feat: replace flat context with tuple-keyed store (#50)

Context keys are now tuples instead of strings, inspired by
React Query's query keys. This prevents context collisions
when multiple instances of the same source type are registered.

Sources write to structured keys like
["aris.google-calendar", "nextEvent", { account: "work" }]
and consumers can query by prefix via context.find().

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

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

@@ -1,8 +1,8 @@
 import { describe, expect, test } from "bun:test"
 
-import type { ActionDefinition, Context, ContextKey, FeedItem, FeedSource } from "./index"
+import type { ActionDefinition, ContextEntry, ContextKey, FeedItem, FeedSource } from "./index"
 
-import { TimeRelevance, UnknownActionError, contextKey, contextValue } from "./index"
+import { Context, TimeRelevance, UnknownActionError, contextKey } from "./index"
 
 // No-op action methods for test sources
 const noActions = {
@@ -47,7 +47,7 @@ interface SimulatedLocationSource extends FeedSource {
 }
 
 function createLocationSource(): SimulatedLocationSource {
-	let callback: ((update: Partial<Context>) => void) | null = null
+	let callback: ((entries: readonly ContextEntry[]) => void) | null = null
 	let currentLocation: Location = { lat: 0, lng: 0 }
 
 	return {
@@ -62,12 +62,12 @@ function createLocationSource(): SimulatedLocationSource {
 		},
 
 		async fetchContext() {
-			return { [LocationKey]: currentLocation }
+			return [[LocationKey, currentLocation]]
 		},
 
 		simulateUpdate(location: Location) {
 			currentLocation = location
-			callback?.({ [LocationKey]: location })
+			callback?.([[LocationKey, location]])
 		},
 	}
 }
@@ -84,15 +84,15 @@ function createWeatherSource(
 		...noActions,
 
 		async fetchContext(context) {
-			const location = contextValue(context, LocationKey)
+			const location = context.get(LocationKey)
 			if (!location) return null
 
 			const weather = await fetchWeather(location)
-			return { [WeatherKey]: weather }
+			return [[WeatherKey, weather]]
 		},
 
 		async fetchItems(context) {
-			const weather = contextValue(context, WeatherKey)
+			const weather = context.get(WeatherKey)
 			if (!weather) return []
 
 			return [
@@ -122,7 +122,7 @@ function createAlertSource(): FeedSource<AlertFeedItem> {
 		},
 
 		async fetchItems(context) {
-			const weather = contextValue(context, WeatherKey)
+			const weather = context.get(WeatherKey)
 			if (!weather) return []
 
 			if (weather.condition === "storm") {
@@ -207,13 +207,13 @@ function buildGraph(sources: FeedSource[]): SourceGraph {
 }
 
 async function refreshGraph(graph: SourceGraph): Promise<{ context: Context; items: FeedItem[] }> {
-	let context: Context = { time: new Date() }
+	const context = new Context()
 
 	// Run fetchContext in topological order
 	for (const source of graph.sorted) {
-		const update = await source.fetchContext(context)
-		if (update) {
-			context = { ...context, ...update }
+		const entries = await source.fetchContext(context)
+		if (entries) {
+			context.set(entries)
 		}
 	}
 
@@ -265,7 +265,7 @@ describe("FeedSource", () => {
 
 		test("source without context returns null from fetchContext", async () => {
 			const source = createAlertSource()
-			const result = await source.fetchContext({ time: new Date() })
+			const result = await source.fetchContext(new Context())
 			expect(result).toBeNull()
 		})
 	})
@@ -369,7 +369,7 @@ describe("FeedSource", () => {
 				...noActions,
 				async fetchContext() {
 					order.push("location")
-					return { [LocationKey]: { lat: 51.5, lng: -0.1 } }
+					return [[LocationKey, { lat: 51.5, lng: -0.1 }]]
 				},
 			}
 
@@ -379,9 +379,9 @@ describe("FeedSource", () => {
 				...noActions,
 				async fetchContext(ctx) {
 					order.push("weather")
-					const loc = contextValue(ctx, LocationKey)
+					const loc = ctx.get(LocationKey)
 					expect(loc).toBeDefined()
-					return { [WeatherKey]: { temperature: 20, condition: "sunny" } }
+					return [[WeatherKey, { temperature: 20, condition: "sunny" }]]
 				},
 			}
 
@@ -400,11 +400,11 @@ describe("FeedSource", () => {
 			const graph = buildGraph([location, weather])
 			const { context } = await refreshGraph(graph)
 
-			expect(contextValue(context, LocationKey)).toEqual({
+			expect(context.get(LocationKey)).toEqual({
 				lat: 51.5,
 				lng: -0.1,
 			})
-			expect(contextValue(context, WeatherKey)).toEqual({
+			expect(context.get(WeatherKey)).toEqual({
 				temperature: 20,
 				condition: "sunny",
 			})
@@ -447,12 +447,10 @@ describe("FeedSource", () => {
 		})
 
 		test("source without location context returns empty items", async () => {
-			// Location source exists but hasn't been updated
 			const location: FeedSource = {
 				id: "location",
 				...noActions,
 				async fetchContext() {
-					// Simulate no location available
 					return null
 				},
 			}
@@ -462,7 +460,7 @@ describe("FeedSource", () => {
 			const graph = buildGraph([location, weather])
 			const { context, items } = await refreshGraph(graph)
 
-			expect(contextValue(context, WeatherKey)).toBeUndefined()
+			expect(context.get(WeatherKey)).toBeUndefined()
 			expect(items).toHaveLength(0)
 		})
 	})
@@ -476,7 +474,7 @@ describe("FeedSource", () => {
 				() => {
 					updateCount++
 				},
-				() => ({ time: new Date() }),
+				() => new Context(),
 			)
 
 			location.simulateUpdate({ lat: 1, lng: 1 })