feat(backend): make FeedSourceProvider async

Make feedSourceForUser and FeedSourceProviderFn return promises.
Use Promise.allSettled to tolerate partial provider failures.
Guard concurrent getOrCreate calls with in-flight promise dedup.
Return 503 from HTTP handlers when session creation fails.

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

apps/aelis-backend/src/engine/http.test.ts

@@ -1,7 +1,7 @@
 import type { ActionDefinition, ContextEntry, FeedItem, FeedSource } from "@aelis/core"
 
 import { contextKey } from "@aelis/core"
-import { describe, expect, test } from "bun:test"
+import { describe, expect, spyOn, test } from "bun:test"
 import { Hono } from "hono"
 
 import { mockAuthSessionMiddleware } from "../auth/session-middleware.ts"
@@ -72,12 +72,12 @@ describe("GET /api/feed", () => {
 			},
 		]
 		const manager = new UserSessionManager({
-			providers: [() => createStubSource("test", items)],
+			providers: [async () => createStubSource("test", items)],
 		})
 		const app = buildTestApp(manager, "user-1")
 
 		// Prime the cache
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 		await session.engine.refresh()
 		expect(session.engine.lastFeed()).not.toBeNull()
 
@@ -105,7 +105,7 @@ describe("GET /api/feed", () => {
 			},
 		]
 		const manager = new UserSessionManager({
-			providers: [() => createStubSource("test", items)],
+			providers: [async () => createStubSource("test", items)],
 		})
 		const app = buildTestApp(manager, "user-1")
 
@@ -136,7 +136,7 @@ describe("GET /api/feed", () => {
 				throw new Error("connection timeout")
 			},
 		}
-		const manager = new UserSessionManager({ providers: [() => failingSource] })
+		const manager = new UserSessionManager({ providers: [async () => failingSource] })
 		const app = buildTestApp(manager, "user-1")
 
 		const res = await app.request("/api/feed")
@@ -148,6 +148,27 @@ describe("GET /api/feed", () => {
 		expect(body.errors[0]!.sourceId).toBe("failing")
 		expect(body.errors[0]!.error).toBe("connection timeout")
 	})
+
+	test("returns 503 when all providers fail", async () => {
+		const manager = new UserSessionManager({
+			providers: [
+				async () => {
+					throw new Error("provider down")
+				},
+			],
+		})
+		const app = buildTestApp(manager, "user-1")
+
+		const spy = spyOn(console, "error").mockImplementation(() => {})
+
+		const res = await app.request("/api/feed")
+
+		expect(res.status).toBe(503)
+		const body = (await res.json()) as { error: string }
+		expect(body.error).toBe("Service unavailable")
+
+		spy.mockRestore()
+	})
 })
 
 describe("GET /api/context", () => {
@@ -158,12 +179,12 @@ describe("GET /api/context", () => {
 	// The mock auth middleware always injects this hardcoded user ID
 	const mockUserId = "k7Gx2mPqRvNwYs9TdLfA4bHcJeUo1iZn"
 
-	function buildContextApp(userId?: string) {
+	async function buildContextApp(userId?: string) {
 		const manager = new UserSessionManager({
-			providers: [() => createStubSource("weather", [], contextEntries)],
+			providers: [async () => createStubSource("weather", [], contextEntries)],
 		})
 		const app = buildTestApp(manager, userId)
-		const session = manager.getOrCreate(mockUserId)
+		const session = await manager.getOrCreate(mockUserId)
 		return { app, session }
 	}
 
@@ -177,7 +198,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("returns 400 when key param is missing", async () => {
-		const { app } = buildContextApp("user-1")
+		const { app } = await buildContextApp("user-1")
 
 		const res = await app.request("/api/context")
 
@@ -187,7 +208,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("returns 400 when key is invalid JSON", async () => {
-		const { app } = buildContextApp("user-1")
+		const { app } = await buildContextApp("user-1")
 
 		const res = await app.request("/api/context?key=notjson")
 
@@ -197,7 +218,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("returns 400 when key is not an array", async () => {
-		const { app } = buildContextApp("user-1")
+		const { app } = await buildContextApp("user-1")
 
 		const res = await app.request('/api/context?key="string"')
 
@@ -207,7 +228,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("returns 400 when key contains invalid element types", async () => {
-		const { app } = buildContextApp("user-1")
+		const { app } = await buildContextApp("user-1")
 
 		const res = await app.request("/api/context?key=[true,null,[1,2]]")
 
@@ -217,7 +238,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("returns 400 when key is an empty array", async () => {
-		const { app } = buildContextApp("user-1")
+		const { app } = await buildContextApp("user-1")
 
 		const res = await app.request("/api/context?key=[]")
 
@@ -227,7 +248,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("returns 400 when match param is invalid", async () => {
-		const { app } = buildContextApp("user-1")
+		const { app } = await buildContextApp("user-1")
 
 		const res = await app.request('/api/context?key=["aelis.weather"]&match=invalid')
 
@@ -237,7 +258,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("returns exact match with match=exact", async () => {
-		const { app, session } = buildContextApp("user-1")
+		const { app, session } = await buildContextApp("user-1")
 		await session.engine.refresh()
 
 		const res = await app.request('/api/context?key=["aelis.weather","weather"]&match=exact')
@@ -249,7 +270,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("returns 404 with match=exact when only prefix would match", async () => {
-		const { app, session } = buildContextApp("user-1")
+		const { app, session } = await buildContextApp("user-1")
 		await session.engine.refresh()
 
 		const res = await app.request('/api/context?key=["aelis.weather"]&match=exact')
@@ -258,7 +279,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("returns prefix match with match=prefix", async () => {
-		const { app, session } = buildContextApp("user-1")
+		const { app, session } = await buildContextApp("user-1")
 		await session.engine.refresh()
 
 		const res = await app.request('/api/context?key=["aelis.weather"]&match=prefix')
@@ -275,7 +296,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("default mode returns exact match when available", async () => {
-		const { app, session } = buildContextApp("user-1")
+		const { app, session } = await buildContextApp("user-1")
 		await session.engine.refresh()
 
 		const res = await app.request('/api/context?key=["aelis.weather","weather"]')
@@ -287,7 +308,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("default mode falls back to prefix when no exact match", async () => {
-		const { app, session } = buildContextApp("user-1")
+		const { app, session } = await buildContextApp("user-1")
 		await session.engine.refresh()
 
 		const res = await app.request('/api/context?key=["aelis.weather"]')
@@ -303,7 +324,7 @@ describe("GET /api/context", () => {
 	})
 
 	test("returns 404 when neither exact nor prefix matches", async () => {
-		const { app, session } = buildContextApp("user-1")
+		const { app, session } = await buildContextApp("user-1")
 		await session.engine.refresh()
 
 		const res = await app.request('/api/context?key=["nonexistent"]')

apps/aelis-backend/src/engine/http.ts

@@ -33,7 +33,14 @@ export function registerFeedHttpHandlers(
 async function handleGetFeed(c: Context<Env>) {
 	const user = c.get("user")!
 	const sessionManager = c.get("sessionManager")
-	const session = sessionManager.getOrCreate(user.id)
+
+	let session
+	try {
+		session = await sessionManager.getOrCreate(user.id)
+	} catch (err) {
+		console.error("[handleGetFeed] Failed to create session:", err)
+		return c.json({ error: "Service unavailable" }, 503)
+	}
 
 	const feed = await session.feed()
 
@@ -46,7 +53,7 @@ async function handleGetFeed(c: Context<Env>) {
 	})
 }
 
-function handleGetContext(c: Context<Env>) {
+async function handleGetContext(c: Context<Env>) {
 	const keyParam = c.req.query("key")
 	if (!keyParam) {
 		return c.json({ error: 'Invalid or missing "key" parameter: must be a JSON array' }, 400)
@@ -70,7 +77,15 @@ function handleGetContext(c: Context<Env>) {
 
 	const user = c.get("user")!
 	const sessionManager = c.get("sessionManager")
-	const session = sessionManager.getOrCreate(user.id)
+
+	let session
+	try {
+		session = await sessionManager.getOrCreate(user.id)
+	} catch (err) {
+		console.error("[handleGetContext] Failed to create session:", err)
+		return c.json({ error: "Service unavailable" }, 503)
+	}
+
 	const context = session.engine.currentContext()
 	const key = contextKey(...parsed)
 

apps/aelis-backend/src/location/http.ts

@@ -44,7 +44,15 @@ async function handleUpdateLocation(c: Context<Env>) {
 
 	const user = c.get("user")!
 	const sessionManager = c.get("sessionManager")
-	const session = sessionManager.getOrCreate(user.id)
+
+	let session
+	try {
+		session = await sessionManager.getOrCreate(user.id)
+	} catch (err) {
+		console.error("[handleUpdateLocation] Failed to create session:", err)
+		return c.json({ error: "Service unavailable" }, 503)
+	}
+
 	await session.engine.executeAction("aelis.location", "update-location", {
 		lat: result.lat,
 		lng: result.lng,

apps/aelis-backend/src/server.ts

@@ -3,9 +3,9 @@ import { Hono } from "hono"
 
 import { registerAuthHandlers } from "./auth/http.ts"
 import { mockAuthSessionMiddleware, requireSession } from "./auth/session-middleware.ts"
+import { registerFeedHttpHandlers } from "./engine/http.ts"
 import { createFeedEnhancer } from "./enhancement/enhance-feed.ts"
 import { createLlmClient } from "./enhancement/llm-client.ts"
-import { registerFeedHttpHandlers } from "./engine/http.ts"
 import { registerLocationHttpHandlers } from "./location/http.ts"
 import { UserSessionManager } from "./session/index.ts"
 import { WeatherSourceProvider } from "./weather/provider.ts"
@@ -26,7 +26,7 @@ function main() {
 
 	const sessionManager = new UserSessionManager({
 		providers: [
-			() => new LocationSource(),
+			async () => new LocationSource(),
 			new WeatherSourceProvider({
 				credentials: {
 					privateKey: process.env.WEATHERKIT_PRIVATE_KEY!,

apps/aelis-backend/src/session/feed-source-provider.ts

@@ -1,9 +1,9 @@
 import type { FeedSource } from "@aelis/core"
 
 export interface FeedSourceProvider {
-	feedSourceForUser(userId: string): FeedSource
+	feedSourceForUser(userId: string): Promise<FeedSource>
 }
 
-export type FeedSourceProviderFn = (userId: string) => FeedSource
+export type FeedSourceProviderFn = (userId: string) => Promise<FeedSource>
 
 export type FeedSourceProviderInput = FeedSourceProvider | FeedSourceProviderFn

apps/aelis-backend/src/session/user-session-manager.test.ts

@@ -1,7 +1,7 @@
 import type { WeatherKitClient, WeatherKitResponse } from "@aelis/source-weatherkit"
 
 import { LocationSource } from "@aelis/source-location"
-import { describe, expect, mock, test } from "bun:test"
+import { describe, expect, mock, spyOn, test } from "bun:test"
 
 import { WeatherSourceProvider } from "../weather/provider.ts"
 import { UserSessionManager } from "./user-session-manager.ts"
@@ -11,38 +11,38 @@ const mockWeatherClient: WeatherKitClient = {
 }
 
 describe("UserSessionManager", () => {
-	test("getOrCreate creates session on first call", () => {
+	test("getOrCreate creates session on first call", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 
 		expect(session).toBeDefined()
 		expect(session.engine).toBeDefined()
 	})
 
-	test("getOrCreate returns same session for same user", () => {
+	test("getOrCreate returns same session for same user", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session1 = manager.getOrCreate("user-1")
+		const session1 = await manager.getOrCreate("user-1")
-		const session2 = manager.getOrCreate("user-1")
+		const session2 = await manager.getOrCreate("user-1")
 
 		expect(session1).toBe(session2)
 	})
 
-	test("getOrCreate returns different sessions for different users", () => {
+	test("getOrCreate returns different sessions for different users", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session1 = manager.getOrCreate("user-1")
+		const session1 = await manager.getOrCreate("user-1")
-		const session2 = manager.getOrCreate("user-2")
+		const session2 = await manager.getOrCreate("user-2")
 
 		expect(session1).not.toBe(session2)
 	})
 
-	test("each user gets independent source instances", () => {
+	test("each user gets independent source instances", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session1 = manager.getOrCreate("user-1")
+		const session1 = await manager.getOrCreate("user-1")
-		const session2 = manager.getOrCreate("user-2")
+		const session2 = await manager.getOrCreate("user-2")
 
 		const source1 = session1.getSource<LocationSource>("aelis.location")
 		const source2 = session2.getSource<LocationSource>("aelis.location")
@@ -50,58 +50,58 @@ describe("UserSessionManager", () => {
 		expect(source1).not.toBe(source2)
 	})
 
-	test("remove destroys session and allows re-creation", () => {
+	test("remove destroys session and allows re-creation", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session1 = manager.getOrCreate("user-1")
+		const session1 = await manager.getOrCreate("user-1")
 		manager.remove("user-1")
-		const session2 = manager.getOrCreate("user-1")
+		const session2 = await manager.getOrCreate("user-1")
 
 		expect(session1).not.toBe(session2)
 	})
 
 	test("remove is no-op for unknown user", () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
 		expect(() => manager.remove("unknown")).not.toThrow()
 	})
 
 	test("accepts function providers", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 		const result = await session.engine.refresh()
 
 		expect(result.errors).toHaveLength(0)
 	})
 
-	test("accepts object providers", () => {
+	test("accepts object providers", async () => {
 		const provider = new WeatherSourceProvider({ client: mockWeatherClient })
 		const manager = new UserSessionManager({
-			providers: [() => new LocationSource(), provider],
+			providers: [async () => new LocationSource(), provider],
 		})
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 
 		expect(session.getSource("aelis.weather")).toBeDefined()
 	})
 
-	test("accepts mixed providers", () => {
+	test("accepts mixed providers", async () => {
 		const provider = new WeatherSourceProvider({ client: mockWeatherClient })
 		const manager = new UserSessionManager({
-			providers: [() => new LocationSource(), provider],
+			providers: [async () => new LocationSource(), provider],
 		})
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 
 		expect(session.getSource("aelis.location")).toBeDefined()
 		expect(session.getSource("aelis.weather")).toBeDefined()
 	})
 
 	test("refresh returns feed result through session", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 		const result = await session.engine.refresh()
 
 		expect(result).toHaveProperty("context")
@@ -111,9 +111,9 @@ describe("UserSessionManager", () => {
 	})
 
 	test("location update via executeAction works", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 		await session.engine.executeAction("aelis.location", "update-location", {
 			lat: 51.5074,
 			lng: -0.1278,
@@ -126,10 +126,10 @@ describe("UserSessionManager", () => {
 	})
 
 	test("subscribe receives updates after location push", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 		const callback = mock()
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 		session.engine.subscribe(callback)
 
 		await session.engine.executeAction("aelis.location", "update-location", {
@@ -146,16 +146,16 @@ describe("UserSessionManager", () => {
 	})
 
 	test("remove stops reactive updates", async () => {
-		const manager = new UserSessionManager({ providers: [() => new LocationSource()] })
+		const manager = new UserSessionManager({ providers: [async () => new LocationSource()] })
 		const callback = mock()
 
-		const session = manager.getOrCreate("user-1")
+		const session = await manager.getOrCreate("user-1")
 		session.engine.subscribe(callback)
 
 		manager.remove("user-1")
 
 		// Create new session and push location — old callback should not fire
-		const session2 = manager.getOrCreate("user-1")
+		const session2 = await manager.getOrCreate("user-1")
 		await session2.engine.executeAction("aelis.location", "update-location", {
 			lat: 51.5074,
 			lng: -0.1278,
@@ -167,4 +167,62 @@ describe("UserSessionManager", () => {
 
 		expect(callback).not.toHaveBeenCalled()
 	})
+
+	test("creates session with successful providers when some fail", async () => {
+		const manager = new UserSessionManager({
+			providers: [
+				async () => new LocationSource(),
+				async () => {
+					throw new Error("provider failed")
+				},
+			],
+		})
+
+		const spy = spyOn(console, "error").mockImplementation(() => {})
+
+		const session = await manager.getOrCreate("user-1")
+
+		expect(session).toBeDefined()
+		expect(session.getSource("aelis.location")).toBeDefined()
+		expect(spy).toHaveBeenCalled()
+
+		spy.mockRestore()
+	})
+
+	test("throws AggregateError when all providers fail", async () => {
+		const manager = new UserSessionManager({
+			providers: [
+				async () => {
+					throw new Error("first failed")
+				},
+				async () => {
+					throw new Error("second failed")
+				},
+			],
+		})
+
+		await expect(manager.getOrCreate("user-1")).rejects.toBeInstanceOf(AggregateError)
+	})
+
+	test("concurrent getOrCreate for same user returns same session", async () => {
+		let callCount = 0
+		const manager = new UserSessionManager({
+			providers: [
+				async () => {
+					callCount++
+					// Simulate async work to widen the race window
+					await new Promise((resolve) => setTimeout(resolve, 10))
+					return new LocationSource()
+				},
+			],
+		})
+
+		const [session1, session2] = await Promise.all([
+			manager.getOrCreate("user-1"),
+			manager.getOrCreate("user-1"),
+		])
+
+		expect(session1).toBe(session2)
+		expect(callCount).toBe(1)
+	})
 })

apps/aelis-backend/src/session/user-session-manager.ts

@@ -1,3 +1,5 @@
+import type { FeedSource } from "@aelis/core"
+
 import type { FeedEnhancer } from "../enhancement/enhance-feed.ts"
 import type { FeedSourceProviderInput } from "./feed-source-provider.ts"
 
@@ -10,6 +12,7 @@ export interface UserSessionManagerConfig {
 
 export class UserSessionManager {
 	private sessions = new Map<string, UserSession>()
+	private pending = new Map<string, Promise<UserSession>>()
 	private readonly providers: FeedSourceProviderInput[]
 	private readonly feedEnhancer: FeedEnhancer | null
 
@@ -18,16 +21,22 @@ export class UserSessionManager {
 		this.feedEnhancer = config.feedEnhancer ?? null
 	}
 
-	getOrCreate(userId: string): UserSession {
+	async getOrCreate(userId: string): Promise<UserSession> {
-		let session = this.sessions.get(userId)
+		const existing = this.sessions.get(userId)
-		if (!session) {
+		if (existing) return existing
-			const sources = this.providers.map((p) =>
+
-				typeof p === "function" ? p(userId) : p.feedSourceForUser(userId),
+		const inflight = this.pending.get(userId)
-			)
+		if (inflight) return inflight
-			session = new UserSession(sources, this.feedEnhancer)
+
+		const promise = this.createSession(userId)
+		this.pending.set(userId, promise)
+		try {
+			const session = await promise
 			this.sessions.set(userId, session)
+			return session
+		} finally {
+			this.pending.delete(userId)
 		}
-		return session
 	}
 
 	remove(userId: string): void {
@@ -37,4 +46,33 @@ export class UserSessionManager {
 			this.sessions.delete(userId)
 		}
 	}
+
+	private async createSession(userId: string): Promise<UserSession> {
+		const results = await Promise.allSettled(
+			this.providers.map((p) =>
+				typeof p === "function" ? p(userId) : p.feedSourceForUser(userId),
+			),
+		)
+
+		const sources: FeedSource[] = []
+		const errors: unknown[] = []
+
+		for (const result of results) {
+			if (result.status === "fulfilled") {
+				sources.push(result.value)
+			} else {
+				errors.push(result.reason)
+			}
+		}
+
+		if (sources.length === 0 && errors.length > 0) {
+			throw new AggregateError(errors, "All feed source providers failed")
+		}
+
+		for (const error of errors) {
+			console.error("[UserSessionManager] Feed source provider failed:", error)
+		}
+
+		return new UserSession(sources, this.feedEnhancer)
+	}
 }

apps/aelis-backend/src/tfl/provider.ts

@@ -13,7 +13,7 @@ export class TflSourceProvider implements FeedSourceProvider {
 		this.options = options
 	}
 
-	feedSourceForUser(_userId: string): TflSource {
+	async feedSourceForUser(_userId: string): Promise<TflSource> {
 		return new TflSource(this.options)
 	}
 }

apps/aelis-backend/src/weather/provider.ts

@@ -9,7 +9,7 @@ export class WeatherSourceProvider implements FeedSourceProvider {
 		this.options = options
 	}
 
-	feedSourceForUser(_userId: string): WeatherSource {
+	async feedSourceForUser(_userId: string): Promise<WeatherSource> {
 		return new WeatherSource(this.options)
 	}
 }