feat: add caching to FeedEngine

Add lastFeed() method that returns cached FeedResult within
a configurable TTL (default 5 min). refresh() always fetches
fresh data and updates the cache. Periodic auto-refresh via
recursive setTimeout when engine is started. Reactive updates
reset the timer to avoid redundant fetches.

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

apps/aris-client/app.json

@@ -46,7 +46,97 @@
 					}
 				}
 			],
-			"expo-font"
+			[
+				"expo-font",
+				{
+					"android": {
+						"fonts": [
+							{
+								"fontFamily": "Inter",
+								"fontDefinitions": [
+									{ "path": "./assets/fonts/Inter_100Thin.ttf", "weight": 100 },
+									{ "path": "./assets/fonts/Inter_100Thin_Italic.ttf", "weight": 100, "style": "italic" },
+									{ "path": "./assets/fonts/Inter_200ExtraLight.ttf", "weight": 200 },
+									{ "path": "./assets/fonts/Inter_200ExtraLight_Italic.ttf", "weight": 200, "style": "italic" },
+									{ "path": "./assets/fonts/Inter_300Light.ttf", "weight": 300 },
+									{ "path": "./assets/fonts/Inter_300Light_Italic.ttf", "weight": 300, "style": "italic" },
+									{ "path": "./assets/fonts/Inter_400Regular.ttf", "weight": 400 },
+									{ "path": "./assets/fonts/Inter_400Regular_Italic.ttf", "weight": 400, "style": "italic" },
+									{ "path": "./assets/fonts/Inter_500Medium.ttf", "weight": 500 },
+									{ "path": "./assets/fonts/Inter_500Medium_Italic.ttf", "weight": 500, "style": "italic" },
+									{ "path": "./assets/fonts/Inter_600SemiBold.ttf", "weight": 600 },
+									{ "path": "./assets/fonts/Inter_600SemiBold_Italic.ttf", "weight": 600, "style": "italic" },
+									{ "path": "./assets/fonts/Inter_700Bold.ttf", "weight": 700 },
+									{ "path": "./assets/fonts/Inter_700Bold_Italic.ttf", "weight": 700, "style": "italic" },
+									{ "path": "./assets/fonts/Inter_800ExtraBold.ttf", "weight": 800 },
+									{ "path": "./assets/fonts/Inter_800ExtraBold_Italic.ttf", "weight": 800, "style": "italic" },
+									{ "path": "./assets/fonts/Inter_900Black.ttf", "weight": 900 },
+									{ "path": "./assets/fonts/Inter_900Black_Italic.ttf", "weight": 900, "style": "italic" }
+								]
+							},
+							{
+								"fontFamily": "Source Serif 4",
+								"fontDefinitions": [
+									{ "path": "./assets/fonts/SourceSerif4_200ExtraLight.ttf", "weight": 200 },
+									{ "path": "./assets/fonts/SourceSerif4_200ExtraLight_Italic.ttf", "weight": 200, "style": "italic" },
+									{ "path": "./assets/fonts/SourceSerif4_300Light.ttf", "weight": 300 },
+									{ "path": "./assets/fonts/SourceSerif4_300Light_Italic.ttf", "weight": 300, "style": "italic" },
+									{ "path": "./assets/fonts/SourceSerif4_400Regular.ttf", "weight": 400 },
+									{ "path": "./assets/fonts/SourceSerif4_400Regular_Italic.ttf", "weight": 400, "style": "italic" },
+									{ "path": "./assets/fonts/SourceSerif4_500Medium.ttf", "weight": 500 },
+									{ "path": "./assets/fonts/SourceSerif4_500Medium_Italic.ttf", "weight": 500, "style": "italic" },
+									{ "path": "./assets/fonts/SourceSerif4_600SemiBold.ttf", "weight": 600 },
+									{ "path": "./assets/fonts/SourceSerif4_600SemiBold_Italic.ttf", "weight": 600, "style": "italic" },
+									{ "path": "./assets/fonts/SourceSerif4_700Bold.ttf", "weight": 700 },
+									{ "path": "./assets/fonts/SourceSerif4_700Bold_Italic.ttf", "weight": 700, "style": "italic" },
+									{ "path": "./assets/fonts/SourceSerif4_800ExtraBold.ttf", "weight": 800 },
+									{ "path": "./assets/fonts/SourceSerif4_800ExtraBold_Italic.ttf", "weight": 800, "style": "italic" },
+									{ "path": "./assets/fonts/SourceSerif4_900Black.ttf", "weight": 900 },
+									{ "path": "./assets/fonts/SourceSerif4_900Black_Italic.ttf", "weight": 900, "style": "italic" }
+								]
+							}
+						]
+					},
+					"ios": {
+						"fonts": [
+							"./assets/fonts/Inter_100Thin.ttf",
+							"./assets/fonts/Inter_100Thin_Italic.ttf",
+							"./assets/fonts/Inter_200ExtraLight.ttf",
+							"./assets/fonts/Inter_200ExtraLight_Italic.ttf",
+							"./assets/fonts/Inter_300Light.ttf",
+							"./assets/fonts/Inter_300Light_Italic.ttf",
+							"./assets/fonts/Inter_400Regular.ttf",
+							"./assets/fonts/Inter_400Regular_Italic.ttf",
+							"./assets/fonts/Inter_500Medium.ttf",
+							"./assets/fonts/Inter_500Medium_Italic.ttf",
+							"./assets/fonts/Inter_600SemiBold.ttf",
+							"./assets/fonts/Inter_600SemiBold_Italic.ttf",
+							"./assets/fonts/Inter_700Bold.ttf",
+							"./assets/fonts/Inter_700Bold_Italic.ttf",
+							"./assets/fonts/Inter_800ExtraBold.ttf",
+							"./assets/fonts/Inter_800ExtraBold_Italic.ttf",
+							"./assets/fonts/Inter_900Black.ttf",
+							"./assets/fonts/Inter_900Black_Italic.ttf",
+							"./assets/fonts/SourceSerif4_200ExtraLight.ttf",
+							"./assets/fonts/SourceSerif4_200ExtraLight_Italic.ttf",
+							"./assets/fonts/SourceSerif4_300Light.ttf",
+							"./assets/fonts/SourceSerif4_300Light_Italic.ttf",
+							"./assets/fonts/SourceSerif4_400Regular.ttf",
+							"./assets/fonts/SourceSerif4_400Regular_Italic.ttf",
+							"./assets/fonts/SourceSerif4_500Medium.ttf",
+							"./assets/fonts/SourceSerif4_500Medium_Italic.ttf",
+							"./assets/fonts/SourceSerif4_600SemiBold.ttf",
+							"./assets/fonts/SourceSerif4_600SemiBold_Italic.ttf",
+							"./assets/fonts/SourceSerif4_700Bold.ttf",
+							"./assets/fonts/SourceSerif4_700Bold_Italic.ttf",
+							"./assets/fonts/SourceSerif4_800ExtraBold.ttf",
+							"./assets/fonts/SourceSerif4_800ExtraBold_Italic.ttf",
+							"./assets/fonts/SourceSerif4_900Black.ttf",
+							"./assets/fonts/SourceSerif4_900Black_Italic.ttf"
+						]
+					}
+				}
+			]
 		],
 		"experiments": {
 			"typedRoutes": true,

apps/aris-client/eas.json

@@ -8,6 +8,12 @@
 			"developmentClient": true,
 			"distribution": "internal"
 		},
+		"development-simulator": {
+			"extends": "development",
+			"ios": {
+				"simulator": "true"
+			}
+		},
 		"preview": {
 			"distribution": "internal"
 		},

apps/aris-client/package.json

@@ -11,10 +11,12 @@
 		"web": "expo start --web",
 		"lint": "expo lint",
 		"build:ios": "eas build --profile development --platform ios --non-interactive",
+		"build:ios-simulator": "eas build --profile development-simulator --platform ios --non-interactive",
 		"debugger": "bun run scripts/open-debugger.ts"
 	},
 	"dependencies": {
 		"@expo-google-fonts/inter": "^0.4.2",
+		"@expo-google-fonts/source-serif-4": "^0.4.1",
 		"@expo/vector-icons": "^15.0.3",
 		"@react-navigation/bottom-tabs": "^7.4.0",
 		"@react-navigation/elements": "^2.6.3",

bun.lock

@@ -35,6 +35,7 @@
       "version": "1.0.0",
       "dependencies": {
         "@expo-google-fonts/inter": "^0.4.2",
+        "@expo-google-fonts/source-serif-4": "^0.4.1",
         "@expo/vector-icons": "^15.0.3",
         "@react-navigation/bottom-tabs": "^7.4.0",
         "@react-navigation/elements": "^2.6.3",
@@ -383,6 +384,8 @@
 
     "@expo-google-fonts/inter": ["@expo-google-fonts/inter@0.4.2", "", {}, "sha512-syfiImMaDmq7cFi0of+waE2M4uSCyd16zgyWxdPOY7fN2VBmSLKEzkfbZgeOjJq61kSqPBNNtXjggiQiSD6gMQ=="],
 
+    "@expo-google-fonts/source-serif-4": ["@expo-google-fonts/source-serif-4@0.4.1", "", {}, "sha512-Ej4UXDjW1kwYPHG8YLq6fK1bqnJGb3K35J3S5atSL0ScKFAFLKvndxoTWeCls7mybtlS9x99hzwDeXCBkiI3rA=="],
+
     "@expo/apple-utils": ["@expo/apple-utils@2.1.13", "", { "bin": { "apple-utils": "bin.js" } }, "sha512-nt3efiJhAWTHl9ikKYrHEuv3dhqCdicsHFRE9LmvtcVsPhXl9bAsm0gbACoLPr7ClP8664H/S6SdVJOD/tw0jg=="],
 
     "@expo/bunyan": ["@expo/bunyan@4.0.1", "", { "dependencies": { "uuid": "^8.0.0" } }, "sha512-+Lla7nYSiHZirgK+U/uYzsLv/X+HaJienbD5AKX1UQZHYfWaP+9uuQluRB4GrEVWF0GZ7vEVp/jzaOT9k/SQlg=="],

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

@@ -638,4 +638,290 @@ describe("FeedEngine", () => {
 			)
 		})
 	})
+
+	describe("lastFeed", () => {
+		test("returns null before any refresh", () => {
+			const engine = new FeedEngine()
+
+			expect(engine.lastFeed()).toBeNull()
+		})
+
+		test("returns cached result after refresh", async () => {
+			const location = createLocationSource()
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			const weather = createWeatherSource()
+			const engine = new FeedEngine().register(location).register(weather)
+
+			const refreshResult = await engine.refresh()
+
+			const cached = engine.lastFeed()
+			expect(cached).not.toBeNull()
+			expect(cached!.items).toEqual(refreshResult.items)
+			expect(cached!.context).toEqual(refreshResult.context)
+		})
+
+		test("returns null after TTL expires", async () => {
+			const engine = new FeedEngine({ cacheTtlMs: 50 })
+			const location = createLocationSource()
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			engine.register(location)
+			await engine.refresh()
+
+			expect(engine.lastFeed()).not.toBeNull()
+
+			await new Promise((resolve) => setTimeout(resolve, 60))
+
+			expect(engine.lastFeed()).toBeNull()
+		})
+
+		test("defaults to 5 minute TTL", async () => {
+			const engine = new FeedEngine()
+			const location = createLocationSource()
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			engine.register(location)
+			await engine.refresh()
+
+			// Should still be cached immediately
+			expect(engine.lastFeed()).not.toBeNull()
+		})
+
+		test("refresh always fetches from sources", async () => {
+			let fetchCount = 0
+			const source: FeedSource = {
+				id: "counter",
+				...noActions,
+				async fetchContext() {
+					fetchCount++
+					return null
+				},
+			}
+
+			const engine = new FeedEngine().register(source)
+
+			await engine.refresh()
+			await engine.refresh()
+			await engine.refresh()
+
+			expect(fetchCount).toBe(3)
+		})
+
+		test("reactive context update refreshes cache", async () => {
+			const location = createLocationSource()
+			const weather = createWeatherSource()
+
+			const engine = new FeedEngine({ cacheTtlMs: 5000 }).register(location).register(weather)
+
+			engine.start()
+
+			// Simulate location update which triggers reactive refresh
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			// Wait for async reactive refresh to complete
+			await new Promise((resolve) => setTimeout(resolve, 50))
+
+			const cached = engine.lastFeed()
+			expect(cached).not.toBeNull()
+			expect(cached!.items.length).toBeGreaterThan(0)
+
+			engine.stop()
+		})
+
+		test("reactive item update refreshes cache", async () => {
+			let itemUpdateCallback: (() => void) | null = null
+
+			const source: FeedSource = {
+				id: "reactive-items",
+				...noActions,
+				async fetchContext() {
+					return null
+				},
+				async fetchItems() {
+					return [
+						{
+							id: "item-1",
+							type: "test",
+							priority: 0.5,
+							timestamp: new Date(),
+							data: {},
+						},
+					]
+				},
+				onItemsUpdate(callback) {
+					itemUpdateCallback = callback
+					return () => {
+						itemUpdateCallback = null
+					}
+				},
+			}
+
+			const engine = new FeedEngine().register(source)
+			engine.start()
+
+			// Trigger item update
+			itemUpdateCallback!()
+
+			// Wait for async refresh
+			await new Promise((resolve) => setTimeout(resolve, 50))
+
+			const cached = engine.lastFeed()
+			expect(cached).not.toBeNull()
+			expect(cached!.items).toHaveLength(1)
+
+			engine.stop()
+		})
+
+		test("TTL resets after reactive update", async () => {
+			const location = createLocationSource()
+			const weather = createWeatherSource()
+
+			const engine = new FeedEngine({ cacheTtlMs: 100 }).register(location).register(weather)
+
+			engine.start()
+
+			// Initial reactive update
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+			await new Promise((resolve) => setTimeout(resolve, 50))
+
+			expect(engine.lastFeed()).not.toBeNull()
+
+			// Wait 70ms (total 120ms from first update, past original TTL)
+			// but trigger another update at 50ms to reset TTL
+			location.simulateUpdate({ lat: 52.0, lng: -0.2 })
+			await new Promise((resolve) => setTimeout(resolve, 50))
+
+			// Should still be cached because TTL was reset by second update
+			expect(engine.lastFeed()).not.toBeNull()
+
+			engine.stop()
+		})
+
+		test("cacheTtlMs is configurable", async () => {
+			const engine = new FeedEngine({ cacheTtlMs: 30 })
+			const location = createLocationSource()
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+
+			engine.register(location)
+			await engine.refresh()
+
+			expect(engine.lastFeed()).not.toBeNull()
+
+			await new Promise((resolve) => setTimeout(resolve, 40))
+
+			expect(engine.lastFeed()).toBeNull()
+		})
+
+		test("auto-refreshes on TTL interval after start", async () => {
+			let fetchCount = 0
+			const source: FeedSource = {
+				id: "counter",
+				...noActions,
+				async fetchContext() {
+					fetchCount++
+					return null
+				},
+				async fetchItems() {
+					return [
+						{
+							id: `item-${fetchCount}`,
+							type: "test",
+							priority: 0.5,
+							timestamp: new Date(),
+							data: {},
+						},
+					]
+				},
+			}
+
+			const engine = new FeedEngine({ cacheTtlMs: 50 }).register(source)
+			engine.start()
+
+			// Wait for two TTL intervals to elapse
+			await new Promise((resolve) => setTimeout(resolve, 120))
+
+			// Should have auto-refreshed at least twice
+			expect(fetchCount).toBeGreaterThanOrEqual(2)
+			expect(engine.lastFeed()).not.toBeNull()
+
+			engine.stop()
+		})
+
+		test("stop cancels periodic refresh", async () => {
+			let fetchCount = 0
+			const source: FeedSource = {
+				id: "counter",
+				...noActions,
+				async fetchContext() {
+					fetchCount++
+					return null
+				},
+			}
+
+			const engine = new FeedEngine({ cacheTtlMs: 50 }).register(source)
+			engine.start()
+			engine.stop()
+
+			const countAfterStop = fetchCount
+
+			// Wait past TTL
+			await new Promise((resolve) => setTimeout(resolve, 80))
+
+			// No additional fetches after stop
+			expect(fetchCount).toBe(countAfterStop)
+		})
+
+		test("reactive update resets periodic refresh timer", async () => {
+			let fetchCount = 0
+			const location = createLocationSource()
+			const countingWeather: FeedSource<WeatherFeedItem> = {
+				id: "weather",
+				dependencies: ["location"],
+				...noActions,
+				async fetchContext(ctx) {
+					fetchCount++
+					const loc = contextValue(ctx, LocationKey)
+					if (!loc) return null
+					return { [WeatherKey]: { temperature: 20, condition: "sunny" } }
+				},
+				async fetchItems(ctx) {
+					const weather = contextValue(ctx, WeatherKey)
+					if (!weather) return []
+					return [
+						{
+							id: `weather-${Date.now()}`,
+							type: "weather",
+							priority: 0.5,
+							timestamp: new Date(),
+							data: { temperature: weather.temperature, condition: weather.condition },
+						},
+					]
+				},
+			}
+
+			const engine = new FeedEngine({ cacheTtlMs: 100 })
+				.register(location)
+				.register(countingWeather)
+
+			engine.start()
+
+			// At 40ms, push a reactive update — this resets the timer
+			await new Promise((resolve) => setTimeout(resolve, 40))
+			const countBeforeUpdate = fetchCount
+			location.simulateUpdate({ lat: 51.5, lng: -0.1 })
+			await new Promise((resolve) => setTimeout(resolve, 20))
+
+			// Reactive update triggered a fetch
+			expect(fetchCount).toBeGreaterThan(countBeforeUpdate)
+			const countAfterUpdate = fetchCount
+
+			// At 100ms from start (60ms after reactive update), the original
+			// timer would have fired, but it was reset. No extra fetch yet.
+			await new Promise((resolve) => setTimeout(resolve, 40))
+			expect(fetchCount).toBe(countAfterUpdate)
+
+			engine.stop()
+		})
+	})
 })

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

@@ -16,6 +16,14 @@ export interface FeedResult<TItem extends FeedItem = FeedItem> {
 
 export type FeedSubscriber<TItem extends FeedItem = FeedItem> = (result: FeedResult<TItem>) => void
 
+const DEFAULT_CACHE_TTL_MS = 300_000 // 5 minutes
+const MIN_CACHE_TTL_MS = 10 // prevent spin from zero/negative values
+
+export interface FeedEngineConfig {
+	/** Cache TTL in milliseconds. Default: 300_000 (5 minutes). Minimum: 10. */
+	cacheTtlMs?: number
+}
+
 interface SourceGraph {
 	sources: Map<string, FeedSource>
 	sorted: FeedSource[]
@@ -59,6 +67,29 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 	private cleanups: Array<() => void> = []
 	private started = false
 
+	private readonly cacheTtlMs: number
+	private cachedResult: FeedResult<TItems> | null = null
+	private cachedAt: number | null = null
+	private refreshTimer: ReturnType<typeof setTimeout> | null = null
+
+	constructor(config?: FeedEngineConfig) {
+		this.cacheTtlMs = Math.max(config?.cacheTtlMs ?? DEFAULT_CACHE_TTL_MS, MIN_CACHE_TTL_MS)
+	}
+
+	/**
+	 * Returns the cached FeedResult if available and not expired.
+	 * Returns null if no refresh has completed or the cache TTL has elapsed.
+	 */
+	lastFeed(): FeedResult<TItems> | null {
+		if (this.cachedResult === null || this.cachedAt === null) {
+			return null
+		}
+		if (Date.now() - this.cachedAt > this.cacheTtlMs) {
+			return null
+		}
+		return this.cachedResult
+	}
+
 	/**
 	 * Registers a FeedSource. Invalidates the cached graph.
 	 */
@@ -124,7 +155,10 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 
 		this.context = context
 
-		return { context, items: items as TItems[], errors }
+		const result: FeedResult<TItems> = { context, items: items as TItems[], errors }
+		this.updateCache(result)
+
+		return result
 	}
 
 	/**
@@ -138,7 +172,7 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 	}
 
 	/**
-	 * Starts reactive subscriptions on all sources.
+	 * Starts reactive subscriptions on all sources and begins periodic refresh.
 	 * Sources with onContextUpdate will trigger re-computation of dependents.
 	 */
 	start(): void {
@@ -168,13 +202,16 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 				this.cleanups.push(cleanup)
 			}
 		}
+
+		this.scheduleNextRefresh()
 	}
 
 	/**
-	 * Stops all reactive subscriptions.
+	 * Stops all reactive subscriptions and the periodic refresh timer.
 	 */
 	stop(): void {
 		this.started = false
+		this.cancelScheduledRefresh()
 		for (const cleanup of this.cleanups) {
 			cleanup()
 		}
@@ -279,11 +316,14 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 
 		items.sort((a, b) => b.priority - a.priority)
 
-		this.notifySubscribers({
+		const result: FeedResult<TItems> = {
 			context: this.context,
 			items: items as TItems[],
 			errors,
-		})
+		}
+		this.updateCache(result)
+
+		this.notifySubscribers(result)
 	}
 
 	private collectDependents(sourceId: string, graph: SourceGraph): string[] {
@@ -307,11 +347,46 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 		return graph.sorted.filter((s) => result.includes(s.id)).map((s) => s.id)
 	}
 
+	private updateCache(result: FeedResult<TItems>): void {
+		this.cachedResult = result
+		this.cachedAt = Date.now()
+		if (this.started) {
+			this.scheduleNextRefresh()
+		}
+	}
+
+	private scheduleNextRefresh(): void {
+		this.cancelScheduledRefresh()
+		this.refreshTimer = setTimeout(() => {
+			this.refresh()
+				.then((result) => {
+					this.notifySubscribers(result)
+				})
+				.catch(() => {
+					// Periodic refresh errors are non-fatal; schedule next attempt
+					if (this.started) {
+						this.scheduleNextRefresh()
+					}
+				})
+		}, this.cacheTtlMs)
+	}
+
+	private cancelScheduledRefresh(): void {
+		if (this.refreshTimer !== null) {
+			clearTimeout(this.refreshTimer)
+			this.refreshTimer = null
+		}
+	}
+
 	private scheduleRefresh(): void {
 		// Simple immediate refresh for now - could add debouncing later
-		this.refresh().then((result) => {
-			this.notifySubscribers(result)
-		})
+		this.refresh()
+			.then((result) => {
+				this.notifySubscribers(result)
+			})
+			.catch(() => {
+				// Reactive refresh errors are non-fatal
+			})
 	}
 
 	private notifySubscribers(result: FeedResult<TItems>): void {

packages/aris-core/src/index.ts

@@ -13,7 +13,7 @@ export type { FeedItem } from "./feed"
 export type { FeedSource } from "./feed-source"
 
 // Feed Engine
-export type { FeedResult, FeedSubscriber, SourceError } from "./feed-engine"
+export type { FeedEngineConfig, FeedResult, FeedSubscriber, SourceError } from "./feed-engine"
 export { FeedEngine } from "./feed-engine"
 
 // =============================================================================