refactor: make fetchContext required on FeedSource

Sources that cannot provide context now return null
instead of omitting the method. The engine checks the
return value rather than method existence.

Co-authored-by: Ona <no-reply@ona.com>

.devcontainer/devcontainer.json

@@ -10,6 +10,7 @@
 		"context": ".",
 		"dockerfile": "Dockerfile"
 	},
+	"postCreateCommand": "bun install",
 	"postStartCommand": "./scripts/setup-git.sh && ./scripts/setup-nvim.sh"
 	// Features add additional features to your environment. See https://containers.dev/features
 	// Beware: features are not supported on all platforms and may have unintended side-effects.

.oxfmtrc.json

@@ -8,5 +8,5 @@
 		"ignoreCase": true,
 		"newlinesBetween": true
 	},
-	"ignorePatterns": []
+	"ignorePatterns": [".claude", "fixtures"]
 }

AGENTS.md

@@ -0,0 +1,42 @@
+# AGENTS.md
+
+## Project
+
+ARIS is an AI-powered personal assistant that aggregates data from various sources into a contextual feed. Monorepo with `packages/` (shared libraries) and `apps/` (applications).
+
+## Commands
+
+- Install: `bun install`
+- Test: `bun test` (run in the specific package directory)
+- Lint: `bun run lint`
+- Format: `bun run format`
+- Type check: `bun tsc --noEmit`
+
+Use Bun exclusively. Do not use npm or yarn.
+
+## Code Style
+
+- File names: kebab-case (`data-source.ts`)
+- Prefer function declarations over arrow functions
+- Never use `any` - use `unknown` and narrow types
+- Enums: use const objects with corresponding types:
+  ```typescript
+  const Priority = {
+  	Low: "Low",
+  	High: "High",
+  } as const
+  type Priority = (typeof Priority)[keyof typeof Priority]
+  ```
+- File organization: types first, then primary functions, then helpers
+
+## Before Committing
+
+1. Format: `bun run format`
+2. Test the modified package: `cd packages/<package> && bun test`
+3. Fix all type errors related to your changes
+
+## Git
+
+- Branch: `feat/<task>`, `fix/<task>`, `ci/<task>`, etc.
+- Commits: conventional commit format, title <= 50 chars
+- Signing: If `GPG_PRIVATE_KEY_PASSPHRASE` env var is available, use it to sign commits with `git commit -S`

README.md

@@ -6,10 +6,25 @@ To install dependencies:
 bun install
 ```
 
-To run:
+## Packages
+
+### @aris/source-tfl
+
+TfL (Transport for London) feed source for tube, overground, and Elizabeth line alerts.
+
+#### Testing
 
 ```bash
-bun run index.ts
+cd packages/aris-source-tfl
+bun run test
 ```
 
-This project was created using `bun init` in bun v1.3.6. [Bun](https://bun.com) is a fast all-in-one JavaScript runtime.
+#### Fixtures
+
+Tests use fixture data from real TfL API responses stored in `fixtures/tfl-responses.json`.
+
+To refresh fixtures:
+
+```bash
+bun run fetch-fixtures
+```

apps/aris-backend/.env.example

@@ -0,0 +1,14 @@
+# PostgreSQL connection string
+DATABASE_URL=postgresql://user:password@localhost:5432/aris
+
+# BetterAuth secret (min 32 chars, generate with: openssl rand -base64 32)
+BETTER_AUTH_SECRET=
+
+# Base URL of the backend
+BETTER_AUTH_URL=http://localhost:3000
+
+# Apple WeatherKit credentials
+WEATHERKIT_PRIVATE_KEY=
+WEATHERKIT_KEY_ID=
+WEATHERKIT_TEAM_ID=
+WEATHERKIT_SERVICE_ID=

apps/aris-backend/package.json

@@ -0,0 +1,26 @@
+{
+	"name": "@aris/backend",
+	"version": "0.0.0",
+	"type": "module",
+	"main": "src/server.ts",
+	"scripts": {
+		"dev": "bun run --watch src/server.ts",
+		"start": "bun run src/server.ts",
+		"test": "bun test src/"
+	},
+	"dependencies": {
+		"@aris/core": "workspace:*",
+		"@aris/source-location": "workspace:*",
+		"@aris/source-tfl": "workspace:*",
+		"@aris/source-weatherkit": "workspace:*",
+		"@hono/trpc-server": "^0.3",
+		"@trpc/server": "^11",
+		"arktype": "^2.1.29",
+		"better-auth": "^1",
+		"hono": "^4",
+		"pg": "^8"
+	},
+	"devDependencies": {
+		"@types/pg": "^8"
+	}
+}

apps/aris-backend/src/auth/http.ts

@@ -0,0 +1,7 @@
+import type { Hono } from "hono"
+
+import { auth } from "./index.ts"
+
+export function registerAuthHandlers(app: Hono): void {
+	app.on(["POST", "GET"], "/api/auth/*", (c) => auth.handler(c.req.raw))
+}

apps/aris-backend/src/auth/index.ts

@@ -0,0 +1,10 @@
+import { betterAuth } from "better-auth"
+
+import { pool } from "../db.ts"
+
+export const auth = betterAuth({
+	database: pool,
+	emailAndPassword: {
+		enabled: true,
+	},
+})

apps/aris-backend/src/auth/session-middleware.ts

@@ -0,0 +1,54 @@
+import type { Context, Next } from "hono"
+
+import { auth } from "./index.ts"
+
+type SessionUser = typeof auth.$Infer.Session.user
+type Session = typeof auth.$Infer.Session.session
+
+export interface SessionVariables {
+	user: SessionUser | null
+	session: Session | null
+}
+
+/**
+ * Middleware that attaches session and user to the context.
+ * Does not reject unauthenticated requests - use requireSession for that.
+ */
+export async function sessionMiddleware(c: Context, next: Next): Promise<void> {
+	const session = await auth.api.getSession({ headers: c.req.raw.headers })
+
+	if (session) {
+		c.set("user", session.user)
+		c.set("session", session.session)
+	} else {
+		c.set("user", null)
+		c.set("session", null)
+	}
+
+	await next()
+}
+
+/**
+ * Middleware that requires a valid session. Returns 401 if not authenticated.
+ */
+export async function requireSession(c: Context, next: Next): Promise<Response | void> {
+	const session = await auth.api.getSession({ headers: c.req.raw.headers })
+
+	if (!session) {
+		return c.json({ error: "Unauthorized" }, 401)
+	}
+
+	c.set("user", session.user)
+	c.set("session", session.session)
+	await next()
+}
+
+/**
+ * Get session from headers. Useful for WebSocket upgrade validation.
+ */
+export async function getSessionFromHeaders(
+	headers: Headers,
+): Promise<{ user: SessionUser; session: Session } | null> {
+	const session = await auth.api.getSession({ headers })
+	return session
+}

apps/aris-backend/src/db.ts

@@ -0,0 +1,5 @@
+import { Pool } from "pg"
+
+export const pool = new Pool({
+	connectionString: process.env.DATABASE_URL,
+})

apps/aris-backend/src/feed/service.test.ts

@@ -0,0 +1,162 @@
+import { describe, expect, mock, test } from "bun:test"
+
+import { LocationService } from "../location/service.ts"
+import { FeedEngineService } from "./service.ts"
+
+describe("FeedEngineService", () => {
+	test("engineForUser creates engine on first call", () => {
+		const locationService = new LocationService()
+		const service = new FeedEngineService([locationService])
+
+		const engine = service.engineForUser("user-1")
+
+		expect(engine).toBeDefined()
+	})
+
+	test("engineForUser returns same engine for same user", () => {
+		const locationService = new LocationService()
+		const service = new FeedEngineService([locationService])
+
+		const engine1 = service.engineForUser("user-1")
+		const engine2 = service.engineForUser("user-1")
+
+		expect(engine1).toBe(engine2)
+	})
+
+	test("engineForUser returns different engines for different users", () => {
+		const locationService = new LocationService()
+		const service = new FeedEngineService([locationService])
+
+		const engine1 = service.engineForUser("user-1")
+		const engine2 = service.engineForUser("user-2")
+
+		expect(engine1).not.toBe(engine2)
+	})
+
+	test("engineForUser registers sources from all providers", async () => {
+		const locationService = new LocationService()
+		const service = new FeedEngineService([locationService])
+
+		const engine = service.engineForUser("user-1")
+		const result = await engine.refresh()
+
+		expect(result.errors).toHaveLength(0)
+	})
+
+	test("engineForUser works with empty providers array", async () => {
+		const service = new FeedEngineService([])
+
+		const engine = service.engineForUser("user-1")
+		const result = await engine.refresh()
+
+		expect(result.errors).toHaveLength(0)
+		expect(result.items).toHaveLength(0)
+	})
+
+	test("refresh returns feed result", async () => {
+		const locationService = new LocationService()
+		const service = new FeedEngineService([locationService])
+
+		const result = await service.refresh("user-1")
+
+		expect(result).toHaveProperty("context")
+		expect(result).toHaveProperty("items")
+		expect(result).toHaveProperty("errors")
+		expect(result.context.time).toBeInstanceOf(Date)
+	})
+
+	test("refresh uses location from LocationService", async () => {
+		const locationService = new LocationService()
+		const service = new FeedEngineService([locationService])
+		const location = {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		}
+
+		// Create engine first, then update location
+		service.engineForUser("user-1")
+		locationService.updateUserLocation("user-1", location)
+
+		const result = await service.refresh("user-1")
+
+		expect(result.context.location).toEqual(location)
+	})
+
+	test("subscribe receives updates", async () => {
+		const locationService = new LocationService()
+		const service = new FeedEngineService([locationService])
+		const callback = mock()
+
+		service.subscribe("user-1", callback)
+
+		// Push location to trigger update
+		locationService.updateUserLocation("user-1", {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		})
+
+		// Wait for async update propagation
+		await new Promise((resolve) => setTimeout(resolve, 10))
+
+		expect(callback).toHaveBeenCalled()
+	})
+
+	test("subscribe returns unsubscribe function", async () => {
+		const locationService = new LocationService()
+		const service = new FeedEngineService([locationService])
+		const callback = mock()
+
+		const unsubscribe = service.subscribe("user-1", callback)
+
+		unsubscribe()
+
+		locationService.updateUserLocation("user-1", {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		})
+
+		await new Promise((resolve) => setTimeout(resolve, 10))
+
+		expect(callback).not.toHaveBeenCalled()
+	})
+
+	test("removeUser stops engine and removes it", async () => {
+		const locationService = new LocationService()
+		const service = new FeedEngineService([locationService])
+		const callback = mock()
+
+		service.subscribe("user-1", callback)
+
+		service.removeUser("user-1")
+
+		// Push location - should not trigger update since engine is stopped
+		locationService.feedSourceForUser("user-1")
+		locationService.updateUserLocation("user-1", {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		})
+
+		await new Promise((resolve) => setTimeout(resolve, 10))
+
+		expect(callback).not.toHaveBeenCalled()
+	})
+
+	test("removeUser allows new engine to be created", () => {
+		const locationService = new LocationService()
+		const service = new FeedEngineService([locationService])
+
+		const engine1 = service.engineForUser("user-1")
+		service.removeUser("user-1")
+		const engine2 = service.engineForUser("user-1")
+
+		expect(engine1).not.toBe(engine2)
+	})
+})

apps/aris-backend/src/feed/service.ts

@@ -0,0 +1,75 @@
+import { FeedEngine, type FeedResult, type FeedSource, type FeedSubscriber } from "@aris/core"
+
+/**
+ * Provides a FeedSource instance for a user.
+ */
+export interface FeedSourceProvider {
+	feedSourceForUser(userId: string): FeedSource
+}
+
+/**
+ * Manages FeedEngine instances per user.
+ *
+ * Receives FeedSource instances from injected providers and wires them
+ * into per-user engines. Engines are auto-started on creation.
+ */
+export class FeedEngineService {
+	private engines = new Map<string, FeedEngine>()
+
+	constructor(private readonly providers: FeedSourceProvider[]) {}
+
+	/**
+	 * Get or create a FeedEngine for a user.
+	 * Automatically registers sources and starts the engine.
+	 */
+	engineForUser(userId: string): FeedEngine {
+		let engine = this.engines.get(userId)
+		if (!engine) {
+			engine = this.createEngine(userId)
+			this.engines.set(userId, engine)
+		}
+		return engine
+	}
+
+	/**
+	 * Refresh a user's feed.
+	 */
+	async refresh(userId: string): Promise<FeedResult> {
+		const engine = this.engineForUser(userId)
+		return engine.refresh()
+	}
+
+	/**
+	 * Subscribe to feed updates for a user.
+	 * Returns unsubscribe function.
+	 */
+	subscribe(userId: string, callback: FeedSubscriber): () => void {
+		const engine = this.engineForUser(userId)
+		return engine.subscribe(callback)
+	}
+
+	/**
+	 * Remove a user's FeedEngine.
+	 * Stops the engine and cleans up resources.
+	 */
+	removeUser(userId: string): void {
+		const engine = this.engines.get(userId)
+		if (engine) {
+			engine.stop()
+			this.engines.delete(userId)
+		}
+	}
+
+	private createEngine(userId: string): FeedEngine {
+		const engine = new FeedEngine()
+
+		for (const provider of this.providers) {
+			const source = provider.feedSourceForUser(userId)
+			engine.register(source)
+		}
+
+		engine.start()
+
+		return engine
+	}
+}

apps/aris-backend/src/lib/error.ts

@@ -0,0 +1,8 @@
+export class UserNotFoundError extends Error {
+	constructor(
+		public readonly userId: string,
+		message?: string,
+	) {
+		super(message ? `${message}: user not found: ${userId}` : `User not found: ${userId}`)
+	}
+}

apps/aris-backend/src/location/router.ts

@@ -0,0 +1,37 @@
+import { TRPCError } from "@trpc/server"
+import { type } from "arktype"
+
+import type { TRPC } from "../trpc/router.ts"
+import type { LocationService } from "./service.ts"
+
+import { UserNotFoundError } from "../lib/error.ts"
+
+const locationInput = type({
+	lat: "number",
+	lng: "number",
+	accuracy: "number",
+	timestamp: "Date",
+})
+
+export function createLocationRouter(
+	t: TRPC,
+	{ locationService }: { locationService: LocationService },
+) {
+	return t.router({
+		update: t.procedure.input(locationInput).mutation(({ input, ctx }) => {
+			try {
+				locationService.updateUserLocation(ctx.user.id, {
+					lat: input.lat,
+					lng: input.lng,
+					accuracy: input.accuracy,
+					timestamp: input.timestamp,
+				})
+			} catch (error) {
+				if (error instanceof UserNotFoundError) {
+					throw new TRPCError({ code: "NOT_FOUND", message: error.message })
+				}
+				throw error
+			}
+		}),
+	})
+}

apps/aris-backend/src/location/service.test.ts

@@ -0,0 +1,111 @@
+import { describe, expect, test } from "bun:test"
+
+import { UserNotFoundError } from "../lib/error.ts"
+import { LocationService } from "./service.ts"
+
+describe("LocationService", () => {
+	test("feedSourceForUser creates source on first call", () => {
+		const service = new LocationService()
+		const source = service.feedSourceForUser("user-1")
+
+		expect(source).toBeDefined()
+		expect(source.id).toBe("location")
+	})
+
+	test("feedSourceForUser returns same source for same user", () => {
+		const service = new LocationService()
+		const source1 = service.feedSourceForUser("user-1")
+		const source2 = service.feedSourceForUser("user-1")
+
+		expect(source1).toBe(source2)
+	})
+
+	test("feedSourceForUser returns different sources for different users", () => {
+		const service = new LocationService()
+		const source1 = service.feedSourceForUser("user-1")
+		const source2 = service.feedSourceForUser("user-2")
+
+		expect(source1).not.toBe(source2)
+	})
+
+	test("updateUserLocation updates the source", () => {
+		const service = new LocationService()
+		const source = service.feedSourceForUser("user-1")
+		const location = {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		}
+
+		service.updateUserLocation("user-1", location)
+
+		expect(source.lastLocation).toEqual(location)
+	})
+
+	test("updateUserLocation throws if source does not exist", () => {
+		const service = new LocationService()
+		const location = {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		}
+
+		expect(() => service.updateUserLocation("user-1", location)).toThrow(UserNotFoundError)
+	})
+
+	test("lastUserLocation returns null for unknown user", () => {
+		const service = new LocationService()
+
+		expect(service.lastUserLocation("unknown")).toBeNull()
+	})
+
+	test("lastUserLocation returns last location", () => {
+		const service = new LocationService()
+		service.feedSourceForUser("user-1")
+		const location1 = {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		}
+		const location2 = {
+			lat: 52.0,
+			lng: -0.2,
+			accuracy: 5,
+			timestamp: new Date(),
+		}
+
+		service.updateUserLocation("user-1", location1)
+		service.updateUserLocation("user-1", location2)
+
+		expect(service.lastUserLocation("user-1")).toEqual(location2)
+	})
+
+	test("removeUser removes the source", () => {
+		const service = new LocationService()
+		service.feedSourceForUser("user-1")
+		const location = {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		}
+
+		service.updateUserLocation("user-1", location)
+		service.removeUser("user-1")
+
+		expect(service.lastUserLocation("user-1")).toBeNull()
+	})
+
+	test("removeUser allows new source to be created", () => {
+		const service = new LocationService()
+		const source1 = service.feedSourceForUser("user-1")
+
+		service.removeUser("user-1")
+		const source2 = service.feedSourceForUser("user-1")
+
+		expect(source1).not.toBe(source2)
+	})
+})

apps/aris-backend/src/location/service.ts

@@ -0,0 +1,57 @@
+import { LocationSource, type Location } from "@aris/source-location"
+
+import type { FeedSourceProvider } from "../feed/service.ts"
+
+import { UserNotFoundError } from "../lib/error.ts"
+
+/**
+ * Manages LocationSource instances per user.
+ */
+export class LocationService implements FeedSourceProvider {
+	private sources = new Map<string, LocationSource>()
+
+	/**
+	 * Get or create a LocationSource for a user.
+	 * @param userId - The user's unique identifier
+	 * @returns The user's LocationSource instance
+	 */
+	feedSourceForUser(userId: string): LocationSource {
+		let source = this.sources.get(userId)
+		if (!source) {
+			source = new LocationSource()
+			this.sources.set(userId, source)
+		}
+		return source
+	}
+
+	/**
+	 * Update location for a user.
+	 * @param userId - The user's unique identifier
+	 * @param location - The new location data
+	 * @throws {UserNotFoundError} If no source exists for the user
+	 */
+	updateUserLocation(userId: string, location: Location): void {
+		const source = this.sources.get(userId)
+		if (!source) {
+			throw new UserNotFoundError(userId)
+		}
+		source.pushLocation(location)
+	}
+
+	/**
+	 * Get last known location for a user.
+	 * @param userId - The user's unique identifier
+	 * @returns The last location, or null if none exists
+	 */
+	lastUserLocation(userId: string): Location | null {
+		return this.sources.get(userId)?.lastLocation ?? null
+	}
+
+	/**
+	 * Remove a user's LocationSource.
+	 * @param userId - The user's unique identifier
+	 */
+	removeUser(userId: string): void {
+		this.sources.delete(userId)
+	}
+}

apps/aris-backend/src/server.ts

@@ -0,0 +1,46 @@
+import { trpcServer } from "@hono/trpc-server"
+import { Hono } from "hono"
+
+import { registerAuthHandlers } from "./auth/http.ts"
+import { LocationService } from "./location/service.ts"
+import { createContext } from "./trpc/context.ts"
+import { createTRPCRouter } from "./trpc/router.ts"
+import { WeatherService } from "./weather/service.ts"
+
+function main() {
+	const locationService = new LocationService()
+
+	const weatherService = new WeatherService({
+		credentials: {
+			privateKey: process.env.WEATHERKIT_PRIVATE_KEY!,
+			keyId: process.env.WEATHERKIT_KEY_ID!,
+			teamId: process.env.WEATHERKIT_TEAM_ID!,
+			serviceId: process.env.WEATHERKIT_SERVICE_ID!,
+		},
+	})
+
+	const trpcRouter = createTRPCRouter({ locationService, weatherService })
+
+	const app = new Hono()
+
+	app.get("/health", (c) => c.json({ status: "ok" }))
+
+	registerAuthHandlers(app)
+
+	app.use(
+		"/trpc/*",
+		trpcServer({
+			router: trpcRouter,
+			createContext,
+		}),
+	)
+
+	return app
+}
+
+const app = main()
+
+export default {
+	port: 3000,
+	fetch: app.fetch,
+}

apps/aris-backend/src/tfl/service.test.ts

@@ -0,0 +1,206 @@
+import type { Context } from "@aris/core"
+import type { ITflApi, StationLocation, TflLineId, TflLineStatus } from "@aris/source-tfl"
+
+import { describe, expect, test } from "bun:test"
+
+import { UserNotFoundError } from "../lib/error.ts"
+import { TflService } from "./service.ts"
+
+class StubTflApi implements ITflApi {
+	private statuses: TflLineStatus[]
+
+	constructor(statuses: TflLineStatus[] = []) {
+		this.statuses = statuses
+	}
+
+	async fetchLineStatuses(lines?: TflLineId[]): Promise<TflLineStatus[]> {
+		if (lines) {
+			return this.statuses.filter((s) => lines.includes(s.lineId))
+		}
+		return this.statuses
+	}
+
+	async fetchStations(): Promise<StationLocation[]> {
+		return [
+			{
+				id: "940GZZLUKSX",
+				name: "King's Cross",
+				lat: 51.5308,
+				lng: -0.1238,
+				lines: ["northern", "victoria"],
+			},
+		]
+	}
+}
+
+function createContext(): Context {
+	return { time: new Date("2026-01-15T12:00:00Z") }
+}
+
+const sampleStatuses: TflLineStatus[] = [
+	{
+		lineId: "northern",
+		lineName: "Northern",
+		severity: "minor-delays",
+		description: "Minor delays on the Northern line",
+	},
+	{
+		lineId: "victoria",
+		lineName: "Victoria",
+		severity: "major-delays",
+		description: "Severe delays on the Victoria line",
+	},
+	{
+		lineId: "central",
+		lineName: "Central",
+		severity: "closure",
+		description: "Central line suspended",
+	},
+]
+
+describe("TflService", () => {
+	test("feedSourceForUser creates source on first call", () => {
+		const service = new TflService(new StubTflApi())
+		const source = service.feedSourceForUser("user-1")
+
+		expect(source).toBeDefined()
+		expect(source.id).toBe("tfl")
+	})
+
+	test("feedSourceForUser returns same source for same user", () => {
+		const service = new TflService(new StubTflApi())
+		const source1 = service.feedSourceForUser("user-1")
+		const source2 = service.feedSourceForUser("user-1")
+
+		expect(source1).toBe(source2)
+	})
+
+	test("feedSourceForUser returns different sources for different users", () => {
+		const service = new TflService(new StubTflApi())
+		const source1 = service.feedSourceForUser("user-1")
+		const source2 = service.feedSourceForUser("user-2")
+
+		expect(source1).not.toBe(source2)
+	})
+
+	test("updateLinesOfInterest mutates the existing source in place", () => {
+		const service = new TflService(new StubTflApi())
+		const original = service.feedSourceForUser("user-1")
+
+		service.updateLinesOfInterest("user-1", ["northern", "victoria"])
+		const after = service.feedSourceForUser("user-1")
+
+		expect(after).toBe(original)
+	})
+
+	test("updateLinesOfInterest throws if source does not exist", () => {
+		const service = new TflService(new StubTflApi())
+
+		expect(() => service.updateLinesOfInterest("user-1", ["northern"])).toThrow(UserNotFoundError)
+	})
+
+	test("removeUser removes the source", () => {
+		const service = new TflService(new StubTflApi())
+		const source1 = service.feedSourceForUser("user-1")
+
+		service.removeUser("user-1")
+		const source2 = service.feedSourceForUser("user-1")
+
+		expect(source1).not.toBe(source2)
+	})
+
+	test("removeUser clears line configuration", async () => {
+		const api = new StubTflApi(sampleStatuses)
+		const service = new TflService(api)
+		service.feedSourceForUser("user-1")
+		service.updateLinesOfInterest("user-1", ["northern"])
+
+		service.removeUser("user-1")
+		const items = await service.feedSourceForUser("user-1").fetchItems(createContext())
+
+		expect(items.length).toBe(3)
+	})
+
+	test("shares single api instance across users", () => {
+		const api = new StubTflApi()
+		const service = new TflService(api)
+
+		service.feedSourceForUser("user-1")
+		service.feedSourceForUser("user-2")
+
+		expect(service.feedSourceForUser("user-1").id).toBe("tfl")
+		expect(service.feedSourceForUser("user-2").id).toBe("tfl")
+	})
+
+	describe("returned source fetches items", () => {
+		test("source returns feed items from api", async () => {
+			const api = new StubTflApi(sampleStatuses)
+			const service = new TflService(api)
+			const source = service.feedSourceForUser("user-1")
+
+			const items = await source.fetchItems(createContext())
+
+			expect(items.length).toBe(3)
+			for (const item of items) {
+				expect(item.type).toBe("tfl-alert")
+				expect(item.id).toMatch(/^tfl-alert-/)
+				expect(typeof item.priority).toBe("number")
+				expect(item.timestamp).toBeInstanceOf(Date)
+			}
+		})
+
+		test("source returns items sorted by priority descending", async () => {
+			const api = new StubTflApi(sampleStatuses)
+			const service = new TflService(api)
+			const source = service.feedSourceForUser("user-1")
+
+			const items = await source.fetchItems(createContext())
+
+			for (let i = 1; i < items.length; i++) {
+				expect(items[i - 1]!.priority).toBeGreaterThanOrEqual(items[i]!.priority)
+			}
+		})
+
+		test("source returns empty array when no disruptions", async () => {
+			const api = new StubTflApi([])
+			const service = new TflService(api)
+			const source = service.feedSourceForUser("user-1")
+
+			const items = await source.fetchItems(createContext())
+
+			expect(items).toEqual([])
+		})
+
+		test("updateLinesOfInterest filters items to configured lines", async () => {
+			const api = new StubTflApi(sampleStatuses)
+			const service = new TflService(api)
+
+			const before = await service.feedSourceForUser("user-1").fetchItems(createContext())
+			expect(before.length).toBe(3)
+
+			service.updateLinesOfInterest("user-1", ["northern"])
+			const after = await service.feedSourceForUser("user-1").fetchItems(createContext())
+
+			expect(after.length).toBe(1)
+			expect(after[0]!.data.line).toBe("northern")
+		})
+
+		test("different users get independent line configs", async () => {
+			const api = new StubTflApi(sampleStatuses)
+			const service = new TflService(api)
+			service.feedSourceForUser("user-1")
+			service.feedSourceForUser("user-2")
+
+			service.updateLinesOfInterest("user-1", ["northern"])
+			service.updateLinesOfInterest("user-2", ["central"])
+
+			const items1 = await service.feedSourceForUser("user-1").fetchItems(createContext())
+			const items2 = await service.feedSourceForUser("user-2").fetchItems(createContext())
+
+			expect(items1.length).toBe(1)
+			expect(items1[0]!.data.line).toBe("northern")
+			expect(items2.length).toBe(1)
+			expect(items2[0]!.data.line).toBe("central")
+		})
+	})
+})

apps/aris-backend/src/tfl/service.ts

@@ -0,0 +1,40 @@
+import { TflSource, type ITflApi, type TflLineId } from "@aris/source-tfl"
+
+import type { FeedSourceProvider } from "../feed/service.ts"
+
+import { UserNotFoundError } from "../lib/error.ts"
+
+/**
+ * Manages per-user TflSource instances with individual line configuration.
+ */
+export class TflService implements FeedSourceProvider {
+	private sources = new Map<string, TflSource>()
+
+	constructor(private readonly api: ITflApi) {}
+
+	feedSourceForUser(userId: string): TflSource {
+		let source = this.sources.get(userId)
+		if (!source) {
+			source = new TflSource({ client: this.api })
+			this.sources.set(userId, source)
+		}
+		return source
+	}
+
+	/**
+	 * Update monitored lines for a user. Mutates the existing TflSource
+	 * so that references held by FeedEngine remain valid.
+	 * @throws {UserNotFoundError} If no source exists for the user
+	 */
+	updateLinesOfInterest(userId: string, lines: TflLineId[]): void {
+		const source = this.sources.get(userId)
+		if (!source) {
+			throw new UserNotFoundError(userId)
+		}
+		source.setLinesOfInterest(lines)
+	}
+
+	removeUser(userId: string): void {
+		this.sources.delete(userId)
+	}
+}

apps/aris-backend/src/trpc/context.ts

@@ -0,0 +1,14 @@
+import type { FetchCreateContextFnOptions } from "@trpc/server/adapters/fetch"
+
+import { auth } from "../auth/index.ts"
+
+export async function createContext(opts: FetchCreateContextFnOptions) {
+	const session = await auth.api.getSession({ headers: opts.req.headers })
+
+	return {
+		user: session?.user ?? null,
+		session: session?.session ?? null,
+	}
+}
+
+export type Context = Awaited<ReturnType<typeof createContext>>

apps/aris-backend/src/trpc/router.ts

@@ -0,0 +1,50 @@
+import { initTRPC, TRPCError } from "@trpc/server"
+
+import type { LocationService } from "../location/service.ts"
+import type { WeatherService } from "../weather/service.ts"
+import type { Context } from "./context.ts"
+
+import { createLocationRouter } from "../location/router.ts"
+
+interface AuthedContext {
+	user: NonNullable<Context["user"]>
+	session: NonNullable<Context["session"]>
+}
+
+function createTRPC() {
+	const t = initTRPC.context<Context>().create()
+
+	const isAuthed = t.middleware(({ ctx, next }) => {
+		if (!ctx.user || !ctx.session) {
+			throw new TRPCError({ code: "UNAUTHORIZED" })
+		}
+		return next({
+			ctx: {
+				user: ctx.user,
+				session: ctx.session,
+			},
+		})
+	})
+
+	return {
+		router: t.router,
+		procedure: t.procedure.use(isAuthed),
+	}
+}
+
+export type TRPC = ReturnType<typeof createTRPC>
+
+export interface TRPCRouterDeps {
+	locationService: LocationService
+	weatherService: WeatherService
+}
+
+export function createTRPCRouter({ locationService }: TRPCRouterDeps) {
+	const t = createTRPC()
+
+	return t.router({
+		location: createLocationRouter(t, { locationService }),
+	})
+}
+
+export type TRPCRouter = ReturnType<typeof createTRPCRouter>

apps/aris-backend/src/weather/service.test.ts

@@ -0,0 +1,116 @@
+import type { Context } from "@aris/core"
+
+import { LocationKey } from "@aris/source-location"
+import {
+	Units,
+	WeatherFeedItemType,
+	type WeatherKitClient,
+	type WeatherKitResponse,
+} from "@aris/source-weatherkit"
+import { describe, expect, test } from "bun:test"
+
+import fixture from "../../../../packages/aris-source-weatherkit/fixtures/san-francisco.json"
+import { WeatherService } from "./service.ts"
+
+const mockClient = createMockClient(fixture.response as WeatherKitResponse)
+
+function createMockClient(response: WeatherKitResponse): WeatherKitClient {
+	return {
+		fetch: async () => response,
+	}
+}
+
+function createMockContext(location?: { lat: number; lng: number }): Context {
+	const ctx: Context = { time: new Date("2026-01-17T00:00:00Z") }
+	if (location) {
+		ctx[LocationKey] = { ...location, accuracy: 10, timestamp: new Date() }
+	}
+	return ctx
+}
+
+describe("WeatherService", () => {
+	test("feedSourceForUser creates source on first call", () => {
+		const service = new WeatherService({ client: mockClient })
+		const source = service.feedSourceForUser("user-1")
+
+		expect(source).toBeDefined()
+		expect(source.id).toBe("weather")
+	})
+
+	test("feedSourceForUser returns same source for same user", () => {
+		const service = new WeatherService({ client: mockClient })
+		const source1 = service.feedSourceForUser("user-1")
+		const source2 = service.feedSourceForUser("user-1")
+
+		expect(source1).toBe(source2)
+	})
+
+	test("feedSourceForUser returns different sources for different users", () => {
+		const service = new WeatherService({ client: mockClient })
+		const source1 = service.feedSourceForUser("user-1")
+		const source2 = service.feedSourceForUser("user-2")
+
+		expect(source1).not.toBe(source2)
+	})
+
+	test("feedSourceForUser applies hourly and daily limits", async () => {
+		const service = new WeatherService({
+			client: mockClient,
+			hourlyLimit: 3,
+			dailyLimit: 2,
+		})
+		const source = service.feedSourceForUser("user-1")
+		const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+		const items = await source.fetchItems(context)
+
+		const hourly = items.filter((i) => i.type === WeatherFeedItemType.hourly)
+		const daily = items.filter((i) => i.type === WeatherFeedItemType.daily)
+
+		expect(hourly).toHaveLength(3)
+		expect(daily).toHaveLength(2)
+	})
+
+	test("feedSourceForUser applies units", async () => {
+		const service = new WeatherService({
+			client: mockClient,
+			units: Units.imperial,
+		})
+		const source = service.feedSourceForUser("user-1")
+		const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+		const items = await source.fetchItems(context)
+		const current = items.find((i) => i.type === WeatherFeedItemType.current)
+
+		expect(current).toBeDefined()
+		// Fixture has ~15.87°C, imperial should be ~60.6°F
+		expect(current!.data.temperature).toBeGreaterThan(50)
+	})
+
+	test("removeUser removes the source", () => {
+		const service = new WeatherService({ client: mockClient })
+		service.feedSourceForUser("user-1")
+
+		service.removeUser("user-1")
+
+		// After removal, feedSourceForUser should create a new instance
+		const source2 = service.feedSourceForUser("user-1")
+		expect(source2).toBeDefined()
+	})
+
+	test("removeUser allows new source to be created", () => {
+		const service = new WeatherService({ client: mockClient })
+		const source1 = service.feedSourceForUser("user-1")
+
+		service.removeUser("user-1")
+		const source2 = service.feedSourceForUser("user-1")
+
+		expect(source1).not.toBe(source2)
+	})
+
+	test("removeUser is no-op for unknown user", () => {
+		const service = new WeatherService({ client: mockClient })
+
+		expect(() => service.removeUser("unknown")).not.toThrow()
+	})
+})

apps/aris-backend/src/weather/service.ts

@@ -0,0 +1,40 @@
+import { WeatherSource, type WeatherSourceOptions } from "@aris/source-weatherkit"
+
+import type { FeedSourceProvider } from "../feed/service.ts"
+
+/**
+ * Options forwarded to every per-user WeatherSource.
+ * Must include either `credentials` or `client` (same requirement as WeatherSourceOptions).
+ */
+export type WeatherServiceOptions = WeatherSourceOptions
+
+/**
+ * Manages WeatherSource instances per user.
+ */
+export class WeatherService implements FeedSourceProvider {
+	private sources = new Map<string, WeatherSource>()
+	private readonly options: WeatherServiceOptions
+
+	constructor(options: WeatherServiceOptions) {
+		this.options = options
+	}
+
+	/**
+	 * Get or create a WeatherSource for a user.
+	 */
+	feedSourceForUser(userId: string): WeatherSource {
+		let source = this.sources.get(userId)
+		if (!source) {
+			source = new WeatherSource(this.options)
+			this.sources.set(userId, source)
+		}
+		return source
+	}
+
+	/**
+	 * Remove a user's WeatherSource.
+	 */
+	removeUser(userId: string): void {
+		this.sources.delete(userId)
+	}
+}

apps/aris-backend/tsconfig.json

@@ -0,0 +1,4 @@
+{
+	"extends": "../../tsconfig.json",
+	"include": ["src"]
+}

bun.lock

@@ -13,14 +13,115 @@
         "typescript": "^5",
       },
     },
+    "apps/aris-backend": {
+      "name": "@aris/backend",
+      "version": "0.0.0",
+      "dependencies": {
+        "@aris/core": "workspace:*",
+        "@aris/source-location": "workspace:*",
+        "@aris/source-tfl": "workspace:*",
+        "@aris/source-weatherkit": "workspace:*",
+        "@hono/trpc-server": "^0.3",
+        "@trpc/server": "^11",
+        "arktype": "^2.1.29",
+        "better-auth": "^1",
+        "hono": "^4",
+        "pg": "^8",
+      },
+      "devDependencies": {
+        "@types/pg": "^8",
+      },
+    },
     "packages/aris-core": {
       "name": "@aris/core",
       "version": "0.0.0",
     },
+    "packages/aris-data-source-weatherkit": {
+      "name": "@aris/data-source-weatherkit",
+      "version": "0.0.0",
+      "dependencies": {
+        "@aris/core": "workspace:*",
+        "arktype": "^2.1.0",
+      },
+    },
+    "packages/aris-source-apple-calendar": {
+      "name": "@aris/source-apple-calendar",
+      "version": "0.0.0",
+      "dependencies": {
+        "@aris/core": "workspace:*",
+        "ical.js": "^2.1.0",
+        "tsdav": "^2.1.7",
+      },
+    },
+    "packages/aris-source-google-calendar": {
+      "name": "@aris/source-google-calendar",
+      "version": "0.0.0",
+      "dependencies": {
+        "@aris/core": "workspace:*",
+        "arktype": "^2.1.0",
+      },
+    },
+    "packages/aris-source-location": {
+      "name": "@aris/source-location",
+      "version": "0.0.0",
+      "dependencies": {
+        "@aris/core": "workspace:*",
+      },
+    },
+    "packages/aris-source-tfl": {
+      "name": "@aris/source-tfl",
+      "version": "0.0.0",
+      "dependencies": {
+        "@aris/core": "workspace:*",
+        "@aris/source-location": "workspace:*",
+        "arktype": "^2.1.0",
+      },
+    },
+    "packages/aris-source-weatherkit": {
+      "name": "@aris/source-weatherkit",
+      "version": "0.0.0",
+      "dependencies": {
+        "@aris/core": "workspace:*",
+        "@aris/source-location": "workspace:*",
+        "arktype": "^2.1.0",
+      },
+    },
   },
   "packages": {
+    "@aris/backend": ["@aris/backend@workspace:apps/aris-backend"],
+
     "@aris/core": ["@aris/core@workspace:packages/aris-core"],
 
+    "@aris/data-source-weatherkit": ["@aris/data-source-weatherkit@workspace:packages/aris-data-source-weatherkit"],
+
+    "@aris/source-apple-calendar": ["@aris/source-apple-calendar@workspace:packages/aris-source-apple-calendar"],
+
+    "@aris/source-google-calendar": ["@aris/source-google-calendar@workspace:packages/aris-source-google-calendar"],
+
+    "@aris/source-location": ["@aris/source-location@workspace:packages/aris-source-location"],
+
+    "@aris/source-tfl": ["@aris/source-tfl@workspace:packages/aris-source-tfl"],
+
+    "@aris/source-weatherkit": ["@aris/source-weatherkit@workspace:packages/aris-source-weatherkit"],
+
+    "@ark/schema": ["@ark/schema@0.56.0", "", { "dependencies": { "@ark/util": "0.56.0" } }, "sha512-ECg3hox/6Z/nLajxXqNhgPtNdHWC9zNsDyskwO28WinoFEnWow4IsERNz9AnXRhTZJnYIlAJ4uGn3nlLk65vZA=="],
+
+    "@ark/util": ["@ark/util@0.56.0", "", {}, "sha512-BghfRC8b9pNs3vBoDJhcta0/c1J1rsoS1+HgVUreMFPdhz/CRAKReAu57YEllNaSy98rWAdY1gE+gFup7OXpgA=="],
+
+    "@better-auth/core": ["@better-auth/core@1.4.18", "", { "dependencies": { "@standard-schema/spec": "^1.0.0", "zod": "^4.3.5" }, "peerDependencies": { "@better-auth/utils": "0.3.0", "@better-fetch/fetch": "1.1.21", "better-call": "1.1.8", "jose": "^6.1.0", "kysely": "^0.28.5", "nanostores": "^1.0.1" } }, "sha512-q+awYgC7nkLEBdx2sW0iJjkzgSHlIxGnOpsN1r/O1+a4m7osJNHtfK2mKJSL1I+GfNyIlxJF8WvD/NLuYMpmcg=="],
+
+    "@better-auth/telemetry": ["@better-auth/telemetry@1.4.18", "", { "dependencies": { "@better-auth/utils": "0.3.0", "@better-fetch/fetch": "1.1.21" }, "peerDependencies": { "@better-auth/core": "1.4.18" } }, "sha512-e5rDF8S4j3Um/0LIVATL2in9dL4lfO2fr2v1Wio4qTMRbfxqnUDTa+6SZtwdeJrbc4O+a3c+IyIpjG9Q/6GpfQ=="],
+
+    "@better-auth/utils": ["@better-auth/utils@0.3.0", "", {}, "sha512-W+Adw6ZA6mgvnSnhOki270rwJ42t4XzSK6YWGF//BbVXL6SwCLWfyzBc1lN2m/4RM28KubdBKQ4X5VMoLRNPQw=="],
+
+    "@better-fetch/fetch": ["@better-fetch/fetch@1.1.21", "", {}, "sha512-/ImESw0sskqlVR94jB+5+Pxjf+xBwDZF/N5+y2/q4EqD7IARUTSpPfIo8uf39SYpCxyOCtbyYpUrZ3F/k0zT4A=="],
+
+    "@hono/trpc-server": ["@hono/trpc-server@0.3.4", "", { "peerDependencies": { "@trpc/server": "^10.10.0 || >11.0.0-rc", "hono": ">=4.*" } }, "sha512-xFOPjUPnII70FgicDzOJy1ufIoBTu8eF578zGiDOrYOrYN8CJe140s9buzuPkX+SwJRYK8LjEBHywqZtxdm8aA=="],
+
+    "@noble/ciphers": ["@noble/ciphers@2.1.1", "", {}, "sha512-bysYuiVfhxNJuldNXlFEitTVdNnYUc+XNJZd7Qm2a5j1vZHgY+fazadNFWFaMK/2vye0JVlxV3gHmC0WDfAOQw=="],
+
+    "@noble/hashes": ["@noble/hashes@2.0.1", "", {}, "sha512-XlOlEbQcE9fmuXxrVTXCTlG2nlRXa9Rj3rr5Ue/+tX+nmkgbX720YHh0VR3hBF9xDvwnb8D2shVGOwNx+ulArw=="],
+
     "@oxfmt/darwin-arm64": ["@oxfmt/darwin-arm64@0.24.0", "", { "os": "darwin", "cpu": "arm64" }, "sha512-aYXuGf/yq8nsyEcHindGhiz9I+GEqLkVq8CfPbd+6VE259CpPEH+CaGHEO1j6vIOmNr8KHRq+IAjeRO2uJpb8A=="],
 
     "@oxfmt/darwin-x64": ["@oxfmt/darwin-x64@0.24.0", "", { "os": "darwin", "cpu": "x64" }, "sha512-vs3b8Bs53hbiNvcNeBilzE/+IhDTWKjSBB3v/ztr664nZk65j0xr+5IHMBNz3CFppmX7o/aBta2PxY+t+4KoPg=="],
@@ -37,36 +138,140 @@
 
     "@oxfmt/win32-x64": ["@oxfmt/win32-x64@0.24.0", "", { "os": "win32", "cpu": "x64" }, "sha512-0tmlNzcyewAnauNeBCq0xmAkmiKzl+H09p0IdHy+QKrTQdtixtf+AOjDAADbRfihkS+heF15Pjc4IyJMdAAJjw=="],
 
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+    "@oxlint/binding-android-arm-eabi": ["@oxlint/binding-android-arm-eabi@1.47.0", "", { "os": "android", "cpu": "arm" }, "sha512-UHqo3te9K/fh29brCuQdHjN+kfpIi9cnTPABuD5S9wb9ykXYRGTOOMVuSV/CK43sOhU4wwb2nT1RVjcbrrQjFw=="],
 
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+    "pg-connection-string": ["pg-connection-string@2.11.0", "", {}, "sha512-kecgoJwhOpxYU21rZjULrmrBJ698U2RxXofKVzOn5UDj61BPj/qMb7diYUR1nLScCDbrztQFl1TaQZT0t1EtzQ=="],
+
+    "pg-int8": ["pg-int8@1.0.1", "", {}, "sha512-WCtabS6t3c8SkpDBUlb1kjOs7l66xsGdKpIPZsg4wR+B3+u9UAum2odSsF9tnvxg80h4ZxLWMy4pRjOsFIqQpw=="],
+
+    "pg-pool": ["pg-pool@3.11.0", "", { "peerDependencies": { "pg": ">=8.0" } }, "sha512-MJYfvHwtGp870aeusDh+hg9apvOe2zmpZJpyt+BMtzUWlVqbhFmMK6bOBXLBUPd7iRtIF9fZplDc7KrPN3PN7w=="],
+
+    "pg-protocol": ["pg-protocol@1.11.0", "", {}, "sha512-pfsxk2M9M3BuGgDOfuy37VNRRX3jmKgMjcvAcWqNDpZSf4cUmv8HSOl5ViRQFsfARFn0KuUQTgLxVMbNq5NW3g=="],
+
+    "pg-types": ["pg-types@2.2.0", "", { "dependencies": { "pg-int8": "1.0.1", "postgres-array": "~2.0.0", "postgres-bytea": "~1.0.0", "postgres-date": "~1.0.4", "postgres-interval": "^1.1.0" } }, "sha512-qTAAlrEsl8s4OiEQY69wDvcMIdQN6wdz5ojQiOy6YRMuynxenON0O5oCpJI6lshc6scgAY8qvJ2On/p+CXY0GA=="],
+
+    "pgpass": ["pgpass@1.0.5", "", { "dependencies": { "split2": "^4.1.0" } }, "sha512-FdW9r/jQZhSeohs1Z3sI1yxFQNFvMcnmfuj4WBMUTxOrAyLMaTcE1aAMBiTlbMNaXvBCQuVi0R7hd8udDSP7ug=="],
+
+    "postgres-array": ["postgres-array@2.0.0", "", {}, "sha512-VpZrUqU5A69eQyW2c5CA1jtLecCsN2U/bD6VilrFDWq5+5UIEVO7nazS3TEcHf1zuPYO/sqGvUvW62g86RXZuA=="],
+
+    "postgres-bytea": ["postgres-bytea@1.0.1", "", {}, "sha512-5+5HqXnsZPE65IJZSMkZtURARZelel2oXUEO8rH83VS/hxH5vv1uHquPg5wZs8yMAfdv971IU+kcPUczi7NVBQ=="],
+
+    "postgres-date": ["postgres-date@1.0.7", "", {}, "sha512-suDmjLVQg78nMK2UZ454hAG+OAW+HQPZ6n++TNDUX+L0+uUlLywnoxJKDou51Zm+zTCjrCl0Nq6J9C5hP9vK/Q=="],
+
+    "postgres-interval": ["postgres-interval@1.2.0", "", { "dependencies": { "xtend": "^4.0.0" } }, "sha512-9ZhXKM/rw350N1ovuWHbGxnGh/SNJ4cnxHiM0rxE4VN41wsg8P8zWn9hv/buK00RP4WvlOyr/RBDiptyxVbkZQ=="],
+
+    "rou3": ["rou3@0.7.12", "", {}, "sha512-iFE4hLDuloSWcD7mjdCDhx2bKcIsYbtOTpfH5MHHLSKMOUyjqQXTeZVa289uuwEGEKFoE/BAPbhaU4B774nceg=="],
+
+    "sax": ["sax@1.4.4", "", {}, "sha512-1n3r/tGXO6b6VXMdFT54SHzT9ytu9yr7TaELowdYpMqY/Ao7EnlQGmAQ1+RatX7Tkkdm6hONI2owqNx2aZj5Sw=="],
+
+    "set-cookie-parser": ["set-cookie-parser@2.7.2", "", {}, "sha512-oeM1lpU/UvhTxw+g3cIfxXHyJRc/uidd3yK1P242gzHds0udQBYzs3y8j4gCCW+ZJ7ad0yctld8RYO+bdurlvw=="],
+
+    "split2": ["split2@4.2.0", "", {}, "sha512-UcjcJOWknrNkF6PLX83qcHM6KHgVKNkV62Y8a5uYDVv9ydGQVwAHMKqHdJje1VTWpljG0WYpCDhrCdAOYH4TWg=="],
 
     "tinypool": ["tinypool@2.0.0", "", {}, "sha512-/RX9RzeH2xU5ADE7n2Ykvmi9ED3FBGPAjw9u3zucrNNaEBIO0HPSYgL0NT7+3p147ojeSdaVu08F6hjpv31HJg=="],
 
+    "tr46": ["tr46@0.0.3", "", {}, "sha512-N3WMsuqV66lT30CrXNbEjx4GEwlow3v6rr4mCcv6prnfwhS01rkgyFdjPNBYd9br7LpXV1+Emh01fHnq2Gdgrw=="],
+
+    "tsdav": ["tsdav@2.1.8", "", { "dependencies": { "base-64": "1.0.0", "cross-fetch": "4.1.0", "debug": "4.4.3", "xml-js": "1.6.11" } }, "sha512-zvQvhZLzTaEmNNgJbBlUYT/JOq9Xpw/xkxCqs7IT2d2/7o7pss0iZOlZXuHJ5VcvSvTny42Vc6+6GyzZcrCJ1g=="],
+
     "typescript": ["typescript@5.9.3", "", { "bin": { "tsc": "bin/tsc", "tsserver": "bin/tsserver" } }, "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw=="],
 
     "undici-types": ["undici-types@7.16.0", "", {}, "sha512-Zz+aZWSj8LE6zoxD+xrjh4VfkIG8Ya6LvYkZqtUQGJPZjYl53ypCaUwWqo7eI0x66KBGeRo+mlBEkMSeSZ38Nw=="],
+
+    "webidl-conversions": ["webidl-conversions@3.0.1", "", {}, "sha512-2JAn3z8AR6rjK8Sm8orRC0h/bcl/DqL7tRPdGZ4I1CjdF+EaMLmYxBHyXuKL849eucPFhvBoxMsflfOb8kxaeQ=="],
+
+    "whatwg-url": ["whatwg-url@5.0.0", "", { "dependencies": { "tr46": "~0.0.3", "webidl-conversions": "^3.0.0" } }, "sha512-saE57nupxk6v3HY35+jzBwYa0rKSy0XR8JSxZPwgLr7ys0IBzhGviA1/TUGJLmSVqs8pb9AnvICXEuOHLprYTw=="],
+
+    "xml-js": ["xml-js@1.6.11", "", { "dependencies": { "sax": "^1.2.4" }, "bin": { "xml-js": "./bin/cli.js" } }, "sha512-7rVi2KMfwfWFl+GpPg6m80IVMWXLRjO+PxTq7V2CDhoGak0wzYzFgUY2m4XJ47OGdXd8eLE8EmwfAmdjw7lC1g=="],
+
+    "xtend": ["xtend@4.0.2", "", {}, "sha512-LKYU1iAXJXUgAXn9URjiu+MWhyUXHsvfp7mcuYm9dSUKK0/CjtrUwFAxD82/mCWbtLsGjFIad0wIsod4zrTAEQ=="],
+
+    "zod": ["zod@4.3.6", "", {}, "sha512-rftlrkhHZOcjDwkGlnUtZZkvaPHCsDATp4pGpuOOMDaTdDDXF91wuVDJoWoPsKX/3YPQ5fHuF3STjcYyKr+Qhg=="],
   }
 }

docs/backend-spec.md

@@ -0,0 +1,193 @@
+# ARIS Backend Specification
+
+## Problem Statement
+
+ARIS needs a backend service that manages per-user FeedEngine instances and delivers real-time feed updates to clients. The backend must handle authentication, maintain WebSocket connections for live updates, and accept context updates (like location) that trigger feed recalculations.
+
+## Requirements
+
+### Authentication
+
+- Email/password authentication using BetterAuth
+- PostgreSQL for session and user storage
+- Session tokens validated via `Authorization: Bearer <token>` header
+- Auth endpoints exposed via BetterAuth's built-in routes
+
+### FeedEngine Management
+
+- Each authenticated user gets their own FeedEngine instance
+- Instances are cached in memory with a 30-minute TTL
+- TTL resets on any activity (WebSocket message, location update)
+- Default sources registered for each user: `LocationSource`, `WeatherSource`, `TflSource`
+- Source configuration is hardcoded initially (customization deferred)
+
+### WebSocket Connection
+
+- Single endpoint: `GET /ws` (upgrades to WebSocket)
+- Authentication via `Authorization: Bearer <token>` header on upgrade request
+- Rejected before upgrade if token is invalid
+- Multiple connections per user allowed (e.g., multiple devices)
+- All connections for a user receive the same feed updates
+- On connect: immediately send current feed state
+
+### JSON-RPC Protocol
+
+All WebSocket communication uses JSON-RPC 2.0.
+
+**Client → Server (Requests):**
+
+```json
+{ "jsonrpc": "2.0", "method": "location.update", "params": { "lat": 51.5, "lng": -0.1, "accuracy": 10, "timestamp": "2025-01-01T12:00:00Z" }, "id": 1 }
+{ "jsonrpc": "2.0", "method": "feed.refresh", "params": {}, "id": 2 }
+```
+
+**Server → Client (Responses):**
+
+```json
+{ "jsonrpc": "2.0", "result": { "ok": true }, "id": 1 }
+```
+
+**Server → Client (Notifications - no id):**
+
+```json
+{ "jsonrpc": "2.0", "method": "feed.update", "params": { "items": [...], "errors": [...] } }
+```
+
+### JSON-RPC Methods
+
+| Method            | Params                              | Description                                 |
+| ----------------- | ----------------------------------- | ------------------------------------------- |
+| `location.update` | `{ lat, lng, accuracy, timestamp }` | Push location update, triggers feed refresh |
+| `feed.refresh`    | `{}`                                | Force manual feed refresh                   |
+
+### Server Notifications
+
+| Method        | Params                       | Description            |
+| ------------- | ---------------------------- | ---------------------- |
+| `feed.update` | `{ context, items, errors }` | Feed state changed     |
+| `error`       | `{ code, message, data? }`   | Source or system error |
+
+### Error Handling
+
+- Source failures during refresh are reported via `error` notification
+- Format: `{ "jsonrpc": "2.0", "method": "error", "params": { "code": -32000, "message": "...", "data": { "sourceId": "weather" } } }`
+
+## Acceptance Criteria
+
+1. **Auth Flow**
+   - [ ] User can sign up with email/password via `POST /api/auth/sign-up`
+   - [ ] User can sign in via `POST /api/auth/sign-in` and receive session token
+   - [ ] Invalid credentials return 401
+
+2. **WebSocket Connection**
+   - [ ] `GET /ws` with valid `Authorization` header upgrades to WebSocket
+   - [ ] `GET /ws` without valid token returns 401 (no upgrade)
+   - [ ] On successful connect, client receives `feed.update` notification with current state
+   - [ ] Multiple connections from same user all receive updates
+
+3. **FeedEngine Lifecycle**
+   - [ ] First connection for a user creates FeedEngine with default sources
+   - [ ] Subsequent connections reuse the same FeedEngine
+   - [ ] FeedEngine is destroyed after 30 minutes of inactivity
+   - [ ] Activity (any WebSocket message) resets the TTL
+
+4. **JSON-RPC Methods**
+   - [ ] `location.update` updates LocationSource and triggers feed refresh
+   - [ ] `feed.refresh` triggers manual refresh
+   - [ ] Both return `{ "ok": true }` on success
+   - [ ] Invalid method returns JSON-RPC error
+
+5. **Feed Updates**
+   - [ ] FeedEngine subscription pushes updates to all user's WebSocket connections
+   - [ ] Updates include `context`, `items`, and `errors`
+
+## Implementation Approach
+
+### Phase 1: Project Setup
+
+1. Create `apps/aris-backend` with Hono
+2. Configure TypeScript, add dependencies (hono, better-auth, postgres driver)
+3. Set up database connection and BetterAuth
+
+### Phase 2: Authentication
+
+4. Configure BetterAuth with email/password provider
+5. Mount BetterAuth routes at `/api/auth/*`
+6. Create session validation helper for extracting user from token
+
+### Phase 3: FeedEngine Manager
+
+7. Create `FeedEngineManager` class:
+   - `getOrCreate(userId): FeedEngine` - returns cached or creates new
+   - `touch(userId)` - resets TTL
+   - `destroy(userId)` - manual cleanup
+   - Internal TTL cleanup loop
+8. Factory function to create FeedEngine with default sources
+
+### Phase 4: WebSocket Handler
+
+9. Create WebSocket upgrade endpoint at `/ws`
+10. Validate `Authorization` header before upgrade
+11. On connect: register connection, send initial feed state
+12. On disconnect: unregister connection
+
+### Phase 5: JSON-RPC Handler
+
+13. Create JSON-RPC message parser and dispatcher
+14. Implement `location.update` method
+15. Implement `feed.refresh` method
+16. Wire FeedEngine subscription to broadcast `feed.update` to all user connections
+
+### Phase 6: Connection Manager
+
+17. Create `ConnectionManager` to track WebSocket connections per user
+18. Broadcast helper to send to all connections for a user
+
+### Phase 7: Integration & Testing
+
+19. Integration test: auth → connect → location update → receive feed
+20. Test multiple connections receive same updates
+21. Test TTL cleanup
+
+## Package Structure
+
+```
+apps/aris-backend/
+├── package.json
+├── src/
+│   ├── index.ts              # Entry point, Hono app
+│   ├── auth.ts               # BetterAuth configuration
+│   ├── db.ts                 # Database connection
+│   ├── ws/
+│   │   ├── handler.ts        # WebSocket upgrade & message handling
+│   │   ├── jsonrpc.ts        # JSON-RPC parser & types
+│   │   └── methods.ts        # Method implementations
+│   ├── feed/
+│   │   ├── manager.ts        # FeedEngineManager (TTL cache)
+│   │   ├── factory.ts        # Creates FeedEngine with default sources
+│   │   └── connections.ts    # ConnectionManager (user → WebSocket[])
+│   └── types.ts              # Shared types
+```
+
+## Dependencies
+
+```json
+{
+	"dependencies": {
+		"hono": "^4",
+		"better-auth": "^1",
+		"postgres": "^3",
+		"@aris/core": "workspace:*",
+		"@aris/source-location": "workspace:*",
+		"@aris/source-weatherkit": "workspace:*",
+		"@aris/data-source-tfl": "workspace:*"
+	}
+}
+```
+
+## Open Questions (Deferred)
+
+- User source configuration storage (database schema)
+- Rate limiting on WebSocket methods
+- Reconnection handling (client-side concern)
+- Horizontal scaling (would need Redis for shared state)

packages/aris-core/README.md

@@ -0,0 +1,186 @@
+# @aris/core
+
+Core orchestration layer for ARIS feed reconciliation.
+
+## Overview
+
+```mermaid
+flowchart TB
+    subgraph Sources["Feed Sources (Graph)"]
+        LS[Location Source]
+        WS[Weather Source]
+        TS[TFL Source]
+        CS[Calendar Source]
+    end
+
+    LS --> WS
+    LS --> TS
+
+    subgraph Controller["FeedController"]
+        direction TB
+        C1[Holds context]
+        C2[Manages source graph]
+        C3[Reconciles on update]
+        C4[Notifies subscribers]
+    end
+
+    Sources --> Controller
+    Controller --> Sub[Subscribers]
+```
+
+## Concepts
+
+### FeedSource
+
+A unified interface for sources that provide context and/or feed items. Sources form a dependency graph.
+
+```ts
+interface FeedSource<TItem extends FeedItem = FeedItem> {
+	readonly id: string
+	readonly dependencies?: readonly string[]
+
+	// Context production (optional)
+	onContextUpdate?(
+		callback: (update: Partial<Context>) => void,
+		getContext: () => Context,
+	): () => void
+	fetchContext?(context: Context): Promise<Partial<Context>>
+
+	// Feed item production (optional)
+	onItemsUpdate?(callback: (items: TItem[]) => void, getContext: () => Context): () => void
+	fetchItems?(context: Context): Promise<TItem[]>
+}
+```
+
+A source may:
+
+- Provide context for other sources (implement `fetchContext`/`onContextUpdate`)
+- Produce feed items (implement `fetchItems`/`onItemsUpdate`)
+- Both
+
+### Context Keys
+
+Each package exports typed context keys for type-safe access:
+
+```ts
+import { contextKey, type ContextKey } from "@aris/core"
+
+interface Location {
+	lat: number
+	lng: number
+}
+
+export const LocationKey: ContextKey<Location> = contextKey("location")
+```
+
+## Usage
+
+### Define a Context-Only Source
+
+```ts
+import type { FeedSource } from "@aris/core"
+
+const locationSource: FeedSource = {
+	id: "location",
+
+	onContextUpdate(callback, _getContext) {
+		const watchId = navigator.geolocation.watchPosition((pos) => {
+			callback({
+				[LocationKey]: { lat: pos.coords.latitude, lng: pos.coords.longitude },
+			})
+		})
+		return () => navigator.geolocation.clearWatch(watchId)
+	},
+
+	async fetchContext() {
+		const pos = await getCurrentPosition()
+		return {
+			[LocationKey]: { lat: pos.coords.latitude, lng: pos.coords.longitude },
+		}
+	},
+}
+```
+
+### Define a Source with Dependencies
+
+```ts
+import type { FeedSource, FeedItem } from "@aris/core"
+import { contextValue } from "@aris/core"
+
+type WeatherItem = FeedItem<"weather", { temp: number; condition: string }>
+
+const weatherSource: FeedSource<WeatherItem> = {
+	id: "weather",
+	dependencies: ["location"],
+
+	async fetchContext(context) {
+		const location = contextValue(context, LocationKey)
+		if (!location) return {}
+
+		const weather = await fetchWeatherApi(location)
+		return { [WeatherKey]: weather }
+	},
+
+	async fetchItems(context) {
+		const weather = contextValue(context, WeatherKey)
+		if (!weather) return []
+
+		return [
+			{
+				id: `weather-${Date.now()}`,
+				type: "weather",
+				priority: 0.5,
+				timestamp: new Date(),
+				data: { temp: weather.temp, condition: weather.condition },
+			},
+		]
+	},
+}
+```
+
+### Graph Behavior
+
+The source graph:
+
+1. Validates all dependencies exist
+2. Detects circular dependencies
+3. Topologically sorts sources
+
+On refresh:
+
+1. `fetchContext` runs in dependency order
+2. `fetchItems` runs on all sources
+3. Combined items returned to subscribers
+
+On reactive update:
+
+1. Source pushes context update via `onContextUpdate` callback
+2. Dependent sources re-run `fetchContext`
+3. Affected sources re-run `fetchItems`
+4. Subscribers notified
+
+## API
+
+### Context
+
+| Export                       | Description                             |
+| ---------------------------- | --------------------------------------- |
+| `ContextKey<T>`              | Branded type for type-safe context keys |
+| `contextKey<T>(key)`         | Creates a typed context key             |
+| `contextValue(context, key)` | Type-safe context value accessor        |
+| `Context`                    | Time + arbitrary key-value bag          |
+
+### Feed
+
+| Export                   | Description              |
+| ------------------------ | ------------------------ |
+| `FeedSource<TItem>`      | Unified source interface |
+| `FeedItem<TType, TData>` | Single item in the feed  |
+
+### Legacy (deprecated)
+
+| Export                       | Description              |
+| ---------------------------- | ------------------------ |
+| `DataSource<TItem, TConfig>` | Use `FeedSource` instead |
+| `ContextProvider<T>`         | Use `FeedSource` instead |
+| `ContextBridge`              | Use source graph instead |

packages/aris-core/context.ts

@@ -1,10 +0,0 @@
-export interface Location {
-	lat: number
-	lng: number
-	accuracy: number
-}
-
-export interface Context {
-	time: Date
-	location?: Location
-}

packages/aris-core/data-source.ts

@@ -1,7 +0,0 @@
-import type { Context } from "./context"
-import type { FeedItem } from "./feed"
-
-export interface DataSource<TItem extends FeedItem = FeedItem, TConfig = unknown> {
-	readonly type: TItem["type"]
-	query(context: Context, config: TConfig): Promise<TItem[]>
-}

packages/aris-core/feed.ts

@@ -1,10 +0,0 @@
-export interface FeedItem<
-	TType extends string = string,
-	TData extends Record<string, unknown> = Record<string, unknown>,
-> {
-	id: string
-	type: TType
-	priority: number
-	timestamp: Date
-	data: TData
-}

packages/aris-core/index.ts

@@ -1,5 +0,0 @@
-export type { Context, Location } from "./context"
-export type { FeedItem } from "./feed"
-export type { DataSource } from "./data-source"
-export type { ReconcilerConfig, ReconcileResult, SourceError } from "./reconciler"
-export { Reconciler } from "./reconciler"

packages/aris-core/package.json

@@ -2,8 +2,8 @@
 	"name": "@aris/core",
 	"version": "0.0.0",
 	"type": "module",
-	"main": "index.ts",
-	"types": "index.ts",
+	"main": "src/index.ts",
+	"types": "src/index.ts",
 	"scripts": {
 		"test": "bun test ."
 	}

packages/aris-core/reconciler.test.ts

@@ -1,240 +0,0 @@
-import { describe, expect, test } from "bun:test"
-
-import type { Context } from "./context"
-import type { DataSource } from "./data-source"
-import type { FeedItem } from "./feed"
-
-import { Reconciler } from "./reconciler"
-
-type WeatherData = { temp: number }
-type WeatherItem = FeedItem<"weather", WeatherData>
-
-type CalendarData = { title: string }
-type CalendarItem = FeedItem<"calendar", CalendarData>
-
-const createMockContext = (): Context => ({
-	time: new Date("2026-01-15T12:00:00Z"),
-})
-
-const createWeatherSource = (items: WeatherItem[], delay = 0): DataSource<WeatherItem> => ({
-	type: "weather",
-	async query() {
-		if (delay > 0) {
-			await new Promise((resolve) => setTimeout(resolve, delay))
-		}
-		return items
-	},
-})
-
-const createCalendarSource = (items: CalendarItem[]): DataSource<CalendarItem> => ({
-	type: "calendar",
-	async query() {
-		return items
-	},
-})
-
-const createFailingSource = (type: string, error: Error): DataSource<FeedItem> => ({
-	type,
-	async query() {
-		throw error
-	},
-})
-
-describe("Reconciler", () => {
-	test("returns empty result when no sources registered", async () => {
-		const reconciler = new Reconciler()
-		const result = await reconciler.reconcile(createMockContext())
-
-		expect(result.items).toEqual([])
-		expect(result.errors).toEqual([])
-	})
-
-	test("collects items from single source", async () => {
-		const items: WeatherItem[] = [
-			{
-				id: "weather-1",
-				type: "weather",
-				priority: 0.5,
-				timestamp: new Date(),
-				data: { temp: 20 },
-			},
-		]
-
-		const reconciler = new Reconciler().register(createWeatherSource(items))
-		const result = await reconciler.reconcile(createMockContext())
-
-		expect(result.items).toEqual(items)
-		expect(result.errors).toEqual([])
-	})
-
-	test("collects items from multiple sources", async () => {
-		const weatherItems: WeatherItem[] = [
-			{
-				id: "weather-1",
-				type: "weather",
-				priority: 0.5,
-				timestamp: new Date(),
-				data: { temp: 20 },
-			},
-		]
-
-		const calendarItems: CalendarItem[] = [
-			{
-				id: "calendar-1",
-				type: "calendar",
-				priority: 0.8,
-				timestamp: new Date(),
-				data: { title: "Meeting" },
-			},
-		]
-
-		const reconciler = new Reconciler()
-			.register(createWeatherSource(weatherItems))
-			.register(createCalendarSource(calendarItems))
-
-		const result = await reconciler.reconcile(createMockContext())
-
-		expect(result.items).toHaveLength(2)
-		expect(result.errors).toEqual([])
-	})
-
-	test("sorts items by priority descending", async () => {
-		const weatherItems: WeatherItem[] = [
-			{
-				id: "weather-1",
-				type: "weather",
-				priority: 0.2,
-				timestamp: new Date(),
-				data: { temp: 20 },
-			},
-		]
-
-		const calendarItems: CalendarItem[] = [
-			{
-				id: "calendar-1",
-				type: "calendar",
-				priority: 0.9,
-				timestamp: new Date(),
-				data: { title: "Meeting" },
-			},
-		]
-
-		const reconciler = new Reconciler()
-			.register(createWeatherSource(weatherItems))
-			.register(createCalendarSource(calendarItems))
-
-		const result = await reconciler.reconcile(createMockContext())
-
-		expect(result.items[0]?.id).toBe("calendar-1")
-		expect(result.items[1]?.id).toBe("weather-1")
-	})
-
-	test("captures errors from failing sources", async () => {
-		const error = new Error("Source failed")
-
-		const reconciler = new Reconciler().register(createFailingSource("failing", error))
-
-		const result = await reconciler.reconcile(createMockContext())
-
-		expect(result.items).toEqual([])
-		expect(result.errors).toHaveLength(1)
-		expect(result.errors[0]?.sourceType).toBe("failing")
-		expect(result.errors[0]?.error.message).toBe("Source failed")
-	})
-
-	test("returns partial results when some sources fail", async () => {
-		const items: WeatherItem[] = [
-			{
-				id: "weather-1",
-				type: "weather",
-				priority: 0.5,
-				timestamp: new Date(),
-				data: { temp: 20 },
-			},
-		]
-
-		const reconciler = new Reconciler()
-			.register(createWeatherSource(items))
-			.register(createFailingSource("failing", new Error("Failed")))
-
-		const result = await reconciler.reconcile(createMockContext())
-
-		expect(result.items).toHaveLength(1)
-		expect(result.errors).toHaveLength(1)
-	})
-
-	test("times out slow sources", async () => {
-		const items: WeatherItem[] = [
-			{
-				id: "weather-1",
-				type: "weather",
-				priority: 0.5,
-				timestamp: new Date(),
-				data: { temp: 20 },
-			},
-		]
-
-		const reconciler = new Reconciler({ timeout: 50 }).register(createWeatherSource(items, 100))
-
-		const result = await reconciler.reconcile(createMockContext())
-
-		expect(result.items).toEqual([])
-		expect(result.errors).toHaveLength(1)
-		expect(result.errors[0]?.sourceType).toBe("weather")
-		expect(result.errors[0]?.error.message).toContain("timed out")
-	})
-
-	test("unregister removes source", async () => {
-		const items: WeatherItem[] = [
-			{
-				id: "weather-1",
-				type: "weather",
-				priority: 0.5,
-				timestamp: new Date(),
-				data: { temp: 20 },
-			},
-		]
-
-		const reconciler = new Reconciler().register(createWeatherSource(items)).unregister("weather")
-
-		const result = await reconciler.reconcile(createMockContext())
-		expect(result.items).toEqual([])
-	})
-
-	test("infers discriminated union type from chained registers", async () => {
-		const weatherItems: WeatherItem[] = [
-			{
-				id: "weather-1",
-				type: "weather",
-				priority: 0.5,
-				timestamp: new Date(),
-				data: { temp: 20 },
-			},
-		]
-
-		const calendarItems: CalendarItem[] = [
-			{
-				id: "calendar-1",
-				type: "calendar",
-				priority: 0.8,
-				timestamp: new Date(),
-				data: { title: "Meeting" },
-			},
-		]
-
-		const reconciler = new Reconciler()
-			.register(createWeatherSource(weatherItems))
-			.register(createCalendarSource(calendarItems))
-
-		const { items } = await reconciler.reconcile(createMockContext())
-
-		// Type narrowing should work
-		for (const item of items) {
-			if (item.type === "weather") {
-				expect(typeof item.data.temp).toBe("number")
-			} else if (item.type === "calendar") {
-				expect(typeof item.data.title).toBe("string")
-			}
-		}
-	})
-})

packages/aris-core/src/context-bridge.ts

@@ -0,0 +1,102 @@
+import type { Context } from "./context"
+import type { ContextProvider } from "./context-provider"
+
+interface ContextUpdatable {
+	pushContextUpdate(update: Partial<Context>): void
+}
+
+export interface ProviderError {
+	key: string
+	error: Error
+}
+
+export interface RefreshResult {
+	errors: ProviderError[]
+}
+
+/**
+ * Bridges context providers to a feed controller.
+ *
+ * Subscribes to provider updates and forwards them to the controller.
+ * Supports manual refresh to gather current values from all providers.
+ *
+ * @example
+ * ```ts
+ * const controller = new FeedController()
+ *   .addDataSource(new WeatherDataSource())
+ *   .addDataSource(new TflDataSource())
+ *
+ * const bridge = new ContextBridge(controller)
+ *   .addProvider(new LocationProvider())
+ *   .addProvider(new MusicProvider())
+ *
+ * // Manual refresh gathers from all providers
+ * await bridge.refresh()
+ *
+ * // Cleanup
+ * bridge.stop()
+ * controller.stop()
+ * ```
+ */
+export class ContextBridge {
+	private controller: ContextUpdatable
+	private providers = new Map<string, ContextProvider>()
+	private cleanups: Array<() => void> = []
+
+	constructor(controller: ContextUpdatable) {
+		this.controller = controller
+	}
+
+	/**
+	 * Registers a context provider. Immediately subscribes to updates.
+	 */
+	addProvider<T>(provider: ContextProvider<T>): this {
+		this.providers.set(provider.key, provider as ContextProvider)
+
+		const cleanup = provider.onUpdate((value) => {
+			this.controller.pushContextUpdate({ [provider.key]: value })
+		})
+		this.cleanups.push(cleanup)
+
+		return this
+	}
+
+	/**
+	 * Gathers current values from all providers and pushes to controller.
+	 * Use for manual refresh when user pulls to refresh.
+	 * Returns errors from providers that failed to fetch.
+	 */
+	async refresh(): Promise<RefreshResult> {
+		const updates: Partial<Context> = {}
+		const errors: ProviderError[] = []
+
+		const entries = Array.from(this.providers.entries())
+		const results = await Promise.allSettled(
+			entries.map(([_, provider]) => provider.fetchCurrentValue()),
+		)
+
+		entries.forEach(([key], i) => {
+			const result = results[i]
+			if (result?.status === "fulfilled") {
+				updates[key] = result.value
+			} else if (result?.status === "rejected") {
+				errors.push({
+					key,
+					error: result.reason instanceof Error ? result.reason : new Error(String(result.reason)),
+				})
+			}
+		})
+
+		this.controller.pushContextUpdate(updates)
+
+		return { errors }
+	}
+
+	/**
+	 * Unsubscribes from all providers.
+	 */
+	stop(): void {
+		this.cleanups.forEach((cleanup) => cleanup())
+		this.cleanups = []
+	}
+}

packages/aris-core/src/context-provider.ts

@@ -0,0 +1,35 @@
+/**
+ * Provides context values reactively and on-demand.
+ *
+ * Implementations push updates when values change (reactive) and
+ * return current values when requested (for manual refresh).
+ *
+ * @example
+ * ```ts
+ * class LocationProvider implements ContextProvider<Location> {
+ *   readonly key = LocationKey
+ *
+ *   onUpdate(callback: (value: Location) => void): () => void {
+ *     const watchId = navigator.geolocation.watchPosition(pos => {
+ *       callback({ lat: pos.coords.latitude, lng: pos.coords.longitude, accuracy: pos.coords.accuracy })
+ *     })
+ *     return () => navigator.geolocation.clearWatch(watchId)
+ *   }
+ *
+ *   async fetchCurrentValue(): Promise<Location> {
+ *     const pos = await getCurrentPosition()
+ *     return { lat: pos.coords.latitude, lng: pos.coords.longitude, accuracy: pos.coords.accuracy }
+ *   }
+ * }
+ * ```
+ */
+export interface ContextProvider<T = unknown> {
+	/** The context key this provider populates */
+	readonly key: string
+
+	/** Subscribe to value changes. Returns cleanup function. */
+	onUpdate(callback: (value: T) => void): () => void
+
+	/** Fetch current value on-demand (used for manual refresh). */
+	fetchCurrentValue(): Promise<T>
+}

packages/aris-core/src/context.ts

@@ -0,0 +1,46 @@
+/**
+ * Branded type for type-safe context keys.
+ *
+ * Each package defines its own keys with associated value types:
+ * ```ts
+ * const LocationKey: ContextKey<Location> = contextKey("location")
+ * ```
+ */
+export type ContextKey<T> = string & { __contextValue?: T }
+
+/**
+ * Creates a typed context key.
+ *
+ * @example
+ * ```ts
+ * interface Location { lat: number; lng: number; accuracy: number }
+ * const LocationKey: ContextKey<Location> = contextKey("location")
+ * ```
+ */
+export function contextKey<T>(key: string): ContextKey<T> {
+	return key as ContextKey<T>
+}
+
+/**
+ * Type-safe accessor for context values.
+ *
+ * @example
+ * ```ts
+ * const location = contextValue(context, LocationKey)
+ * if (location) {
+ *   console.log(location.lat, location.lng)
+ * }
+ * ```
+ */
+export function contextValue<T>(context: Context, key: ContextKey<T>): T | undefined {
+	return context[key] as T | undefined
+}
+
+/**
+ * Arbitrary key-value bag representing the current state.
+ * Always includes `time`. Other keys are added by context providers.
+ */
+export interface Context {
+	time: Date
+	[key: string]: unknown
+}

packages/aris-core/src/data-source.ts

@@ -0,0 +1,35 @@
+import type { Context } from "./context"
+import type { FeedItem } from "./feed"
+
+/**
+ * Produces feed items from an external source.
+ *
+ * @example
+ * ```ts
+ * type WeatherItem = FeedItem<"weather", { temp: number }>
+ *
+ * class WeatherDataSource implements DataSource<WeatherItem> {
+ *   readonly type = "weather"
+ *
+ *   async query(context: Context): Promise<WeatherItem[]> {
+ *     const location = contextValue(context, LocationKey)
+ *     if (!location) return []
+ *     const data = await fetchWeather(location)
+ *     return [{
+ *       id: `weather-${Date.now()}`,
+ *       type: this.type,
+ *       priority: 0.5,
+ *       timestamp: context.time,
+ *       data: { temp: data.temperature },
+ *     }]
+ *   }
+ * }
+ * ```
+ */
+export interface DataSource<TItem extends FeedItem = FeedItem, TConfig = unknown> {
+	/** Unique identifier for this source type */
+	readonly type: TItem["type"]
+
+	/** Queries the source and returns feed items */
+	query(context: Context, config: TConfig): Promise<TItem[]>
+}

packages/aris-core/src/feed-controller.ts

@@ -0,0 +1,161 @@
+import type { Context } from "./context"
+import type { DataSource } from "./data-source"
+import type { FeedItem } from "./feed"
+import type { ReconcileResult } from "./reconciler"
+
+import { Reconciler } from "./reconciler"
+
+export interface FeedControllerConfig {
+	/** Timeout for each data source query in milliseconds */
+	timeout?: number
+	/** Debounce window for batching context updates (default: 100ms) */
+	debounceMs?: number
+	/** Initial context state */
+	initialContext?: Context
+}
+
+export type FeedSubscriber<TItems extends FeedItem> = (result: ReconcileResult<TItems>) => void
+
+interface RegisteredSource {
+	source: DataSource<FeedItem, unknown>
+	config: unknown
+}
+
+const DEFAULT_DEBOUNCE_MS = 100
+
+/**
+ * Orchestrates feed reconciliation in response to context updates.
+ *
+ * Holds context state, debounces updates, queries data sources, and
+ * notifies subscribers. Each user should have their own instance.
+ *
+ * @example
+ * ```ts
+ * const controller = new FeedController({ debounceMs: 100 })
+ *   .addDataSource(new WeatherDataSource())
+ *   .addDataSource(new TflDataSource())
+ *
+ * controller.subscribe((result) => {
+ *   console.log(result.items)
+ * })
+ *
+ * // Context update triggers debounced reconcile
+ * controller.pushContextUpdate({ [LocationKey]: location })
+ *
+ * // Direct reconcile (no debounce)
+ * const result = await controller.reconcile()
+ *
+ * // Cleanup
+ * controller.stop()
+ * ```
+ */
+export class FeedController<TItems extends FeedItem = never> {
+	private sources = new Map<string, RegisteredSource>()
+	private subscribers = new Set<FeedSubscriber<TItems>>()
+	private context: Context
+	private debounceMs: number
+	private timeout: number | undefined
+	private pendingTimeout: ReturnType<typeof setTimeout> | null = null
+	private stopped = false
+
+	constructor(config?: FeedControllerConfig) {
+		this.context = config?.initialContext ?? { time: new Date() }
+		this.debounceMs = config?.debounceMs ?? DEFAULT_DEBOUNCE_MS
+		this.timeout = config?.timeout
+	}
+
+	/** Registers a data source. */
+	addDataSource<TItem extends FeedItem, TConfig>(
+		source: DataSource<TItem, TConfig>,
+		config?: TConfig,
+	): FeedController<TItems | TItem> {
+		this.sources.set(source.type, {
+			source: source as DataSource<FeedItem, unknown>,
+			config,
+		})
+		return this as FeedController<TItems | TItem>
+	}
+
+	/** Removes a data source by type. */
+	removeDataSource<T extends TItems["type"]>(
+		sourceType: T,
+	): FeedController<Exclude<TItems, { type: T }>> {
+		this.sources.delete(sourceType)
+		return this as unknown as FeedController<Exclude<TItems, { type: T }>>
+	}
+
+	/** Stops the controller and cancels pending reconciles. */
+	stop(): void {
+		this.stopped = true
+
+		if (this.pendingTimeout) {
+			clearTimeout(this.pendingTimeout)
+			this.pendingTimeout = null
+		}
+	}
+
+	/** Merges update into context and schedules a debounced reconcile. */
+	pushContextUpdate(update: Partial<Context>): void {
+		this.context = { ...this.context, ...update, time: new Date() }
+		this.scheduleReconcile()
+	}
+
+	/** Subscribes to feed updates. Returns unsubscribe function. */
+	subscribe(callback: FeedSubscriber<TItems>): () => void {
+		this.subscribers.add(callback)
+
+		return () => {
+			this.subscribers.delete(callback)
+		}
+	}
+
+	/** Immediately reconciles with current or provided context. */
+	async reconcile(context?: Context): Promise<ReconcileResult<TItems>> {
+		const ctx = context ?? this.context
+		const reconciler = this.createReconciler()
+		return reconciler.reconcile(ctx)
+	}
+
+	/** Returns current context. */
+	getContext(): Context {
+		return this.context
+	}
+
+	private scheduleReconcile(): void {
+		if (this.pendingTimeout) return
+
+		this.pendingTimeout = setTimeout(() => {
+			this.flushPending()
+		}, this.debounceMs)
+	}
+
+	private async flushPending(): Promise<void> {
+		this.pendingTimeout = null
+
+		if (this.stopped) return
+		if (this.sources.size === 0) return
+
+		const reconciler = this.createReconciler()
+		const result = await reconciler.reconcile(this.context)
+
+		this.notifySubscribers(result)
+	}
+
+	private createReconciler(): Reconciler<TItems> {
+		const reconciler = new Reconciler<TItems>({ timeout: this.timeout })
+		Array.from(this.sources.values()).forEach(({ source, config }) => {
+			reconciler.register(source, config)
+		})
+		return reconciler as Reconciler<TItems>
+	}
+
+	private notifySubscribers(result: ReconcileResult<TItems>): void {
+		this.subscribers.forEach((callback) => {
+			try {
+				callback(result)
+			} catch {
+				// Subscriber errors shouldn't break other subscribers
+			}
+		})
+	}
+}

packages/aris-core/src/feed-engine.test.ts

@@ -0,0 +1,501 @@
+import { describe, expect, test } from "bun:test"
+
+import type { Context, ContextKey, FeedItem, FeedSource } from "./index"
+
+import { FeedEngine } from "./feed-engine"
+import { contextKey, contextValue } from "./index"
+
+// =============================================================================
+// CONTEXT KEYS
+// =============================================================================
+
+interface Location {
+	lat: number
+	lng: number
+}
+
+interface Weather {
+	temperature: number
+	condition: string
+}
+
+const LocationKey: ContextKey<Location> = contextKey("location")
+const WeatherKey: ContextKey<Weather> = contextKey("weather")
+
+// =============================================================================
+// FEED ITEMS
+// =============================================================================
+
+type WeatherFeedItem = FeedItem<"weather", { temperature: number; condition: string }>
+type AlertFeedItem = FeedItem<"alert", { message: string }>
+
+// =============================================================================
+// TEST HELPERS
+// =============================================================================
+
+interface SimulatedLocationSource extends FeedSource {
+	simulateUpdate(location: Location): void
+}
+
+function createLocationSource(): SimulatedLocationSource {
+	let callback: ((update: Partial<Context>) => void) | null = null
+	let currentLocation: Location = { lat: 0, lng: 0 }
+
+	return {
+		id: "location",
+
+		onContextUpdate(cb) {
+			callback = cb
+			return () => {
+				callback = null
+			}
+		},
+
+		async fetchContext() {
+			return { [LocationKey]: currentLocation }
+		},
+
+		simulateUpdate(location: Location) {
+			currentLocation = location
+			callback?.({ [LocationKey]: location })
+		},
+	}
+}
+
+function createWeatherSource(
+	fetchWeather: (location: Location) => Promise<Weather> = async () => ({
+		temperature: 20,
+		condition: "sunny",
+	}),
+): FeedSource<WeatherFeedItem> {
+	return {
+		id: "weather",
+		dependencies: ["location"],
+
+		async fetchContext(context) {
+			const location = contextValue(context, LocationKey)
+			if (!location) return null
+
+			const weather = await fetchWeather(location)
+			return { [WeatherKey]: weather }
+		},
+
+		async fetchItems(context) {
+			const weather = contextValue(context, WeatherKey)
+			if (!weather) return []
+
+			return [
+				{
+					id: `weather-${Date.now()}`,
+					type: "weather",
+					priority: 0.5,
+					timestamp: new Date(),
+					data: {
+						temperature: weather.temperature,
+						condition: weather.condition,
+					},
+				},
+			]
+		},
+	}
+}
+
+function createAlertSource(): FeedSource<AlertFeedItem> {
+	return {
+		id: "alert",
+		dependencies: ["weather"],
+
+		async fetchContext() {
+			return null
+		},
+
+		async fetchItems(context) {
+			const weather = contextValue(context, WeatherKey)
+			if (!weather) return []
+
+			if (weather.condition === "storm") {
+				return [
+					{
+						id: "alert-storm",
+						type: "alert",
+						priority: 1.0,
+						timestamp: new Date(),
+						data: { message: "Storm warning!" },
+					},
+				]
+			}
+
+			return []
+		},
+	}
+}
+
+// =============================================================================
+// TESTS
+// =============================================================================
+
+describe("FeedEngine", () => {
+	describe("registration", () => {
+		test("registers sources", () => {
+			const engine = new FeedEngine()
+			const location = createLocationSource()
+
+			engine.register(location)
+
+			// Can refresh without error
+			expect(engine.refresh()).resolves.toBeDefined()
+		})
+
+		test("unregisters sources", async () => {
+			const engine = new FeedEngine()
+			const location = createLocationSource()
+
+			engine.register(location)
+			engine.unregister("location")
+
+			const result = await engine.refresh()
+			expect(result.items).toHaveLength(0)
+		})
+
+		test("allows chained registration", () => {
+			const engine = new FeedEngine()
+				.register(createLocationSource())
+				.register(createWeatherSource())
+				.register(createAlertSource())
+
+			expect(engine.refresh()).resolves.toBeDefined()
+		})
+	})
+
+	describe("graph validation", () => {
+		test("throws on missing dependency", () => {
+			const engine = new FeedEngine()
+			const orphan: FeedSource = {
+				id: "orphan",
+				dependencies: ["nonexistent"],
+				async fetchContext() {
+					return null
+				},
+			}
+
+			engine.register(orphan)
+
+			expect(engine.refresh()).rejects.toThrow(
+				'Source "orphan" depends on "nonexistent" which is not registered',
+			)
+		})
+
+		test("throws on circular dependency", () => {
+			const engine = new FeedEngine()
+			const a: FeedSource = {
+				id: "a",
+				dependencies: ["b"],
+				async fetchContext() {
+					return null
+				},
+			}
+			const b: FeedSource = {
+				id: "b",
+				dependencies: ["a"],
+				async fetchContext() {
+					return null
+				},
+			}
+
+			engine.register(a).register(b)
+
+			expect(engine.refresh()).rejects.toThrow("Circular dependency detected: a → b → a")
+		})
+
+		test("throws on longer cycles", () => {
+			const engine = new FeedEngine()
+			const a: FeedSource = {
+				id: "a",
+				dependencies: ["c"],
+				async fetchContext() {
+					return null
+				},
+			}
+			const b: FeedSource = {
+				id: "b",
+				dependencies: ["a"],
+				async fetchContext() {
+					return null
+				},
+			}
+			const c: FeedSource = {
+				id: "c",
+				dependencies: ["b"],
+				async fetchContext() {
+					return null
+				},
+			}
+
+			engine.register(a).register(b).register(c)
+
+			expect(engine.refresh()).rejects.toThrow("Circular dependency detected")
+		})
+	})
+
+	describe("refresh", () => {
+		test("runs fetchContext in dependency order", async () => {
+			const order: string[] = []
+
+			const location: FeedSource = {
+				id: "location",
+				async fetchContext() {
+					order.push("location")
+					return { [LocationKey]: { lat: 51.5, lng: -0.1 } }
+				},
+			}
+
+			const weather: FeedSource = {
+				id: "weather",
+				dependencies: ["location"],
+				async fetchContext(ctx) {
+					order.push("weather")
+					const loc = contextValue(ctx, LocationKey)
+					expect(loc).toBeDefined()
+					return { [WeatherKey]: { temperature: 20, condition: "sunny" } }
+				},
+			}
+
+			const engine = new FeedEngine().register(weather).register(location)
+
+			await engine.refresh()
+
+			expect(order).toEqual(["location", "weather"])
+		})
+
+		test("accumulates context across sources", async () => {
+			const location = createLocationSource()
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			const weather = createWeatherSource()
+
+			const engine = new FeedEngine().register(location).register(weather)
+
+			const { context } = await engine.refresh()
+
+			expect(contextValue(context, LocationKey)).toEqual({ lat: 51.5, lng: -0.1 })
+			expect(contextValue(context, WeatherKey)).toEqual({ temperature: 20, condition: "sunny" })
+		})
+
+		test("collects items from all sources", async () => {
+			const location = createLocationSource()
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			const weather = createWeatherSource()
+
+			const engine = new FeedEngine().register(location).register(weather)
+
+			const { items } = await engine.refresh()
+
+			expect(items).toHaveLength(1)
+			expect(items[0]!.type).toBe("weather")
+		})
+
+		test("sorts items by priority descending", async () => {
+			const location = createLocationSource()
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			const weather = createWeatherSource(async () => ({
+				temperature: 15,
+				condition: "storm",
+			}))
+
+			const alert = createAlertSource()
+
+			const engine = new FeedEngine().register(location).register(weather).register(alert)
+
+			const { items } = await engine.refresh()
+
+			expect(items).toHaveLength(2)
+			expect(items[0]!.type).toBe("alert") // priority 1.0
+			expect(items[1]!.type).toBe("weather") // priority 0.5
+		})
+
+		test("handles missing upstream context gracefully", async () => {
+			const location: FeedSource = {
+				id: "location",
+				async fetchContext() {
+					return null // No location available
+				},
+			}
+
+			const weather = createWeatherSource()
+
+			const engine = new FeedEngine().register(location).register(weather)
+
+			const { context, items } = await engine.refresh()
+
+			expect(contextValue(context, WeatherKey)).toBeUndefined()
+			expect(items).toHaveLength(0)
+		})
+
+		test("captures errors from fetchContext", async () => {
+			const failing: FeedSource = {
+				id: "failing",
+				async fetchContext() {
+					throw new Error("Context fetch failed")
+				},
+			}
+
+			const engine = new FeedEngine().register(failing)
+
+			const { errors } = await engine.refresh()
+
+			expect(errors).toHaveLength(1)
+			expect(errors[0]!.sourceId).toBe("failing")
+			expect(errors[0]!.error.message).toBe("Context fetch failed")
+		})
+
+		test("captures errors from fetchItems", async () => {
+			const failing: FeedSource = {
+				id: "failing",
+				async fetchContext() {
+					return null
+				},
+				async fetchItems() {
+					throw new Error("Items fetch failed")
+				},
+			}
+
+			const engine = new FeedEngine().register(failing)
+
+			const { errors } = await engine.refresh()
+
+			expect(errors).toHaveLength(1)
+			expect(errors[0]!.sourceId).toBe("failing")
+			expect(errors[0]!.error.message).toBe("Items fetch failed")
+		})
+
+		test("continues after source error", async () => {
+			const failing: FeedSource = {
+				id: "failing",
+				async fetchContext() {
+					throw new Error("Failed")
+				},
+			}
+
+			const working: FeedSource = {
+				id: "working",
+				async fetchContext() {
+					return null
+				},
+				async fetchItems() {
+					return [
+						{
+							id: "item-1",
+							type: "test",
+							priority: 0.5,
+							timestamp: new Date(),
+							data: {},
+						},
+					]
+				},
+			}
+
+			const engine = new FeedEngine().register(failing).register(working)
+
+			const { items, errors } = await engine.refresh()
+
+			expect(errors).toHaveLength(1)
+			expect(items).toHaveLength(1)
+		})
+	})
+
+	describe("currentContext", () => {
+		test("returns initial context before refresh", () => {
+			const engine = new FeedEngine()
+
+			const context = engine.currentContext()
+
+			expect(context.time).toBeInstanceOf(Date)
+		})
+
+		test("returns accumulated context after refresh", async () => {
+			const location = createLocationSource()
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			const engine = new FeedEngine().register(location)
+
+			await engine.refresh()
+
+			const context = engine.currentContext()
+			expect(contextValue(context, LocationKey)).toEqual({ lat: 51.5, lng: -0.1 })
+		})
+	})
+
+	describe("subscribe", () => {
+		test("returns unsubscribe function", () => {
+			const engine = new FeedEngine()
+			let callCount = 0
+
+			const unsubscribe = engine.subscribe(() => {
+				callCount++
+			})
+
+			unsubscribe()
+
+			// Subscriber should not be called after unsubscribe
+			expect(callCount).toBe(0)
+		})
+	})
+
+	describe("reactive updates", () => {
+		test("start subscribes to onContextUpdate", async () => {
+			const location = createLocationSource()
+			const weather = createWeatherSource()
+
+			const engine = new FeedEngine().register(location).register(weather)
+
+			const results: Array<{ items: FeedItem[] }> = []
+			engine.subscribe((result) => {
+				results.push({ items: result.items })
+			})
+
+			engine.start()
+
+			// Simulate location update
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			// Wait for async refresh
+			await new Promise((resolve) => setTimeout(resolve, 50))
+
+			expect(results.length).toBeGreaterThan(0)
+			expect(results[0]!.items[0]!.type).toBe("weather")
+		})
+
+		test("stop unsubscribes from all sources", async () => {
+			const location = createLocationSource()
+
+			const engine = new FeedEngine().register(location)
+
+			let callCount = 0
+			engine.subscribe(() => {
+				callCount++
+			})
+
+			engine.start()
+			engine.stop()
+
+			// Simulate update after stop
+			location.simulateUpdate({ lat: 1, lng: 1 })
+
+			await new Promise((resolve) => setTimeout(resolve, 50))
+
+			expect(callCount).toBe(0)
+		})
+
+		test("start is idempotent", () => {
+			const location = createLocationSource()
+			const engine = new FeedEngine().register(location)
+
+			// Should not throw or double-subscribe
+			engine.start()
+			engine.start()
+			engine.stop()
+		})
+	})
+})

packages/aris-core/src/feed-engine.ts

@@ -0,0 +1,337 @@
+import type { Context } from "./context"
+import type { FeedItem } from "./feed"
+import type { FeedSource } from "./feed-source"
+
+export interface SourceError {
+	sourceId: string
+	error: Error
+}
+
+export interface FeedResult<TItem extends FeedItem = FeedItem> {
+	context: Context
+	items: TItem[]
+	errors: SourceError[]
+}
+
+export type FeedSubscriber<TItem extends FeedItem = FeedItem> = (result: FeedResult<TItem>) => void
+
+interface SourceGraph {
+	sources: Map<string, FeedSource>
+	sorted: FeedSource[]
+	dependents: Map<string, string[]>
+}
+
+/**
+ * Orchestrates FeedSources, managing the dependency graph and context flow.
+ *
+ * Sources declare dependencies on other sources. The engine:
+ * - Validates the dependency graph (no missing deps, no cycles)
+ * - Runs fetchContext() in topological order during refresh
+ * - Runs fetchItems() on all sources with accumulated context
+ * - Subscribes to reactive updates via onContextUpdate/onItemsUpdate
+ *
+ * @example
+ * ```ts
+ * const engine = new FeedEngine()
+ *   .register(locationSource)
+ *   .register(weatherSource)
+ *   .register(alertSource)
+ *
+ * // Pull-based refresh
+ * const { context, items, errors } = await engine.refresh()
+ *
+ * // Reactive updates
+ * engine.subscribe((result) => {
+ *   console.log(result.items)
+ * })
+ * engine.start()
+ *
+ * // Cleanup
+ * engine.stop()
+ * ```
+ */
+export class FeedEngine<TItems extends FeedItem = FeedItem> {
+	private sources = new Map<string, FeedSource>()
+	private graph: SourceGraph | null = null
+	private context: Context = { time: new Date() }
+	private subscribers = new Set<FeedSubscriber<TItems>>()
+	private cleanups: Array<() => void> = []
+	private started = false
+
+	/**
+	 * Registers a FeedSource. Invalidates the cached graph.
+	 */
+	register<TItem extends FeedItem>(source: FeedSource<TItem>): FeedEngine<TItems | TItem> {
+		this.sources.set(source.id, source)
+		this.graph = null
+		return this as FeedEngine<TItems | TItem>
+	}
+
+	/**
+	 * Unregisters a FeedSource by ID. Invalidates the cached graph.
+	 */
+	unregister(sourceId: string): this {
+		this.sources.delete(sourceId)
+		this.graph = null
+		return this
+	}
+
+	/**
+	 * Refreshes the feed by running all sources in dependency order.
+	 * Calls fetchContext() then fetchItems() on each source.
+	 */
+	async refresh(): Promise<FeedResult<TItems>> {
+		const graph = this.ensureGraph()
+		const errors: SourceError[] = []
+
+		// Reset context with fresh time
+		let context: Context = { time: new Date() }
+
+		// Run fetchContext in topological order
+		for (const source of graph.sorted) {
+			try {
+				const update = await source.fetchContext(context)
+				if (update) {
+					context = { ...context, ...update }
+				}
+			} catch (err) {
+				errors.push({
+					sourceId: source.id,
+					error: err instanceof Error ? err : new Error(String(err)),
+				})
+			}
+		}
+
+		// Run fetchItems on all sources
+		const items: FeedItem[] = []
+		for (const source of graph.sorted) {
+			if (source.fetchItems) {
+				try {
+					const sourceItems = await source.fetchItems(context)
+					items.push(...sourceItems)
+				} catch (err) {
+					errors.push({
+						sourceId: source.id,
+						error: err instanceof Error ? err : new Error(String(err)),
+					})
+				}
+			}
+		}
+
+		// Sort by priority descending
+		items.sort((a, b) => b.priority - a.priority)
+
+		this.context = context
+
+		return { context, items: items as TItems[], errors }
+	}
+
+	/**
+	 * Subscribes to feed updates. Returns unsubscribe function.
+	 */
+	subscribe(callback: FeedSubscriber<TItems>): () => void {
+		this.subscribers.add(callback)
+		return () => {
+			this.subscribers.delete(callback)
+		}
+	}
+
+	/**
+	 * Starts reactive subscriptions on all sources.
+	 * Sources with onContextUpdate will trigger re-computation of dependents.
+	 */
+	start(): void {
+		if (this.started) return
+
+		this.started = true
+		const graph = this.ensureGraph()
+
+		for (const source of graph.sorted) {
+			if (source.onContextUpdate) {
+				const cleanup = source.onContextUpdate(
+					(update) => {
+						this.handleContextUpdate(source.id, update)
+					},
+					() => this.context,
+				)
+				this.cleanups.push(cleanup)
+			}
+
+			if (source.onItemsUpdate) {
+				const cleanup = source.onItemsUpdate(
+					() => {
+						this.scheduleRefresh()
+					},
+					() => this.context,
+				)
+				this.cleanups.push(cleanup)
+			}
+		}
+	}
+
+	/**
+	 * Stops all reactive subscriptions.
+	 */
+	stop(): void {
+		this.started = false
+		for (const cleanup of this.cleanups) {
+			cleanup()
+		}
+		this.cleanups = []
+	}
+
+	/**
+	 * Returns the current accumulated context.
+	 */
+	currentContext(): Context {
+		return this.context
+	}
+
+	private ensureGraph(): SourceGraph {
+		if (!this.graph) {
+			this.graph = buildGraph(Array.from(this.sources.values()))
+		}
+		return this.graph
+	}
+
+	private handleContextUpdate(sourceId: string, update: Partial<Context>): void {
+		this.context = { ...this.context, ...update, time: new Date() }
+
+		// Re-run dependents and notify
+		this.refreshDependents(sourceId)
+	}
+
+	private async refreshDependents(sourceId: string): Promise<void> {
+		const graph = this.ensureGraph()
+		const toRefresh = this.collectDependents(sourceId, graph)
+
+		// Re-run fetchContext for dependents in order
+		for (const id of toRefresh) {
+			const source = graph.sources.get(id)
+			if (source) {
+				try {
+					const update = await source.fetchContext(this.context)
+					if (update) {
+						this.context = { ...this.context, ...update }
+					}
+				} catch {
+					// Errors during reactive updates are logged but don't stop propagation
+				}
+			}
+		}
+
+		// Collect items from all sources
+		const items: FeedItem[] = []
+		const errors: SourceError[] = []
+
+		for (const source of graph.sorted) {
+			if (source.fetchItems) {
+				try {
+					const sourceItems = await source.fetchItems(this.context)
+					items.push(...sourceItems)
+				} catch (err) {
+					errors.push({
+						sourceId: source.id,
+						error: err instanceof Error ? err : new Error(String(err)),
+					})
+				}
+			}
+		}
+
+		items.sort((a, b) => b.priority - a.priority)
+
+		this.notifySubscribers({ context: this.context, items: items as TItems[], errors })
+	}
+
+	private collectDependents(sourceId: string, graph: SourceGraph): string[] {
+		const result: string[] = []
+		const visited = new Set<string>()
+
+		const collect = (id: string): void => {
+			const deps = graph.dependents.get(id) ?? []
+			for (const dep of deps) {
+				if (!visited.has(dep)) {
+					visited.add(dep)
+					result.push(dep)
+					collect(dep)
+				}
+			}
+		}
+
+		collect(sourceId)
+
+		// Return in topological order
+		return graph.sorted.filter((s) => result.includes(s.id)).map((s) => s.id)
+	}
+
+	private scheduleRefresh(): void {
+		// Simple immediate refresh for now - could add debouncing later
+		this.refresh().then((result) => {
+			this.notifySubscribers(result)
+		})
+	}
+
+	private notifySubscribers(result: FeedResult<TItems>): void {
+		this.subscribers.forEach((callback) => {
+			try {
+				callback(result)
+			} catch {
+				// Subscriber errors shouldn't break other subscribers
+			}
+		})
+	}
+}
+
+function buildGraph(sources: FeedSource[]): SourceGraph {
+	const byId = new Map<string, FeedSource>()
+	for (const source of sources) {
+		byId.set(source.id, source)
+	}
+
+	// Validate dependencies exist
+	for (const source of sources) {
+		for (const dep of source.dependencies ?? []) {
+			if (!byId.has(dep)) {
+				throw new Error(`Source "${source.id}" depends on "${dep}" which is not registered`)
+			}
+		}
+	}
+
+	// Check for cycles and topologically sort
+	const visited = new Set<string>()
+	const visiting = new Set<string>()
+	const sorted: FeedSource[] = []
+
+	function visit(id: string, path: string[]): void {
+		if (visiting.has(id)) {
+			const cycle = [...path.slice(path.indexOf(id)), id].join(" → ")
+			throw new Error(`Circular dependency detected: ${cycle}`)
+		}
+		if (visited.has(id)) return
+
+		visiting.add(id)
+		const source = byId.get(id)!
+		for (const dep of source.dependencies ?? []) {
+			visit(dep, [...path, id])
+		}
+		visiting.delete(id)
+		visited.add(id)
+		sorted.push(source)
+	}
+
+	for (const source of sources) {
+		visit(source.id, [])
+	}
+
+	// Build reverse dependency map
+	const dependents = new Map<string, string[]>()
+	for (const source of sources) {
+		for (const dep of source.dependencies ?? []) {
+			const list = dependents.get(dep) ?? []
+			list.push(source.id)
+			dependents.set(dep, list)
+		}
+	}
+
+	return { sources: byId, sorted, dependents }
+}

packages/aris-core/src/feed-source.test.ts

@@ -0,0 +1,465 @@
+import { describe, expect, test } from "bun:test"
+
+import type { Context, ContextKey, FeedItem, FeedSource } from "./index"
+
+import { contextKey, contextValue } from "./index"
+
+// =============================================================================
+// CONTEXT KEYS
+// =============================================================================
+
+interface Location {
+	lat: number
+	lng: number
+}
+
+interface Weather {
+	temperature: number
+	condition: string
+}
+
+const LocationKey: ContextKey<Location> = contextKey("location")
+const WeatherKey: ContextKey<Weather> = contextKey("weather")
+
+// =============================================================================
+// FEED ITEMS
+// =============================================================================
+
+type WeatherFeedItem = FeedItem<"weather", { temperature: number; condition: string }>
+type AlertFeedItem = FeedItem<"alert", { message: string }>
+
+// =============================================================================
+// TEST HELPERS
+// =============================================================================
+
+interface SimulatedLocationSource extends FeedSource {
+	simulateUpdate(location: Location): void
+}
+
+function createLocationSource(): SimulatedLocationSource {
+	let callback: ((update: Partial<Context>) => void) | null = null
+	let currentLocation: Location = { lat: 0, lng: 0 }
+
+	return {
+		id: "location",
+
+		onContextUpdate(cb) {
+			callback = cb
+			return () => {
+				callback = null
+			}
+		},
+
+		async fetchContext() {
+			return { [LocationKey]: currentLocation }
+		},
+
+		simulateUpdate(location: Location) {
+			currentLocation = location
+			callback?.({ [LocationKey]: location })
+		},
+	}
+}
+
+function createWeatherSource(
+	fetchWeather: (location: Location) => Promise<Weather> = async () => ({
+		temperature: 20,
+		condition: "sunny",
+	}),
+): FeedSource<WeatherFeedItem> {
+	return {
+		id: "weather",
+		dependencies: ["location"],
+
+		async fetchContext(context) {
+			const location = contextValue(context, LocationKey)
+			if (!location) return null
+
+			const weather = await fetchWeather(location)
+			return { [WeatherKey]: weather }
+		},
+
+		async fetchItems(context) {
+			const weather = contextValue(context, WeatherKey)
+			if (!weather) return []
+
+			return [
+				{
+					id: `weather-${Date.now()}`,
+					type: "weather",
+					priority: 0.5,
+					timestamp: new Date(),
+					data: {
+						temperature: weather.temperature,
+						condition: weather.condition,
+					},
+				},
+			]
+		},
+	}
+}
+
+function createAlertSource(): FeedSource<AlertFeedItem> {
+	return {
+		id: "alert",
+		dependencies: ["weather"],
+
+		async fetchContext() {
+			return null
+		},
+
+		async fetchItems(context) {
+			const weather = contextValue(context, WeatherKey)
+			if (!weather) return []
+
+			if (weather.condition === "storm") {
+				return [
+					{
+						id: "alert-storm",
+						type: "alert",
+						priority: 1.0,
+						timestamp: new Date(),
+						data: { message: "Storm warning!" },
+					},
+				]
+			}
+
+			return []
+		},
+	}
+}
+
+// =============================================================================
+// GRAPH SIMULATION (until FeedController is updated)
+// =============================================================================
+
+interface SourceGraph {
+	sources: Map<string, FeedSource>
+	sorted: FeedSource[]
+	dependents: Map<string, string[]>
+}
+
+function buildGraph(sources: FeedSource[]): SourceGraph {
+	const byId = new Map<string, FeedSource>()
+	for (const source of sources) {
+		byId.set(source.id, source)
+	}
+
+	// Validate dependencies exist
+	for (const source of sources) {
+		for (const dep of source.dependencies ?? []) {
+			if (!byId.has(dep)) {
+				throw new Error(`Source "${source.id}" depends on "${dep}" which is not registered`)
+			}
+		}
+	}
+
+	// Check for cycles and topologically sort
+	const visited = new Set<string>()
+	const visiting = new Set<string>()
+	const sorted: FeedSource[] = []
+
+	function visit(id: string, path: string[]): void {
+		if (visiting.has(id)) {
+			const cycle = [...path.slice(path.indexOf(id)), id].join(" → ")
+			throw new Error(`Circular dependency detected: ${cycle}`)
+		}
+		if (visited.has(id)) return
+
+		visiting.add(id)
+		const source = byId.get(id)!
+		for (const dep of source.dependencies ?? []) {
+			visit(dep, [...path, id])
+		}
+		visiting.delete(id)
+		visited.add(id)
+		sorted.push(source)
+	}
+
+	for (const source of sources) {
+		visit(source.id, [])
+	}
+
+	// Build reverse dependency map
+	const dependents = new Map<string, string[]>()
+	for (const source of sources) {
+		for (const dep of source.dependencies ?? []) {
+			const list = dependents.get(dep) ?? []
+			list.push(source.id)
+			dependents.set(dep, list)
+		}
+	}
+
+	return { sources: byId, sorted, dependents }
+}
+
+async function refreshGraph(graph: SourceGraph): Promise<{ context: Context; items: FeedItem[] }> {
+	let context: Context = { time: new Date() }
+
+	// Run fetchContext in topological order
+	for (const source of graph.sorted) {
+		const update = await source.fetchContext(context)
+		if (update) {
+			context = { ...context, ...update }
+		}
+	}
+
+	// Run fetchItems on all sources
+	const items: FeedItem[] = []
+	for (const source of graph.sorted) {
+		if (source.fetchItems) {
+			const sourceItems = await source.fetchItems(context)
+			items.push(...sourceItems)
+		}
+	}
+
+	// Sort by priority descending
+	items.sort((a, b) => b.priority - a.priority)
+
+	return { context, items }
+}
+
+// =============================================================================
+// TESTS
+// =============================================================================
+
+describe("FeedSource", () => {
+	describe("interface", () => {
+		test("source with only context production", () => {
+			const source = createLocationSource()
+
+			expect(source.id).toBe("location")
+			expect(source.dependencies).toBeUndefined()
+			expect(source.fetchContext).toBeDefined()
+			expect(source.onContextUpdate).toBeDefined()
+			expect(source.fetchItems).toBeUndefined()
+		})
+
+		test("source with dependencies and both context and items", () => {
+			const source = createWeatherSource()
+
+			expect(source.id).toBe("weather")
+			expect(source.dependencies).toEqual(["location"])
+			expect(source.fetchContext).toBeDefined()
+			expect(source.fetchItems).toBeDefined()
+		})
+
+		test("source with only item production", () => {
+			const source = createAlertSource()
+
+			expect(source.id).toBe("alert")
+			expect(source.dependencies).toEqual(["weather"])
+			expect(source.fetchContext).toBeDefined()
+			expect(source.fetchItems).toBeDefined()
+		})
+
+		test("source without context returns null from fetchContext", async () => {
+			const source = createAlertSource()
+			const result = await source.fetchContext({ time: new Date() })
+			expect(result).toBeNull()
+		})
+	})
+
+	describe("graph validation", () => {
+		test("validates all dependencies exist", () => {
+			const orphan: FeedSource = {
+				id: "orphan",
+				dependencies: ["nonexistent"],
+				async fetchContext() {
+					return null
+				},
+			}
+
+			expect(() => buildGraph([orphan])).toThrow(
+				'Source "orphan" depends on "nonexistent" which is not registered',
+			)
+		})
+
+		test("detects circular dependencies", () => {
+			const a: FeedSource = {
+				id: "a",
+				dependencies: ["b"],
+				async fetchContext() {
+					return null
+				},
+			}
+			const b: FeedSource = {
+				id: "b",
+				dependencies: ["a"],
+				async fetchContext() {
+					return null
+				},
+			}
+
+			expect(() => buildGraph([a, b])).toThrow("Circular dependency detected: a → b → a")
+		})
+
+		test("detects longer cycles", () => {
+			const a: FeedSource = {
+				id: "a",
+				dependencies: ["c"],
+				async fetchContext() {
+					return null
+				},
+			}
+			const b: FeedSource = {
+				id: "b",
+				dependencies: ["a"],
+				async fetchContext() {
+					return null
+				},
+			}
+			const c: FeedSource = {
+				id: "c",
+				dependencies: ["b"],
+				async fetchContext() {
+					return null
+				},
+			}
+
+			expect(() => buildGraph([a, b, c])).toThrow("Circular dependency detected")
+		})
+
+		test("topologically sorts sources", () => {
+			const location = createLocationSource()
+			const weather = createWeatherSource()
+			const alert = createAlertSource()
+
+			// Register in wrong order
+			const graph = buildGraph([alert, weather, location])
+
+			expect(graph.sorted.map((s) => s.id)).toEqual(["location", "weather", "alert"])
+		})
+
+		test("builds reverse dependency map", () => {
+			const location = createLocationSource()
+			const weather = createWeatherSource()
+			const alert = createAlertSource()
+
+			const graph = buildGraph([location, weather, alert])
+
+			expect(graph.dependents.get("location")).toEqual(["weather"])
+			expect(graph.dependents.get("weather")).toEqual(["alert"])
+			expect(graph.dependents.get("alert")).toBeUndefined()
+		})
+	})
+
+	describe("graph refresh", () => {
+		test("runs fetchContext in dependency order", async () => {
+			const order: string[] = []
+
+			const location: FeedSource = {
+				id: "location",
+				async fetchContext() {
+					order.push("location")
+					return { [LocationKey]: { lat: 51.5, lng: -0.1 } }
+				},
+			}
+
+			const weather: FeedSource = {
+				id: "weather",
+				dependencies: ["location"],
+				async fetchContext(ctx) {
+					order.push("weather")
+					const loc = contextValue(ctx, LocationKey)
+					expect(loc).toBeDefined()
+					return { [WeatherKey]: { temperature: 20, condition: "sunny" } }
+				},
+			}
+
+			const graph = buildGraph([weather, location])
+			await refreshGraph(graph)
+
+			expect(order).toEqual(["location", "weather"])
+		})
+
+		test("accumulates context across sources", async () => {
+			const location = createLocationSource()
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			const weather = createWeatherSource()
+
+			const graph = buildGraph([location, weather])
+			const { context } = await refreshGraph(graph)
+
+			expect(contextValue(context, LocationKey)).toEqual({ lat: 51.5, lng: -0.1 })
+			expect(contextValue(context, WeatherKey)).toEqual({ temperature: 20, condition: "sunny" })
+		})
+
+		test("collects items from all sources", async () => {
+			const location = createLocationSource()
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			const weather = createWeatherSource()
+
+			const graph = buildGraph([location, weather])
+			const { items } = await refreshGraph(graph)
+
+			expect(items).toHaveLength(1)
+			expect(items[0]!.type).toBe("weather")
+		})
+
+		test("downstream source receives upstream context", async () => {
+			const location = createLocationSource()
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			const weather = createWeatherSource(async () => ({
+				temperature: 15,
+				condition: "storm",
+			}))
+
+			const alert = createAlertSource()
+
+			const graph = buildGraph([location, weather, alert])
+			const { items } = await refreshGraph(graph)
+
+			expect(items).toHaveLength(2)
+			expect(items[0]!.type).toBe("alert") // priority 1.0
+			expect(items[1]!.type).toBe("weather") // priority 0.5
+		})
+
+		test("source without location context returns empty items", async () => {
+			// Location source exists but hasn't been updated
+			const location: FeedSource = {
+				id: "location",
+				async fetchContext() {
+					// Simulate no location available
+					return null
+				},
+			}
+
+			const weather = createWeatherSource()
+
+			const graph = buildGraph([location, weather])
+			const { context, items } = await refreshGraph(graph)
+
+			expect(contextValue(context, WeatherKey)).toBeUndefined()
+			expect(items).toHaveLength(0)
+		})
+	})
+
+	describe("reactive updates", () => {
+		test("onContextUpdate receives callback and returns cleanup", () => {
+			const location = createLocationSource()
+			let updateCount = 0
+
+			const cleanup = location.onContextUpdate!(
+				() => {
+					updateCount++
+				},
+				() => ({ time: new Date() }),
+			)
+
+			location.simulateUpdate({ lat: 1, lng: 1 })
+			expect(updateCount).toBe(1)
+
+			location.simulateUpdate({ lat: 2, lng: 2 })
+			expect(updateCount).toBe(2)
+
+			cleanup()
+
+			location.simulateUpdate({ lat: 3, lng: 3 })
+			expect(updateCount).toBe(2) // no more updates after cleanup
+		})
+	})
+})

packages/aris-core/src/feed-source.ts

@@ -0,0 +1,84 @@
+import type { Context } from "./context"
+import type { FeedItem } from "./feed"
+
+/**
+ * Unified interface for sources that provide context and/or feed items.
+ *
+ * Sources form a dependency graph - a source declares which other sources
+ * it depends on, and the graph ensures dependencies are resolved before
+ * dependents run.
+ *
+ * A source may:
+ * - Provide context for other sources (implement fetchContext/onContextUpdate)
+ * - Produce feed items (implement fetchItems/onItemsUpdate)
+ * - Both
+ *
+ * @example
+ * ```ts
+ * // Location source - provides context only
+ * const locationSource: FeedSource = {
+ *   id: "location",
+ *   fetchContext: async () => {
+ *     const pos = await getCurrentPosition()
+ *     return { location: { lat: pos.coords.latitude, lng: pos.coords.longitude } }
+ *   },
+ * }
+ *
+ * // Weather source - depends on location, provides both context and items
+ * const weatherSource: FeedSource<WeatherFeedItem> = {
+ *   id: "weather",
+ *   dependencies: ["location"],
+ *   fetchContext: async (ctx) => {
+ *     const weather = await fetchWeather(ctx.location)
+ *     return { weather }
+ *   },
+ *   fetchItems: async (ctx) => {
+ *     return createWeatherFeedItems(ctx.weather)
+ *   },
+ * }
+ *
+ * // TFL source - no context to provide
+ * const tflSource: FeedSource<TflFeedItem> = {
+ *   id: "tfl",
+ *   fetchContext: async () => null,
+ *   fetchItems: async (ctx) => { ... },
+ * }
+ * ```
+ */
+export interface FeedSource<TItem extends FeedItem = FeedItem> {
+	/** Unique identifier for this source */
+	readonly id: string
+
+	/** IDs of sources this source depends on */
+	readonly dependencies?: readonly string[]
+
+	/**
+	 * Subscribe to reactive context updates.
+	 * Called when the source can push context changes proactively.
+	 * Returns cleanup function.
+	 */
+	onContextUpdate?(
+		callback: (update: Partial<Context>) => void,
+		getContext: () => Context,
+	): () => void
+
+	/**
+	 * Fetch context on-demand.
+	 * Called during manual refresh or initial load.
+	 * Return null if this source cannot provide context.
+	 */
+	fetchContext(context: Context): Promise<Partial<Context> | null>
+
+	/**
+	 * Subscribe to reactive feed item updates.
+	 * Called when the source can push item changes proactively.
+	 * Returns cleanup function.
+	 */
+	onItemsUpdate?(callback: (items: TItem[]) => void, getContext: () => Context): () => void
+
+	/**
+	 * Fetch feed items on-demand.
+	 * Called during manual refresh or when dependencies update.
+	 */
+	fetchItems?(context: Context): Promise<TItem[]>
+}

packages/aris-core/src/feed.ts

@@ -0,0 +1,31 @@
+/**
+ * A single item in the feed.
+ *
+ * @example
+ * ```ts
+ * type WeatherItem = FeedItem<"weather", { temp: number; condition: string }>
+ *
+ * const item: WeatherItem = {
+ *   id: "weather-123",
+ *   type: "weather",
+ *   priority: 0.5,
+ *   timestamp: new Date(),
+ *   data: { temp: 18, condition: "cloudy" },
+ * }
+ * ```
+ */
+export interface FeedItem<
+	TType extends string = string,
+	TData extends Record<string, unknown> = Record<string, unknown>,
+> {
+	/** Unique identifier */
+	id: string
+	/** Item type, matches the data source type */
+	type: TType
+	/** Sort priority (higher = more important, shown first) */
+	priority: number
+	/** When this item was generated */
+	timestamp: Date
+	/** Type-specific payload */
+	data: TData
+}

packages/aris-core/src/index.ts

@@ -0,0 +1,42 @@
+// Context
+export type { Context, ContextKey } from "./context"
+export { contextKey, contextValue } from "./context"
+
+// Feed
+export type { FeedItem } from "./feed"
+
+// Feed Source
+export type { FeedSource } from "./feed-source"
+
+// Feed Engine
+export type { FeedResult, FeedSubscriber, SourceError } from "./feed-engine"
+export { FeedEngine } from "./feed-engine"
+
+// =============================================================================
+// DEPRECATED - Use FeedSource + FeedEngine instead
+// =============================================================================
+
+// Data Source (deprecated - use FeedSource)
+export type { DataSource } from "./data-source"
+
+// Context Provider (deprecated - use FeedSource)
+export type { ContextProvider } from "./context-provider"
+
+// Context Bridge (deprecated - use FeedEngine)
+export type { ProviderError, RefreshResult } from "./context-bridge"
+export { ContextBridge } from "./context-bridge"
+
+// Reconciler (deprecated - use FeedEngine)
+export type {
+	ReconcileResult,
+	ReconcilerConfig,
+	SourceError as ReconcilerSourceError,
+} from "./reconciler"
+export { Reconciler } from "./reconciler"
+
+// Feed Controller (deprecated - use FeedEngine)
+export type {
+	FeedControllerConfig,
+	FeedSubscriber as FeedControllerSubscriber,
+} from "./feed-controller"
+export { FeedController } from "./feed-controller"

packages/aris-data-source-weatherkit/.env.example

@@ -0,0 +1,4 @@
+WEATHERKIT_PRIVATE_KEY="-----BEGIN PRIVATE KEY-----\n...\n-----END PRIVATE KEY-----"
+WEATHERKIT_KEY_ID=ABC123DEFG
+WEATHERKIT_TEAM_ID=TEAM123456
+WEATHERKIT_SERVICE_ID=com.example.weatherkit.test

packages/aris-data-source-weatherkit/README.md

@@ -0,0 +1,58 @@
+# @aris/data-source-weatherkit
+
+Weather data source using Apple WeatherKit REST API.
+
+## Usage
+
+```typescript
+import { WeatherKitDataSource, Units } from "@aris/data-source-weatherkit"
+
+const dataSource = new WeatherKitDataSource({
+	credentials: {
+		privateKey: "-----BEGIN PRIVATE KEY-----\n...",
+		keyId: "ABC123",
+		teamId: "DEF456",
+		serviceId: "com.example.weatherkit",
+	},
+	hourlyLimit: 12, // optional, default: 12
+	dailyLimit: 7, // optional, default: 7
+})
+
+const items = await dataSource.query(context, {
+	units: Units.metric, // or Units.imperial
+})
+```
+
+## Feed Items
+
+The data source returns four types of feed items:
+
+| Type              | Description                |
+| ----------------- | -------------------------- |
+| `weather-current` | Current weather conditions |
+| `weather-hourly`  | Hourly forecast            |
+| `weather-daily`   | Daily forecast             |
+| `weather-alert`   | Weather alerts             |
+
+## Priority
+
+Base priorities are adjusted based on weather conditions:
+
+- Severe conditions (tornado, hurricane, blizzard, etc.): +0.3
+- Moderate conditions (thunderstorm, heavy rain, etc.): +0.15
+- Alert severity: extreme=1.0, severe=0.9, moderate=0.75, minor=0.7
+
+## Authentication
+
+WeatherKit requires Apple Developer credentials. Generate a private key in the Apple Developer portal under Certificates, Identifiers & Profiles > Keys.
+
+## Validation
+
+API responses are validated using [arktype](https://arktype.io) schemas.
+
+## Generating Test Fixtures
+
+To regenerate fixture data from the real API:
+
+1. Create a `.env` file with your credentials (see `.env.example`)
+2. Run `bun run scripts/generate-fixtures.ts`

packages/aris-data-source-weatherkit/package.json

@@ -0,0 +1,14 @@
+{
+	"name": "@aris/data-source-weatherkit",
+	"version": "0.0.0",
+	"type": "module",
+	"main": "src/index.ts",
+	"types": "src/index.ts",
+	"scripts": {
+		"test": "bun test ."
+	},
+	"dependencies": {
+		"@aris/core": "workspace:*",
+		"arktype": "^2.1.0"
+	}
+}

packages/aris-data-source-weatherkit/scripts/generate-fixtures.ts

@@ -0,0 +1,60 @@
+import { DefaultWeatherKitClient } from "../src/weatherkit"
+
+function loadEnv(): Record<string, string> {
+	const content = require("fs").readFileSync(".env", "utf-8")
+	const env: Record<string, string> = {}
+
+	for (const line of content.split("\n")) {
+		const trimmed = line.trim()
+		if (!trimmed || trimmed.startsWith("#")) continue
+
+		const eqIndex = trimmed.indexOf("=")
+		if (eqIndex === -1) continue
+
+		const key = trimmed.slice(0, eqIndex)
+		let value = trimmed.slice(eqIndex + 1)
+
+		if (value.startsWith('"') && value.endsWith('"')) {
+			value = value.slice(1, -1)
+		}
+
+		env[key] = value.replace(/\\n/g, "\n")
+	}
+
+	return env
+}
+
+const env = loadEnv()
+
+const client = new DefaultWeatherKitClient({
+	privateKey: env.WEATHERKIT_PRIVATE_KEY!,
+	keyId: env.WEATHERKIT_KEY_ID!,
+	teamId: env.WEATHERKIT_TEAM_ID!,
+	serviceId: env.WEATHERKIT_SERVICE_ID!,
+})
+
+const locations = {
+	sanFrancisco: { lat: 37.7749, lng: -122.4194 },
+}
+
+async function main() {
+	console.log("Fetching weather data for San Francisco...")
+
+	const response = await client.fetch({
+		lat: locations.sanFrancisco.lat,
+		lng: locations.sanFrancisco.lng,
+	})
+
+	const fixture = {
+		generatedAt: new Date().toISOString(),
+		location: locations.sanFrancisco,
+		response,
+	}
+
+	const output = JSON.stringify(fixture)
+	await Bun.write("fixtures/san-francisco.json", output)
+
+	console.log("Fixture written to fixtures/san-francisco.json")
+}
+
+main().catch(console.error)

packages/aris-data-source-weatherkit/src/data-source.test.ts

@@ -0,0 +1,210 @@
+import type { Context } from "@aris/core"
+
+import { describe, expect, test } from "bun:test"
+
+import type { WeatherKitClient, WeatherKitResponse } from "./weatherkit"
+
+import fixture from "../fixtures/san-francisco.json"
+import { WeatherKitDataSource, Units } from "./data-source"
+import { WeatherFeedItemType } from "./feed-items"
+
+const mockCredentials = {
+	privateKey: "mock",
+	keyId: "mock",
+	teamId: "mock",
+	serviceId: "mock",
+}
+
+const createMockClient = (response: WeatherKitResponse): WeatherKitClient => ({
+	fetch: async () => response,
+})
+
+const createMockContext = (location?: { lat: number; lng: number }): Context => ({
+	time: new Date("2026-01-17T00:00:00Z"),
+	location: location ? { ...location, accuracy: 10 } : undefined,
+})
+
+describe("WeatherKitDataSource", () => {
+	test("returns empty array when location is missing", async () => {
+		const dataSource = new WeatherKitDataSource({ credentials: mockCredentials })
+		const items = await dataSource.query(createMockContext())
+
+		expect(items).toEqual([])
+	})
+
+	test("type is weather-current", () => {
+		const dataSource = new WeatherKitDataSource({ credentials: mockCredentials })
+
+		expect(dataSource.type).toBe(WeatherFeedItemType.current)
+	})
+
+	test("throws error if neither client nor credentials provided", () => {
+		expect(() => new WeatherKitDataSource({})).toThrow(
+			"Either client or credentials must be provided",
+		)
+	})
+})
+
+describe("WeatherKitDataSource with fixture", () => {
+	const response = fixture.response
+
+	test("parses current weather from fixture", () => {
+		const current = response.currentWeather
+
+		expect(typeof current.conditionCode).toBe("string")
+		expect(typeof current.temperature).toBe("number")
+		expect(typeof current.humidity).toBe("number")
+		expect(current.pressureTrend).toMatch(/^(rising|falling|steady)$/)
+	})
+
+	test("parses hourly forecast from fixture", () => {
+		const hours = response.forecastHourly.hours
+
+		expect(hours.length).toBeGreaterThan(0)
+
+		const firstHour = hours[0]!
+		expect(firstHour.forecastStart).toBeDefined()
+		expect(typeof firstHour.temperature).toBe("number")
+		expect(typeof firstHour.precipitationChance).toBe("number")
+	})
+
+	test("parses daily forecast from fixture", () => {
+		const days = response.forecastDaily.days
+
+		expect(days.length).toBeGreaterThan(0)
+
+		const firstDay = days[0]!
+		expect(firstDay.forecastStart).toBeDefined()
+		expect(typeof firstDay.temperatureMax).toBe("number")
+		expect(typeof firstDay.temperatureMin).toBe("number")
+		expect(firstDay.sunrise).toBeDefined()
+		expect(firstDay.sunset).toBeDefined()
+	})
+
+	test("hourly limit is respected", () => {
+		const dataSource = new WeatherKitDataSource({
+			credentials: mockCredentials,
+			hourlyLimit: 6,
+		})
+
+		expect(dataSource["hourlyLimit"]).toBe(6)
+	})
+
+	test("daily limit is respected", () => {
+		const dataSource = new WeatherKitDataSource({
+			credentials: mockCredentials,
+			dailyLimit: 3,
+		})
+
+		expect(dataSource["dailyLimit"]).toBe(3)
+	})
+
+	test("default limits are applied", () => {
+		const dataSource = new WeatherKitDataSource({ credentials: mockCredentials })
+
+		expect(dataSource["hourlyLimit"]).toBe(12)
+		expect(dataSource["dailyLimit"]).toBe(7)
+	})
+})
+
+describe("unit conversion", () => {
+	test("Units enum has metric and imperial", () => {
+		expect(Units.metric).toBe("metric")
+		expect(Units.imperial).toBe("imperial")
+	})
+})
+
+describe("query() with mocked client", () => {
+	const mockClient = createMockClient(fixture.response as WeatherKitResponse)
+
+	test("transforms API response into feed items", async () => {
+		const dataSource = new WeatherKitDataSource({ client: mockClient })
+		const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+		const items = await dataSource.query(context)
+
+		expect(items.length).toBeGreaterThan(0)
+		expect(items.some((i) => i.type === WeatherFeedItemType.current)).toBe(true)
+		expect(items.some((i) => i.type === WeatherFeedItemType.hourly)).toBe(true)
+		expect(items.some((i) => i.type === WeatherFeedItemType.daily)).toBe(true)
+	})
+
+	test("applies hourly and daily limits", async () => {
+		const dataSource = new WeatherKitDataSource({
+			client: mockClient,
+			hourlyLimit: 3,
+			dailyLimit: 2,
+		})
+		const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+		const items = await dataSource.query(context)
+
+		const hourlyItems = items.filter((i) => i.type === WeatherFeedItemType.hourly)
+		const dailyItems = items.filter((i) => i.type === WeatherFeedItemType.daily)
+
+		expect(hourlyItems.length).toBe(3)
+		expect(dailyItems.length).toBe(2)
+	})
+
+	test("sets timestamp from context.time", async () => {
+		const dataSource = new WeatherKitDataSource({ client: mockClient })
+		const queryTime = new Date("2026-01-17T12:00:00Z")
+		const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+		context.time = queryTime
+
+		const items = await dataSource.query(context)
+
+		for (const item of items) {
+			expect(item.timestamp).toEqual(queryTime)
+		}
+	})
+
+	test("converts temperatures to imperial", async () => {
+		const dataSource = new WeatherKitDataSource({ client: mockClient })
+		const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+		const metricItems = await dataSource.query(context, { units: Units.metric })
+		const imperialItems = await dataSource.query(context, { units: Units.imperial })
+
+		const metricCurrent = metricItems.find((i) => i.type === WeatherFeedItemType.current)
+		const imperialCurrent = imperialItems.find((i) => i.type === WeatherFeedItemType.current)
+
+		expect(metricCurrent).toBeDefined()
+		expect(imperialCurrent).toBeDefined()
+
+		const metricTemp = (metricCurrent!.data as { temperature: number }).temperature
+		const imperialTemp = (imperialCurrent!.data as { temperature: number }).temperature
+
+		// Verify conversion: F = C * 9/5 + 32
+		const expectedImperial = (metricTemp * 9) / 5 + 32
+		expect(imperialTemp).toBeCloseTo(expectedImperial, 2)
+	})
+
+	test("assigns priority based on weather conditions", async () => {
+		const dataSource = new WeatherKitDataSource({ client: mockClient })
+		const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+		const items = await dataSource.query(context)
+
+		for (const item of items) {
+			expect(item.priority).toBeGreaterThanOrEqual(0)
+			expect(item.priority).toBeLessThanOrEqual(1)
+		}
+
+		const currentItem = items.find((i) => i.type === WeatherFeedItemType.current)
+		expect(currentItem).toBeDefined()
+		// Base priority for current is 0.5, may be adjusted for conditions
+		expect(currentItem!.priority).toBeGreaterThanOrEqual(0.5)
+	})
+
+	test("generates unique IDs for each item", async () => {
+		const dataSource = new WeatherKitDataSource({ client: mockClient })
+		const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+		const items = await dataSource.query(context)
+		const ids = items.map((i) => i.id)
+		const uniqueIds = new Set(ids)
+
+		expect(uniqueIds.size).toBe(ids.length)
+	})
+})

packages/aris-data-source-weatherkit/src/data-source.ts

@@ -0,0 +1,306 @@
+import type { Context, DataSource } from "@aris/core"
+
+import {
+	WeatherFeedItemType,
+	type CurrentWeatherFeedItem,
+	type DailyWeatherFeedItem,
+	type HourlyWeatherFeedItem,
+	type WeatherAlertFeedItem,
+	type WeatherFeedItem,
+} from "./feed-items"
+import {
+	ConditionCode,
+	DefaultWeatherKitClient,
+	Severity,
+	type CurrentWeather,
+	type DailyForecast,
+	type HourlyForecast,
+	type WeatherAlert,
+	type WeatherKitClient,
+	type WeatherKitCredentials,
+} from "./weatherkit"
+
+export const Units = {
+	metric: "metric",
+	imperial: "imperial",
+} as const
+
+export type Units = (typeof Units)[keyof typeof Units]
+
+export interface WeatherKitDataSourceOptions {
+	credentials?: WeatherKitCredentials
+	client?: WeatherKitClient
+	hourlyLimit?: number
+	dailyLimit?: number
+}
+
+export interface WeatherKitQueryConfig {
+	units?: Units
+}
+
+export class WeatherKitDataSource implements DataSource<WeatherFeedItem, WeatherKitQueryConfig> {
+	private readonly DEFAULT_HOURLY_LIMIT = 12
+	private readonly DEFAULT_DAILY_LIMIT = 7
+
+	readonly type = WeatherFeedItemType.current
+	private readonly client: WeatherKitClient
+	private readonly hourlyLimit: number
+	private readonly dailyLimit: number
+
+	constructor(options: WeatherKitDataSourceOptions) {
+		if (!options.client && !options.credentials) {
+			throw new Error("Either client or credentials must be provided")
+		}
+		this.client = options.client ?? new DefaultWeatherKitClient(options.credentials!)
+		this.hourlyLimit = options.hourlyLimit ?? this.DEFAULT_HOURLY_LIMIT
+		this.dailyLimit = options.dailyLimit ?? this.DEFAULT_DAILY_LIMIT
+	}
+
+	async query(context: Context, config: WeatherKitQueryConfig = {}): Promise<WeatherFeedItem[]> {
+		if (!context.location) {
+			return []
+		}
+
+		const units = config.units ?? Units.metric
+		const timestamp = context.time
+
+		const response = await this.client.fetch({
+			lat: context.location.lat,
+			lng: context.location.lng,
+		})
+
+		const items: WeatherFeedItem[] = []
+
+		if (response.currentWeather) {
+			items.push(createCurrentWeatherFeedItem(response.currentWeather, timestamp, units))
+		}
+
+		if (response.forecastHourly?.hours) {
+			const hours = response.forecastHourly.hours.slice(0, this.hourlyLimit)
+			for (let i = 0; i < hours.length; i++) {
+				const hour = hours[i]
+				if (hour) {
+					items.push(createHourlyWeatherFeedItem(hour, i, timestamp, units))
+				}
+			}
+		}
+
+		if (response.forecastDaily?.days) {
+			const days = response.forecastDaily.days.slice(0, this.dailyLimit)
+			for (let i = 0; i < days.length; i++) {
+				const day = days[i]
+				if (day) {
+					items.push(createDailyWeatherFeedItem(day, i, timestamp, units))
+				}
+			}
+		}
+
+		if (response.weatherAlerts?.alerts) {
+			for (const alert of response.weatherAlerts.alerts) {
+				items.push(createWeatherAlertFeedItem(alert, timestamp))
+			}
+		}
+
+		return items
+	}
+}
+
+const BASE_PRIORITY = {
+	current: 0.5,
+	hourly: 0.3,
+	daily: 0.2,
+	alert: 0.7,
+} as const
+
+const SEVERE_CONDITIONS = new Set<ConditionCode>([
+	ConditionCode.SevereThunderstorm,
+	ConditionCode.Hurricane,
+	ConditionCode.Tornado,
+	ConditionCode.TropicalStorm,
+	ConditionCode.Blizzard,
+	ConditionCode.FreezingRain,
+	ConditionCode.Hail,
+	ConditionCode.Frigid,
+	ConditionCode.Hot,
+])
+
+const MODERATE_CONDITIONS = new Set<ConditionCode>([
+	ConditionCode.Thunderstorm,
+	ConditionCode.IsolatedThunderstorms,
+	ConditionCode.ScatteredThunderstorms,
+	ConditionCode.HeavyRain,
+	ConditionCode.HeavySnow,
+	ConditionCode.FreezingDrizzle,
+	ConditionCode.BlowingSnow,
+])
+
+function adjustPriorityForCondition(basePriority: number, conditionCode: ConditionCode): number {
+	if (SEVERE_CONDITIONS.has(conditionCode)) {
+		return Math.min(1, basePriority + 0.3)
+	}
+	if (MODERATE_CONDITIONS.has(conditionCode)) {
+		return Math.min(1, basePriority + 0.15)
+	}
+	return basePriority
+}
+
+function adjustPriorityForAlertSeverity(severity: Severity): number {
+	switch (severity) {
+		case Severity.Extreme:
+			return 1
+		case Severity.Severe:
+			return 0.9
+		case Severity.Moderate:
+			return 0.75
+		case Severity.Minor:
+			return BASE_PRIORITY.alert
+	}
+}
+
+function convertTemperature(celsius: number, units: Units): number {
+	if (units === Units.imperial) {
+		return (celsius * 9) / 5 + 32
+	}
+	return celsius
+}
+
+function convertSpeed(kmh: number, units: Units): number {
+	if (units === Units.imperial) {
+		return kmh * 0.621371
+	}
+	return kmh
+}
+
+function convertDistance(km: number, units: Units): number {
+	if (units === Units.imperial) {
+		return km * 0.621371
+	}
+	return km
+}
+
+function convertPrecipitation(mm: number, units: Units): number {
+	if (units === Units.imperial) {
+		return mm * 0.0393701
+	}
+	return mm
+}
+
+function convertPressure(mb: number, units: Units): number {
+	if (units === Units.imperial) {
+		return mb * 0.02953
+	}
+	return mb
+}
+
+function createCurrentWeatherFeedItem(
+	current: CurrentWeather,
+	timestamp: Date,
+	units: Units,
+): CurrentWeatherFeedItem {
+	const priority = adjustPriorityForCondition(BASE_PRIORITY.current, current.conditionCode)
+
+	return {
+		id: `weather-current-${timestamp.getTime()}`,
+		type: WeatherFeedItemType.current,
+		priority,
+		timestamp,
+		data: {
+			conditionCode: current.conditionCode,
+			daylight: current.daylight,
+			humidity: current.humidity,
+			precipitationIntensity: convertPrecipitation(current.precipitationIntensity, units),
+			pressure: convertPressure(current.pressure, units),
+			pressureTrend: current.pressureTrend,
+			temperature: convertTemperature(current.temperature, units),
+			temperatureApparent: convertTemperature(current.temperatureApparent, units),
+			uvIndex: current.uvIndex,
+			visibility: convertDistance(current.visibility, units),
+			windDirection: current.windDirection,
+			windGust: convertSpeed(current.windGust, units),
+			windSpeed: convertSpeed(current.windSpeed, units),
+		},
+	}
+}
+
+function createHourlyWeatherFeedItem(
+	hourly: HourlyForecast,
+	index: number,
+	timestamp: Date,
+	units: Units,
+): HourlyWeatherFeedItem {
+	const priority = adjustPriorityForCondition(BASE_PRIORITY.hourly, hourly.conditionCode)
+
+	return {
+		id: `weather-hourly-${timestamp.getTime()}-${index}`,
+		type: WeatherFeedItemType.hourly,
+		priority,
+		timestamp,
+		data: {
+			forecastTime: new Date(hourly.forecastStart),
+			conditionCode: hourly.conditionCode,
+			daylight: hourly.daylight,
+			humidity: hourly.humidity,
+			precipitationAmount: convertPrecipitation(hourly.precipitationAmount, units),
+			precipitationChance: hourly.precipitationChance,
+			precipitationType: hourly.precipitationType,
+			temperature: convertTemperature(hourly.temperature, units),
+			temperatureApparent: convertTemperature(hourly.temperatureApparent, units),
+			uvIndex: hourly.uvIndex,
+			windDirection: hourly.windDirection,
+			windGust: convertSpeed(hourly.windGust, units),
+			windSpeed: convertSpeed(hourly.windSpeed, units),
+		},
+	}
+}
+
+function createDailyWeatherFeedItem(
+	daily: DailyForecast,
+	index: number,
+	timestamp: Date,
+	units: Units,
+): DailyWeatherFeedItem {
+	const priority = adjustPriorityForCondition(BASE_PRIORITY.daily, daily.conditionCode)
+
+	return {
+		id: `weather-daily-${timestamp.getTime()}-${index}`,
+		type: WeatherFeedItemType.daily,
+		priority,
+		timestamp,
+		data: {
+			forecastDate: new Date(daily.forecastStart),
+			conditionCode: daily.conditionCode,
+			maxUvIndex: daily.maxUvIndex,
+			precipitationAmount: convertPrecipitation(daily.precipitationAmount, units),
+			precipitationChance: daily.precipitationChance,
+			precipitationType: daily.precipitationType,
+			snowfallAmount: convertPrecipitation(daily.snowfallAmount, units),
+			sunrise: new Date(daily.sunrise),
+			sunset: new Date(daily.sunset),
+			temperatureMax: convertTemperature(daily.temperatureMax, units),
+			temperatureMin: convertTemperature(daily.temperatureMin, units),
+		},
+	}
+}
+
+function createWeatherAlertFeedItem(alert: WeatherAlert, timestamp: Date): WeatherAlertFeedItem {
+	const priority = adjustPriorityForAlertSeverity(alert.severity)
+
+	return {
+		id: `weather-alert-${alert.id}`,
+		type: WeatherFeedItemType.alert,
+		priority,
+		timestamp,
+		data: {
+			alertId: alert.id,
+			areaName: alert.areaName,
+			certainty: alert.certainty,
+			description: alert.description,
+			detailsUrl: alert.detailsUrl,
+			effectiveTime: new Date(alert.effectiveTime),
+			expireTime: new Date(alert.expireTime),
+			severity: alert.severity,
+			source: alert.source,
+			urgency: alert.urgency,
+		},
+	}
+}

packages/aris-data-source-weatherkit/src/feed-items.ts

@@ -0,0 +1,97 @@
+import type { FeedItem } from "@aris/core"
+
+import type { Certainty, ConditionCode, PrecipitationType, Severity, Urgency } from "./weatherkit"
+
+export const WeatherFeedItemType = {
+	current: "weather-current",
+	hourly: "weather-hourly",
+	daily: "weather-daily",
+	alert: "weather-alert",
+} as const
+
+export type WeatherFeedItemType = (typeof WeatherFeedItemType)[keyof typeof WeatherFeedItemType]
+
+export type CurrentWeatherData = {
+	conditionCode: ConditionCode
+	daylight: boolean
+	humidity: number
+	precipitationIntensity: number
+	pressure: number
+	pressureTrend: "rising" | "falling" | "steady"
+	temperature: number
+	temperatureApparent: number
+	uvIndex: number
+	visibility: number
+	windDirection: number
+	windGust: number
+	windSpeed: number
+}
+
+export interface CurrentWeatherFeedItem extends FeedItem<
+	typeof WeatherFeedItemType.current,
+	CurrentWeatherData
+> {}
+
+export type HourlyWeatherData = {
+	forecastTime: Date
+	conditionCode: ConditionCode
+	daylight: boolean
+	humidity: number
+	precipitationAmount: number
+	precipitationChance: number
+	precipitationType: PrecipitationType
+	temperature: number
+	temperatureApparent: number
+	uvIndex: number
+	windDirection: number
+	windGust: number
+	windSpeed: number
+}
+
+export interface HourlyWeatherFeedItem extends FeedItem<
+	typeof WeatherFeedItemType.hourly,
+	HourlyWeatherData
+> {}
+
+export type DailyWeatherData = {
+	forecastDate: Date
+	conditionCode: ConditionCode
+	maxUvIndex: number
+	precipitationAmount: number
+	precipitationChance: number
+	precipitationType: PrecipitationType
+	snowfallAmount: number
+	sunrise: Date
+	sunset: Date
+	temperatureMax: number
+	temperatureMin: number
+}
+
+export interface DailyWeatherFeedItem extends FeedItem<
+	typeof WeatherFeedItemType.daily,
+	DailyWeatherData
+> {}
+
+export type WeatherAlertData = {
+	alertId: string
+	areaName: string
+	certainty: Certainty
+	description: string
+	detailsUrl: string
+	effectiveTime: Date
+	expireTime: Date
+	severity: Severity
+	source: string
+	urgency: Urgency
+}
+
+export interface WeatherAlertFeedItem extends FeedItem<
+	typeof WeatherFeedItemType.alert,
+	WeatherAlertData
+> {}
+
+export type WeatherFeedItem =
+	| CurrentWeatherFeedItem
+	| HourlyWeatherFeedItem
+	| DailyWeatherFeedItem
+	| WeatherAlertFeedItem

packages/aris-data-source-weatherkit/src/index.ts

@@ -0,0 +1,38 @@
+export {
+	WeatherKitDataSource,
+	Units,
+	type Units as UnitsType,
+	type WeatherKitDataSourceOptions,
+	type WeatherKitQueryConfig,
+} from "./data-source"
+
+export {
+	WeatherFeedItemType,
+	type WeatherFeedItemType as WeatherFeedItemTypeType,
+	type CurrentWeatherData,
+	type CurrentWeatherFeedItem,
+	type DailyWeatherData,
+	type DailyWeatherFeedItem,
+	type HourlyWeatherData,
+	type HourlyWeatherFeedItem,
+	type WeatherAlertData,
+	type WeatherAlertFeedItem,
+	type WeatherFeedItem,
+} from "./feed-items"
+
+export {
+	Severity,
+	Urgency,
+	Certainty,
+	PrecipitationType,
+	ConditionCode,
+	DefaultWeatherKitClient,
+	type Severity as SeverityType,
+	type Urgency as UrgencyType,
+	type Certainty as CertaintyType,
+	type PrecipitationType as PrecipitationTypeType,
+	type ConditionCode as ConditionCodeType,
+	type WeatherKitCredentials,
+	type WeatherKitClient,
+	type WeatherKitQueryOptions,
+} from "./weatherkit"

packages/aris-data-source-weatherkit/src/weatherkit.ts

@@ -0,0 +1,367 @@
+// WeatherKit REST API client and response types
+// https://developer.apple.com/documentation/weatherkitrestapi
+
+import { type } from "arktype"
+
+export interface WeatherKitCredentials {
+	privateKey: string
+	keyId: string
+	teamId: string
+	serviceId: string
+}
+
+export interface WeatherKitQueryOptions {
+	lat: number
+	lng: number
+	language?: string
+	timezone?: string
+}
+
+export interface WeatherKitClient {
+	fetch(query: WeatherKitQueryOptions): Promise<WeatherKitResponse>
+}
+
+export class DefaultWeatherKitClient implements WeatherKitClient {
+	private readonly credentials: WeatherKitCredentials
+
+	constructor(credentials: WeatherKitCredentials) {
+		this.credentials = credentials
+	}
+
+	async fetch(query: WeatherKitQueryOptions): Promise<WeatherKitResponse> {
+		const token = await generateJwt(this.credentials)
+
+		const dataSets = ["currentWeather", "forecastHourly", "forecastDaily", "weatherAlerts"].join(
+			",",
+		)
+
+		const url = new URL(
+			`${WEATHERKIT_API_BASE}/weather/${query.language ?? "en"}/${query.lat}/${query.lng}`,
+		)
+		url.searchParams.set("dataSets", dataSets)
+		if (query.timezone) {
+			url.searchParams.set("timezone", query.timezone)
+		}
+
+		const response = await fetch(url.toString(), {
+			headers: {
+				Authorization: `Bearer ${token}`,
+			},
+		})
+
+		if (!response.ok) {
+			const body = await response.text()
+			throw new Error(`WeatherKit API error: ${response.status} ${response.statusText}: ${body}`)
+		}
+
+		const json = await response.json()
+		const result = weatherKitResponseSchema(json)
+
+		if (result instanceof type.errors) {
+			throw new Error(`WeatherKit API response validation failed: ${result.summary}`)
+		}
+
+		return result
+	}
+}
+
+export const Severity = {
+	Minor: "minor",
+	Moderate: "moderate",
+	Severe: "severe",
+	Extreme: "extreme",
+} as const
+
+export type Severity = (typeof Severity)[keyof typeof Severity]
+
+export const Urgency = {
+	Immediate: "immediate",
+	Expected: "expected",
+	Future: "future",
+	Past: "past",
+	Unknown: "unknown",
+} as const
+
+export type Urgency = (typeof Urgency)[keyof typeof Urgency]
+
+export const Certainty = {
+	Observed: "observed",
+	Likely: "likely",
+	Possible: "possible",
+	Unlikely: "unlikely",
+	Unknown: "unknown",
+} as const
+
+export type Certainty = (typeof Certainty)[keyof typeof Certainty]
+
+export const PrecipitationType = {
+	Clear: "clear",
+	Precipitation: "precipitation",
+	Rain: "rain",
+	Snow: "snow",
+	Sleet: "sleet",
+	Hail: "hail",
+	Mixed: "mixed",
+} as const
+
+export type PrecipitationType = (typeof PrecipitationType)[keyof typeof PrecipitationType]
+
+export const ConditionCode = {
+	Clear: "Clear",
+	Cloudy: "Cloudy",
+	Dust: "Dust",
+	Fog: "Fog",
+	Haze: "Haze",
+	MostlyClear: "MostlyClear",
+	MostlyCloudy: "MostlyCloudy",
+	PartlyCloudy: "PartlyCloudy",
+	ScatteredThunderstorms: "ScatteredThunderstorms",
+	Smoke: "Smoke",
+	Breezy: "Breezy",
+	Windy: "Windy",
+	Drizzle: "Drizzle",
+	HeavyRain: "HeavyRain",
+	Rain: "Rain",
+	Showers: "Showers",
+	Flurries: "Flurries",
+	HeavySnow: "HeavySnow",
+	MixedRainAndSleet: "MixedRainAndSleet",
+	MixedRainAndSnow: "MixedRainAndSnow",
+	MixedRainfall: "MixedRainfall",
+	MixedSnowAndSleet: "MixedSnowAndSleet",
+	ScatteredShowers: "ScatteredShowers",
+	ScatteredSnowShowers: "ScatteredSnowShowers",
+	Sleet: "Sleet",
+	Snow: "Snow",
+	SnowShowers: "SnowShowers",
+	Blizzard: "Blizzard",
+	BlowingSnow: "BlowingSnow",
+	FreezingDrizzle: "FreezingDrizzle",
+	FreezingRain: "FreezingRain",
+	Frigid: "Frigid",
+	Hail: "Hail",
+	Hot: "Hot",
+	Hurricane: "Hurricane",
+	IsolatedThunderstorms: "IsolatedThunderstorms",
+	SevereThunderstorm: "SevereThunderstorm",
+	Thunderstorm: "Thunderstorm",
+	Tornado: "Tornado",
+	TropicalStorm: "TropicalStorm",
+} as const
+
+export type ConditionCode = (typeof ConditionCode)[keyof typeof ConditionCode]
+
+const WEATHERKIT_API_BASE = "https://weatherkit.apple.com/api/v1"
+
+const severitySchema = type.enumerated(
+	Severity.Minor,
+	Severity.Moderate,
+	Severity.Severe,
+	Severity.Extreme,
+)
+
+const urgencySchema = type.enumerated(
+	Urgency.Immediate,
+	Urgency.Expected,
+	Urgency.Future,
+	Urgency.Past,
+	Urgency.Unknown,
+)
+
+const certaintySchema = type.enumerated(
+	Certainty.Observed,
+	Certainty.Likely,
+	Certainty.Possible,
+	Certainty.Unlikely,
+	Certainty.Unknown,
+)
+
+const precipitationTypeSchema = type.enumerated(
+	PrecipitationType.Clear,
+	PrecipitationType.Precipitation,
+	PrecipitationType.Rain,
+	PrecipitationType.Snow,
+	PrecipitationType.Sleet,
+	PrecipitationType.Hail,
+	PrecipitationType.Mixed,
+)
+
+const conditionCodeSchema = type.enumerated(...Object.values(ConditionCode))
+
+const pressureTrendSchema = type.enumerated("rising", "falling", "steady")
+
+const currentWeatherSchema = type({
+	asOf: "string",
+	conditionCode: conditionCodeSchema,
+	daylight: "boolean",
+	humidity: "number",
+	precipitationIntensity: "number",
+	pressure: "number",
+	pressureTrend: pressureTrendSchema,
+	temperature: "number",
+	temperatureApparent: "number",
+	temperatureDewPoint: "number",
+	uvIndex: "number",
+	visibility: "number",
+	windDirection: "number",
+	windGust: "number",
+	windSpeed: "number",
+})
+
+export type CurrentWeather = typeof currentWeatherSchema.infer
+
+const hourlyForecastSchema = type({
+	forecastStart: "string",
+	conditionCode: conditionCodeSchema,
+	daylight: "boolean",
+	humidity: "number",
+	precipitationAmount: "number",
+	precipitationChance: "number",
+	precipitationType: precipitationTypeSchema,
+	pressure: "number",
+	snowfallIntensity: "number",
+	temperature: "number",
+	temperatureApparent: "number",
+	temperatureDewPoint: "number",
+	uvIndex: "number",
+	visibility: "number",
+	windDirection: "number",
+	windGust: "number",
+	windSpeed: "number",
+})
+
+export type HourlyForecast = typeof hourlyForecastSchema.infer
+
+const dayWeatherConditionsSchema = type({
+	conditionCode: conditionCodeSchema,
+	humidity: "number",
+	precipitationAmount: "number",
+	precipitationChance: "number",
+	precipitationType: precipitationTypeSchema,
+	snowfallAmount: "number",
+	temperatureMax: "number",
+	temperatureMin: "number",
+	windDirection: "number",
+	"windGust?": "number",
+	windSpeed: "number",
+})
+
+export type DayWeatherConditions = typeof dayWeatherConditionsSchema.infer
+
+const dailyForecastSchema = type({
+	forecastStart: "string",
+	forecastEnd: "string",
+	conditionCode: conditionCodeSchema,
+	maxUvIndex: "number",
+	moonPhase: "string",
+	"moonrise?": "string",
+	"moonset?": "string",
+	precipitationAmount: "number",
+	precipitationChance: "number",
+	precipitationType: precipitationTypeSchema,
+	snowfallAmount: "number",
+	sunrise: "string",
+	sunriseCivil: "string",
+	sunriseNautical: "string",
+	sunriseAstronomical: "string",
+	sunset: "string",
+	sunsetCivil: "string",
+	sunsetNautical: "string",
+	sunsetAstronomical: "string",
+	temperatureMax: "number",
+	temperatureMin: "number",
+	"daytimeForecast?": dayWeatherConditionsSchema,
+	"overnightForecast?": dayWeatherConditionsSchema,
+})
+
+export type DailyForecast = typeof dailyForecastSchema.infer
+
+const weatherAlertSchema = type({
+	id: "string",
+	areaId: "string",
+	areaName: "string",
+	certainty: certaintySchema,
+	countryCode: "string",
+	description: "string",
+	detailsUrl: "string",
+	effectiveTime: "string",
+	expireTime: "string",
+	issuedTime: "string",
+	responses: "string[]",
+	severity: severitySchema,
+	source: "string",
+	urgency: urgencySchema,
+})
+
+export type WeatherAlert = typeof weatherAlertSchema.infer
+
+const weatherKitResponseSchema = type({
+	"currentWeather?": currentWeatherSchema,
+	"forecastHourly?": type({
+		hours: hourlyForecastSchema.array(),
+	}),
+	"forecastDaily?": type({
+		days: dailyForecastSchema.array(),
+	}),
+	"weatherAlerts?": type({
+		alerts: weatherAlertSchema.array(),
+	}),
+})
+
+export type WeatherKitResponse = typeof weatherKitResponseSchema.infer
+
+async function generateJwt(credentials: WeatherKitCredentials): Promise<string> {
+	const header = {
+		alg: "ES256",
+		kid: credentials.keyId,
+		id: `${credentials.teamId}.${credentials.serviceId}`,
+	}
+
+	const now = Math.floor(Date.now() / 1000)
+	const payload = {
+		iss: credentials.teamId,
+		iat: now,
+		exp: now + 3600,
+		sub: credentials.serviceId,
+	}
+
+	const encoder = new TextEncoder()
+	const headerB64 = btoa(JSON.stringify(header))
+		.replace(/\+/g, "-")
+		.replace(/\//g, "_")
+		.replace(/=+$/, "")
+	const payloadB64 = btoa(JSON.stringify(payload))
+		.replace(/\+/g, "-")
+		.replace(/\//g, "_")
+		.replace(/=+$/, "")
+
+	const signingInput = `${headerB64}.${payloadB64}`
+
+	const pemContents = credentials.privateKey
+		.replace(/-----BEGIN PRIVATE KEY-----/, "")
+		.replace(/-----END PRIVATE KEY-----/, "")
+		.replace(/\s/g, "")
+
+	const binaryKey = Uint8Array.from(atob(pemContents), (c) => c.charCodeAt(0))
+
+	const cryptoKey = await crypto.subtle.importKey(
+		"pkcs8",
+		binaryKey,
+		{ name: "ECDSA", namedCurve: "P-256" },
+		false,
+		["sign"],
+	)
+
+	const signature = await crypto.subtle.sign(
+		{ name: "ECDSA", hash: "SHA-256" },
+		cryptoKey,
+		encoder.encode(signingInput),
+	)
+
+	const signatureB64 = btoa(String.fromCharCode(...new Uint8Array(signature)))
+		.replace(/\+/g, "-")
+		.replace(/\//g, "_")
+		.replace(/=+$/, "")
+
+	return `${signingInput}.${signatureB64}`
+}

packages/aris-source-apple-calendar/fixtures/all-day-event.ics

@@ -0,0 +1,11 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Test//Test//EN
+BEGIN:VEVENT
+UID:all-day-001@test
+DTSTART;VALUE=DATE:20260115
+DTEND;VALUE=DATE:20260116
+SUMMARY:Company Holiday
+STATUS:CONFIRMED
+END:VEVENT
+END:VCALENDAR

packages/aris-source-apple-calendar/fixtures/cancelled-event.ics

@@ -0,0 +1,11 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Test//Test//EN
+BEGIN:VEVENT
+UID:cancelled-001@test
+DTSTART:20260115T120000Z
+DTEND:20260115T130000Z
+SUMMARY:Cancelled Meeting
+STATUS:CANCELLED
+END:VEVENT
+END:VCALENDAR

packages/aris-source-apple-calendar/fixtures/minimal-event.ics

@@ -0,0 +1,10 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Test//Test//EN
+BEGIN:VEVENT
+UID:minimal-001@test
+DTSTART:20260115T180000Z
+DTEND:20260115T190000Z
+SUMMARY:Quick Chat
+END:VEVENT
+END:VCALENDAR

packages/aris-source-apple-calendar/fixtures/recurring-event.ics

@@ -0,0 +1,20 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Test//Test//EN
+BEGIN:VEVENT
+UID:recurring-001@test
+DTSTART:20260115T090000Z
+DTEND:20260115T093000Z
+SUMMARY:Weekly Sync
+RRULE:FREQ=WEEKLY;COUNT=4
+STATUS:CONFIRMED
+END:VEVENT
+BEGIN:VEVENT
+UID:recurring-001@test
+RECURRENCE-ID:20260122T090000Z
+DTSTART:20260122T100000Z
+DTEND:20260122T103000Z
+SUMMARY:Weekly Sync (moved)
+STATUS:CONFIRMED
+END:VEVENT
+END:VCALENDAR

packages/aris-source-apple-calendar/fixtures/single-event.ics

@@ -0,0 +1,26 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Test//Test//EN
+BEGIN:VEVENT
+UID:single-event-001@test
+DTSTART:20260115T140000Z
+DTEND:20260115T150000Z
+SUMMARY:Team Standup
+LOCATION:Conference Room A
+DESCRIPTION:Daily standup meeting
+STATUS:CONFIRMED
+URL:https://example.com/meeting/123
+ORGANIZER;CN=Alice Smith:mailto:alice@example.com
+ATTENDEE;CN=Bob Jones;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED:mailto:bob@example.com
+ATTENDEE;CN=Carol White;ROLE=OPT-PARTICIPANT;PARTSTAT=TENTATIVE:mailto:carol@example.com
+BEGIN:VALARM
+TRIGGER:-PT15M
+ACTION:DISPLAY
+DESCRIPTION:Reminder
+END:VALARM
+BEGIN:VALARM
+TRIGGER:-PT5M
+ACTION:AUDIO
+END:VALARM
+END:VEVENT
+END:VCALENDAR

packages/aris-source-apple-calendar/package.json

@@ -0,0 +1,15 @@
+{
+	"name": "@aris/source-apple-calendar",
+	"version": "0.0.0",
+	"type": "module",
+	"main": "src/index.ts",
+	"types": "src/index.ts",
+	"scripts": {
+		"test": "bun test ."
+	},
+	"dependencies": {
+		"@aris/core": "workspace:*",
+		"ical.js": "^2.1.0",
+		"tsdav": "^2.1.7"
+	}
+}

packages/aris-source-apple-calendar/src/calendar-context.ts

@@ -0,0 +1,24 @@
+import type { ContextKey } from "@aris/core"
+
+import { contextKey } from "@aris/core"
+
+import type { CalendarEventData } from "./types.ts"
+
+/**
+ * Calendar context for downstream sources.
+ *
+ * Provides a snapshot of the user's upcoming events so other sources
+ * can adapt (e.g. a commute source checking if there's a meeting soon).
+ */
+export interface CalendarContext {
+	/** Events happening right now */
+	inProgress: CalendarEventData[]
+	/** Next upcoming event, if any */
+	nextEvent: CalendarEventData | null
+	/** Whether the user has any events today */
+	hasTodayEvents: boolean
+	/** Total number of events today */
+	todayEventCount: number
+}
+
+export const CalendarKey: ContextKey<CalendarContext> = contextKey("calendar")

packages/aris-source-apple-calendar/src/calendar-source.test.ts

@@ -0,0 +1,460 @@
+import type { Context } from "@aris/core"
+
+import { contextValue } from "@aris/core"
+import { describe, expect, test } from "bun:test"
+import { readFileSync } from "node:fs"
+import { join } from "node:path"
+
+import type {
+	CalendarCredentialProvider,
+	CalendarCredentials,
+	CalendarDAVCalendar,
+	CalendarDAVClient,
+	CalendarDAVObject,
+	CalendarEventData,
+} from "./types.ts"
+
+import { CalendarKey } from "./calendar-context.ts"
+import { CalendarSource, computePriority } from "./calendar-source.ts"
+
+function loadFixture(name: string): string {
+	return readFileSync(join(import.meta.dir, "..", "fixtures", name), "utf-8")
+}
+
+function createContext(time: Date): Context {
+	return { time }
+}
+
+const mockCredentials: CalendarCredentials = {
+	accessToken: "mock-access-token",
+	refreshToken: "mock-refresh-token",
+	expiresAt: Date.now() + 3600000,
+	tokenUrl: "https://appleid.apple.com/auth/token",
+	clientId: "com.example.aris",
+	clientSecret: "mock-secret",
+}
+
+class NullCredentialProvider implements CalendarCredentialProvider {
+	async fetchCredentials(_userId: string): Promise<CalendarCredentials | null> {
+		return null
+	}
+}
+
+class MockCredentialProvider implements CalendarCredentialProvider {
+	async fetchCredentials(_userId: string): Promise<CalendarCredentials | null> {
+		return mockCredentials
+	}
+}
+
+class MockDAVClient implements CalendarDAVClient {
+	credentials: Record<string, unknown> = {}
+	fetchCalendarsCallCount = 0
+	private calendars: CalendarDAVCalendar[]
+	private objectsByCalendarUrl: Record<string, CalendarDAVObject[]>
+
+	constructor(
+		calendars: CalendarDAVCalendar[],
+		objectsByCalendarUrl: Record<string, CalendarDAVObject[]>,
+	) {
+		this.calendars = calendars
+		this.objectsByCalendarUrl = objectsByCalendarUrl
+	}
+
+	async login(): Promise<void> {}
+
+	async fetchCalendars(): Promise<CalendarDAVCalendar[]> {
+		this.fetchCalendarsCallCount++
+		return this.calendars
+	}
+
+	async fetchCalendarObjects(params: {
+		calendar: CalendarDAVCalendar
+		timeRange: { start: string; end: string }
+	}): Promise<CalendarDAVObject[]> {
+		return this.objectsByCalendarUrl[params.calendar.url] ?? []
+	}
+}
+
+describe("CalendarSource", () => {
+	test("has correct id", () => {
+		const source = new CalendarSource(new NullCredentialProvider(), "user-1")
+		expect(source.id).toBe("apple-calendar")
+	})
+
+	test("returns empty array when credentials are null", async () => {
+		const source = new CalendarSource(new NullCredentialProvider(), "user-1")
+		const items = await source.fetchItems(createContext(new Date("2026-01-15T12:00:00Z")))
+		expect(items).toEqual([])
+	})
+
+	test("returns empty array when no calendars exist", async () => {
+		const client = new MockDAVClient([], {})
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+		const items = await source.fetchItems(createContext(new Date("2026-01-15T12:00:00Z")))
+		expect(items).toEqual([])
+	})
+
+	test("returns feed items from a single calendar", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [{ url: "/cal/work/event1.ics", data: loadFixture("single-event.ics") }],
+		}
+		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		const items = await source.fetchItems(createContext(new Date("2026-01-15T12:00:00Z")))
+
+		expect(items).toHaveLength(1)
+		expect(items[0]!.type).toBe("calendar-event")
+		expect(items[0]!.id).toBe("calendar-event-single-event-001@test")
+		expect(items[0]!.data.title).toBe("Team Standup")
+		expect(items[0]!.data.location).toBe("Conference Room A")
+		expect(items[0]!.data.calendarName).toBe("Work")
+		expect(items[0]!.data.attendees).toHaveLength(2)
+		expect(items[0]!.data.alarms).toHaveLength(2)
+	})
+
+	test("returns feed items from multiple calendars", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [{ url: "/cal/work/event1.ics", data: loadFixture("single-event.ics") }],
+			"/cal/personal": [
+				{ url: "/cal/personal/event2.ics", data: loadFixture("all-day-event.ics") },
+			],
+		}
+		const client = new MockDAVClient(
+			[
+				{ url: "/cal/work", displayName: "Work" },
+				{ url: "/cal/personal", displayName: "Personal" },
+			],
+			objects,
+		)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		const items = await source.fetchItems(createContext(new Date("2026-01-15T12:00:00Z")))
+
+		expect(items).toHaveLength(2)
+
+		const standup = items.find((i) => i.data.title === "Team Standup")
+		const holiday = items.find((i) => i.data.title === "Company Holiday")
+
+		expect(standup).toBeDefined()
+		expect(standup!.data.calendarName).toBe("Work")
+
+		expect(holiday).toBeDefined()
+		expect(holiday!.data.calendarName).toBe("Personal")
+		expect(holiday!.data.isAllDay).toBe(true)
+	})
+
+	test("skips objects with non-string data", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [
+				{ url: "/cal/work/event1.ics", data: loadFixture("single-event.ics") },
+				{ url: "/cal/work/bad.ics", data: 12345 },
+				{ url: "/cal/work/empty.ics" },
+			],
+		}
+		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		const items = await source.fetchItems(createContext(new Date("2026-01-15T12:00:00Z")))
+		expect(items).toHaveLength(1)
+		expect(items[0]!.data.title).toBe("Team Standup")
+	})
+
+	test("uses context time as feed item timestamp", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [{ url: "/cal/work/event1.ics", data: loadFixture("single-event.ics") }],
+		}
+		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		const now = new Date("2026-01-15T12:00:00Z")
+		const items = await source.fetchItems(createContext(now))
+		expect(items[0]!.timestamp).toEqual(now)
+	})
+
+	test("assigns priority based on event proximity", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [
+				{ url: "/cal/work/event1.ics", data: loadFixture("single-event.ics") },
+				{ url: "/cal/work/allday.ics", data: loadFixture("all-day-event.ics") },
+			],
+		}
+		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		// 2 hours before the event at 14:00
+		const items = await source.fetchItems(createContext(new Date("2026-01-15T12:00:00Z")))
+
+		const standup = items.find((i) => i.data.title === "Team Standup")
+		const holiday = items.find((i) => i.data.title === "Company Holiday")
+
+		expect(standup!.priority).toBe(0.7) // within 2 hours
+		expect(holiday!.priority).toBe(0.3) // all-day
+	})
+
+	test("handles calendar with non-string displayName", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/weird": [{ url: "/cal/weird/event1.ics", data: loadFixture("minimal-event.ics") }],
+		}
+		const client = new MockDAVClient(
+			[{ url: "/cal/weird", displayName: { _cdata: "Weird Calendar" } }],
+			objects,
+		)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		const items = await source.fetchItems(createContext(new Date("2026-01-15T12:00:00Z")))
+		expect(items[0]!.data.calendarName).toBeNull()
+	})
+
+	test("handles recurring events with exceptions", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [{ url: "/cal/work/recurring.ics", data: loadFixture("recurring-event.ics") }],
+		}
+		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		const items = await source.fetchItems(createContext(new Date("2026-01-15T08:00:00Z")))
+
+		expect(items).toHaveLength(2)
+
+		const base = items.find((i) => i.data.title === "Weekly Sync")
+		const exception = items.find((i) => i.data.title === "Weekly Sync (moved)")
+
+		expect(base).toBeDefined()
+		expect(base!.data.recurrenceId).toBeNull()
+
+		expect(exception).toBeDefined()
+		expect(exception!.data.recurrenceId).not.toBeNull()
+		expect(exception!.id).toContain("-")
+	})
+
+	test("caches events within the same refresh cycle", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [{ url: "/cal/work/event1.ics", data: loadFixture("single-event.ics") }],
+		}
+		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		const context = createContext(new Date("2026-01-15T12:00:00Z"))
+
+		await source.fetchContext(context)
+		await source.fetchItems(context)
+
+		// Same context.time reference — fetchEvents should only hit the client once
+		expect(client.fetchCalendarsCallCount).toBe(1)
+	})
+
+	test("refetches events for a different context time", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [{ url: "/cal/work/event1.ics", data: loadFixture("single-event.ics") }],
+		}
+		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		await source.fetchItems(createContext(new Date("2026-01-15T12:00:00Z")))
+		await source.fetchItems(createContext(new Date("2026-01-15T13:00:00Z")))
+
+		// Different context.time references — should fetch twice
+		expect(client.fetchCalendarsCallCount).toBe(2)
+	})
+})
+
+describe("CalendarSource.fetchContext", () => {
+	test("returns empty context when credentials are null", async () => {
+		const source = new CalendarSource(new NullCredentialProvider(), "user-1")
+		const ctx = await source.fetchContext(createContext(new Date("2026-01-15T12:00:00Z")))
+		const calendar = contextValue(ctx as Context, CalendarKey)
+
+		expect(calendar).toBeDefined()
+		expect(calendar!.inProgress).toEqual([])
+		expect(calendar!.nextEvent).toBeNull()
+		expect(calendar!.hasTodayEvents).toBe(false)
+		expect(calendar!.todayEventCount).toBe(0)
+	})
+
+	test("identifies in-progress events", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [{ url: "/cal/work/event1.ics", data: loadFixture("single-event.ics") }],
+		}
+		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		// 14:30 is during the 14:00-15:00 event
+		const ctx = await source.fetchContext(createContext(new Date("2026-01-15T14:30:00Z")))
+		const calendar = contextValue(ctx as Context, CalendarKey)
+
+		expect(calendar!.inProgress).toHaveLength(1)
+		expect(calendar!.inProgress[0]!.title).toBe("Team Standup")
+	})
+
+	test("identifies next upcoming event", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [{ url: "/cal/work/event1.ics", data: loadFixture("single-event.ics") }],
+		}
+		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		// 12:00 is before the 14:00 event
+		const ctx = await source.fetchContext(createContext(new Date("2026-01-15T12:00:00Z")))
+		const calendar = contextValue(ctx as Context, CalendarKey)
+
+		expect(calendar!.inProgress).toHaveLength(0)
+		expect(calendar!.nextEvent).not.toBeNull()
+		expect(calendar!.nextEvent!.title).toBe("Team Standup")
+	})
+
+	test("excludes all-day events from inProgress and nextEvent", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [{ url: "/cal/work/allday.ics", data: loadFixture("all-day-event.ics") }],
+		}
+		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		const ctx = await source.fetchContext(createContext(new Date("2026-01-15T12:00:00Z")))
+		const calendar = contextValue(ctx as Context, CalendarKey)
+
+		expect(calendar!.inProgress).toHaveLength(0)
+		expect(calendar!.nextEvent).toBeNull()
+		expect(calendar!.hasTodayEvents).toBe(true)
+		expect(calendar!.todayEventCount).toBe(1)
+	})
+
+	test("counts all events including all-day in todayEventCount", async () => {
+		const objects: Record<string, CalendarDAVObject[]> = {
+			"/cal/work": [
+				{ url: "/cal/work/event1.ics", data: loadFixture("single-event.ics") },
+				{ url: "/cal/work/allday.ics", data: loadFixture("all-day-event.ics") },
+			],
+		}
+		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
+		const source = new CalendarSource(new MockCredentialProvider(), "user-1", {
+			davClient: client,
+		})
+
+		const ctx = await source.fetchContext(createContext(new Date("2026-01-15T12:00:00Z")))
+		const calendar = contextValue(ctx as Context, CalendarKey)
+
+		expect(calendar!.todayEventCount).toBe(2)
+		expect(calendar!.hasTodayEvents).toBe(true)
+	})
+})
+
+describe("computePriority", () => {
+	const now = new Date("2026-01-15T12:00:00Z")
+
+	function makeEvent(overrides: Partial<CalendarEventData>): CalendarEventData {
+		return {
+			uid: "test-uid",
+			title: "Test",
+			startDate: new Date("2026-01-15T14:00:00Z"),
+			endDate: new Date("2026-01-15T15:00:00Z"),
+			isAllDay: false,
+			location: null,
+			description: null,
+			calendarName: null,
+			status: null,
+			url: null,
+			organizer: null,
+			attendees: [],
+			alarms: [],
+			recurrenceId: null,
+			...overrides,
+		}
+	}
+
+	test("all-day events get priority 0.3", () => {
+		const event = makeEvent({ isAllDay: true })
+		expect(computePriority(event, now)).toBe(0.3)
+	})
+
+	test("events starting within 30 minutes get priority 0.9", () => {
+		const event = makeEvent({
+			startDate: new Date("2026-01-15T12:20:00Z"),
+		})
+		expect(computePriority(event, now)).toBe(0.9)
+	})
+
+	test("events starting exactly at 30 minutes get priority 0.9", () => {
+		const event = makeEvent({
+			startDate: new Date("2026-01-15T12:30:00Z"),
+		})
+		expect(computePriority(event, now)).toBe(0.9)
+	})
+
+	test("events starting within 2 hours get priority 0.7", () => {
+		const event = makeEvent({
+			startDate: new Date("2026-01-15T13:00:00Z"),
+		})
+		expect(computePriority(event, now)).toBe(0.7)
+	})
+
+	test("events later today get priority 0.5", () => {
+		const event = makeEvent({
+			startDate: new Date("2026-01-15T20:00:00Z"),
+		})
+		expect(computePriority(event, now)).toBe(0.5)
+	})
+
+	test("in-progress events get priority 0.8", () => {
+		const event = makeEvent({
+			startDate: new Date("2026-01-15T11:00:00Z"),
+			endDate: new Date("2026-01-15T13:00:00Z"),
+		})
+		expect(computePriority(event, now)).toBe(0.8)
+	})
+
+	test("fully past events get priority 0.2", () => {
+		const event = makeEvent({
+			startDate: new Date("2026-01-15T09:00:00Z"),
+			endDate: new Date("2026-01-15T10:00:00Z"),
+		})
+		expect(computePriority(event, now)).toBe(0.2)
+	})
+
+	test("events on future days get priority 0.2", () => {
+		const event = makeEvent({
+			startDate: new Date("2026-01-16T10:00:00Z"),
+		})
+		expect(computePriority(event, now)).toBe(0.2)
+	})
+
+	test("priority boundaries are correct", () => {
+		// 31 minutes from now should be 0.7 (within 2 hours, not within 30 min)
+		const event31min = makeEvent({
+			startDate: new Date("2026-01-15T12:31:00Z"),
+		})
+		expect(computePriority(event31min, now)).toBe(0.7)
+
+		// 2 hours 1 minute from now should be 0.5 (later today, not within 2 hours)
+		const event2h1m = makeEvent({
+			startDate: new Date("2026-01-15T14:01:00Z"),
+		})
+		expect(computePriority(event2h1m, now)).toBe(0.5)
+	})
+})

packages/aris-source-apple-calendar/src/calendar-source.ts

@@ -0,0 +1,242 @@
+import type { Context, FeedSource } from "@aris/core"
+
+import { DAVClient } from "tsdav"
+
+import type {
+	CalendarCredentialProvider,
+	CalendarCredentials,
+	CalendarDAVClient,
+	CalendarEventData,
+	CalendarFeedItem,
+} from "./types.ts"
+
+export interface CalendarSourceOptions {
+	/** Number of additional days beyond today to fetch. Default: 0 (today only). */
+	lookAheadDays?: number
+	/** Optional DAVClient instance for testing. Uses tsdav DAVClient by default. */
+	davClient?: CalendarDAVClient
+}
+
+import { CalendarKey, type CalendarContext } from "./calendar-context.ts"
+import { parseICalEvents } from "./ical-parser.ts"
+
+const ICLOUD_CALDAV_URL = "https://caldav.icloud.com"
+const DEFAULT_LOOK_AHEAD_DAYS = 0
+
+/**
+ * A FeedSource that fetches Apple Calendar events via CalDAV.
+ *
+ * Credentials are provided by an injected CalendarCredentialProvider.
+ * The server is responsible for managing OAuth tokens and storage.
+ *
+ * @example
+ * ```ts
+ * const source = new CalendarSource(credentialProvider, "user-123")
+ * const engine = new FeedEngine()
+ * engine.register(source)
+ * ```
+ */
+export class CalendarSource implements FeedSource<CalendarFeedItem> {
+	readonly id = "apple-calendar"
+
+	private readonly credentialProvider: CalendarCredentialProvider
+	private readonly userId: string
+	private readonly lookAheadDays: number
+	private readonly injectedClient: CalendarDAVClient | null
+	private davClient: CalendarDAVClient | null = null
+	private lastAccessToken: string | null = null
+	private cachedEvents: { time: Date; events: CalendarEventData[] } | null = null
+
+	constructor(
+		credentialProvider: CalendarCredentialProvider,
+		userId: string,
+		options?: CalendarSourceOptions,
+	) {
+		this.credentialProvider = credentialProvider
+		this.userId = userId
+		this.lookAheadDays = options?.lookAheadDays ?? DEFAULT_LOOK_AHEAD_DAYS
+		this.injectedClient = options?.davClient ?? null
+	}
+
+	async fetchContext(context: Context): Promise<Partial<Context> | null> {
+		const events = await this.fetchEvents(context)
+		if (events.length === 0) {
+			return {
+				[CalendarKey]: {
+					inProgress: [],
+					nextEvent: null,
+					hasTodayEvents: false,
+					todayEventCount: 0,
+				},
+			}
+		}
+
+		const now = context.time
+		const inProgress = events.filter((e) => !e.isAllDay && e.startDate <= now && e.endDate > now)
+
+		const upcoming = events
+			.filter((e) => !e.isAllDay && e.startDate > now)
+			.sort((a, b) => a.startDate.getTime() - b.startDate.getTime())
+
+		const calendarContext: CalendarContext = {
+			inProgress,
+			nextEvent: upcoming[0] ?? null,
+			hasTodayEvents: events.length > 0,
+			todayEventCount: events.length,
+		}
+
+		return { [CalendarKey]: calendarContext }
+	}
+
+	async fetchItems(context: Context): Promise<CalendarFeedItem[]> {
+		const now = context.time
+		const events = await this.fetchEvents(context)
+		return events.map((event) => createFeedItem(event, now))
+	}
+
+	private async fetchEvents(context: Context): Promise<CalendarEventData[]> {
+		if (this.cachedEvents && this.cachedEvents.time === context.time) {
+			return this.cachedEvents.events
+		}
+
+		const credentials = await this.credentialProvider.fetchCredentials(this.userId)
+		if (!credentials) {
+			return []
+		}
+
+		const client = await this.connectClient(credentials)
+		const calendars = await client.fetchCalendars()
+
+		const { start, end } = computeTimeRange(context.time, this.lookAheadDays)
+
+		const results = await Promise.allSettled(
+			calendars.map(async (calendar) => {
+				const objects = await client.fetchCalendarObjects({
+					calendar,
+					timeRange: {
+						start: start.toISOString(),
+						end: end.toISOString(),
+					},
+				})
+				// tsdav types displayName as string | Record<string, unknown> | undefined
+				// because the XML parser can return an object for some responses
+				const calendarName = typeof calendar.displayName === "string" ? calendar.displayName : null
+				return { objects, calendarName }
+			}),
+		)
+
+		const allEvents: CalendarEventData[] = []
+		for (const result of results) {
+			if (result.status !== "fulfilled") continue
+			const { objects, calendarName } = result.value
+			for (const obj of objects) {
+				if (typeof obj.data !== "string") continue
+
+				const events = parseICalEvents(obj.data, calendarName)
+				for (const event of events) {
+					allEvents.push(event)
+				}
+			}
+		}
+
+		this.cachedEvents = { time: context.time, events: allEvents }
+		return allEvents
+	}
+
+	/**
+	 * Returns a ready-to-use DAVClient. Creates and logs in a new client
+	 * on first call; reuses the existing one on subsequent calls, updating
+	 * credentials if the access token has changed.
+	 */
+	private async connectClient(credentials: CalendarCredentials): Promise<CalendarDAVClient> {
+		if (this.injectedClient) {
+			return this.injectedClient
+		}
+
+		const davCredentials = {
+			tokenUrl: credentials.tokenUrl,
+			refreshToken: credentials.refreshToken,
+			accessToken: credentials.accessToken,
+			expiration: credentials.expiresAt,
+			clientId: credentials.clientId,
+			clientSecret: credentials.clientSecret,
+		}
+
+		if (!this.davClient) {
+			this.davClient = new DAVClient({
+				serverUrl: ICLOUD_CALDAV_URL,
+				credentials: davCredentials,
+				authMethod: "Oauth",
+				defaultAccountType: "caldav",
+			})
+			await this.davClient.login()
+			this.lastAccessToken = credentials.accessToken
+			return this.davClient
+		}
+
+		if (credentials.accessToken !== this.lastAccessToken) {
+			this.davClient.credentials = davCredentials
+			this.lastAccessToken = credentials.accessToken
+		}
+
+		return this.davClient
+	}
+}
+
+function computeTimeRange(now: Date, lookAheadDays: number): { start: Date; end: Date } {
+	const start = new Date(now)
+	start.setUTCHours(0, 0, 0, 0)
+
+	const end = new Date(start)
+	end.setUTCDate(end.getUTCDate() + 1 + lookAheadDays)
+
+	return { start, end }
+}
+
+export function computePriority(event: CalendarEventData, now: Date): number {
+	if (event.isAllDay) {
+		return 0.3
+	}
+
+	const msUntilStart = event.startDate.getTime() - now.getTime()
+
+	// Event already started
+	if (msUntilStart < 0) {
+		const isInProgress = now.getTime() < event.endDate.getTime()
+		// Currently happening events are high priority; fully past events are low
+		return isInProgress ? 0.8 : 0.2
+	}
+
+	// Starting within 30 minutes
+	if (msUntilStart <= 30 * 60 * 1000) {
+		return 0.9
+	}
+
+	// Starting within 2 hours
+	if (msUntilStart <= 2 * 60 * 60 * 1000) {
+		return 0.7
+	}
+
+	// Later today (within 24 hours from start of day)
+	const startOfDay = new Date(now)
+	startOfDay.setUTCHours(0, 0, 0, 0)
+	const endOfDay = new Date(startOfDay)
+	endOfDay.setUTCDate(endOfDay.getUTCDate() + 1)
+
+	if (event.startDate.getTime() < endOfDay.getTime()) {
+		return 0.5
+	}
+
+	// Future days
+	return 0.2
+}
+
+function createFeedItem(event: CalendarEventData, now: Date): CalendarFeedItem {
+	return {
+		id: `calendar-event-${event.uid}${event.recurrenceId ? `-${event.recurrenceId}` : ""}`,
+		type: "calendar-event",
+		priority: computePriority(event, now),
+		timestamp: now,
+		data: event,
+	}
+}

packages/aris-source-apple-calendar/src/ical-parser.test.ts

@@ -0,0 +1,107 @@
+import { describe, expect, test } from "bun:test"
+import { readFileSync } from "node:fs"
+import { join } from "node:path"
+
+import { parseICalEvents } from "./ical-parser.ts"
+
+function loadFixture(name: string): string {
+	return readFileSync(join(import.meta.dir, "..", "fixtures", name), "utf-8")
+}
+
+describe("parseICalEvents", () => {
+	test("parses a full event with all fields", () => {
+		const events = parseICalEvents(loadFixture("single-event.ics"), "Work")
+
+		expect(events).toHaveLength(1)
+		const event = events[0]!
+
+		expect(event.uid).toBe("single-event-001@test")
+		expect(event.title).toBe("Team Standup")
+		expect(event.startDate).toEqual(new Date("2026-01-15T14:00:00Z"))
+		expect(event.endDate).toEqual(new Date("2026-01-15T15:00:00Z"))
+		expect(event.isAllDay).toBe(false)
+		expect(event.location).toBe("Conference Room A")
+		expect(event.description).toBe("Daily standup meeting")
+		expect(event.calendarName).toBe("Work")
+		expect(event.status).toBe("confirmed")
+		expect(event.url).toBe("https://example.com/meeting/123")
+		expect(event.organizer).toBe("Alice Smith")
+		expect(event.recurrenceId).toBeNull()
+
+		expect(event.attendees).toHaveLength(2)
+		expect(event.attendees[0]).toEqual({
+			name: "Bob Jones",
+			email: "bob@example.com",
+			role: "required",
+			status: "accepted",
+		})
+		expect(event.attendees[1]).toEqual({
+			name: "Carol White",
+			email: "carol@example.com",
+			role: "optional",
+			status: "tentative",
+		})
+
+		expect(event.alarms).toHaveLength(2)
+		expect(event.alarms[0]).toEqual({ trigger: "-PT15M", action: "DISPLAY" })
+		expect(event.alarms[1]).toEqual({ trigger: "-PT5M", action: "AUDIO" })
+	})
+
+	test("parses an all-day event with optional fields as null", () => {
+		const events = parseICalEvents(loadFixture("all-day-event.ics"), null)
+
+		expect(events).toHaveLength(1)
+		const event = events[0]!
+
+		expect(event.isAllDay).toBe(true)
+		expect(event.title).toBe("Company Holiday")
+		expect(event.calendarName).toBeNull()
+		expect(event.location).toBeNull()
+		expect(event.description).toBeNull()
+		expect(event.url).toBeNull()
+		expect(event.organizer).toBeNull()
+		expect(event.attendees).toEqual([])
+		expect(event.alarms).toEqual([])
+	})
+
+	test("parses recurring event with exception", () => {
+		const events = parseICalEvents(loadFixture("recurring-event.ics"), "Team")
+
+		expect(events).toHaveLength(2)
+		expect(events[0]!.uid).toBe("recurring-001@test")
+		expect(events[1]!.uid).toBe("recurring-001@test")
+
+		const base = events.find((e) => e.title === "Weekly Sync")
+		expect(base).toBeDefined()
+		expect(base!.recurrenceId).toBeNull()
+
+		const exception = events.find((e) => e.title === "Weekly Sync (moved)")
+		expect(exception).toBeDefined()
+		expect(exception!.recurrenceId).not.toBeNull()
+	})
+
+	test("parses minimal event with defaults", () => {
+		const events = parseICalEvents(loadFixture("minimal-event.ics"), null)
+
+		expect(events).toHaveLength(1)
+		const event = events[0]!
+
+		expect(event.uid).toBe("minimal-001@test")
+		expect(event.title).toBe("Quick Chat")
+		expect(event.startDate).toEqual(new Date("2026-01-15T18:00:00Z"))
+		expect(event.endDate).toEqual(new Date("2026-01-15T19:00:00Z"))
+		expect(event.location).toBeNull()
+		expect(event.description).toBeNull()
+		expect(event.status).toBeNull()
+		expect(event.url).toBeNull()
+		expect(event.organizer).toBeNull()
+		expect(event.attendees).toEqual([])
+		expect(event.alarms).toEqual([])
+		expect(event.recurrenceId).toBeNull()
+	})
+
+	test("parses cancelled status", () => {
+		const events = parseICalEvents(loadFixture("cancelled-event.ics"), null)
+		expect(events[0]!.status).toBe("cancelled")
+	})
+})

packages/aris-source-apple-calendar/src/ical-parser.ts

@@ -0,0 +1,150 @@
+import ICAL from "ical.js"
+
+import {
+	AttendeeRole,
+	AttendeeStatus,
+	CalendarEventStatus,
+	type CalendarAlarm,
+	type CalendarAttendee,
+	type CalendarEventData,
+} from "./types.ts"
+
+/**
+ * Parses a raw iCalendar string and extracts all VEVENT components
+ * into CalendarEventData objects.
+ *
+ * @param icsData - Raw iCalendar string from a CalDAV response
+ * @param calendarName - Display name of the calendar this event belongs to
+ */
+export function parseICalEvents(icsData: string, calendarName: string | null): CalendarEventData[] {
+	const jcal = ICAL.parse(icsData)
+	const comp = new ICAL.Component(jcal)
+	const vevents = comp.getAllSubcomponents("vevent")
+
+	return vevents.map((vevent: InstanceType<typeof ICAL.Component>) =>
+		parseVEvent(vevent, calendarName),
+	)
+}
+
+function parseVEvent(
+	vevent: InstanceType<typeof ICAL.Component>,
+	calendarName: string | null,
+): CalendarEventData {
+	const event = new ICAL.Event(vevent)
+
+	return {
+		uid: event.uid ?? "",
+		title: event.summary ?? "",
+		startDate: event.startDate?.toJSDate() ?? new Date(0),
+		endDate: event.endDate?.toJSDate() ?? new Date(0),
+		isAllDay: event.startDate?.isDate ?? false,
+		location: event.location ?? null,
+		description: event.description ?? null,
+		calendarName,
+		status: parseStatus(asStringOrNull(vevent.getFirstPropertyValue("status"))),
+		url: asStringOrNull(vevent.getFirstPropertyValue("url")),
+		organizer: parseOrganizer(asStringOrNull(event.organizer), vevent),
+		attendees: parseAttendees(Array.isArray(event.attendees) ? event.attendees : []),
+		alarms: parseAlarms(vevent),
+		recurrenceId: event.recurrenceId ? event.recurrenceId.toString() : null,
+	}
+}
+
+function parseStatus(raw: string | null): CalendarEventStatus | null {
+	if (!raw) return null
+	switch (raw.toLowerCase()) {
+		case "confirmed":
+			return CalendarEventStatus.Confirmed
+		case "tentative":
+			return CalendarEventStatus.Tentative
+		case "cancelled":
+			return CalendarEventStatus.Cancelled
+		default:
+			return null
+	}
+}
+
+function parseOrganizer(
+	value: string | null,
+	vevent: InstanceType<typeof ICAL.Component>,
+): string | null {
+	if (!value) return null
+
+	// Try CN parameter first
+	const prop = vevent.getFirstProperty("organizer")
+	if (prop) {
+		const cn = prop.getParameter("cn") as string | undefined
+		if (cn) return cn
+	}
+
+	// Fall back to mailto: value
+	return value.replace(/^mailto:/i, "")
+}
+
+function parseAttendees(properties: unknown[]): CalendarAttendee[] {
+	if (properties.length === 0) return []
+
+	return properties.map((prop) => {
+		const p = prop as InstanceType<typeof ICAL.Property>
+		const value = asStringOrNull(p.getFirstValue())
+		const cn = asStringOrNull(p.getParameter("cn"))
+		const role = asStringOrNull(p.getParameter("role"))
+		const partstat = asStringOrNull(p.getParameter("partstat"))
+
+		return {
+			name: cn,
+			email: value ? value.replace(/^mailto:/i, "") : null,
+			role: parseAttendeeRole(role),
+			status: parseAttendeeStatus(partstat),
+		}
+	})
+}
+
+function parseAttendeeRole(raw: string | null): AttendeeRole | null {
+	if (!raw) return null
+	switch (raw.toUpperCase()) {
+		case "CHAIR":
+			return AttendeeRole.Chair
+		case "REQ-PARTICIPANT":
+			return AttendeeRole.Required
+		case "OPT-PARTICIPANT":
+			return AttendeeRole.Optional
+		default:
+			return null
+	}
+}
+
+function parseAttendeeStatus(raw: string | null): AttendeeStatus | null {
+	if (!raw) return null
+	switch (raw.toUpperCase()) {
+		case "ACCEPTED":
+			return AttendeeStatus.Accepted
+		case "DECLINED":
+			return AttendeeStatus.Declined
+		case "TENTATIVE":
+			return AttendeeStatus.Tentative
+		case "NEEDS-ACTION":
+			return AttendeeStatus.NeedsAction
+		default:
+			return null
+	}
+}
+
+function parseAlarms(vevent: InstanceType<typeof ICAL.Component>): CalendarAlarm[] {
+	const valarms = vevent.getAllSubcomponents("valarm")
+	if (!valarms || valarms.length === 0) return []
+
+	return valarms.map((valarm: InstanceType<typeof ICAL.Component>) => {
+		const trigger = valarm.getFirstPropertyValue("trigger")
+		const action = asStringOrNull(valarm.getFirstPropertyValue("action"))
+
+		return {
+			trigger: trigger ? trigger.toString() : "",
+			action: action ?? "DISPLAY",
+		}
+	})
+}
+
+function asStringOrNull(value: unknown): string | null {
+	return typeof value === "string" ? value : null
+}

packages/aris-source-apple-calendar/src/index.ts

@@ -0,0 +1,16 @@
+export { CalendarKey, type CalendarContext } from "./calendar-context.ts"
+export { CalendarSource, type CalendarSourceOptions } from "./calendar-source.ts"
+export {
+	CalendarEventStatus,
+	AttendeeRole,
+	AttendeeStatus,
+	type CalendarCredentials,
+	type CalendarCredentialProvider,
+	type CalendarDAVClient,
+	type CalendarDAVCalendar,
+	type CalendarDAVObject,
+	type CalendarAttendee,
+	type CalendarAlarm,
+	type CalendarEventData,
+	type CalendarFeedItem,
+} from "./types.ts"

packages/aris-source-apple-calendar/src/types.ts

@@ -0,0 +1,101 @@
+import type { FeedItem } from "@aris/core"
+
+// -- Credential provider --
+
+export interface CalendarCredentials {
+	accessToken: string
+	refreshToken: string
+	/** Unix timestamp in milliseconds when the access token expires */
+	expiresAt: number
+	tokenUrl: string
+	clientId: string
+	clientSecret: string
+}
+
+export interface CalendarCredentialProvider {
+	fetchCredentials(userId: string): Promise<CalendarCredentials | null>
+}
+
+// -- Feed item types --
+
+export const CalendarEventStatus = {
+	Confirmed: "confirmed",
+	Tentative: "tentative",
+	Cancelled: "cancelled",
+} as const
+
+export type CalendarEventStatus = (typeof CalendarEventStatus)[keyof typeof CalendarEventStatus]
+
+export const AttendeeRole = {
+	Chair: "chair",
+	Required: "required",
+	Optional: "optional",
+} as const
+
+export type AttendeeRole = (typeof AttendeeRole)[keyof typeof AttendeeRole]
+
+export const AttendeeStatus = {
+	Accepted: "accepted",
+	Declined: "declined",
+	Tentative: "tentative",
+	NeedsAction: "needs-action",
+} as const
+
+export type AttendeeStatus = (typeof AttendeeStatus)[keyof typeof AttendeeStatus]
+
+export interface CalendarAttendee {
+	name: string | null
+	email: string | null
+	role: AttendeeRole | null
+	status: AttendeeStatus | null
+}
+
+export interface CalendarAlarm {
+	/** ISO 8601 duration relative to event start, e.g. "-PT15M" */
+	trigger: string
+	/** e.g. "DISPLAY", "AUDIO" */
+	action: string
+}
+
+export interface CalendarEventData extends Record<string, unknown> {
+	uid: string
+	title: string
+	startDate: Date
+	endDate: Date
+	isAllDay: boolean
+	location: string | null
+	description: string | null
+	calendarName: string | null
+	status: CalendarEventStatus | null
+	url: string | null
+	organizer: string | null
+	attendees: CalendarAttendee[]
+	alarms: CalendarAlarm[]
+	recurrenceId: string | null
+}
+
+export type CalendarFeedItem = FeedItem<"calendar-event", CalendarEventData>
+
+// -- DAV client interface --
+
+export interface CalendarDAVObject {
+	data?: unknown
+	etag?: string
+	url: string
+}
+
+export interface CalendarDAVCalendar {
+	displayName?: string | Record<string, unknown>
+	url: string
+}
+
+/** Subset of DAVClient used by CalendarSource. */
+export interface CalendarDAVClient {
+	login(): Promise<void>
+	fetchCalendars(): Promise<CalendarDAVCalendar[]>
+	fetchCalendarObjects(params: {
+		calendar: CalendarDAVCalendar
+		timeRange: { start: string; end: string }
+	}): Promise<CalendarDAVObject[]>
+	credentials: Record<string, unknown>
+}

packages/aris-source-google-calendar/fixtures/events.json

@@ -0,0 +1,72 @@
+{
+	"kind": "calendar#events",
+	"summary": "primary",
+	"items": [
+		{
+			"id": "evt-ongoing",
+			"status": "confirmed",
+			"htmlLink": "https://calendar.google.com/event?eid=evt-ongoing",
+			"summary": "Team Standup",
+			"description": "Daily standup meeting",
+			"location": "Room 3A",
+			"start": {
+				"dateTime": "2026-01-20T09:30:00Z"
+			},
+			"end": {
+				"dateTime": "2026-01-20T10:15:00Z"
+			}
+		},
+		{
+			"id": "evt-soon",
+			"status": "confirmed",
+			"htmlLink": "https://calendar.google.com/event?eid=evt-soon",
+			"summary": "1:1 with Manager",
+			"start": {
+				"dateTime": "2026-01-20T10:10:00Z"
+			},
+			"end": {
+				"dateTime": "2026-01-20T10:40:00Z"
+			}
+		},
+		{
+			"id": "evt-later",
+			"status": "confirmed",
+			"htmlLink": "https://calendar.google.com/event?eid=evt-later",
+			"summary": "Design Review",
+			"description": "Review new dashboard designs",
+			"location": "Conference Room B",
+			"start": {
+				"dateTime": "2026-01-20T14:00:00Z"
+			},
+			"end": {
+				"dateTime": "2026-01-20T15:00:00Z"
+			}
+		},
+		{
+			"id": "evt-tentative",
+			"status": "tentative",
+			"htmlLink": "https://calendar.google.com/event?eid=evt-tentative",
+			"summary": "Lunch with Alex",
+			"location": "Cafe Nero",
+			"start": {
+				"dateTime": "2026-01-20T12:00:00Z"
+			},
+			"end": {
+				"dateTime": "2026-01-20T13:00:00Z"
+			}
+		},
+		{
+			"id": "evt-allday",
+			"status": "confirmed",
+			"htmlLink": "https://calendar.google.com/event?eid=evt-allday",
+			"summary": "Company Holiday",
+			"description": "Office closed",
+			"start": {
+				"date": "2026-01-20"
+			},
+			"end": {
+				"date": "2026-01-21"
+			}
+		}
+	]
+}

packages/aris-source-google-calendar/package.json

@@ -0,0 +1,14 @@
+{
+	"name": "@aris/source-google-calendar",
+	"version": "0.0.0",
+	"type": "module",
+	"main": "src/index.ts",
+	"types": "src/index.ts",
+	"scripts": {
+		"test": "bun test ."
+	},
+	"dependencies": {
+		"@aris/core": "workspace:*",
+		"arktype": "^2.1.0"
+	}
+}

packages/aris-source-google-calendar/src/calendar-context.ts

@@ -0,0 +1,13 @@
+import type { ContextKey } from "@aris/core"
+
+import { contextKey } from "@aris/core"
+
+export interface NextEvent {
+	title: string
+	startTime: Date
+	endTime: Date
+	minutesUntilStart: number
+	location: string | null
+}
+
+export const NextEventKey: ContextKey<NextEvent> = contextKey("nextEvent")

packages/aris-source-google-calendar/src/feed-items.ts

@@ -0,0 +1,22 @@
+import type { FeedItem } from "@aris/core"
+
+import type { CalendarEventData } from "./types"
+
+export const CalendarFeedItemType = {
+	event: "calendar-event",
+	allDay: "calendar-all-day",
+} as const
+
+export type CalendarFeedItemType = (typeof CalendarFeedItemType)[keyof typeof CalendarFeedItemType]
+
+export interface CalendarEventFeedItem extends FeedItem<
+	typeof CalendarFeedItemType.event,
+	CalendarEventData
+> {}
+
+export interface CalendarAllDayFeedItem extends FeedItem<
+	typeof CalendarFeedItemType.allDay,
+	CalendarEventData
+> {}
+
+export type CalendarFeedItem = CalendarEventFeedItem | CalendarAllDayFeedItem

packages/aris-source-google-calendar/src/google-calendar-api.ts

@@ -0,0 +1,122 @@
+// Google Calendar REST API v3 client
+// https://developers.google.com/calendar/api/v3/reference/events/list
+
+import { type } from "arktype"
+
+import type {
+	ApiCalendarEvent,
+	GoogleCalendarClient,
+	GoogleOAuthProvider,
+	ListEventsOptions,
+} from "./types"
+
+import { EventStatus } from "./types"
+
+const eventStatusSchema = type.enumerated(
+	EventStatus.Confirmed,
+	EventStatus.Tentative,
+	EventStatus.Cancelled,
+)
+
+const eventDateTimeSchema = type({
+	"dateTime?": "string",
+	"date?": "string",
+	"timeZone?": "string",
+})
+
+const eventSchema = type({
+	id: "string",
+	status: eventStatusSchema,
+	htmlLink: "string",
+	"summary?": "string",
+	"description?": "string",
+	"location?": "string",
+	start: eventDateTimeSchema,
+	end: eventDateTimeSchema,
+})
+
+const calendarListEntrySchema = type({
+	id: "string",
+})
+
+const calendarListResponseSchema = type({
+	"items?": calendarListEntrySchema.array(),
+	"nextPageToken?": "string",
+})
+
+const eventsResponseSchema = type({
+	"items?": eventSchema.array(),
+	"nextPageToken?": "string",
+})
+
+export class DefaultGoogleCalendarClient implements GoogleCalendarClient {
+	private static readonly API_BASE = "https://www.googleapis.com/calendar/v3"
+
+	private readonly oauthProvider: GoogleOAuthProvider
+
+	constructor(oauthProvider: GoogleOAuthProvider) {
+		this.oauthProvider = oauthProvider
+	}
+
+	async listCalendarIds(): Promise<string[]> {
+		const url = `${DefaultGoogleCalendarClient.API_BASE}/users/me/calendarList?fields=items(id)`
+		const json = await this.request(url)
+		const result = calendarListResponseSchema(json)
+
+		if (result instanceof type.errors) {
+			throw new Error(`Google Calendar API response validation failed: ${result.summary}`)
+		}
+
+		if (!result.items) {
+			return []
+		}
+		return result.items.map((entry) => entry.id)
+	}
+
+	async listEvents(options: ListEventsOptions): Promise<ApiCalendarEvent[]> {
+		const url = new URL(
+			`${DefaultGoogleCalendarClient.API_BASE}/calendars/${encodeURIComponent(options.calendarId)}/events`,
+		)
+		url.searchParams.set("timeMin", options.timeMin.toISOString())
+		url.searchParams.set("timeMax", options.timeMax.toISOString())
+		url.searchParams.set("singleEvents", "true")
+		url.searchParams.set("orderBy", "startTime")
+
+		const json = await this.request(url.toString())
+		const result = eventsResponseSchema(json)
+
+		if (result instanceof type.errors) {
+			throw new Error(`Google Calendar API response validation failed: ${result.summary}`)
+		}
+
+		if (!result.items) {
+			return []
+		}
+
+		return result.items
+	}
+
+	/** Authenticated GET with auto token refresh on 401. */
+	private async request(url: string): Promise<unknown> {
+		const token = await this.oauthProvider.fetchAccessToken()
+		let response = await fetch(url, {
+			headers: { Authorization: `Bearer ${token}` },
+		})
+
+		if (response.status === 401) {
+			const newToken = await this.oauthProvider.refresh()
+			response = await fetch(url, {
+				headers: { Authorization: `Bearer ${newToken}` },
+			})
+		}
+
+		if (!response.ok) {
+			const body = await response.text()
+			throw new Error(
+				`Google Calendar API error: ${response.status} ${response.statusText}: ${body}`,
+			)
+		}
+
+		return response.json()
+	}
+}

packages/aris-source-google-calendar/src/google-calendar-source.test.ts

@@ -0,0 +1,292 @@
+import { contextValue, type Context } from "@aris/core"
+import { describe, expect, test } from "bun:test"
+
+import type { ApiCalendarEvent, GoogleCalendarClient, ListEventsOptions } from "./types"
+
+import fixture from "../fixtures/events.json"
+import { NextEventKey } from "./calendar-context"
+import { CalendarFeedItemType } from "./feed-items"
+import { GoogleCalendarSource } from "./google-calendar-source"
+
+const NOW = new Date("2026-01-20T10:00:00Z")
+
+function fixtureEvents(): ApiCalendarEvent[] {
+	return fixture.items as unknown as ApiCalendarEvent[]
+}
+
+function createMockClient(
+	eventsByCalendar: Record<string, ApiCalendarEvent[]>,
+): GoogleCalendarClient {
+	return {
+		listCalendarIds: async () => Object.keys(eventsByCalendar),
+		listEvents: async (options: ListEventsOptions) => {
+			const events = eventsByCalendar[options.calendarId] ?? []
+			return events.filter((e) => {
+				const startRaw = e.start.dateTime ?? e.start.date ?? ""
+				const endRaw = e.end.dateTime ?? e.end.date ?? ""
+				return (
+					new Date(startRaw).getTime() < options.timeMax.getTime() &&
+					new Date(endRaw).getTime() > options.timeMin.getTime()
+				)
+			})
+		},
+	}
+}
+
+function defaultMockClient(): GoogleCalendarClient {
+	return createMockClient({ primary: fixtureEvents() })
+}
+
+function createContext(time?: Date): Context {
+	return { time: time ?? NOW }
+}
+
+describe("GoogleCalendarSource", () => {
+	describe("constructor", () => {
+		test("has correct id", () => {
+			const source = new GoogleCalendarSource({ client: defaultMockClient() })
+			expect(source.id).toBe("google-calendar")
+		})
+	})
+
+	describe("fetchItems", () => {
+		test("returns empty array when no events", async () => {
+			const source = new GoogleCalendarSource({ client: createMockClient({ primary: [] }) })
+			const items = await source.fetchItems(createContext())
+			expect(items).toEqual([])
+		})
+
+		test("returns feed items for all events in window", async () => {
+			const source = new GoogleCalendarSource({ client: defaultMockClient() })
+			const items = await source.fetchItems(createContext())
+
+			expect(items.length).toBe(fixture.items.length)
+		})
+
+		test("assigns calendar-event type to timed events", async () => {
+			const source = new GoogleCalendarSource({ client: defaultMockClient() })
+			const items = await source.fetchItems(createContext())
+
+			const timedItems = items.filter((i) => i.type === CalendarFeedItemType.event)
+			expect(timedItems.length).toBe(4)
+		})
+
+		test("assigns calendar-all-day type to all-day events", async () => {
+			const source = new GoogleCalendarSource({ client: defaultMockClient() })
+			const items = await source.fetchItems(createContext())
+
+			const allDayItems = items.filter((i) => i.type === CalendarFeedItemType.allDay)
+			expect(allDayItems.length).toBe(1)
+		})
+
+		test("ongoing events get highest priority (1.0)", async () => {
+			const source = new GoogleCalendarSource({ client: defaultMockClient() })
+			const items = await source.fetchItems(createContext())
+
+			const ongoing = items.find((i) => i.data.eventId === "evt-ongoing")
+			expect(ongoing).toBeDefined()
+			expect(ongoing!.priority).toBe(1.0)
+		})
+
+		test("upcoming events get higher priority when sooner", async () => {
+			const source = new GoogleCalendarSource({ client: defaultMockClient() })
+			const items = await source.fetchItems(createContext())
+
+			const soon = items.find((i) => i.data.eventId === "evt-soon")
+			const later = items.find((i) => i.data.eventId === "evt-later")
+
+			expect(soon).toBeDefined()
+			expect(later).toBeDefined()
+			expect(soon!.priority).toBeGreaterThan(later!.priority)
+		})
+
+		test("all-day events get flat priority (0.4)", async () => {
+			const source = new GoogleCalendarSource({ client: defaultMockClient() })
+			const items = await source.fetchItems(createContext())
+
+			const allDay = items.find((i) => i.data.eventId === "evt-allday")
+			expect(allDay).toBeDefined()
+			expect(allDay!.priority).toBe(0.4)
+		})
+
+		test("generates unique IDs for each item", async () => {
+			const source = new GoogleCalendarSource({ client: defaultMockClient() })
+			const items = await source.fetchItems(createContext())
+
+			const ids = items.map((i) => i.id)
+			const uniqueIds = new Set(ids)
+			expect(uniqueIds.size).toBe(ids.length)
+		})
+
+		test("sets timestamp from context.time", async () => {
+			const source = new GoogleCalendarSource({ client: defaultMockClient() })
+			const items = await source.fetchItems(createContext())
+
+			for (const item of items) {
+				expect(item.timestamp).toEqual(NOW)
+			}
+		})
+
+		test("respects lookaheadHours", async () => {
+			// Only 2 hours lookahead from 10:00 → events before 12:00
+			const source = new GoogleCalendarSource({
+				client: defaultMockClient(),
+				lookaheadHours: 2,
+			})
+			const items = await source.fetchItems(createContext())
+
+			// Should include: ongoing (09:30-10:15), soon (10:10-10:40), allday (00:00-next day)
+			// Should exclude: later (14:00), tentative lunch (12:00)
+			const eventIds = items.map((i) => i.data.eventId)
+			expect(eventIds).toContain("evt-ongoing")
+			expect(eventIds).toContain("evt-soon")
+			expect(eventIds).toContain("evt-allday")
+			expect(eventIds).not.toContain("evt-later")
+			expect(eventIds).not.toContain("evt-tentative")
+		})
+
+		test("defaults to all user calendars via listCalendarIds", async () => {
+			const workEvent: ApiCalendarEvent = {
+				id: "evt-work",
+				status: "confirmed",
+				htmlLink: "https://calendar.google.com/event?eid=evt-work",
+				summary: "Work Meeting",
+				start: { dateTime: "2026-01-20T11:00:00Z" },
+				end: { dateTime: "2026-01-20T12:00:00Z" },
+			}
+
+			const client = createMockClient({
+				primary: fixtureEvents(),
+				"work@example.com": [workEvent],
+			})
+
+			// No calendarIds provided — should discover both calendars
+			const source = new GoogleCalendarSource({ client })
+			const items = await source.fetchItems(createContext())
+
+			const eventIds = items.map((i) => i.data.eventId)
+			expect(eventIds).toContain("evt-work")
+			expect(eventIds).toContain("evt-ongoing")
+		})
+
+		test("fetches from explicit calendar IDs", async () => {
+			const workEvent: ApiCalendarEvent = {
+				id: "evt-work",
+				status: "confirmed",
+				htmlLink: "https://calendar.google.com/event?eid=evt-work",
+				summary: "Work Meeting",
+				start: { dateTime: "2026-01-20T11:00:00Z" },
+				end: { dateTime: "2026-01-20T12:00:00Z" },
+			}
+
+			const client = createMockClient({
+				primary: fixtureEvents(),
+				"work@example.com": [workEvent],
+			})
+
+			const source = new GoogleCalendarSource({
+				client,
+				calendarIds: ["primary", "work@example.com"],
+			})
+			const items = await source.fetchItems(createContext())
+
+			const eventIds = items.map((i) => i.data.eventId)
+			expect(eventIds).toContain("evt-work")
+			expect(eventIds).toContain("evt-ongoing")
+		})
+	})
+
+	describe("fetchContext", () => {
+		test("returns null when no events", async () => {
+			const source = new GoogleCalendarSource({ client: createMockClient({ primary: [] }) })
+			const result = await source.fetchContext(createContext())
+			expect(result).toBeNull()
+		})
+
+		test("returns null when only all-day events", async () => {
+			const allDayOnly: ApiCalendarEvent[] = [
+				{
+					id: "evt-allday",
+					status: "confirmed",
+					htmlLink: "https://calendar.google.com/event?eid=evt-allday",
+					summary: "Holiday",
+					start: { date: "2026-01-20" },
+					end: { date: "2026-01-21" },
+				},
+			]
+			const source = new GoogleCalendarSource({
+				client: createMockClient({ primary: allDayOnly }),
+			})
+			const result = await source.fetchContext(createContext())
+			expect(result).toBeNull()
+		})
+
+		test("returns next upcoming timed event (not ongoing)", async () => {
+			const source = new GoogleCalendarSource({ client: defaultMockClient() })
+			const result = await source.fetchContext(createContext())
+
+			expect(result).not.toBeNull()
+			const nextEvent = contextValue(result! as Context, NextEventKey)
+			expect(nextEvent).toBeDefined()
+			// evt-soon starts at 10:10, which is the nearest future timed event
+			expect(nextEvent!.title).toBe("1:1 with Manager")
+			expect(nextEvent!.minutesUntilStart).toBe(10)
+			expect(nextEvent!.location).toBeNull()
+		})
+
+		test("includes location when available", async () => {
+			const events: ApiCalendarEvent[] = [
+				{
+					id: "evt-loc",
+					status: "confirmed",
+					htmlLink: "https://calendar.google.com/event?eid=evt-loc",
+					summary: "Offsite",
+					location: "123 Main St",
+					start: { dateTime: "2026-01-20T11:00:00Z" },
+					end: { dateTime: "2026-01-20T12:00:00Z" },
+				},
+			]
+			const source = new GoogleCalendarSource({
+				client: createMockClient({ primary: events }),
+			})
+			const result = await source.fetchContext(createContext())
+
+			expect(result).not.toBeNull()
+			const nextEvent = contextValue(result! as Context, NextEventKey)
+			expect(nextEvent).toBeDefined()
+			expect(nextEvent!.location).toBe("123 Main St")
+		})
+
+		test("skips ongoing events for next-event context", async () => {
+			const events: ApiCalendarEvent[] = [
+				{
+					id: "evt-now",
+					status: "confirmed",
+					htmlLink: "https://calendar.google.com/event?eid=evt-now",
+					summary: "Current Meeting",
+					start: { dateTime: "2026-01-20T09:30:00Z" },
+					end: { dateTime: "2026-01-20T10:30:00Z" },
+				},
+			]
+			const source = new GoogleCalendarSource({
+				client: createMockClient({ primary: events }),
+			})
+			const result = await source.fetchContext(createContext())
+			expect(result).toBeNull()
+		})
+	})
+
+	describe("priority ordering", () => {
+		test("ongoing > upcoming > all-day", async () => {
+			const source = new GoogleCalendarSource({ client: defaultMockClient() })
+			const items = await source.fetchItems(createContext())
+
+			const ongoing = items.find((i) => i.data.eventId === "evt-ongoing")!
+			const upcoming = items.find((i) => i.data.eventId === "evt-soon")!
+			const allDay = items.find((i) => i.data.eventId === "evt-allday")!
+
+			expect(ongoing.priority).toBeGreaterThan(upcoming.priority)
+			expect(upcoming.priority).toBeGreaterThan(allDay.priority)
+		})
+	})
+})

packages/aris-source-google-calendar/src/google-calendar-source.ts

@@ -0,0 +1,202 @@
+import type { Context, FeedSource } from "@aris/core"
+
+import type {
+	ApiCalendarEvent,
+	CalendarEventData,
+	GoogleCalendarClient,
+	GoogleOAuthProvider,
+} from "./types"
+
+import { NextEventKey, type NextEvent } from "./calendar-context"
+
+interface GoogleCalendarSourceBaseOptions {
+	calendarIds?: string[]
+	/** Default: 24 */
+	lookaheadHours?: number
+}
+
+interface GoogleCalendarSourceWithProvider extends GoogleCalendarSourceBaseOptions {
+	oauthProvider: GoogleOAuthProvider
+	client?: never
+}
+
+interface GoogleCalendarSourceWithClient extends GoogleCalendarSourceBaseOptions {
+	oauthProvider?: never
+	client: GoogleCalendarClient
+}
+
+export type GoogleCalendarSourceOptions =
+	| GoogleCalendarSourceWithProvider
+	| GoogleCalendarSourceWithClient
+import { CalendarFeedItemType, type CalendarFeedItem } from "./feed-items"
+import { DefaultGoogleCalendarClient } from "./google-calendar-api"
+
+const DEFAULT_LOOKAHEAD_HOURS = 24
+
+const PRIORITY_ONGOING = 1.0
+const PRIORITY_UPCOMING_MAX = 0.9
+const PRIORITY_UPCOMING_MIN = 0.3
+const PRIORITY_ALL_DAY = 0.4
+
+/**
+ * A FeedSource that provides Google Calendar events and next-event context.
+ *
+ * Fetches upcoming and all-day events within a configurable lookahead window.
+ * Provides a NextEvent context for downstream sources to react to the user's schedule.
+ *
+ * @example
+ * ```ts
+ * const calendarSource = new GoogleCalendarSource({
+ *   oauthProvider: myOAuthProvider,
+ *   calendarIds: ["primary", "work@example.com"],
+ *   lookaheadHours: 12,
+ * })
+ *
+ * const engine = new FeedEngine()
+ *   .register(calendarSource)
+ *
+ * // Access next-event context in downstream sources
+ * const next = contextValue(context, NextEventKey)
+ * if (next && next.minutesUntilStart < 15) {
+ *   // remind user
+ * }
+ * ```
+ */
+export class GoogleCalendarSource implements FeedSource<CalendarFeedItem> {
+	readonly id = "google-calendar"
+
+	private readonly client: GoogleCalendarClient
+	private readonly calendarIds: string[] | undefined
+	private readonly lookaheadHours: number
+
+	constructor(options: GoogleCalendarSourceOptions) {
+		this.client = options.client ?? new DefaultGoogleCalendarClient(options.oauthProvider)
+		this.calendarIds = options.calendarIds
+		this.lookaheadHours = options.lookaheadHours ?? DEFAULT_LOOKAHEAD_HOURS
+	}
+
+	async fetchContext(context: Context): Promise<Partial<Context> | null> {
+		const events = await this.fetchAllEvents(context.time)
+
+		const now = context.time.getTime()
+		const nextTimedEvent = events.find((e) => !e.isAllDay && e.startTime.getTime() > now)
+
+		if (!nextTimedEvent) {
+			return null
+		}
+
+		const minutesUntilStart = (nextTimedEvent.startTime.getTime() - now) / 60_000
+
+		const nextEvent: NextEvent = {
+			title: nextTimedEvent.title,
+			startTime: nextTimedEvent.startTime,
+			endTime: nextTimedEvent.endTime,
+			minutesUntilStart,
+			location: nextTimedEvent.location,
+		}
+
+		return { [NextEventKey]: nextEvent }
+	}
+
+	async fetchItems(context: Context): Promise<CalendarFeedItem[]> {
+		const events = await this.fetchAllEvents(context.time)
+		const now = context.time.getTime()
+		const lookaheadMs = this.lookaheadHours * 60 * 60 * 1000
+
+		return events.map((event) => createFeedItem(event, now, lookaheadMs))
+	}
+
+	private async resolveCalendarIds(): Promise<string[]> {
+		if (this.calendarIds) {
+			return this.calendarIds
+		}
+		return this.client.listCalendarIds()
+	}
+
+	private async fetchAllEvents(time: Date): Promise<CalendarEventData[]> {
+		const timeMax = new Date(time.getTime() + this.lookaheadHours * 60 * 60 * 1000)
+		const calendarIds = await this.resolveCalendarIds()
+
+		const results = await Promise.all(
+			calendarIds.map(async (calendarId) => {
+				const raw = await this.client.listEvents({
+					calendarId,
+					timeMin: time,
+					timeMax,
+				})
+				return raw.map((event) => parseEvent(event, calendarId))
+			}),
+		)
+
+		const allEvents = results.flat()
+
+		// Sort by start time ascending
+		allEvents.sort((a, b) => a.startTime.getTime() - b.startTime.getTime())
+
+		return allEvents
+	}
+}
+
+function parseEvent(event: ApiCalendarEvent, calendarId: string): CalendarEventData {
+	const startRaw = event.start.dateTime ?? event.start.date
+	const endRaw = event.end.dateTime ?? event.end.date
+
+	if (!startRaw || !endRaw) {
+		throw new Error(`Event ${event.id} is missing start or end date`)
+	}
+
+	const isAllDay = !event.start.dateTime
+
+	return {
+		eventId: event.id,
+		calendarId,
+		title: event.summary ?? "(No title)",
+		description: event.description ?? null,
+		location: event.location ?? null,
+		startTime: new Date(startRaw),
+		endTime: new Date(endRaw),
+		isAllDay,
+		status: event.status,
+		htmlLink: event.htmlLink,
+	}
+}
+
+function computePriority(event: CalendarEventData, nowMs: number, lookaheadMs: number): number {
+	if (event.isAllDay) {
+		return PRIORITY_ALL_DAY
+	}
+
+	const startMs = event.startTime.getTime()
+	const endMs = event.endTime.getTime()
+
+	// Ongoing: start <= now < end
+	if (startMs <= nowMs && nowMs < endMs) {
+		return PRIORITY_ONGOING
+	}
+
+	// Upcoming: linear decay from PRIORITY_UPCOMING_MAX to PRIORITY_UPCOMING_MIN
+	const msUntilStart = startMs - nowMs
+	if (msUntilStart <= 0) {
+		return PRIORITY_UPCOMING_MIN
+	}
+
+	const ratio = Math.min(msUntilStart / lookaheadMs, 1)
+	return PRIORITY_UPCOMING_MAX - ratio * (PRIORITY_UPCOMING_MAX - PRIORITY_UPCOMING_MIN)
+}
+
+function createFeedItem(
+	event: CalendarEventData,
+	nowMs: number,
+	lookaheadMs: number,
+): CalendarFeedItem {
+	const priority = computePriority(event, nowMs, lookaheadMs)
+	const itemType = event.isAllDay ? CalendarFeedItemType.allDay : CalendarFeedItemType.event
+
+	return {
+		id: `calendar-${event.calendarId}-${event.eventId}`,
+		type: itemType,
+		priority,
+		timestamp: new Date(nowMs),
+		data: event,
+	}
+}

packages/aris-source-google-calendar/src/index.ts

@@ -0,0 +1,20 @@
+export { NextEventKey, type NextEvent } from "./calendar-context"
+export {
+	CalendarFeedItemType,
+	type CalendarFeedItemType as CalendarFeedItemTypeType,
+	type CalendarAllDayFeedItem,
+	type CalendarEventFeedItem,
+	type CalendarFeedItem,
+} from "./feed-items"
+export { DefaultGoogleCalendarClient } from "./google-calendar-api"
+export { GoogleCalendarSource, type GoogleCalendarSourceOptions } from "./google-calendar-source"
+export {
+	EventStatus,
+	type EventStatus as EventStatusType,
+	type ApiCalendarEvent,
+	type ApiEventDateTime,
+	type CalendarEventData,
+	type GoogleCalendarClient,
+	type GoogleOAuthProvider,
+	type ListEventsOptions,
+} from "./types"

packages/aris-source-google-calendar/src/types.ts

@@ -0,0 +1,55 @@
+export interface GoogleOAuthProvider {
+	fetchAccessToken(): Promise<string>
+	refresh(): Promise<string>
+	revoke(): Promise<void>
+}
+
+export const EventStatus = {
+	Confirmed: "confirmed",
+	Tentative: "tentative",
+	Cancelled: "cancelled",
+} as const
+
+export type EventStatus = (typeof EventStatus)[keyof typeof EventStatus]
+
+/** Exactly one of dateTime or date is present. */
+export interface ApiEventDateTime {
+	dateTime?: string
+	date?: string
+	timeZone?: string
+}
+
+export interface ApiCalendarEvent {
+	id: string
+	status: EventStatus
+	htmlLink: string
+	summary?: string
+	description?: string
+	location?: string
+	start: ApiEventDateTime
+	end: ApiEventDateTime
+}
+
+export type CalendarEventData = {
+	eventId: string
+	calendarId: string
+	title: string
+	description: string | null
+	location: string | null
+	startTime: Date
+	endTime: Date
+	isAllDay: boolean
+	status: EventStatus
+	htmlLink: string
+}
+
+export interface ListEventsOptions {
+	calendarId: string
+	timeMin: Date
+	timeMax: Date
+}
+
+export interface GoogleCalendarClient {
+	listCalendarIds(): Promise<string[]>
+	listEvents(options: ListEventsOptions): Promise<ApiCalendarEvent[]>
+}

packages/aris-source-location/README.md

@@ -0,0 +1,112 @@
+# @aris/source-location
+
+A FeedSource that provides location context to the ARIS feed graph.
+
+## Overview
+
+This source accepts external location pushes and does not query location itself. It provides location context to downstream sources (e.g., weather, transit) but does not produce feed items.
+
+## Installation
+
+```bash
+bun add @aris/source-location
+```
+
+## Usage
+
+```ts
+import { LocationSource, LocationKey, type Location } from "@aris/source-location"
+import { contextValue } from "@aris/core"
+
+// Create source with default history size (1)
+const locationSource = new LocationSource()
+
+// Or keep last 10 locations
+const locationSource = new LocationSource({ historySize: 10 })
+
+// Push location from external provider (GPS, network, etc.)
+locationSource.pushLocation({
+	lat: 37.7749,
+	lng: -122.4194,
+	accuracy: 10,
+	timestamp: new Date(),
+})
+
+// Access current location
+locationSource.lastLocation // { lat, lng, accuracy, timestamp } | null
+
+// Access location history (oldest first)
+locationSource.locationHistory // readonly Location[]
+```
+
+### With FeedController
+
+```ts
+import { FeedController } from "@aris/core"
+import { LocationSource } from "@aris/source-location"
+
+const locationSource = new LocationSource()
+
+const controller = new FeedController({
+	sources: [locationSource, weatherSource, transitSource],
+})
+
+// Push location updates - downstream sources will re-fetch
+locationSource.pushLocation({
+	lat: 37.7749,
+	lng: -122.4194,
+	accuracy: 10,
+	timestamp: new Date(),
+})
+```
+
+### Reading Location in Downstream Sources
+
+```ts
+import { contextValue, type FeedSource } from "@aris/core"
+import { LocationKey } from "@aris/source-location"
+
+const weatherSource: FeedSource = {
+	id: "weather",
+	dependencies: ["location"],
+
+	async fetchContext(context) {
+		const location = contextValue(context, LocationKey)
+		if (!location) return {}
+
+		const weather = await fetchWeather(location.lat, location.lng)
+		return { [WeatherKey]: weather }
+	},
+}
+```
+
+## API
+
+### `LocationSource`
+
+| Member                   | Type                  | Description                           |
+| ------------------------ | --------------------- | ------------------------------------- |
+| `id`                     | `"location"`          | Source identifier                     |
+| `constructor(options?)`  |                       | Create with optional `historySize`    |
+| `pushLocation(location)` | `void`                | Push new location, notifies listeners |
+| `lastLocation`           | `Location \| null`    | Most recent location                  |
+| `locationHistory`        | `readonly Location[]` | All retained locations, oldest first  |
+
+### `Location`
+
+```ts
+interface Location {
+	lat: number
+	lng: number
+	accuracy: number // meters
+	timestamp: Date
+}
+```
+
+### `LocationKey`
+
+Typed context key for accessing location in downstream sources:
+
+```ts
+const location = contextValue(context, LocationKey)
+```

packages/aris-source-location/package.json

@@ -0,0 +1,13 @@
+{
+	"name": "@aris/source-location",
+	"version": "0.0.0",
+	"type": "module",
+	"main": "src/index.ts",
+	"types": "src/index.ts",
+	"scripts": {
+		"test": "bun test src/"
+	},
+	"dependencies": {
+		"@aris/core": "workspace:*"
+	}
+}

packages/aris-source-location/src/index.ts

@@ -0,0 +1,6 @@
+export {
+	LocationSource,
+	LocationKey,
+	type Location,
+	type LocationSourceOptions,
+} from "./location-source.ts"

packages/aris-source-location/src/location-source.test.ts

@@ -0,0 +1,150 @@
+import { describe, expect, mock, test } from "bun:test"
+
+import { LocationKey, LocationSource, type Location } from "./location-source.ts"
+
+function createLocation(overrides: Partial<Location> = {}): Location {
+	return {
+		lat: 37.7749,
+		lng: -122.4194,
+		accuracy: 10,
+		timestamp: new Date(),
+		...overrides,
+	}
+}
+
+describe("LocationSource", () => {
+	describe("FeedSource interface", () => {
+		test("has correct id", () => {
+			const source = new LocationSource()
+			expect(source.id).toBe("location")
+		})
+
+		test("fetchItems always returns empty array", async () => {
+			const source = new LocationSource()
+			source.pushLocation(createLocation())
+
+			const items = await source.fetchItems()
+			expect(items).toEqual([])
+		})
+
+		test("fetchContext returns null when no location", async () => {
+			const source = new LocationSource()
+
+			const context = await source.fetchContext()
+			expect(context).toBeNull()
+		})
+
+		test("fetchContext returns location when available", async () => {
+			const source = new LocationSource()
+			const location = createLocation()
+			source.pushLocation(location)
+
+			const context = await source.fetchContext()
+			expect(context).toEqual({ [LocationKey]: location })
+		})
+	})
+
+	describe("pushLocation", () => {
+		test("updates lastLocation", () => {
+			const source = new LocationSource()
+			expect(source.lastLocation).toBeNull()
+
+			const location = createLocation()
+			source.pushLocation(location)
+
+			expect(source.lastLocation).toEqual(location)
+		})
+
+		test("notifies listeners", () => {
+			const source = new LocationSource()
+			const listener = mock()
+
+			source.onContextUpdate(listener)
+
+			const location = createLocation()
+			source.pushLocation(location)
+
+			expect(listener).toHaveBeenCalledTimes(1)
+			expect(listener).toHaveBeenCalledWith({ [LocationKey]: location })
+		})
+	})
+
+	describe("history", () => {
+		test("default historySize is 1", () => {
+			const source = new LocationSource()
+
+			source.pushLocation(createLocation({ lat: 1 }))
+			source.pushLocation(createLocation({ lat: 2 }))
+
+			expect(source.locationHistory).toHaveLength(1)
+			expect(source.lastLocation?.lat).toBe(2)
+		})
+
+		test("respects configured historySize", () => {
+			const source = new LocationSource({ historySize: 3 })
+
+			const loc1 = createLocation({ lat: 1 })
+			const loc2 = createLocation({ lat: 2 })
+			const loc3 = createLocation({ lat: 3 })
+
+			source.pushLocation(loc1)
+			source.pushLocation(loc2)
+			source.pushLocation(loc3)
+
+			expect(source.locationHistory).toEqual([loc1, loc2, loc3])
+		})
+
+		test("evicts oldest when exceeding historySize", () => {
+			const source = new LocationSource({ historySize: 2 })
+
+			const loc1 = createLocation({ lat: 1 })
+			const loc2 = createLocation({ lat: 2 })
+			const loc3 = createLocation({ lat: 3 })
+
+			source.pushLocation(loc1)
+			source.pushLocation(loc2)
+			source.pushLocation(loc3)
+
+			expect(source.locationHistory).toEqual([loc2, loc3])
+		})
+
+		test("locationHistory is readonly", () => {
+			const source = new LocationSource({ historySize: 3 })
+			source.pushLocation(createLocation())
+
+			const history = source.locationHistory
+			expect(Array.isArray(history)).toBe(true)
+		})
+	})
+
+	describe("onContextUpdate", () => {
+		test("returns cleanup function", () => {
+			const source = new LocationSource()
+			const listener = mock()
+
+			const cleanup = source.onContextUpdate(listener)
+
+			source.pushLocation(createLocation({ lat: 1 }))
+			expect(listener).toHaveBeenCalledTimes(1)
+
+			cleanup()
+
+			source.pushLocation(createLocation({ lat: 2 }))
+			expect(listener).toHaveBeenCalledTimes(1)
+		})
+
+		test("supports multiple listeners", () => {
+			const source = new LocationSource()
+			const listener1 = mock()
+			const listener2 = mock()
+
+			source.onContextUpdate(listener1)
+			source.onContextUpdate(listener2)
+
+			source.pushLocation(createLocation())
+
+			expect(listener1).toHaveBeenCalledTimes(1)
+			expect(listener2).toHaveBeenCalledTimes(1)
+		})
+	})
+})

packages/aris-source-location/src/location-source.ts

@@ -0,0 +1,86 @@
+import type { Context, FeedSource } from "@aris/core"
+
+import { contextKey, type ContextKey } from "@aris/core"
+
+/**
+ * Geographic coordinates with accuracy and timestamp.
+ */
+export interface Location {
+	lat: number
+	lng: number
+	/** Accuracy in meters */
+	accuracy: number
+	timestamp: Date
+}
+
+export interface LocationSourceOptions {
+	/** Number of locations to retain in history. Defaults to 1. */
+	historySize?: number
+}
+
+export const LocationKey: ContextKey<Location> = contextKey("location")
+
+/**
+ * A FeedSource that provides location context.
+ *
+ * This source accepts external location pushes and does not query location itself.
+ * Use `pushLocation` to update the location from an external provider (e.g., GPS, network).
+ *
+ * Does not produce feed items - always returns empty array from `fetchItems`.
+ */
+export class LocationSource implements FeedSource {
+	readonly id = "location"
+
+	private readonly historySize: number
+	private locations: Location[] = []
+	private listeners = new Set<(update: Partial<Context>) => void>()
+
+	constructor(options: LocationSourceOptions = {}) {
+		this.historySize = options.historySize ?? 1
+	}
+
+	/**
+	 * Push a new location update. Notifies all context listeners.
+	 */
+	pushLocation(location: Location): void {
+		this.locations.push(location)
+		if (this.locations.length > this.historySize) {
+			this.locations.shift()
+		}
+		this.listeners.forEach((listener) => {
+			listener({ [LocationKey]: location })
+		})
+	}
+
+	/**
+	 * Most recent location, or null if none pushed.
+	 */
+	get lastLocation(): Location | null {
+		return this.locations[this.locations.length - 1] ?? null
+	}
+
+	/**
+	 * Location history, oldest first. Length limited by `historySize`.
+	 */
+	get locationHistory(): readonly Location[] {
+		return this.locations
+	}
+
+	onContextUpdate(callback: (update: Partial<Context>) => void): () => void {
+		this.listeners.add(callback)
+		return () => {
+			this.listeners.delete(callback)
+		}
+	}
+
+	async fetchContext(): Promise<Partial<Context> | null> {
+		if (this.lastLocation) {
+			return { [LocationKey]: this.lastLocation }
+		}
+		return null
+	}
+
+	async fetchItems(): Promise<[]> {
+		return []
+	}
+}

packages/aris-source-tfl/package.json

@@ -0,0 +1,16 @@
+{
+	"name": "@aris/source-tfl",
+	"version": "0.0.0",
+	"type": "module",
+	"main": "src/index.ts",
+	"types": "src/index.ts",
+	"scripts": {
+		"test": "bun test src/",
+		"fetch-fixtures": "bun run scripts/fetch-fixtures.ts"
+	},
+	"dependencies": {
+		"@aris/core": "workspace:*",
+		"@aris/source-location": "workspace:*",
+		"arktype": "^2.1.0"
+	}
+}

packages/aris-source-tfl/scripts/fetch-fixtures.ts

@@ -0,0 +1,35 @@
+// Fetches real TfL API responses and saves them as test fixtures
+
+const TEST_LINES = ["northern", "central", "elizabeth"]
+const BASE_URL = "https://api.tfl.gov.uk"
+
+async function fetchFixtures() {
+	console.log("Fetching line statuses...")
+	const statusRes = await fetch(`${BASE_URL}/Line/${TEST_LINES.join(",")}/Status`)
+	const lineStatuses = await statusRes.json()
+
+	console.log("Fetching stop points...")
+	const stopPoints: Record<string, unknown> = {}
+	for (const lineId of TEST_LINES) {
+		console.log(`  Fetching ${lineId}...`)
+		const res = await fetch(`${BASE_URL}/Line/${lineId}/StopPoints`)
+		stopPoints[lineId] = await res.json()
+	}
+
+	const fixtures = {
+		fetchedAt: new Date().toISOString(),
+		lineStatuses,
+		stopPoints,
+	}
+
+	const path = new URL("../fixtures/tfl-responses.json", import.meta.url)
+	await Bun.write(path, JSON.stringify(fixtures))
+
+	console.log(`\nFixtures saved to fixtures/tfl-responses.json`)
+	console.log(`  Line statuses: ${(lineStatuses as unknown[]).length} lines`)
+	for (const [lineId, stops] of Object.entries(stopPoints)) {
+		console.log(`  ${lineId} stops: ${(stops as unknown[]).length}`)
+	}
+}
+
+fetchFixtures().catch(console.error)

packages/aris-source-tfl/src/index.ts

@@ -0,0 +1,12 @@
+export { TflSource } from "./tfl-source.ts"
+export { TflApi } from "./tfl-api.ts"
+export type { TflLineId } from "./tfl-api.ts"
+export type {
+	ITflApi,
+	StationLocation,
+	TflAlertData,
+	TflAlertFeedItem,
+	TflAlertSeverity,
+	TflLineStatus,
+	TflSourceOptions,
+} from "./types.ts"

packages/aris-source-tfl/src/tfl-api.ts

@@ -0,0 +1,172 @@
+import { type } from "arktype"
+
+import type { StationLocation, TflAlertSeverity, TflLineStatus } from "./types.ts"
+
+const TFL_API_BASE = "https://api.tfl.gov.uk"
+
+const ALL_LINE_IDS: TflLineId[] = [
+	"bakerloo",
+	"central",
+	"circle",
+	"district",
+	"hammersmith-city",
+	"jubilee",
+	"metropolitan",
+	"northern",
+	"piccadilly",
+	"victoria",
+	"waterloo-city",
+	"lioness",
+	"mildmay",
+	"windrush",
+	"weaver",
+	"suffragette",
+	"liberty",
+	"elizabeth",
+]
+
+// TfL severity codes: https://api.tfl.gov.uk/Line/Meta/Severity
+// 0 = Special Service, 1 = Closed, 6 = Severe Delays, 9 = Minor Delays, 10 = Good Service
+const SEVERITY_MAP: Record<number, TflAlertSeverity | null> = {
+	1: "closure",
+	2: "closure", // Suspended
+	3: "closure", // Part Suspended
+	4: "closure", // Planned Closure
+	5: "closure", // Part Closure
+	6: "major-delays", // Severe Delays
+	7: "major-delays", // Reduced Service
+	8: "major-delays", // Bus Service
+	9: "minor-delays", // Minor Delays
+	10: null, // Good Service
+	11: null, // Part Closed
+	12: null, // Exit Only
+	13: null, // No Step Free Access
+	14: null, // Change of frequency
+	15: null, // Diverted
+	16: null, // Not Running
+	17: null, // Issues Reported
+	18: null, // No Issues
+	19: null, // Information
+	20: null, // Service Closed
+}
+
+export class TflApi {
+	private apiKey: string
+	private stationsCache: StationLocation[] | null = null
+
+	constructor(apiKey: string) {
+		this.apiKey = apiKey
+	}
+
+	private async fetch<T>(path: string): Promise<T> {
+		const url = new URL(path, TFL_API_BASE)
+		url.searchParams.set("app_key", this.apiKey)
+		const response = await fetch(url.toString())
+		if (!response.ok) {
+			throw new Error(`TfL API error: ${response.status} ${response.statusText}`)
+		}
+		return response.json() as Promise<T>
+	}
+
+	async fetchLineStatuses(lines?: TflLineId[]): Promise<TflLineStatus[]> {
+		const lineIds = lines ?? ALL_LINE_IDS
+		const data = await this.fetch<unknown>(`/Line/${lineIds.join(",")}/Status`)
+
+		const parsed = lineResponseArray(data)
+		if (parsed instanceof type.errors) {
+			throw new Error(`Invalid TfL API response: ${parsed.summary}`)
+		}
+
+		const statuses: TflLineStatus[] = []
+
+		for (const line of parsed) {
+			for (const status of line.lineStatuses) {
+				const severity = SEVERITY_MAP[status.statusSeverity]
+				if (severity) {
+					statuses.push({
+						lineId: line.id,
+						lineName: line.name,
+						severity,
+						description: status.reason ?? status.statusSeverityDescription,
+					})
+				}
+			}
+		}
+
+		return statuses
+	}
+
+	async fetchStations(): Promise<StationLocation[]> {
+		if (this.stationsCache) {
+			return this.stationsCache
+		}
+
+		// Fetch stations for all lines in parallel
+		const responses = await Promise.all(
+			ALL_LINE_IDS.map(async (id) => {
+				const data = await this.fetch<unknown>(`/Line/${id}/StopPoints`)
+				const parsed = lineStopPointsArray(data)
+				if (parsed instanceof type.errors) {
+					throw new Error(`Invalid TfL API response for line ${id}: ${parsed.summary}`)
+				}
+				return { lineId: id, stops: parsed }
+			}),
+		)
+
+		// Merge stations, combining lines for shared stations
+		const stationMap = new Map<string, StationLocation>()
+
+		for (const { lineId: currentLineId, stops } of responses) {
+			for (const stop of stops) {
+				const existing = stationMap.get(stop.naptanId)
+				if (existing) {
+					if (!existing.lines.includes(currentLineId)) {
+						existing.lines.push(currentLineId)
+					}
+				} else {
+					stationMap.set(stop.naptanId, {
+						id: stop.naptanId,
+						name: stop.commonName,
+						lat: stop.lat,
+						lng: stop.lon,
+						lines: [currentLineId],
+					})
+				}
+			}
+		}
+
+		this.stationsCache = Array.from(stationMap.values())
+		return this.stationsCache
+	}
+}
+
+// Schemas
+
+const lineId = type(
+	"'bakerloo' | 'central' | 'circle' | 'district' | 'hammersmith-city' | 'jubilee' | 'metropolitan' | 'northern' | 'piccadilly' | 'victoria' | 'waterloo-city' | 'lioness' | 'mildmay' | 'windrush' | 'weaver' | 'suffragette' | 'liberty' | 'elizabeth'",
+)
+
+export type TflLineId = typeof lineId.infer
+
+const lineStatus = type({
+	statusSeverity: "number",
+	statusSeverityDescription: "string",
+	"reason?": "string",
+})
+
+const lineResponse = type({
+	id: lineId,
+	name: "string",
+	lineStatuses: lineStatus.array(),
+})
+
+const lineResponseArray = lineResponse.array()
+
+const lineStopPoint = type({
+	naptanId: "string",
+	commonName: "string",
+	lat: "number",
+	lon: "number",
+})
+
+const lineStopPointsArray = lineStopPoint.array()

packages/aris-source-tfl/src/tfl-source.test.ts

@@ -0,0 +1,286 @@
+import type { Context } from "@aris/core"
+
+import { LocationKey, type Location } from "@aris/source-location"
+import { describe, expect, test } from "bun:test"
+
+import type {
+	ITflApi,
+	StationLocation,
+	TflAlertSeverity,
+	TflLineId,
+	TflLineStatus,
+} from "./types.ts"
+
+import fixtures from "../fixtures/tfl-responses.json"
+import { TflSource } from "./tfl-source.ts"
+
+// Mock API that returns fixture data
+class FixtureTflApi implements ITflApi {
+	async fetchLineStatuses(_lines?: TflLineId[]): Promise<TflLineStatus[]> {
+		const statuses: TflLineStatus[] = []
+
+		for (const line of fixtures.lineStatuses as Record<string, unknown>[]) {
+			for (const status of line.lineStatuses as Record<string, unknown>[]) {
+				const severityCode = status.statusSeverity as number
+				const severity = this.mapSeverity(severityCode)
+				if (severity) {
+					statuses.push({
+						lineId: line.id as TflLineId,
+						lineName: line.name as string,
+						severity,
+						description: (status.reason as string) ?? (status.statusSeverityDescription as string),
+					})
+				}
+			}
+		}
+
+		return statuses
+	}
+
+	async fetchStations(): Promise<StationLocation[]> {
+		const stationMap = new Map<string, StationLocation>()
+
+		for (const [lineId, stops] of Object.entries(fixtures.stopPoints)) {
+			for (const stop of stops as Record<string, unknown>[]) {
+				const id = stop.naptanId as string
+				const existing = stationMap.get(id)
+				if (existing) {
+					if (!existing.lines.includes(lineId as TflLineId)) {
+						existing.lines.push(lineId as TflLineId)
+					}
+				} else {
+					stationMap.set(id, {
+						id,
+						name: stop.commonName as string,
+						lat: stop.lat as number,
+						lng: stop.lon as number,
+						lines: [lineId as TflLineId],
+					})
+				}
+			}
+		}
+
+		return Array.from(stationMap.values())
+	}
+
+	private mapSeverity(code: number): TflAlertSeverity | null {
+		const map: Record<number, TflAlertSeverity | null> = {
+			1: "closure",
+			2: "closure",
+			3: "closure",
+			4: "closure",
+			5: "closure",
+			6: "major-delays",
+			7: "major-delays",
+			8: "major-delays",
+			9: "minor-delays",
+			10: null,
+		}
+		return map[code] ?? null
+	}
+}
+
+function createContext(location?: Location): Context {
+	const ctx: Context = { time: new Date("2026-01-15T12:00:00Z") }
+	if (location) {
+		ctx[LocationKey] = location
+	}
+	return ctx
+}
+
+describe("TflSource", () => {
+	const api = new FixtureTflApi()
+
+	describe("interface", () => {
+		test("has correct id", () => {
+			const source = new TflSource({ client: api })
+			expect(source.id).toBe("tfl")
+		})
+
+		test("depends on location", () => {
+			const source = new TflSource({ client: api })
+			expect(source.dependencies).toEqual(["location"])
+		})
+
+		test("implements fetchItems", () => {
+			const source = new TflSource({ client: api })
+			expect(source.fetchItems).toBeDefined()
+		})
+
+		test("throws if neither client nor apiKey provided", () => {
+			expect(() => new TflSource({})).toThrow("Either client or apiKey must be provided")
+		})
+	})
+
+	describe("setLinesOfInterest", () => {
+		const lineFilteringApi: ITflApi = {
+			async fetchLineStatuses(lines?: TflLineId[]): Promise<TflLineStatus[]> {
+				const all: TflLineStatus[] = [
+					{
+						lineId: "northern",
+						lineName: "Northern",
+						severity: "minor-delays",
+						description: "Delays",
+					},
+					{ lineId: "central", lineName: "Central", severity: "closure", description: "Closed" },
+				]
+				return lines ? all.filter((s) => lines.includes(s.lineId)) : all
+			},
+			async fetchStations(): Promise<StationLocation[]> {
+				return []
+			},
+		}
+
+		test("changes which lines are fetched", async () => {
+			const source = new TflSource({ client: lineFilteringApi })
+			const before = await source.fetchItems(createContext())
+			expect(before.length).toBe(2)
+
+			source.setLinesOfInterest(["northern"])
+			const after = await source.fetchItems(createContext())
+
+			expect(after.length).toBe(1)
+			expect(after[0]!.data.line).toBe("northern")
+		})
+
+		test("DEFAULT_LINES_OF_INTEREST restores all lines", async () => {
+			const source = new TflSource({ client: lineFilteringApi, lines: ["northern"] })
+			const filtered = await source.fetchItems(createContext())
+			expect(filtered.length).toBe(1)
+
+			source.setLinesOfInterest([...TflSource.DEFAULT_LINES_OF_INTEREST])
+			const all = await source.fetchItems(createContext())
+
+			expect(all.length).toBe(2)
+		})
+	})
+
+	describe("fetchItems", () => {
+		test("returns feed items array", async () => {
+			const source = new TflSource({ client: api })
+			const items = await source.fetchItems(createContext())
+			expect(Array.isArray(items)).toBe(true)
+		})
+
+		test("feed items have correct base structure", async () => {
+			const source = new TflSource({ client: api })
+			const location: Location = { lat: 51.5074, lng: -0.1278, accuracy: 10, timestamp: new Date() }
+			const items = await source.fetchItems(createContext(location))
+
+			for (const item of items) {
+				expect(typeof item.id).toBe("string")
+				expect(item.id).toMatch(/^tfl-alert-/)
+				expect(item.type).toBe("tfl-alert")
+				expect(typeof item.priority).toBe("number")
+				expect(item.timestamp).toBeInstanceOf(Date)
+			}
+		})
+
+		test("feed items have correct data structure", async () => {
+			const source = new TflSource({ client: api })
+			const location: Location = { lat: 51.5074, lng: -0.1278, accuracy: 10, timestamp: new Date() }
+			const items = await source.fetchItems(createContext(location))
+
+			for (const item of items) {
+				expect(typeof item.data.line).toBe("string")
+				expect(typeof item.data.lineName).toBe("string")
+				expect(["minor-delays", "major-delays", "closure"]).toContain(item.data.severity)
+				expect(typeof item.data.description).toBe("string")
+				expect(
+					item.data.closestStationDistance === null ||
+						typeof item.data.closestStationDistance === "number",
+				).toBe(true)
+			}
+		})
+
+		test("feed item ids are unique", async () => {
+			const source = new TflSource({ client: api })
+			const items = await source.fetchItems(createContext())
+
+			const ids = items.map((item) => item.id)
+			const uniqueIds = new Set(ids)
+			expect(uniqueIds.size).toBe(ids.length)
+		})
+
+		test("feed items are sorted by priority descending", async () => {
+			const source = new TflSource({ client: api })
+			const items = await source.fetchItems(createContext())
+
+			for (let i = 1; i < items.length; i++) {
+				const prev = items[i - 1]!
+				const curr = items[i]!
+				expect(prev.priority).toBeGreaterThanOrEqual(curr.priority)
+			}
+		})
+
+		test("priority values match severity levels", async () => {
+			const source = new TflSource({ client: api })
+			const items = await source.fetchItems(createContext())
+
+			const severityPriority: Record<string, number> = {
+				closure: 1.0,
+				"major-delays": 0.8,
+				"minor-delays": 0.6,
+			}
+
+			for (const item of items) {
+				expect(item.priority).toBe(severityPriority[item.data.severity]!)
+			}
+		})
+
+		test("closestStationDistance is number when location provided", async () => {
+			const source = new TflSource({ client: api })
+			const location: Location = { lat: 51.5074, lng: -0.1278, accuracy: 10, timestamp: new Date() }
+			const items = await source.fetchItems(createContext(location))
+
+			for (const item of items) {
+				expect(typeof item.data.closestStationDistance).toBe("number")
+				expect(item.data.closestStationDistance!).toBeGreaterThan(0)
+			}
+		})
+
+		test("closestStationDistance is null when no location provided", async () => {
+			const source = new TflSource({ client: api })
+			const items = await source.fetchItems(createContext())
+
+			for (const item of items) {
+				expect(item.data.closestStationDistance).toBeNull()
+			}
+		})
+	})
+})
+
+describe("TfL Fixture Data Shape", () => {
+	test("fixtures have expected structure", () => {
+		expect(typeof fixtures.fetchedAt).toBe("string")
+		expect(Array.isArray(fixtures.lineStatuses)).toBe(true)
+		expect(typeof fixtures.stopPoints).toBe("object")
+	})
+
+	test("line statuses have required fields", () => {
+		for (const line of fixtures.lineStatuses as Record<string, unknown>[]) {
+			expect(typeof line.id).toBe("string")
+			expect(typeof line.name).toBe("string")
+			expect(Array.isArray(line.lineStatuses)).toBe(true)
+
+			for (const status of line.lineStatuses as Record<string, unknown>[]) {
+				expect(typeof status.statusSeverity).toBe("number")
+				expect(typeof status.statusSeverityDescription).toBe("string")
+			}
+		}
+	})
+
+	test("stop points have required fields", () => {
+		for (const [lineId, stops] of Object.entries(fixtures.stopPoints)) {
+			expect(typeof lineId).toBe("string")
+			expect(Array.isArray(stops)).toBe(true)
+
+			for (const stop of stops as Record<string, unknown>[]) {
+				expect(typeof stop.naptanId).toBe("string")
+				expect(typeof stop.commonName).toBe("string")
+				expect(typeof stop.lat).toBe("number")
+				expect(typeof stop.lon).toBe("number")
+			}
+		}
+	})
+})

packages/aris-source-tfl/src/tfl-source.ts

@@ -0,0 +1,168 @@
+import type { Context, FeedSource } from "@aris/core"
+
+import { contextValue } from "@aris/core"
+import { LocationKey } from "@aris/source-location"
+
+import type {
+	ITflApi,
+	StationLocation,
+	TflAlertData,
+	TflAlertFeedItem,
+	TflAlertSeverity,
+	TflLineId,
+	TflSourceOptions,
+} from "./types.ts"
+
+import { TflApi } from "./tfl-api.ts"
+
+const SEVERITY_PRIORITY: Record<TflAlertSeverity, number> = {
+	closure: 1.0,
+	"major-delays": 0.8,
+	"minor-delays": 0.6,
+}
+
+/**
+ * A FeedSource that provides TfL (Transport for London) service alerts.
+ *
+ * Depends on location source for proximity-based sorting. Produces feed items
+ * for tube, overground, and Elizabeth line disruptions.
+ *
+ * @example
+ * ```ts
+ * const tflSource = new TflSource({
+ *   apiKey: process.env.TFL_API_KEY!,
+ *   lines: ["northern", "victoria", "jubilee"],
+ * })
+ *
+ * const engine = new FeedEngine()
+ *   .register(locationSource)
+ *   .register(tflSource)
+ *
+ * const { items } = await engine.refresh()
+ * ```
+ */
+export class TflSource implements FeedSource<TflAlertFeedItem> {
+	static readonly DEFAULT_LINES_OF_INTEREST: readonly TflLineId[] = [
+		"bakerloo",
+		"central",
+		"circle",
+		"district",
+		"hammersmith-city",
+		"jubilee",
+		"metropolitan",
+		"northern",
+		"piccadilly",
+		"victoria",
+		"waterloo-city",
+		"lioness",
+		"mildmay",
+		"windrush",
+		"weaver",
+		"suffragette",
+		"liberty",
+		"elizabeth",
+	]
+
+	readonly id = "tfl"
+	readonly dependencies = ["location"]
+
+	private readonly client: ITflApi
+	private lines: TflLineId[]
+
+	constructor(options: TflSourceOptions) {
+		if (!options.client && !options.apiKey) {
+			throw new Error("Either client or apiKey must be provided")
+		}
+		this.client = options.client ?? new TflApi(options.apiKey!)
+		this.lines = options.lines ?? [...TflSource.DEFAULT_LINES_OF_INTEREST]
+	}
+
+	async fetchContext(): Promise<null> {
+		return null
+	}
+
+	/**
+	 * Update the set of monitored lines. Takes effect on the next fetchItems call.
+	 */
+	setLinesOfInterest(lines: TflLineId[]): void {
+		this.lines = lines
+	}
+
+	async fetchItems(context: Context): Promise<TflAlertFeedItem[]> {
+		const [statuses, stations] = await Promise.all([
+			this.client.fetchLineStatuses(this.lines),
+			this.client.fetchStations(),
+		])
+
+		const location = contextValue(context, LocationKey)
+
+		const items: TflAlertFeedItem[] = statuses.map((status) => {
+			const closestStationDistance = location
+				? findClosestStationDistance(status.lineId, stations, location.lat, location.lng)
+				: null
+
+			const data: TflAlertData = {
+				line: status.lineId,
+				lineName: status.lineName,
+				severity: status.severity,
+				description: status.description,
+				closestStationDistance,
+			}
+
+			return {
+				id: `tfl-alert-${status.lineId}-${status.severity}`,
+				type: "tfl-alert",
+				priority: SEVERITY_PRIORITY[status.severity],
+				timestamp: context.time,
+				data,
+			}
+		})
+
+		// Sort by severity (desc), then by proximity (asc) if location available
+		items.sort((a, b) => {
+			if (b.priority !== a.priority) {
+				return b.priority - a.priority
+			}
+			if (a.data.closestStationDistance !== null && b.data.closestStationDistance !== null) {
+				return a.data.closestStationDistance - b.data.closestStationDistance
+			}
+			return 0
+		})
+
+		return items
+	}
+}
+
+function haversineDistance(lat1: number, lng1: number, lat2: number, lng2: number): number {
+	const R = 6371 // Earth's radius in km
+	const dLat = ((lat2 - lat1) * Math.PI) / 180
+	const dLng = ((lng2 - lng1) * Math.PI) / 180
+	const a =
+		Math.sin(dLat / 2) * Math.sin(dLat / 2) +
+		Math.cos((lat1 * Math.PI) / 180) *
+			Math.cos((lat2 * Math.PI) / 180) *
+			Math.sin(dLng / 2) *
+			Math.sin(dLng / 2)
+	const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a))
+	return R * c
+}
+
+function findClosestStationDistance(
+	lineId: TflLineId,
+	stations: StationLocation[],
+	userLat: number,
+	userLng: number,
+): number | null {
+	const lineStations = stations.filter((s) => s.lines.includes(lineId))
+	if (lineStations.length === 0) return null
+
+	let minDistance = Infinity
+	for (const station of lineStations) {
+		const distance = haversineDistance(userLat, userLng, station.lat, station.lng)
+		if (distance < minDistance) {
+			minDistance = distance
+		}
+	}
+
+	return minDistance
+}

packages/aris-source-tfl/src/types.ts

@@ -0,0 +1,50 @@
+import type { FeedItem } from "@aris/core"
+
+import type { TflLineId } from "./tfl-api.ts"
+
+export type { TflLineId } from "./tfl-api.ts"
+
+export const TflAlertSeverity = {
+	MinorDelays: "minor-delays",
+	MajorDelays: "major-delays",
+	Closure: "closure",
+} as const
+
+export type TflAlertSeverity = (typeof TflAlertSeverity)[keyof typeof TflAlertSeverity]
+
+export interface TflAlertData extends Record<string, unknown> {
+	line: TflLineId
+	lineName: string
+	severity: TflAlertSeverity
+	description: string
+	closestStationDistance: number | null
+}
+
+export type TflAlertFeedItem = FeedItem<"tfl-alert", TflAlertData>
+
+export interface TflSourceOptions {
+	apiKey?: string
+	client?: ITflApi
+	/** Lines to monitor. Defaults to all lines. */
+	lines?: TflLineId[]
+}
+
+export interface StationLocation {
+	id: string
+	name: string
+	lat: number
+	lng: number
+	lines: TflLineId[]
+}
+
+export interface ITflApi {
+	fetchLineStatuses(lines?: TflLineId[]): Promise<TflLineStatus[]>
+	fetchStations(): Promise<StationLocation[]>
+}
+
+export interface TflLineStatus {
+	lineId: TflLineId
+	lineName: string
+	severity: TflAlertSeverity
+	description: string
+}

packages/aris-source-weatherkit/README.md

@@ -0,0 +1,101 @@
+# @aris/source-weatherkit
+
+Weather feed source using Apple WeatherKit API.
+
+## Usage
+
+### Basic Setup
+
+```ts
+import { WeatherSource, Units } from "@aris/source-weatherkit"
+
+const weatherSource = new WeatherSource({
+	credentials: {
+		privateKey: process.env.WEATHERKIT_PRIVATE_KEY!,
+		keyId: process.env.WEATHERKIT_KEY_ID!,
+		teamId: process.env.WEATHERKIT_TEAM_ID!,
+		serviceId: process.env.WEATHERKIT_SERVICE_ID!,
+	},
+	units: Units.metric,
+})
+```
+
+### With Feed Source Graph
+
+```ts
+import { LocationSource } from "@aris/source-location"
+import { WeatherSource } from "@aris/source-weatherkit"
+
+const locationSource = new LocationSource()
+const weatherSource = new WeatherSource({ credentials })
+
+// Weather depends on location - graph handles ordering
+const sources = [locationSource, weatherSource]
+```
+
+### Reading Weather Context
+
+Downstream sources can access weather data:
+
+```ts
+import { contextValue } from "@aris/core"
+import { WeatherKey } from "@aris/source-weatherkit"
+
+async function fetchContext(context: Context) {
+	const weather = contextValue(context, WeatherKey)
+
+	if (weather?.condition === "Rain") {
+		// Suggest umbrella, indoor activities, etc.
+	}
+
+	if (weather && weather.uvIndex > 7) {
+		// Suggest sunscreen
+	}
+}
+```
+
+## Exports
+
+| Export          | Description                             |
+| --------------- | --------------------------------------- |
+| `WeatherSource` | FeedSource implementation               |
+| `WeatherKey`    | Context key for simplified weather data |
+| `Weather`       | Type for weather context                |
+| `Units`         | `metric` or `imperial`                  |
+
+## Options
+
+| Option        | Default  | Description                |
+| ------------- | -------- | -------------------------- |
+| `credentials` | -        | WeatherKit API credentials |
+| `client`      | -        | Custom WeatherKit client   |
+| `hourlyLimit` | `12`     | Max hourly forecasts       |
+| `dailyLimit`  | `7`      | Max daily forecasts        |
+| `units`       | `metric` | Temperature/speed units    |
+
+## Context
+
+Provides simplified weather context for downstream sources:
+
+```ts
+interface Weather {
+	temperature: number
+	temperatureApparent: number
+	condition: ConditionCode
+	humidity: number
+	uvIndex: number
+	windSpeed: number
+	daylight: boolean
+}
+```
+
+## Feed Items
+
+Produces feed items:
+
+- `weather-current` - Current conditions
+- `weather-hourly` - Hourly forecasts (up to `hourlyLimit`)
+- `weather-daily` - Daily forecasts (up to `dailyLimit`)
+- `weather-alert` - Weather alerts when present
+
+Priority is adjusted based on weather severity (storms, extreme temperatures).

packages/aris-source-weatherkit/package.json

@@ -0,0 +1,15 @@
+{
+	"name": "@aris/source-weatherkit",
+	"version": "0.0.0",
+	"type": "module",
+	"main": "src/index.ts",
+	"types": "src/index.ts",
+	"scripts": {
+		"test": "bun test ."
+	},
+	"dependencies": {
+		"@aris/core": "workspace:*",
+		"@aris/source-location": "workspace:*",
+		"arktype": "^2.1.0"
+	}
+}

packages/aris-source-weatherkit/src/feed-items.ts

@@ -0,0 +1,97 @@
+import type { FeedItem } from "@aris/core"
+
+import type { Certainty, ConditionCode, PrecipitationType, Severity, Urgency } from "./weatherkit"
+
+export const WeatherFeedItemType = {
+	current: "weather-current",
+	hourly: "weather-hourly",
+	daily: "weather-daily",
+	alert: "weather-alert",
+} as const
+
+export type WeatherFeedItemType = (typeof WeatherFeedItemType)[keyof typeof WeatherFeedItemType]
+
+export type CurrentWeatherData = {
+	conditionCode: ConditionCode
+	daylight: boolean
+	humidity: number
+	precipitationIntensity: number
+	pressure: number
+	pressureTrend: "rising" | "falling" | "steady"
+	temperature: number
+	temperatureApparent: number
+	uvIndex: number
+	visibility: number
+	windDirection: number
+	windGust: number
+	windSpeed: number
+}
+
+export interface CurrentWeatherFeedItem extends FeedItem<
+	typeof WeatherFeedItemType.current,
+	CurrentWeatherData
+> {}
+
+export type HourlyWeatherData = {
+	forecastTime: Date
+	conditionCode: ConditionCode
+	daylight: boolean
+	humidity: number
+	precipitationAmount: number
+	precipitationChance: number
+	precipitationType: PrecipitationType
+	temperature: number
+	temperatureApparent: number
+	uvIndex: number
+	windDirection: number
+	windGust: number
+	windSpeed: number
+}
+
+export interface HourlyWeatherFeedItem extends FeedItem<
+	typeof WeatherFeedItemType.hourly,
+	HourlyWeatherData
+> {}
+
+export type DailyWeatherData = {
+	forecastDate: Date
+	conditionCode: ConditionCode
+	maxUvIndex: number
+	precipitationAmount: number
+	precipitationChance: number
+	precipitationType: PrecipitationType
+	snowfallAmount: number
+	sunrise: Date
+	sunset: Date
+	temperatureMax: number
+	temperatureMin: number
+}
+
+export interface DailyWeatherFeedItem extends FeedItem<
+	typeof WeatherFeedItemType.daily,
+	DailyWeatherData
+> {}
+
+export type WeatherAlertData = {
+	alertId: string
+	areaName: string
+	certainty: Certainty
+	description: string
+	detailsUrl: string
+	effectiveTime: Date
+	expireTime: Date
+	severity: Severity
+	source: string
+	urgency: Urgency
+}
+
+export interface WeatherAlertFeedItem extends FeedItem<
+	typeof WeatherFeedItemType.alert,
+	WeatherAlertData
+> {}
+
+export type WeatherFeedItem =
+	| CurrentWeatherFeedItem
+	| HourlyWeatherFeedItem
+	| DailyWeatherFeedItem
+	| WeatherAlertFeedItem

packages/aris-source-weatherkit/src/index.ts

@@ -0,0 +1,39 @@
+export { WeatherKey, type Weather } from "./weather-context"
+export {
+	WeatherSource,
+	Units,
+	type Units as UnitsType,
+	type WeatherSourceOptions,
+} from "./weather-source"
+
+export {
+	WeatherFeedItemType,
+	type WeatherFeedItemType as WeatherFeedItemTypeType,
+	type WeatherFeedItem,
+	type CurrentWeatherFeedItem,
+	type CurrentWeatherData,
+	type HourlyWeatherFeedItem,
+	type HourlyWeatherData,
+	type DailyWeatherFeedItem,
+	type DailyWeatherData,
+	type WeatherAlertFeedItem,
+	type WeatherAlertData,
+} from "./feed-items"
+
+export {
+	ConditionCode,
+	Severity,
+	Urgency,
+	Certainty,
+	PrecipitationType,
+	DefaultWeatherKitClient,
+	type ConditionCode as ConditionCodeType,
+	type Severity as SeverityType,
+	type Urgency as UrgencyType,
+	type Certainty as CertaintyType,
+	type PrecipitationType as PrecipitationTypeType,
+	type WeatherKitClient,
+	type WeatherKitCredentials,
+	type WeatherKitQueryOptions,
+	type WeatherKitResponse,
+} from "./weatherkit"

packages/aris-source-weatherkit/src/weather-context.ts

@@ -0,0 +1,27 @@
+import type { ContextKey } from "@aris/core"
+
+import { contextKey } from "@aris/core"
+
+import type { ConditionCode } from "./weatherkit"
+
+/**
+ * Simplified weather context for downstream sources.
+ */
+export interface Weather {
+	/** Current temperature */
+	temperature: number
+	/** Feels-like temperature */
+	temperatureApparent: number
+	/** Weather condition */
+	condition: ConditionCode
+	/** Relative humidity (0-1) */
+	humidity: number
+	/** UV index */
+	uvIndex: number
+	/** Wind speed */
+	windSpeed: number
+	/** Is it currently daytime */
+	daylight: boolean
+}
+
+export const WeatherKey: ContextKey<Weather> = contextKey("weather")

packages/aris-source-weatherkit/src/weather-source.test.ts

@@ -0,0 +1,184 @@
+import { contextValue, type Context } from "@aris/core"
+import { LocationKey } from "@aris/source-location"
+import { describe, expect, test } from "bun:test"
+
+import type { WeatherKitClient, WeatherKitResponse } from "./weatherkit"
+
+import fixture from "../fixtures/san-francisco.json"
+import { WeatherFeedItemType } from "./feed-items"
+import { WeatherKey } from "./weather-context"
+import { WeatherSource, Units } from "./weather-source"
+
+const mockCredentials = {
+	privateKey: "mock",
+	keyId: "mock",
+	teamId: "mock",
+	serviceId: "mock",
+}
+
+function createMockClient(response: WeatherKitResponse): WeatherKitClient {
+	return {
+		fetch: async () => response,
+	}
+}
+
+function createMockContext(location?: { lat: number; lng: number }): Context {
+	const ctx: Context = { time: new Date("2026-01-17T00:00:00Z") }
+	if (location) {
+		ctx[LocationKey] = { ...location, accuracy: 10, timestamp: new Date() }
+	}
+	return ctx
+}
+
+describe("WeatherSource", () => {
+	describe("properties", () => {
+		test("has correct id", () => {
+			const source = new WeatherSource({ credentials: mockCredentials })
+			expect(source.id).toBe("weather")
+		})
+
+		test("depends on location", () => {
+			const source = new WeatherSource({ credentials: mockCredentials })
+			expect(source.dependencies).toEqual(["location"])
+		})
+
+		test("throws error if neither client nor credentials provided", () => {
+			expect(() => new WeatherSource({} as never)).toThrow(
+				"Either client or credentials must be provided",
+			)
+		})
+	})
+
+	describe("fetchContext", () => {
+		const mockClient = createMockClient(fixture.response as WeatherKitResponse)
+
+		test("returns null when no location", async () => {
+			const source = new WeatherSource({ client: mockClient })
+			const result = await source.fetchContext(createMockContext())
+
+			expect(result).toBeNull()
+		})
+
+		test("returns simplified weather context", async () => {
+			const source = new WeatherSource({ client: mockClient })
+			const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+			const result = await source.fetchContext(context)
+			expect(result).not.toBeNull()
+			const weather = contextValue(result! as Context, WeatherKey)
+
+			expect(weather).toBeDefined()
+			expect(typeof weather!.temperature).toBe("number")
+			expect(typeof weather!.temperatureApparent).toBe("number")
+			expect(typeof weather!.condition).toBe("string")
+			expect(typeof weather!.humidity).toBe("number")
+			expect(typeof weather!.uvIndex).toBe("number")
+			expect(typeof weather!.windSpeed).toBe("number")
+			expect(typeof weather!.daylight).toBe("boolean")
+		})
+
+		test("converts temperature to imperial", async () => {
+			const source = new WeatherSource({ client: mockClient, units: Units.imperial })
+			const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+			const result = await source.fetchContext(context)
+			expect(result).not.toBeNull()
+			const weather = contextValue(result! as Context, WeatherKey)
+
+			// Fixture has temperature around 10°C, imperial should be around 50°F
+			expect(weather!.temperature).toBeGreaterThan(40)
+		})
+	})
+
+	describe("fetchItems", () => {
+		const mockClient = createMockClient(fixture.response as WeatherKitResponse)
+
+		test("returns empty array when no location", async () => {
+			const source = new WeatherSource({ client: mockClient })
+			const items = await source.fetchItems(createMockContext())
+
+			expect(items).toEqual([])
+		})
+
+		test("returns feed items with all types", async () => {
+			const source = new WeatherSource({ client: mockClient })
+			const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+			const items = await source.fetchItems(context)
+
+			expect(items.length).toBeGreaterThan(0)
+			expect(items.some((i) => i.type === WeatherFeedItemType.current)).toBe(true)
+			expect(items.some((i) => i.type === WeatherFeedItemType.hourly)).toBe(true)
+			expect(items.some((i) => i.type === WeatherFeedItemType.daily)).toBe(true)
+		})
+
+		test("applies hourly and daily limits", async () => {
+			const source = new WeatherSource({
+				client: mockClient,
+				hourlyLimit: 3,
+				dailyLimit: 2,
+			})
+			const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+			const items = await source.fetchItems(context)
+
+			const hourlyItems = items.filter((i) => i.type === WeatherFeedItemType.hourly)
+			const dailyItems = items.filter((i) => i.type === WeatherFeedItemType.daily)
+
+			expect(hourlyItems.length).toBe(3)
+			expect(dailyItems.length).toBe(2)
+		})
+
+		test("sets timestamp from context.time", async () => {
+			const source = new WeatherSource({ client: mockClient })
+			const queryTime = new Date("2026-01-17T12:00:00Z")
+			const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+			context.time = queryTime
+
+			const items = await source.fetchItems(context)
+
+			for (const item of items) {
+				expect(item.timestamp).toEqual(queryTime)
+			}
+		})
+
+		test("assigns priority based on weather conditions", async () => {
+			const source = new WeatherSource({ client: mockClient })
+			const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+			const items = await source.fetchItems(context)
+
+			for (const item of items) {
+				expect(item.priority).toBeGreaterThanOrEqual(0)
+				expect(item.priority).toBeLessThanOrEqual(1)
+			}
+
+			const currentItem = items.find((i) => i.type === WeatherFeedItemType.current)
+			expect(currentItem).toBeDefined()
+			expect(currentItem!.priority).toBeGreaterThanOrEqual(0.5)
+		})
+
+		test("generates unique IDs for each item", async () => {
+			const source = new WeatherSource({ client: mockClient })
+			const context = createMockContext({ lat: 37.7749, lng: -122.4194 })
+
+			const items = await source.fetchItems(context)
+			const ids = items.map((i) => i.id)
+			const uniqueIds = new Set(ids)
+
+			expect(uniqueIds.size).toBe(ids.length)
+		})
+	})
+
+	describe("no reactive methods", () => {
+		test("does not implement onContextUpdate", () => {
+			const source = new WeatherSource({ credentials: mockCredentials })
+			expect(source.onContextUpdate).toBeUndefined()
+		})
+
+		test("does not implement onItemsUpdate", () => {
+			const source = new WeatherSource({ credentials: mockCredentials })
+			expect(source.onItemsUpdate).toBeUndefined()
+		})
+	})
+})

packages/aris-source-weatherkit/src/weather-source.ts

@@ -0,0 +1,363 @@
+import type { Context, FeedSource } from "@aris/core"
+
+import { contextValue } from "@aris/core"
+import { LocationKey } from "@aris/source-location"
+
+import { WeatherFeedItemType, type WeatherFeedItem } from "./feed-items"
+import { WeatherKey, type Weather } from "./weather-context"
+import {
+	DefaultWeatherKitClient,
+	type ConditionCode,
+	type CurrentWeather,
+	type DailyForecast,
+	type HourlyForecast,
+	type Severity,
+	type WeatherAlert,
+	type WeatherKitClient,
+	type WeatherKitCredentials,
+} from "./weatherkit"
+
+export const Units = {
+	metric: "metric",
+	imperial: "imperial",
+} as const
+
+export type Units = (typeof Units)[keyof typeof Units]
+
+export interface WeatherSourceOptions {
+	credentials?: WeatherKitCredentials
+	client?: WeatherKitClient
+	/** Number of hourly forecasts to include (default: 12) */
+	hourlyLimit?: number
+	/** Number of daily forecasts to include (default: 7) */
+	dailyLimit?: number
+	/** Units for temperature and measurements (default: metric) */
+	units?: Units
+}
+
+const DEFAULT_HOURLY_LIMIT = 12
+const DEFAULT_DAILY_LIMIT = 7
+
+const BASE_PRIORITY = {
+	current: 0.5,
+	hourly: 0.3,
+	daily: 0.2,
+	alert: 0.7,
+} as const
+
+const SEVERE_CONDITIONS = new Set<ConditionCode>([
+	"SevereThunderstorm",
+	"Hurricane",
+	"Tornado",
+	"TropicalStorm",
+	"Blizzard",
+	"FreezingRain",
+	"Hail",
+	"Frigid",
+	"Hot",
+])
+
+const MODERATE_CONDITIONS = new Set<ConditionCode>([
+	"Thunderstorm",
+	"IsolatedThunderstorms",
+	"ScatteredThunderstorms",
+	"HeavyRain",
+	"HeavySnow",
+	"FreezingDrizzle",
+	"BlowingSnow",
+])
+
+/**
+ * A FeedSource that provides weather context and feed items using Apple WeatherKit.
+ *
+ * Depends on location source for coordinates. Provides simplified weather context
+ * for downstream sources and produces weather feed items (current, hourly, daily, alerts).
+ *
+ * @example
+ * ```ts
+ * const weatherSource = new WeatherSource({
+ *   credentials: {
+ *     privateKey: process.env.WEATHERKIT_PRIVATE_KEY!,
+ *     keyId: process.env.WEATHERKIT_KEY_ID!,
+ *     teamId: process.env.WEATHERKIT_TEAM_ID!,
+ *     serviceId: process.env.WEATHERKIT_SERVICE_ID!,
+ *   },
+ *   units: Units.metric,
+ * })
+ *
+ * // Access weather context in downstream sources
+ * const weather = contextValue(context, WeatherKey)
+ * if (weather?.condition === "Rain") {
+ *   // suggest umbrella
+ * }
+ * ```
+ */
+export class WeatherSource implements FeedSource<WeatherFeedItem> {
+	readonly id = "weather"
+	readonly dependencies = ["location"]
+
+	private readonly client: WeatherKitClient
+	private readonly hourlyLimit: number
+	private readonly dailyLimit: number
+	private readonly units: Units
+
+	constructor(options: WeatherSourceOptions) {
+		if (!options.client && !options.credentials) {
+			throw new Error("Either client or credentials must be provided")
+		}
+		this.client = options.client ?? new DefaultWeatherKitClient(options.credentials!)
+		this.hourlyLimit = options.hourlyLimit ?? DEFAULT_HOURLY_LIMIT
+		this.dailyLimit = options.dailyLimit ?? DEFAULT_DAILY_LIMIT
+		this.units = options.units ?? Units.metric
+	}
+
+	async fetchContext(context: Context): Promise<Partial<Context> | null> {
+		const location = contextValue(context, LocationKey)
+		if (!location) {
+			return null
+		}
+
+		const response = await this.client.fetch({
+			lat: location.lat,
+			lng: location.lng,
+		})
+
+		if (!response.currentWeather) {
+			return null
+		}
+
+		const weather: Weather = {
+			temperature: convertTemperature(response.currentWeather.temperature, this.units),
+			temperatureApparent: convertTemperature(
+				response.currentWeather.temperatureApparent,
+				this.units,
+			),
+			condition: response.currentWeather.conditionCode,
+			humidity: response.currentWeather.humidity,
+			uvIndex: response.currentWeather.uvIndex,
+			windSpeed: convertSpeed(response.currentWeather.windSpeed, this.units),
+			daylight: response.currentWeather.daylight,
+		}
+
+		return { [WeatherKey]: weather }
+	}
+
+	async fetchItems(context: Context): Promise<WeatherFeedItem[]> {
+		const location = contextValue(context, LocationKey)
+		if (!location) {
+			return []
+		}
+
+		const timestamp = context.time
+
+		const response = await this.client.fetch({
+			lat: location.lat,
+			lng: location.lng,
+		})
+
+		const items: WeatherFeedItem[] = []
+
+		if (response.currentWeather) {
+			items.push(createCurrentWeatherFeedItem(response.currentWeather, timestamp, this.units))
+		}
+
+		if (response.forecastHourly?.hours) {
+			const hours = response.forecastHourly.hours.slice(0, this.hourlyLimit)
+			for (let i = 0; i < hours.length; i++) {
+				const hour = hours[i]
+				if (hour) {
+					items.push(createHourlyWeatherFeedItem(hour, i, timestamp, this.units))
+				}
+			}
+		}
+
+		if (response.forecastDaily?.days) {
+			const days = response.forecastDaily.days.slice(0, this.dailyLimit)
+			for (let i = 0; i < days.length; i++) {
+				const day = days[i]
+				if (day) {
+					items.push(createDailyWeatherFeedItem(day, i, timestamp, this.units))
+				}
+			}
+		}
+
+		if (response.weatherAlerts?.alerts) {
+			for (const alert of response.weatherAlerts.alerts) {
+				items.push(createWeatherAlertFeedItem(alert, timestamp))
+			}
+		}
+
+		return items
+	}
+}
+
+function adjustPriorityForCondition(basePriority: number, conditionCode: ConditionCode): number {
+	if (SEVERE_CONDITIONS.has(conditionCode)) {
+		return Math.min(1, basePriority + 0.3)
+	}
+	if (MODERATE_CONDITIONS.has(conditionCode)) {
+		return Math.min(1, basePriority + 0.15)
+	}
+	return basePriority
+}
+
+function adjustPriorityForAlertSeverity(severity: Severity): number {
+	switch (severity) {
+		case "extreme":
+			return 1
+		case "severe":
+			return 0.9
+		case "moderate":
+			return 0.75
+		case "minor":
+			return BASE_PRIORITY.alert
+	}
+}
+
+function convertTemperature(celsius: number, units: Units): number {
+	if (units === Units.imperial) {
+		return (celsius * 9) / 5 + 32
+	}
+	return celsius
+}
+
+function convertSpeed(kmh: number, units: Units): number {
+	if (units === Units.imperial) {
+		return kmh * 0.621371
+	}
+	return kmh
+}
+
+function convertDistance(km: number, units: Units): number {
+	if (units === Units.imperial) {
+		return km * 0.621371
+	}
+	return km
+}
+
+function convertPrecipitation(mm: number, units: Units): number {
+	if (units === Units.imperial) {
+		return mm * 0.0393701
+	}
+	return mm
+}
+
+function convertPressure(mb: number, units: Units): number {
+	if (units === Units.imperial) {
+		return mb * 0.02953
+	}
+	return mb
+}
+
+function createCurrentWeatherFeedItem(
+	current: CurrentWeather,
+	timestamp: Date,
+	units: Units,
+): WeatherFeedItem {
+	const priority = adjustPriorityForCondition(BASE_PRIORITY.current, current.conditionCode)
+
+	return {
+		id: `weather-current-${timestamp.getTime()}`,
+		type: WeatherFeedItemType.current,
+		priority,
+		timestamp,
+		data: {
+			conditionCode: current.conditionCode,
+			daylight: current.daylight,
+			humidity: current.humidity,
+			precipitationIntensity: convertPrecipitation(current.precipitationIntensity, units),
+			pressure: convertPressure(current.pressure, units),
+			pressureTrend: current.pressureTrend,
+			temperature: convertTemperature(current.temperature, units),
+			temperatureApparent: convertTemperature(current.temperatureApparent, units),
+			uvIndex: current.uvIndex,
+			visibility: convertDistance(current.visibility, units),
+			windDirection: current.windDirection,
+			windGust: convertSpeed(current.windGust, units),
+			windSpeed: convertSpeed(current.windSpeed, units),
+		},
+	}
+}
+
+function createHourlyWeatherFeedItem(
+	hourly: HourlyForecast,
+	index: number,
+	timestamp: Date,
+	units: Units,
+): WeatherFeedItem {
+	const priority = adjustPriorityForCondition(BASE_PRIORITY.hourly, hourly.conditionCode)
+
+	return {
+		id: `weather-hourly-${timestamp.getTime()}-${index}`,
+		type: WeatherFeedItemType.hourly,
+		priority,
+		timestamp,
+		data: {
+			forecastTime: new Date(hourly.forecastStart),
+			conditionCode: hourly.conditionCode,
+			daylight: hourly.daylight,
+			humidity: hourly.humidity,
+			precipitationAmount: convertPrecipitation(hourly.precipitationAmount, units),
+			precipitationChance: hourly.precipitationChance,
+			precipitationType: hourly.precipitationType,
+			temperature: convertTemperature(hourly.temperature, units),
+			temperatureApparent: convertTemperature(hourly.temperatureApparent, units),
+			uvIndex: hourly.uvIndex,
+			windDirection: hourly.windDirection,
+			windGust: convertSpeed(hourly.windGust, units),
+			windSpeed: convertSpeed(hourly.windSpeed, units),
+		},
+	}
+}
+
+function createDailyWeatherFeedItem(
+	daily: DailyForecast,
+	index: number,
+	timestamp: Date,
+	units: Units,
+): WeatherFeedItem {
+	const priority = adjustPriorityForCondition(BASE_PRIORITY.daily, daily.conditionCode)
+
+	return {
+		id: `weather-daily-${timestamp.getTime()}-${index}`,
+		type: WeatherFeedItemType.daily,
+		priority,
+		timestamp,
+		data: {
+			forecastDate: new Date(daily.forecastStart),
+			conditionCode: daily.conditionCode,
+			maxUvIndex: daily.maxUvIndex,
+			precipitationAmount: convertPrecipitation(daily.precipitationAmount, units),
+			precipitationChance: daily.precipitationChance,
+			precipitationType: daily.precipitationType,
+			snowfallAmount: convertPrecipitation(daily.snowfallAmount, units),
+			sunrise: new Date(daily.sunrise),
+			sunset: new Date(daily.sunset),
+			temperatureMax: convertTemperature(daily.temperatureMax, units),
+			temperatureMin: convertTemperature(daily.temperatureMin, units),
+		},
+	}
+}
+
+function createWeatherAlertFeedItem(alert: WeatherAlert, timestamp: Date): WeatherFeedItem {
+	const priority = adjustPriorityForAlertSeverity(alert.severity)
+
+	return {
+		id: `weather-alert-${alert.id}`,
+		type: WeatherFeedItemType.alert,
+		priority,
+		timestamp,
+		data: {
+			alertId: alert.id,
+			areaName: alert.areaName,
+			certainty: alert.certainty,
+			description: alert.description,
+			detailsUrl: alert.detailsUrl,
+			effectiveTime: new Date(alert.effectiveTime),
+			expireTime: new Date(alert.expireTime),
+			severity: alert.severity,
+			source: alert.source,
+			urgency: alert.urgency,
+		},
+	}
+}

packages/aris-source-weatherkit/src/weatherkit.ts

@@ -0,0 +1,367 @@
+// WeatherKit REST API client and response types
+// https://developer.apple.com/documentation/weatherkitrestapi
+
+import { type } from "arktype"
+
+export interface WeatherKitCredentials {
+	privateKey: string
+	keyId: string
+	teamId: string
+	serviceId: string
+}
+
+export interface WeatherKitQueryOptions {
+	lat: number
+	lng: number
+	language?: string
+	timezone?: string
+}
+
+export interface WeatherKitClient {
+	fetch(query: WeatherKitQueryOptions): Promise<WeatherKitResponse>
+}
+
+export class DefaultWeatherKitClient implements WeatherKitClient {
+	private readonly credentials: WeatherKitCredentials
+
+	constructor(credentials: WeatherKitCredentials) {
+		this.credentials = credentials
+	}
+
+	async fetch(query: WeatherKitQueryOptions): Promise<WeatherKitResponse> {
+		const token = await generateJwt(this.credentials)
+
+		const dataSets = ["currentWeather", "forecastHourly", "forecastDaily", "weatherAlerts"].join(
+			",",
+		)
+
+		const url = new URL(
+			`${WEATHERKIT_API_BASE}/weather/${query.language ?? "en"}/${query.lat}/${query.lng}`,
+		)
+		url.searchParams.set("dataSets", dataSets)
+		if (query.timezone) {
+			url.searchParams.set("timezone", query.timezone)
+		}
+
+		const response = await fetch(url.toString(), {
+			headers: {
+				Authorization: `Bearer ${token}`,
+			},
+		})
+
+		if (!response.ok) {
+			const body = await response.text()
+			throw new Error(`WeatherKit API error: ${response.status} ${response.statusText}: ${body}`)
+		}
+
+		const json = await response.json()
+		const result = weatherKitResponseSchema(json)
+
+		if (result instanceof type.errors) {
+			throw new Error(`WeatherKit API response validation failed: ${result.summary}`)
+		}
+
+		return result
+	}
+}
+
+export const Severity = {
+	Minor: "minor",
+	Moderate: "moderate",
+	Severe: "severe",
+	Extreme: "extreme",
+} as const
+
+export type Severity = (typeof Severity)[keyof typeof Severity]
+
+export const Urgency = {
+	Immediate: "immediate",
+	Expected: "expected",
+	Future: "future",
+	Past: "past",
+	Unknown: "unknown",
+} as const
+
+export type Urgency = (typeof Urgency)[keyof typeof Urgency]
+
+export const Certainty = {
+	Observed: "observed",
+	Likely: "likely",
+	Possible: "possible",
+	Unlikely: "unlikely",
+	Unknown: "unknown",
+} as const
+
+export type Certainty = (typeof Certainty)[keyof typeof Certainty]
+
+export const PrecipitationType = {
+	Clear: "clear",
+	Precipitation: "precipitation",
+	Rain: "rain",
+	Snow: "snow",
+	Sleet: "sleet",
+	Hail: "hail",
+	Mixed: "mixed",
+} as const
+
+export type PrecipitationType = (typeof PrecipitationType)[keyof typeof PrecipitationType]
+
+export const ConditionCode = {
+	Clear: "Clear",
+	Cloudy: "Cloudy",
+	Dust: "Dust",
+	Fog: "Fog",
+	Haze: "Haze",
+	MostlyClear: "MostlyClear",
+	MostlyCloudy: "MostlyCloudy",
+	PartlyCloudy: "PartlyCloudy",
+	ScatteredThunderstorms: "ScatteredThunderstorms",
+	Smoke: "Smoke",
+	Breezy: "Breezy",
+	Windy: "Windy",
+	Drizzle: "Drizzle",
+	HeavyRain: "HeavyRain",
+	Rain: "Rain",
+	Showers: "Showers",
+	Flurries: "Flurries",
+	HeavySnow: "HeavySnow",
+	MixedRainAndSleet: "MixedRainAndSleet",
+	MixedRainAndSnow: "MixedRainAndSnow",
+	MixedRainfall: "MixedRainfall",
+	MixedSnowAndSleet: "MixedSnowAndSleet",
+	ScatteredShowers: "ScatteredShowers",
+	ScatteredSnowShowers: "ScatteredSnowShowers",
+	Sleet: "Sleet",
+	Snow: "Snow",
+	SnowShowers: "SnowShowers",
+	Blizzard: "Blizzard",
+	BlowingSnow: "BlowingSnow",
+	FreezingDrizzle: "FreezingDrizzle",
+	FreezingRain: "FreezingRain",
+	Frigid: "Frigid",
+	Hail: "Hail",
+	Hot: "Hot",
+	Hurricane: "Hurricane",
+	IsolatedThunderstorms: "IsolatedThunderstorms",
+	SevereThunderstorm: "SevereThunderstorm",
+	Thunderstorm: "Thunderstorm",
+	Tornado: "Tornado",
+	TropicalStorm: "TropicalStorm",
+} as const
+
+export type ConditionCode = (typeof ConditionCode)[keyof typeof ConditionCode]
+
+const WEATHERKIT_API_BASE = "https://weatherkit.apple.com/api/v1"
+
+const severitySchema = type.enumerated(
+	Severity.Minor,
+	Severity.Moderate,
+	Severity.Severe,
+	Severity.Extreme,
+)
+
+const urgencySchema = type.enumerated(
+	Urgency.Immediate,
+	Urgency.Expected,
+	Urgency.Future,
+	Urgency.Past,
+	Urgency.Unknown,
+)
+
+const certaintySchema = type.enumerated(
+	Certainty.Observed,
+	Certainty.Likely,
+	Certainty.Possible,
+	Certainty.Unlikely,
+	Certainty.Unknown,
+)
+
+const precipitationTypeSchema = type.enumerated(
+	PrecipitationType.Clear,
+	PrecipitationType.Precipitation,
+	PrecipitationType.Rain,
+	PrecipitationType.Snow,
+	PrecipitationType.Sleet,
+	PrecipitationType.Hail,
+	PrecipitationType.Mixed,
+)
+
+const conditionCodeSchema = type.enumerated(...Object.values(ConditionCode))
+
+const pressureTrendSchema = type.enumerated("rising", "falling", "steady")
+
+const currentWeatherSchema = type({
+	asOf: "string",
+	conditionCode: conditionCodeSchema,
+	daylight: "boolean",
+	humidity: "number",
+	precipitationIntensity: "number",
+	pressure: "number",
+	pressureTrend: pressureTrendSchema,
+	temperature: "number",
+	temperatureApparent: "number",
+	temperatureDewPoint: "number",
+	uvIndex: "number",
+	visibility: "number",
+	windDirection: "number",
+	windGust: "number",
+	windSpeed: "number",
+})
+
+export type CurrentWeather = typeof currentWeatherSchema.infer
+
+const hourlyForecastSchema = type({
+	forecastStart: "string",
+	conditionCode: conditionCodeSchema,
+	daylight: "boolean",
+	humidity: "number",
+	precipitationAmount: "number",
+	precipitationChance: "number",
+	precipitationType: precipitationTypeSchema,
+	pressure: "number",
+	snowfallIntensity: "number",
+	temperature: "number",
+	temperatureApparent: "number",
+	temperatureDewPoint: "number",
+	uvIndex: "number",
+	visibility: "number",
+	windDirection: "number",
+	windGust: "number",
+	windSpeed: "number",
+})
+
+export type HourlyForecast = typeof hourlyForecastSchema.infer
+
+const dayWeatherConditionsSchema = type({
+	conditionCode: conditionCodeSchema,
+	humidity: "number",
+	precipitationAmount: "number",
+	precipitationChance: "number",
+	precipitationType: precipitationTypeSchema,
+	snowfallAmount: "number",
+	temperatureMax: "number",
+	temperatureMin: "number",
+	windDirection: "number",
+	"windGust?": "number",
+	windSpeed: "number",
+})
+
+export type DayWeatherConditions = typeof dayWeatherConditionsSchema.infer
+
+const dailyForecastSchema = type({
+	forecastStart: "string",
+	forecastEnd: "string",
+	conditionCode: conditionCodeSchema,
+	maxUvIndex: "number",
+	moonPhase: "string",
+	"moonrise?": "string",
+	"moonset?": "string",
+	precipitationAmount: "number",
+	precipitationChance: "number",
+	precipitationType: precipitationTypeSchema,
+	snowfallAmount: "number",
+	sunrise: "string",
+	sunriseCivil: "string",
+	sunriseNautical: "string",
+	sunriseAstronomical: "string",
+	sunset: "string",
+	sunsetCivil: "string",
+	sunsetNautical: "string",
+	sunsetAstronomical: "string",
+	temperatureMax: "number",
+	temperatureMin: "number",
+	"daytimeForecast?": dayWeatherConditionsSchema,
+	"overnightForecast?": dayWeatherConditionsSchema,
+})
+
+export type DailyForecast = typeof dailyForecastSchema.infer
+
+const weatherAlertSchema = type({
+	id: "string",
+	areaId: "string",
+	areaName: "string",
+	certainty: certaintySchema,
+	countryCode: "string",
+	description: "string",
+	detailsUrl: "string",
+	effectiveTime: "string",
+	expireTime: "string",
+	issuedTime: "string",
+	responses: "string[]",
+	severity: severitySchema,
+	source: "string",
+	urgency: urgencySchema,
+})
+
+export type WeatherAlert = typeof weatherAlertSchema.infer
+
+const weatherKitResponseSchema = type({
+	"currentWeather?": currentWeatherSchema,
+	"forecastHourly?": type({
+		hours: hourlyForecastSchema.array(),
+	}),
+	"forecastDaily?": type({
+		days: dailyForecastSchema.array(),
+	}),
+	"weatherAlerts?": type({
+		alerts: weatherAlertSchema.array(),
+	}),
+})
+
+export type WeatherKitResponse = typeof weatherKitResponseSchema.infer
+
+async function generateJwt(credentials: WeatherKitCredentials): Promise<string> {
+	const header = {
+		alg: "ES256",
+		kid: credentials.keyId,
+		id: `${credentials.teamId}.${credentials.serviceId}`,
+	}
+
+	const now = Math.floor(Date.now() / 1000)
+	const payload = {
+		iss: credentials.teamId,
+		iat: now,
+		exp: now + 3600,
+		sub: credentials.serviceId,
+	}
+
+	const encoder = new TextEncoder()
+	const headerB64 = btoa(JSON.stringify(header))
+		.replace(/\+/g, "-")
+		.replace(/\//g, "_")
+		.replace(/=+$/, "")
+	const payloadB64 = btoa(JSON.stringify(payload))
+		.replace(/\+/g, "-")
+		.replace(/\//g, "_")
+		.replace(/=+$/, "")
+
+	const signingInput = `${headerB64}.${payloadB64}`
+
+	const pemContents = credentials.privateKey
+		.replace(/-----BEGIN PRIVATE KEY-----/, "")
+		.replace(/-----END PRIVATE KEY-----/, "")
+		.replace(/\s/g, "")
+
+	const binaryKey = Uint8Array.from(atob(pemContents), (c) => c.charCodeAt(0))
+
+	const cryptoKey = await crypto.subtle.importKey(
+		"pkcs8",
+		binaryKey,
+		{ name: "ECDSA", namedCurve: "P-256" },
+		false,
+		["sign"],
+	)
+
+	const signature = await crypto.subtle.sign(
+		{ name: "ECDSA", hash: "SHA-256" },
+		cryptoKey,
+		encoder.encode(signingInput),
+	)
+
+	const signatureB64 = btoa(String.fromCharCode(...new Uint8Array(signature)))
+		.replace(/\+/g, "-")
+		.replace(/\//g, "_")
+		.replace(/=+$/, "")
+
+	return `${signingInput}.${signatureB64}`
+}