diff --git a/apps/aris-backend/src/feed/http.test.ts b/apps/aris-backend/src/feed/http.test.ts
index 48fbca2..a87c522 100644
--- a/apps/aris-backend/src/feed/http.test.ts
+++ b/apps/aris-backend/src/feed/http.test.ts
@@ -1,4 +1,4 @@
-import type { ActionDefinition, Context, FeedItem, FeedSource } from "@aris/core"
+import type { ActionDefinition, ContextEntry, FeedItem, FeedSource } from "@aris/core"
 
 import { describe, expect, test } from "bun:test"
 import { Hono } from "hono"
@@ -27,7 +27,7 @@ function createStubSource(id: string, items: FeedItem[] = []): FeedSource {
 		async executeAction(): Promise<unknown> {
 			return undefined
 		},
-		async fetchContext(): Promise<Partial<Context> | null> {
+		async fetchContext(): Promise<readonly ContextEntry[] | null> {
 			return null
 		},
 		async fetchItems() {
diff --git a/apps/aris-backend/src/session/user-session.test.ts b/apps/aris-backend/src/session/user-session.test.ts
index 33c92da..794221d 100644
--- a/apps/aris-backend/src/session/user-session.test.ts
+++ b/apps/aris-backend/src/session/user-session.test.ts
@@ -1,4 +1,4 @@
-import type { ActionDefinition, Context, FeedSource } from "@aris/core"
+import type { ActionDefinition, ContextEntry, FeedSource } from "@aris/core"
 
 import { LocationSource } from "@aris/source-location"
 import { describe, expect, test } from "bun:test"
@@ -14,7 +14,7 @@ function createStubSource(id: string): FeedSource {
 		async executeAction(): Promise<unknown> {
 			return undefined
 		},
-		async fetchContext(): Promise<Partial<Context> | null> {
+		async fetchContext(): Promise<readonly ContextEntry[] | null> {
 			return null
 		},
 		async fetchItems() {
diff --git a/packages/aris-core/src/context-bridge.ts b/packages/aris-core/src/context-bridge.ts
index 2599e6c..d3fb286 100644
--- a/packages/aris-core/src/context-bridge.ts
+++ b/packages/aris-core/src/context-bridge.ts
@@ -1,8 +1,10 @@
-import type { Context } from "./context"
+import type { ContextEntry } from "./context"
 import type { ContextProvider } from "./context-provider"
 
+import { contextKey } from "./context"
+
 interface ContextUpdatable {
-	pushContextUpdate(update: Partial<Context>): void
+	pushContextUpdate(entries: readonly ContextEntry[]): void
 }
 
 export interface ProviderError {
@@ -54,7 +56,7 @@ export class ContextBridge {
 		this.providers.set(provider.key, provider as ContextProvider)
 
 		const cleanup = provider.onUpdate((value) => {
-			this.controller.pushContextUpdate({ [provider.key]: value })
+			this.controller.pushContextUpdate([[contextKey(provider.key), value]])
 		})
 		this.cleanups.push(cleanup)
 
@@ -67,7 +69,7 @@ export class ContextBridge {
 	 * Returns errors from providers that failed to fetch.
 	 */
 	async refresh(): Promise<RefreshResult> {
-		const updates: Partial<Context> = {}
+		const collected: ContextEntry[] = []
 		const errors: ProviderError[] = []
 
 		const entries = Array.from(this.providers.entries())
@@ -78,7 +80,7 @@ export class ContextBridge {
 		entries.forEach(([key], i) => {
 			const result = results[i]
 			if (result?.status === "fulfilled") {
-				updates[key] = result.value
+				collected.push([contextKey(key), result.value])
 			} else if (result?.status === "rejected") {
 				errors.push({
 					key,
@@ -87,7 +89,7 @@ export class ContextBridge {
 			}
 		})
 
-		this.controller.pushContextUpdate(updates)
+		this.controller.pushContextUpdate(collected)
 
 		return { errors }
 	}
diff --git a/packages/aris-core/src/context.test.ts b/packages/aris-core/src/context.test.ts
new file mode 100644
index 0000000..81ea212
--- /dev/null
+++ b/packages/aris-core/src/context.test.ts
@@ -0,0 +1,184 @@
+import { describe, expect, test } from "bun:test"
+
+import type { ContextKey } from "./context"
+
+import { Context, contextKey } from "./context"
+
+interface Weather {
+	temperature: number
+}
+
+interface NextEvent {
+	title: string
+}
+
+const WeatherKey: ContextKey<Weather> = contextKey("aris.weather", "current")
+const NextEventKey: ContextKey<NextEvent> = contextKey("aris.google-calendar", "nextEvent")
+
+describe("Context", () => {
+	describe("get", () => {
+		test("returns undefined for missing key", () => {
+			const ctx = new Context()
+			expect(ctx.get(WeatherKey)).toBeUndefined()
+		})
+
+		test("returns value for exact key match", () => {
+			const ctx = new Context()
+			const weather: Weather = { temperature: 20 }
+			ctx.set([[WeatherKey, weather]])
+
+			expect(ctx.get(WeatherKey)).toEqual(weather)
+		})
+
+		test("distinguishes keys with different parts", () => {
+			const ctx = new Context()
+			ctx.set([
+				[WeatherKey, { temperature: 20 }],
+				[NextEventKey, { title: "Standup" }],
+			])
+
+			expect(ctx.get(WeatherKey)).toEqual({ temperature: 20 })
+			expect(ctx.get(NextEventKey)).toEqual({ title: "Standup" })
+		})
+
+		test("last write wins for same key", () => {
+			const ctx = new Context()
+			ctx.set([[WeatherKey, { temperature: 20 }]])
+			ctx.set([[WeatherKey, { temperature: 25 }]])
+
+			expect(ctx.get(WeatherKey)).toEqual({ temperature: 25 })
+		})
+	})
+
+	describe("find", () => {
+		test("returns empty array when no keys match", () => {
+			const ctx = new Context()
+			expect(ctx.find(WeatherKey)).toEqual([])
+		})
+
+		test("returns exact match as single result", () => {
+			const ctx = new Context()
+			ctx.set([[NextEventKey, { title: "Standup" }]])
+
+			const results = ctx.find(NextEventKey)
+			expect(results).toHaveLength(1)
+			expect(results[0]!.value).toEqual({ title: "Standup" })
+		})
+
+		test("prefix match returns multiple instances", () => {
+			const workKey = contextKey<NextEvent>("aris.google-calendar", "nextEvent", {
+				account: "work",
+			})
+			const personalKey = contextKey<NextEvent>("aris.google-calendar", "nextEvent", {
+				account: "personal",
+			})
+
+			const ctx = new Context()
+			ctx.set([
+				[workKey, { title: "Sprint Planning" }],
+				[personalKey, { title: "Dentist" }],
+			])
+
+			const prefix = contextKey<NextEvent>("aris.google-calendar", "nextEvent")
+			const results = ctx.find(prefix)
+
+			expect(results).toHaveLength(2)
+			const titles = results.map((r) => r.value.title).sort()
+			expect(titles).toEqual(["Dentist", "Sprint Planning"])
+		})
+
+		test("prefix match includes exact match and longer keys", () => {
+			const baseKey = contextKey<NextEvent>("aris.google-calendar", "nextEvent")
+			const instanceKey = contextKey<NextEvent>("aris.google-calendar", "nextEvent", {
+				account: "work",
+			})
+
+			const ctx = new Context()
+			ctx.set([
+				[baseKey, { title: "Base" }],
+				[instanceKey, { title: "Instance" }],
+			])
+
+			const results = ctx.find(baseKey)
+			expect(results).toHaveLength(2)
+		})
+
+		test("does not match keys that share a string prefix but differ at segment boundary", () => {
+			const keyA = contextKey<string>("aris.calendar", "next")
+			const keyB = contextKey<string>("aris.calendar", "nextEvent")
+
+			const ctx = new Context()
+			ctx.set([
+				[keyA, "a"],
+				[keyB, "b"],
+			])
+
+			const results = ctx.find(keyA)
+			expect(results).toHaveLength(1)
+			expect(results[0]!.value).toBe("a")
+		})
+
+		test("object key parts with different property order match", () => {
+			const key1 = contextKey<string>("source", "ctx", { b: 2, a: 1 })
+			const key2 = contextKey<string>("source", "ctx", { a: 1, b: 2 })
+
+			const ctx = new Context()
+			ctx.set([[key1, "value"]])
+
+			// Exact match via get should work regardless of property order
+			expect(ctx.get(key2)).toBe("value")
+
+			// find with the reordered key as prefix should also match
+			const prefix = contextKey<string>("source", "ctx")
+			const results = ctx.find(prefix)
+			expect(results).toHaveLength(1)
+		})
+
+		test("single-segment prefix matches all keys starting with that segment", () => {
+			const ctx = new Context()
+			ctx.set([
+				[contextKey("aris.weather", "current"), { temperature: 20 }],
+				[contextKey("aris.weather", "forecast"), { high: 25 }],
+				[contextKey("aris.calendar", "nextEvent"), { title: "Meeting" }],
+			])
+
+			const results = ctx.find(contextKey("aris.weather"))
+			expect(results).toHaveLength(2)
+		})
+
+		test("does not match shorter keys", () => {
+			const ctx = new Context()
+			ctx.set([[contextKey("aris.weather"), "short"]])
+
+			const results = ctx.find(contextKey("aris.weather", "current"))
+			expect(results).toHaveLength(0)
+		})
+
+		test("numeric key parts match correctly", () => {
+			const ctx = new Context()
+			ctx.set([
+				[contextKey("source", 1, "data"), "one"],
+				[contextKey("source", 2, "data"), "two"],
+			])
+
+			const results = ctx.find(contextKey("source", 1))
+			expect(results).toHaveLength(1)
+			expect(results[0]!.value).toBe("one")
+		})
+	})
+
+	describe("size", () => {
+		test("returns 0 for empty context", () => {
+			expect(new Context().size).toBe(0)
+		})
+
+		test("reflects number of entries", () => {
+			const ctx = new Context()
+			ctx.set([
+				[WeatherKey, { temperature: 20 }],
+				[NextEventKey, { title: "Standup" }],
+			])
+			expect(ctx.size).toBe(2)
+		})
+	})
+})
diff --git a/packages/aris-core/src/context.ts b/packages/aris-core/src/context.ts
index 8d1c8fc..5d1ba22 100644
--- a/packages/aris-core/src/context.ts
+++ b/packages/aris-core/src/context.ts
@@ -1,46 +1,131 @@
 /**
- * Branded type for type-safe context keys.
+ * Tuple-keyed context system inspired by React Query's query keys.
  *
- * Each package defines its own keys with associated value types:
- * ```ts
- * const LocationKey: ContextKey<Location> = contextKey("location")
- * ```
+ * Context keys are arrays that form a hierarchy. Sources write to specific
+ * keys (e.g., ["aris.google-calendar", "nextEvent", { account: "work" }])
+ * and consumers can query by exact match or prefix match to get all values
+ * of a given type across source instances.
  */
-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>
+// -- Key types --
+
+/** A single segment of a context key: string, number, or a record of primitives. */
+export type ContextKeyPart = string | number | Record<string, unknown>
+
+/** A context key is a readonly tuple of parts, branded with the value type. */
+export type ContextKey<T> = readonly ContextKeyPart[] & { __contextValue?: T }
+
+/** Creates a typed context key. */
+export function contextKey<T>(...parts: ContextKeyPart[]): ContextKey<T> {
+	return parts 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
-}
+// -- Serialization --
 
 /**
- * Arbitrary key-value bag representing the current state.
- * Always includes `time`. Other keys are added by context providers.
+ * Deterministic serialization of a context key for use as a Map key.
+ * Object parts have their keys sorted for stable comparison.
  */
-export interface Context {
+export function serializeKey(key: readonly ContextKeyPart[]): string {
+	return JSON.stringify(key, (_key, value) => {
+		if (value !== null && typeof value === "object" && !Array.isArray(value)) {
+			const sorted: Record<string, unknown> = {}
+			for (const k of Object.keys(value).sort()) {
+				sorted[k] = value[k]
+			}
+			return sorted
+		}
+		return value
+	})
+}
+
+// -- Key matching --
+
+/** Returns true if `key` starts with all parts of `prefix`. */
+function keyStartsWith(key: readonly ContextKeyPart[], prefix: readonly ContextKeyPart[]): boolean {
+	if (key.length < prefix.length) return false
+
+	for (let i = 0; i < prefix.length; i++) {
+		if (!partsEqual(key[i]!, prefix[i]!)) return false
+	}
+
+	return true
+}
+
+/** Recursive structural equality, matching React Query's partialMatchKey approach. */
+function partsEqual(a: unknown, b: unknown): boolean {
+	if (a === b) return true
+	if (typeof a !== typeof b) return false
+	if (a && b && typeof a === "object" && typeof b === "object") {
+		const aKeys = Object.keys(a)
+		const bKeys = Object.keys(b)
+		if (aKeys.length !== bKeys.length) return false
+		return aKeys.every((key) =>
+			partsEqual(
+				(a as Record<string, unknown>)[key],
+				(b as Record<string, unknown>)[key],
+			),
+		)
+	}
+	return false
+}
+
+// -- Context store --
+
+/** A single context entry: a key-value pair. */
+export type ContextEntry<T = unknown> = readonly [ContextKey<T>, T]
+
+/**
+ * Mutable context store with tuple keys.
+ *
+ * Supports exact-match lookups and prefix-match queries.
+ * Sources write context in topological order during refresh.
+ */
+export class Context {
 	time: Date
-	[key: string]: unknown
+	private readonly store: Map<string, { key: readonly ContextKeyPart[]; value: unknown }>
+
+	constructor(time: Date = new Date()) {
+		this.time = time
+		this.store = new Map()
+	}
+
+	/** Merges entries into this context. */
+	set(entries: readonly ContextEntry[]): void {
+		for (const [key, value] of entries) {
+			this.store.set(serializeKey(key), { key, value })
+		}
+	}
+
+	/** Exact-match lookup. Returns the value for the given key, or undefined. */
+	get<T>(key: ContextKey<T>): T | undefined {
+		const entry = this.store.get(serializeKey(key))
+		return entry?.value as T | undefined
+	}
+
+	/**
+	 * Prefix-match query. Returns all entries whose key starts with the given prefix.
+	 *
+	 * @example
+	 * ```ts
+	 * // Get all "nextEvent" values across calendar source instances
+	 * const events = context.find(contextKey("nextEvent"))
+	 * ```
+	 */
+	find<T>(prefix: ContextKey<T>): Array<{ key: readonly ContextKeyPart[]; value: T }> {
+		const results: Array<{ key: readonly ContextKeyPart[]; value: T }> = []
+
+		for (const entry of this.store.values()) {
+			if (keyStartsWith(entry.key, prefix)) {
+				results.push({ key: entry.key, value: entry.value as T })
+			}
+		}
+
+		return results
+	}
+
+	/** Returns the number of entries (excluding time). */
+	get size(): number {
+		return this.store.size
+	}
 }
diff --git a/packages/aris-core/src/data-source.ts b/packages/aris-core/src/data-source.ts
index 71ee4d1..2e0561e 100644
--- a/packages/aris-core/src/data-source.ts
+++ b/packages/aris-core/src/data-source.ts
@@ -12,7 +12,7 @@ import type { FeedItem } from "./feed"
  *   readonly type = "weather"
  *
  *   async query(context: Context): Promise<WeatherItem[]> {
- *     const location = contextValue(context, LocationKey)
+ *     const location = context.get(LocationKey)
  *     if (!location) return []
  *     const data = await fetchWeather(location)
  *     return [{
diff --git a/packages/aris-core/src/feed-controller.ts b/packages/aris-core/src/feed-controller.ts
index 25aaf08..984423b 100644
--- a/packages/aris-core/src/feed-controller.ts
+++ b/packages/aris-core/src/feed-controller.ts
@@ -1,8 +1,9 @@
-import type { Context } from "./context"
+import type { ContextEntry } from "./context"
 import type { DataSource } from "./data-source"
 import type { FeedItem } from "./feed"
 import type { ReconcileResult } from "./reconciler"
 
+import { Context } from "./context"
 import { Reconciler } from "./reconciler"
 
 export interface FeedControllerConfig {
@@ -40,7 +41,7 @@ const DEFAULT_DEBOUNCE_MS = 100
  * })
  *
  * // Context update triggers debounced reconcile
- * controller.pushContextUpdate({ [LocationKey]: location })
+ * controller.pushContextUpdate([[LocationKey, location]])
  *
  * // Direct reconcile (no debounce)
  * const result = await controller.reconcile()
@@ -59,7 +60,7 @@ export class FeedController<TItems extends FeedItem = never> {
 	private stopped = false
 
 	constructor(config?: FeedControllerConfig) {
-		this.context = config?.initialContext ?? { time: new Date() }
+		this.context = config?.initialContext ?? new Context()
 		this.debounceMs = config?.debounceMs ?? DEFAULT_DEBOUNCE_MS
 		this.timeout = config?.timeout
 	}
@@ -94,9 +95,10 @@ export class FeedController<TItems extends FeedItem = never> {
 		}
 	}
 
-	/** Merges update into context and schedules a debounced reconcile. */
-	pushContextUpdate(update: Partial<Context>): void {
-		this.context = { ...this.context, ...update, time: new Date() }
+	/** Merges entries into context and schedules a debounced reconcile. */
+	pushContextUpdate(entries: readonly ContextEntry[]): void {
+		this.context.time = new Date()
+		this.context.set(entries)
 		this.scheduleReconcile()
 	}
 
diff --git a/packages/aris-core/src/feed-engine.test.ts b/packages/aris-core/src/feed-engine.test.ts
index e506f5b..0df1035 100644
--- a/packages/aris-core/src/feed-engine.test.ts
+++ b/packages/aris-core/src/feed-engine.test.ts
@@ -1,9 +1,9 @@
 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 { FeedEngine } from "./feed-engine"
-import { TimeRelevance, UnknownActionError, contextKey, contextValue } from "./index"
+import { Context, TimeRelevance, UnknownActionError, contextKey } from "./index"
 
 // No-op action methods for test sources
 const noActions = {
@@ -48,7 +48,7 @@ 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 {
@@ -63,12 +63,12 @@ function createLocationSource(): SimulatedLocationSource {
 		},
 
 		async fetchContext() {
-			return { [LocationKey]: currentLocation }
+			return [[LocationKey, currentLocation]]
 		},
 
 		simulateUpdate(location: Location) {
 			currentLocation = location
-			callback?.({ [LocationKey]: location })
+			callback?.([[LocationKey, location]])
 		},
 	}
 }
@@ -85,15 +85,15 @@ 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 [
@@ -123,7 +123,7 @@ function createAlertSource(): FeedSource<AlertFeedItem> {
 		},
 
 		async fetchItems(context) {
-			const weather = contextValue(context, WeatherKey)
+			const weather = context.get(WeatherKey)
 			if (!weather) return []
 
 			if (weather.condition === "storm") {
@@ -265,7 +265,7 @@ describe("FeedEngine", () => {
 				...noActions,
 				async fetchContext() {
 					order.push("location")
-					return { [LocationKey]: { lat: 51.5, lng: -0.1 } }
+					return [[LocationKey, { lat: 51.5, lng: -0.1 }]]
 				},
 			}
 
@@ -275,9 +275,9 @@ describe("FeedEngine", () => {
 				...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" }]]
 				},
 			}
 
@@ -298,11 +298,11 @@ describe("FeedEngine", () => {
 
 			const { context } = await engine.refresh()
 
-			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",
 			})
@@ -361,7 +361,7 @@ describe("FeedEngine", () => {
 
 			const { context, items } = await engine.refresh()
 
-			expect(contextValue(context, WeatherKey)).toBeUndefined()
+			expect(context.get(WeatherKey)).toBeUndefined()
 			expect(items).toHaveLength(0)
 		})
 
@@ -459,7 +459,7 @@ describe("FeedEngine", () => {
 			await engine.refresh()
 
 			const context = engine.currentContext()
-			expect(contextValue(context, LocationKey)).toEqual({
+			expect(context.get(LocationKey)).toEqual({
 				lat: 51.5,
 				lng: -0.1,
 			})
@@ -734,7 +734,7 @@ describe("FeedEngine", () => {
 		})
 
 		test("reactive item update refreshes cache", async () => {
-			let itemUpdateCallback: (() => void) | null = null
+			let itemUpdateCallback: ((items: FeedItem[]) => void) | null = null
 
 			const source: FeedSource = {
 				id: "reactive-items",
@@ -765,7 +765,7 @@ describe("FeedEngine", () => {
 			engine.start()
 
 			// Trigger item update
-			itemUpdateCallback!()
+			itemUpdateCallback!([])
 
 			// Wait for async refresh
 			await new Promise((resolve) => setTimeout(resolve, 50))
@@ -885,12 +885,12 @@ describe("FeedEngine", () => {
 				...noActions,
 				async fetchContext(ctx) {
 					fetchCount++
-					const loc = contextValue(ctx, LocationKey)
+					const loc = ctx.get(LocationKey)
 					if (!loc) return null
-					return { [WeatherKey]: { temperature: 20, condition: "sunny" } }
+					return [[WeatherKey, { temperature: 20, condition: "sunny" }]]
 				},
 				async fetchItems(ctx) {
-					const weather = contextValue(ctx, WeatherKey)
+					const weather = ctx.get(WeatherKey)
 					if (!weather) return []
 					return [
 						{
diff --git a/packages/aris-core/src/feed-engine.ts b/packages/aris-core/src/feed-engine.ts
index 97c9d62..f1baf6f 100644
--- a/packages/aris-core/src/feed-engine.ts
+++ b/packages/aris-core/src/feed-engine.ts
@@ -1,9 +1,11 @@
 import type { ActionDefinition } from "./action"
-import type { Context } from "./context"
+import type { ContextEntry } from "./context"
 import type { FeedItem } from "./feed"
 import type { FeedPostProcessor, ItemGroup } from "./feed-post-processor"
 import type { FeedSource } from "./feed-source"
 
+import { Context } from "./context"
+
 export interface SourceError {
 	sourceId: string
 	error: Error
@@ -65,7 +67,7 @@ interface SourceGraph {
 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 context: Context = new Context()
 	private subscribers = new Set<FeedSubscriber<TItems>>()
 	private cleanups: Array<() => void> = []
 	private started = false
@@ -138,14 +140,14 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 		const errors: SourceError[] = []
 
 		// Reset context with fresh time
-		let context: Context = { time: new Date() }
+		const context = new Context()
 
 		// Run fetchContext in topological order
 		for (const source of graph.sorted) {
 			try {
-				const update = await source.fetchContext(context)
-				if (update) {
-					context = { ...context, ...update }
+				const entries = await source.fetchContext(context)
+				if (entries) {
+					context.set(entries)
 				}
 			} catch (err) {
 				errors.push({
@@ -213,8 +215,8 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 		for (const source of graph.sorted) {
 			if (source.onContextUpdate) {
 				const cleanup = source.onContextUpdate(
-					(update) => {
-						this.handleContextUpdate(source.id, update)
+					(entries) => {
+						this.handleContextUpdate(source.id, entries)
 					},
 					() => this.context,
 				)
@@ -365,8 +367,9 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 		return this.graph
 	}
 
-	private handleContextUpdate(sourceId: string, update: Partial<Context>): void {
-		this.context = { ...this.context, ...update, time: new Date() }
+	private handleContextUpdate(sourceId: string, entries: readonly ContextEntry[]): void {
+		this.context.time = new Date()
+		this.context.set(entries)
 
 		// Re-run dependents and notify
 		this.refreshDependents(sourceId)
@@ -381,9 +384,9 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 			const source = graph.sources.get(id)
 			if (source) {
 				try {
-					const update = await source.fetchContext(this.context)
-					if (update) {
-						this.context = { ...this.context, ...update }
+					const entries = await source.fetchContext(this.context)
+					if (entries) {
+						this.context.set(entries)
 					}
 				} catch {
 					// Errors during reactive updates are logged but don't stop propagation
diff --git a/packages/aris-core/src/feed-post-processor.test.ts b/packages/aris-core/src/feed-post-processor.test.ts
index d350907..03abd41 100644
--- a/packages/aris-core/src/feed-post-processor.test.ts
+++ b/packages/aris-core/src/feed-post-processor.test.ts
@@ -1,6 +1,12 @@
 import { describe, expect, mock, test } from "bun:test"
 
-import type { ActionDefinition, FeedItem, FeedPostProcessor, FeedSource } from "./index"
+import type {
+	ActionDefinition,
+	ContextEntry,
+	FeedItem,
+	FeedPostProcessor,
+	FeedSource,
+} from "./index"
 
 import { FeedEngine } from "./feed-engine"
 import { UnknownActionError } from "./index"
@@ -471,7 +477,7 @@ describe("FeedPostProcessor", () => {
 		test("post-processors run during reactive context updates", async () => {
 			let callCount = 0
 
-			let triggerUpdate: ((update: Record<string, unknown>) => void) | null = null
+			let triggerUpdate: ((entries: readonly ContextEntry[]) => void) | null = null
 
 			const source: FeedSource = {
 				id: "aris.reactive",
@@ -502,7 +508,7 @@ describe("FeedPostProcessor", () => {
 			const countAfterStart = callCount
 
 			// Trigger a reactive context update
-			triggerUpdate!({ foo: "bar" })
+			triggerUpdate!([])
 			await new Promise((resolve) => setTimeout(resolve, 50))
 
 			expect(callCount).toBeGreaterThan(countAfterStart)
@@ -513,7 +519,7 @@ describe("FeedPostProcessor", () => {
 		test("post-processors run during reactive item updates", async () => {
 			let callCount = 0
 
-			let triggerItemsUpdate: (() => void) | null = null
+			let triggerItemsUpdate: ((items: FeedItem[]) => void) | null = null
 
 			const source: FeedSource = {
 				id: "aris.reactive",
@@ -543,7 +549,7 @@ describe("FeedPostProcessor", () => {
 			const countAfterStart = callCount
 
 			// Trigger a reactive items update
-			triggerItemsUpdate!()
+			triggerItemsUpdate!([weatherItem("w1", 25)])
 			await new Promise((resolve) => setTimeout(resolve, 50))
 
 			expect(callCount).toBeGreaterThan(countAfterStart)
diff --git a/packages/aris-core/src/feed-source.test.ts b/packages/aris-core/src/feed-source.test.ts
index 0b4785a..becf57d 100644
--- a/packages/aris-core/src/feed-source.test.ts
+++ b/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 })
diff --git a/packages/aris-core/src/feed-source.ts b/packages/aris-core/src/feed-source.ts
index df577ff..cb95c31 100644
--- a/packages/aris-core/src/feed-source.ts
+++ b/packages/aris-core/src/feed-source.ts
@@ -1,5 +1,5 @@
 import type { ActionDefinition } from "./action"
-import type { Context } from "./context"
+import type { Context, ContextEntry } from "./context"
 import type { FeedItem } from "./feed"
 
 /**
@@ -57,7 +57,7 @@ export interface FeedSource<TItem extends FeedItem = FeedItem> {
 	 * Maps to: source/contextUpdated (notification, source → host)
 	 */
 	onContextUpdate?(
-		callback: (update: Partial<Context>) => void,
+		callback: (entries: readonly ContextEntry[]) => void,
 		getContext: () => Context,
 	): () => void
 
@@ -67,7 +67,7 @@ export interface FeedSource<TItem extends FeedItem = FeedItem> {
 	 * Return null if this source cannot provide context.
 	 * Maps to: source/fetchContext
 	 */
-	fetchContext(context: Context): Promise<Partial<Context> | null>
+	fetchContext(context: Context): Promise<readonly ContextEntry[] | null>
 
 	/**
 	 * Subscribe to reactive feed item updates.
diff --git a/packages/aris-core/src/index.ts b/packages/aris-core/src/index.ts
index ecd3348..f9e4158 100644
--- a/packages/aris-core/src/index.ts
+++ b/packages/aris-core/src/index.ts
@@ -1,6 +1,6 @@
 // Context
-export type { Context, ContextKey } from "./context"
-export { contextKey, contextValue } from "./context"
+export type { ContextEntry, ContextKey, ContextKeyPart } from "./context"
+export { Context, contextKey, serializeKey } from "./context"
 
 // Actions
 export type { ActionDefinition } from "./action"
diff --git a/packages/aris-data-source-weatherkit/src/data-source.test.ts b/packages/aris-data-source-weatherkit/src/data-source.test.ts
index e791f11..58b66f1 100644
--- a/packages/aris-data-source-weatherkit/src/data-source.test.ts
+++ b/packages/aris-data-source-weatherkit/src/data-source.test.ts
@@ -1,5 +1,6 @@
-import type { Context } from "@aris/core"
+import type { ContextKey } from "@aris/core"
 
+import { Context, contextKey } from "@aris/core"
 import { describe, expect, test } from "bun:test"
 
 import type { WeatherKitClient, WeatherKitResponse } from "./weatherkit"
@@ -15,14 +16,25 @@ const mockCredentials = {
 	serviceId: "mock",
 }
 
+interface LocationData {
+	lat: number
+	lng: number
+	accuracy: number
+}
+
+const LocationKey: ContextKey<LocationData> = contextKey("aris.location", "location")
+
 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,
-})
+function createMockContext(location?: { lat: number; lng: number }): Context {
+	const ctx = new Context(new Date("2026-01-17T00:00:00Z"))
+	if (location) {
+		ctx.set([[LocationKey, { ...location, accuracy: 10 }]])
+	}
+	return ctx
+}
 
 describe("WeatherKitDataSource", () => {
 	test("returns empty array when location is missing", async () => {
diff --git a/packages/aris-data-source-weatherkit/src/data-source.ts b/packages/aris-data-source-weatherkit/src/data-source.ts
index dce1c91..b2f8de9 100644
--- a/packages/aris-data-source-weatherkit/src/data-source.ts
+++ b/packages/aris-data-source-weatherkit/src/data-source.ts
@@ -1,6 +1,6 @@
-import type { Context, DataSource, FeedItemSignals } from "@aris/core"
+import type { Context, ContextKey, DataSource, FeedItemSignals } from "@aris/core"
 
-import { TimeRelevance } from "@aris/core"
+import { TimeRelevance, contextKey } from "@aris/core"
 
 import {
 	WeatherFeedItemType,
@@ -40,6 +40,13 @@ export interface WeatherKitQueryConfig {
 	units?: Units
 }
 
+interface LocationData {
+	lat: number
+	lng: number
+}
+
+const LocationKey: ContextKey<LocationData> = contextKey("aris.location", "location")
+
 export class WeatherKitDataSource implements DataSource<WeatherFeedItem, WeatherKitQueryConfig> {
 	private readonly DEFAULT_HOURLY_LIMIT = 12
 	private readonly DEFAULT_DAILY_LIMIT = 7
@@ -59,7 +66,8 @@ export class WeatherKitDataSource implements DataSource<WeatherFeedItem, Weather
 	}
 
 	async query(context: Context, config: WeatherKitQueryConfig = {}): Promise<WeatherFeedItem[]> {
-		if (!context.location) {
+		const location = context.get(LocationKey)
+		if (!location) {
 			return []
 		}
 
@@ -67,8 +75,8 @@ export class WeatherKitDataSource implements DataSource<WeatherFeedItem, Weather
 		const timestamp = context.time
 
 		const response = await this.client.fetch({
-			lat: context.location.lat,
-			lng: context.location.lng,
+			lat: location.lat,
+			lng: location.lng,
 		})
 
 		const items: WeatherFeedItem[] = []
diff --git a/packages/aris-source-caldav/scripts/test-live.ts b/packages/aris-source-caldav/scripts/test-live.ts
index 070a987..c2b1617 100644
--- a/packages/aris-source-caldav/scripts/test-live.ts
+++ b/packages/aris-source-caldav/scripts/test-live.ts
@@ -5,6 +5,8 @@
  *   bun run test-live.ts
  */
 
+import { Context } from "@aris/core"
+
 import { CalDavSource } from "../src/index.ts"
 
 const serverUrl = prompt("CalDAV server URL:")
@@ -27,7 +29,7 @@ const source = new CalDavSource({
 	lookAheadDays,
 })
 
-const context = { time: new Date() }
+const context = new Context()
 
 console.log(`\nFetching from ${serverUrl} as ${username} (lookAheadDays=${lookAheadDays})...\n`)
 
diff --git a/packages/aris-source-caldav/src/caldav-source.test.ts b/packages/aris-source-caldav/src/caldav-source.test.ts
index 130417e..d5c70e7 100644
--- a/packages/aris-source-caldav/src/caldav-source.test.ts
+++ b/packages/aris-source-caldav/src/caldav-source.test.ts
@@ -1,6 +1,6 @@
-import type { Context } from "@aris/core"
+import type { ContextEntry } from "@aris/core"
 
-import { TimeRelevance, contextValue } from "@aris/core"
+import { Context, TimeRelevance } from "@aris/core"
 import { describe, expect, test } from "bun:test"
 import { readFileSync } from "node:fs"
 import { join } from "node:path"
@@ -13,14 +13,21 @@ import type {
 } from "./types.ts"
 
 import { CalDavSource, computeSignals } from "./caldav-source.ts"
-import { CalDavCalendarKey } from "./calendar-context.ts"
+import { CalDavCalendarKey, type CalendarContext } from "./calendar-context.ts"
 
 function loadFixture(name: string): string {
 	return readFileSync(join(import.meta.dir, "..", "fixtures", name), "utf-8")
 }
 
 function createContext(time: Date): Context {
-	return { time }
+	return new Context(time)
+}
+
+/** Extract the CalendarContext value from fetchContext entries. */
+function extractCalendar(entries: readonly ContextEntry[] | null): CalendarContext | undefined {
+	if (!entries) return undefined
+	const entry = entries.find(([key]) => key === CalDavCalendarKey)
+	return entry?.[1] as CalendarContext | undefined
 }
 
 class MockDAVClient implements CalDavDAVClient {
@@ -302,8 +309,8 @@ describe("CalDavSource.fetchContext", () => {
 	test("returns empty context when no calendars exist", async () => {
 		const client = new MockDAVClient([], {})
 		const source = createSource(client)
-		const ctx = await source.fetchContext(createContext(new Date("2026-01-15T12:00:00Z")))
-		const calendar = contextValue(ctx as Context, CalDavCalendarKey)
+		const entries = await source.fetchContext(createContext(new Date("2026-01-15T12:00:00Z")))
+		const calendar = extractCalendar(entries)
 
 		expect(calendar).toBeDefined()
 		expect(calendar!.inProgress).toEqual([])
@@ -320,8 +327,8 @@ describe("CalDavSource.fetchContext", () => {
 		const source = createSource(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, CalDavCalendarKey)
+		const entries = await source.fetchContext(createContext(new Date("2026-01-15T14:30:00Z")))
+		const calendar = extractCalendar(entries)
 
 		expect(calendar!.inProgress).toHaveLength(1)
 		expect(calendar!.inProgress[0]!.title).toBe("Team Standup")
@@ -335,8 +342,8 @@ describe("CalDavSource.fetchContext", () => {
 		const source = createSource(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, CalDavCalendarKey)
+		const entries = await source.fetchContext(createContext(new Date("2026-01-15T12:00:00Z")))
+		const calendar = extractCalendar(entries)
 
 		expect(calendar!.inProgress).toHaveLength(0)
 		expect(calendar!.nextEvent).not.toBeNull()
@@ -350,8 +357,8 @@ describe("CalDavSource.fetchContext", () => {
 		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
 		const source = createSource(client)
 
-		const ctx = await source.fetchContext(createContext(new Date("2026-01-15T12:00:00Z")))
-		const calendar = contextValue(ctx as Context, CalDavCalendarKey)
+		const entries = await source.fetchContext(createContext(new Date("2026-01-15T12:00:00Z")))
+		const calendar = extractCalendar(entries)
 
 		expect(calendar!.inProgress).toHaveLength(0)
 		expect(calendar!.nextEvent).toBeNull()
@@ -369,8 +376,8 @@ describe("CalDavSource.fetchContext", () => {
 		const client = new MockDAVClient([{ url: "/cal/work", displayName: "Work" }], objects)
 		const source = createSource(client)
 
-		const ctx = await source.fetchContext(createContext(new Date("2026-01-15T12:00:00Z")))
-		const calendar = contextValue(ctx as Context, CalDavCalendarKey)
+		const entries = await source.fetchContext(createContext(new Date("2026-01-15T12:00:00Z")))
+		const calendar = extractCalendar(entries)
 
 		expect(calendar!.todayEventCount).toBe(2)
 		expect(calendar!.hasTodayEvents).toBe(true)
diff --git a/packages/aris-source-caldav/src/caldav-source.ts b/packages/aris-source-caldav/src/caldav-source.ts
index d0f3d37..9020680 100644
--- a/packages/aris-source-caldav/src/caldav-source.ts
+++ b/packages/aris-source-caldav/src/caldav-source.ts
@@ -1,6 +1,6 @@
-import type { ActionDefinition, Context, FeedItemSignals, FeedSource } from "@aris/core"
+import type { ActionDefinition, ContextEntry, FeedItemSignals, FeedSource } from "@aris/core"
 
-import { TimeRelevance, UnknownActionError } from "@aris/core"
+import { Context, TimeRelevance, UnknownActionError } from "@aris/core"
 import { DAVClient } from "tsdav"
 
 import type { CalDavDAVClient, CalDavEventData, CalDavFeedItem } from "./types.ts"
@@ -93,17 +93,20 @@ export class CalDavSource implements FeedSource<CalDavFeedItem> {
 		throw new UnknownActionError(actionId)
 	}
 
-	async fetchContext(context: Context): Promise<Partial<Context> | null> {
+	async fetchContext(context: Context): Promise<readonly ContextEntry[] | null> {
 		const events = await this.fetchEvents(context)
 		if (events.length === 0) {
-			return {
-				[CalDavCalendarKey]: {
-					inProgress: [],
-					nextEvent: null,
-					hasTodayEvents: false,
-					todayEventCount: 0,
-				},
-			}
+			return [
+				[
+					CalDavCalendarKey,
+					{
+						inProgress: [],
+						nextEvent: null,
+						hasTodayEvents: false,
+						todayEventCount: 0,
+					},
+				],
+			]
 		}
 
 		const now = context.time
@@ -121,7 +124,7 @@ export class CalDavSource implements FeedSource<CalDavFeedItem> {
 			todayEventCount: events.length,
 		}
 
-		return { [CalDavCalendarKey]: calendarContext }
+		return [[CalDavCalendarKey, calendarContext]]
 	}
 
 	async fetchItems(context: Context): Promise<CalDavFeedItem[]> {
diff --git a/packages/aris-source-caldav/src/calendar-context.ts b/packages/aris-source-caldav/src/calendar-context.ts
index b1245db..95e149e 100644
--- a/packages/aris-source-caldav/src/calendar-context.ts
+++ b/packages/aris-source-caldav/src/calendar-context.ts
@@ -21,4 +21,4 @@ export interface CalendarContext {
 	todayEventCount: number
 }
 
-export const CalDavCalendarKey: ContextKey<CalendarContext> = contextKey("caldavCalendar")
+export const CalDavCalendarKey: ContextKey<CalendarContext> = contextKey("aris.caldav", "calendar")
diff --git a/packages/aris-source-google-calendar/src/calendar-context.ts b/packages/aris-source-google-calendar/src/calendar-context.ts
index cd1a942..c8133da 100644
--- a/packages/aris-source-google-calendar/src/calendar-context.ts
+++ b/packages/aris-source-google-calendar/src/calendar-context.ts
@@ -10,4 +10,4 @@ export interface NextEvent {
 	location: string | null
 }
 
-export const NextEventKey: ContextKey<NextEvent> = contextKey("nextEvent")
+export const NextEventKey: ContextKey<NextEvent> = contextKey("aris.google-calendar", "nextEvent")
diff --git a/packages/aris-source-google-calendar/src/google-calendar-source.test.ts b/packages/aris-source-google-calendar/src/google-calendar-source.test.ts
index 904e795..2ddfe33 100644
--- a/packages/aris-source-google-calendar/src/google-calendar-source.test.ts
+++ b/packages/aris-source-google-calendar/src/google-calendar-source.test.ts
@@ -1,10 +1,10 @@
-import { TimeRelevance, contextValue, type Context } from "@aris/core"
+import { Context, TimeRelevance } 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 { NextEventKey, type NextEvent } from "./calendar-context"
 import { CalendarFeedItemType } from "./feed-items"
 import { GoogleCalendarSource } from "./google-calendar-source"
 
@@ -38,7 +38,7 @@ function defaultMockClient(): GoogleCalendarClient {
 }
 
 function createContext(time?: Date): Context {
-	return { time: time ?? NOW }
+	return new Context(time ?? NOW)
 }
 
 describe("GoogleCalendarSource", () => {
@@ -229,15 +229,16 @@ describe("GoogleCalendarSource", () => {
 
 		test("returns next upcoming timed event (not ongoing)", async () => {
 			const source = new GoogleCalendarSource({ client: defaultMockClient() })
-			const result = await source.fetchContext(createContext())
+			const entries = await source.fetchContext(createContext())
 
-			expect(result).not.toBeNull()
-			const nextEvent = contextValue(result! as Context, NextEventKey)
-			expect(nextEvent).toBeDefined()
+			expect(entries).not.toBeNull()
+			expect(entries).toHaveLength(1)
+			const [key, nextEvent] = entries![0]! as [typeof NextEventKey, NextEvent]
+			expect(key).toEqual(NextEventKey)
 			// 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()
+			expect(nextEvent.title).toBe("1:1 with Manager")
+			expect(nextEvent.minutesUntilStart).toBe(10)
+			expect(nextEvent.location).toBeNull()
 		})
 
 		test("includes location when available", async () => {
@@ -255,12 +256,11 @@ describe("GoogleCalendarSource", () => {
 			const source = new GoogleCalendarSource({
 				client: createMockClient({ primary: events }),
 			})
-			const result = await source.fetchContext(createContext())
+			const entries = 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")
+			expect(entries).not.toBeNull()
+			const [, nextEvent] = entries![0]! as [typeof NextEventKey, NextEvent]
+			expect(nextEvent.location).toBe("123 Main St")
 		})
 
 		test("skips ongoing events for next-event context", async () => {
diff --git a/packages/aris-source-google-calendar/src/google-calendar-source.ts b/packages/aris-source-google-calendar/src/google-calendar-source.ts
index 678818e..2f43c02 100644
--- a/packages/aris-source-google-calendar/src/google-calendar-source.ts
+++ b/packages/aris-source-google-calendar/src/google-calendar-source.ts
@@ -1,6 +1,6 @@
-import type { ActionDefinition, Context, FeedItemSignals, FeedSource } from "@aris/core"
+import type { ActionDefinition, ContextEntry, FeedItemSignals, FeedSource } from "@aris/core"
 
-import { TimeRelevance, UnknownActionError } from "@aris/core"
+import { Context, TimeRelevance, UnknownActionError } from "@aris/core"
 
 import type {
 	ApiCalendarEvent,
@@ -58,7 +58,7 @@ const URGENCY_ALL_DAY = 0.4
  *   .register(calendarSource)
  *
  * // Access next-event context in downstream sources
- * const next = contextValue(context, NextEventKey)
+ * const next = context.get(NextEventKey)
  * if (next && next.minutesUntilStart < 15) {
  *   // remind user
  * }
@@ -85,7 +85,7 @@ export class GoogleCalendarSource implements FeedSource<CalendarFeedItem> {
 		throw new UnknownActionError(actionId)
 	}
 
-	async fetchContext(context: Context): Promise<Partial<Context> | null> {
+	async fetchContext(context: Context): Promise<readonly ContextEntry[] | null> {
 		const events = await this.fetchAllEvents(context.time)
 
 		const now = context.time.getTime()
@@ -105,7 +105,7 @@ export class GoogleCalendarSource implements FeedSource<CalendarFeedItem> {
 			location: nextTimedEvent.location,
 		}
 
-		return { [NextEventKey]: nextEvent }
+		return [[NextEventKey, nextEvent]]
 	}
 
 	async fetchItems(context: Context): Promise<CalendarFeedItem[]> {
diff --git a/packages/aris-source-location/src/location-source.test.ts b/packages/aris-source-location/src/location-source.test.ts
index af76707..8e287a2 100644
--- a/packages/aris-source-location/src/location-source.test.ts
+++ b/packages/aris-source-location/src/location-source.test.ts
@@ -1,6 +1,8 @@
 import { describe, expect, mock, test } from "bun:test"
 
-import { LocationKey, LocationSource, type Location } from "./location-source.ts"
+import type { Location } from "./types.ts"
+
+import { LocationKey, LocationSource } from "./location-source.ts"
 
 function createLocation(overrides: Partial<Location> = {}): Location {
 	return {
@@ -39,8 +41,8 @@ describe("LocationSource", () => {
 			const location = createLocation()
 			source.pushLocation(location)
 
-			const context = await source.fetchContext()
-			expect(context).toEqual({ [LocationKey]: location })
+			const entries = await source.fetchContext()
+			expect(entries).toEqual([[LocationKey, location]])
 		})
 	})
 
@@ -65,7 +67,7 @@ describe("LocationSource", () => {
 			source.pushLocation(location)
 
 			expect(listener).toHaveBeenCalledTimes(1)
-			expect(listener).toHaveBeenCalledWith({ [LocationKey]: location })
+			expect(listener).toHaveBeenCalledWith([[LocationKey, location]])
 		})
 	})
 
diff --git a/packages/aris-source-location/src/location-source.ts b/packages/aris-source-location/src/location-source.ts
index 20e6ec2..78f9cfc 100644
--- a/packages/aris-source-location/src/location-source.ts
+++ b/packages/aris-source-location/src/location-source.ts
@@ -1,11 +1,11 @@
-import type { ActionDefinition, Context, FeedSource } from "@aris/core"
+import type { ActionDefinition, ContextEntry, FeedSource } from "@aris/core"
 
-import { UnknownActionError, contextKey, type ContextKey } from "@aris/core"
+import { Context, UnknownActionError, contextKey, type ContextKey } from "@aris/core"
 import { type } from "arktype"
 
 import { Location, type LocationSourceOptions } from "./types.ts"
 
-export const LocationKey: ContextKey<Location> = contextKey("location")
+export const LocationKey: ContextKey<Location> = contextKey("aris.location", "location")
 
 /**
  * A FeedSource that provides location context.
@@ -20,7 +20,7 @@ export class LocationSource implements FeedSource {
 
 	private readonly historySize: number
 	private locations: Location[] = []
-	private listeners = new Set<(update: Partial<Context>) => void>()
+	private listeners = new Set<(entries: readonly ContextEntry[]) => void>()
 
 	constructor(options: LocationSourceOptions = {}) {
 		this.historySize = options.historySize ?? 1
@@ -59,8 +59,9 @@ export class LocationSource implements FeedSource {
 		if (this.locations.length > this.historySize) {
 			this.locations.shift()
 		}
+		const entries: readonly ContextEntry[] = [[LocationKey, location]]
 		this.listeners.forEach((listener) => {
-			listener({ [LocationKey]: location })
+			listener(entries)
 		})
 	}
 
@@ -78,16 +79,16 @@ export class LocationSource implements FeedSource {
 		return this.locations
 	}
 
-	onContextUpdate(callback: (update: Partial<Context>) => void): () => void {
+	onContextUpdate(callback: (entries: readonly ContextEntry[]) => void): () => void {
 		this.listeners.add(callback)
 		return () => {
 			this.listeners.delete(callback)
 		}
 	}
 
-	async fetchContext(): Promise<Partial<Context> | null> {
+	async fetchContext(): Promise<readonly ContextEntry[] | null> {
 		if (this.lastLocation) {
-			return { [LocationKey]: this.lastLocation }
+			return [[LocationKey, this.lastLocation]]
 		}
 		return null
 	}
diff --git a/packages/aris-source-tfl/src/tfl-source.test.ts b/packages/aris-source-tfl/src/tfl-source.test.ts
index 9653f85..cbd368a 100644
--- a/packages/aris-source-tfl/src/tfl-source.test.ts
+++ b/packages/aris-source-tfl/src/tfl-source.test.ts
@@ -1,5 +1,4 @@
-import type { Context } from "@aris/core"
-
+import { Context } from "@aris/core"
 import { LocationKey, type Location } from "@aris/source-location"
 import { describe, expect, test } from "bun:test"
 
@@ -81,9 +80,9 @@ class FixtureTflApi implements ITflApi {
 }
 
 function createContext(location?: Location): Context {
-	const ctx: Context = { time: new Date("2026-01-15T12:00:00Z") }
+	const ctx = new Context(new Date("2026-01-15T12:00:00Z"))
 	if (location) {
-		ctx[LocationKey] = location
+		ctx.set([[LocationKey, location]])
 	}
 	return ctx
 }
diff --git a/packages/aris-source-tfl/src/tfl-source.ts b/packages/aris-source-tfl/src/tfl-source.ts
index 3ac2f7d..aa6f1bc 100644
--- a/packages/aris-source-tfl/src/tfl-source.ts
+++ b/packages/aris-source-tfl/src/tfl-source.ts
@@ -1,6 +1,6 @@
-import type { ActionDefinition, Context, FeedItemSignals, FeedSource } from "@aris/core"
+import type { ActionDefinition, ContextEntry, FeedItemSignals, FeedSource } from "@aris/core"
 
-import { TimeRelevance, UnknownActionError, contextValue } from "@aris/core"
+import { Context, TimeRelevance, UnknownActionError } from "@aris/core"
 import { LocationKey } from "@aris/source-location"
 import { type } from "arktype"
 
@@ -112,7 +112,7 @@ export class TflSource implements FeedSource<TflAlertFeedItem> {
 		}
 	}
 
-	async fetchContext(): Promise<null> {
+	async fetchContext(): Promise<readonly ContextEntry[] | null> {
 		return null
 	}
 
@@ -129,7 +129,7 @@ export class TflSource implements FeedSource<TflAlertFeedItem> {
 			this.client.fetchStations(),
 		])
 
-		const location = contextValue(context, LocationKey)
+		const location = context.get(LocationKey)
 
 		const items: TflAlertFeedItem[] = statuses.map((status) => {
 			const closestStationDistance = location
diff --git a/packages/aris-source-weatherkit/src/weather-context.ts b/packages/aris-source-weatherkit/src/weather-context.ts
index 11a027e..eadf53e 100644
--- a/packages/aris-source-weatherkit/src/weather-context.ts
+++ b/packages/aris-source-weatherkit/src/weather-context.ts
@@ -24,4 +24,4 @@ export interface Weather {
 	daylight: boolean
 }
 
-export const WeatherKey: ContextKey<Weather> = contextKey("weather")
+export const WeatherKey: ContextKey<Weather> = contextKey("aris.weather", "weather")
diff --git a/packages/aris-source-weatherkit/src/weather-source.test.ts b/packages/aris-source-weatherkit/src/weather-source.test.ts
index 18749c2..88b4994 100644
--- a/packages/aris-source-weatherkit/src/weather-source.test.ts
+++ b/packages/aris-source-weatherkit/src/weather-source.test.ts
@@ -1,4 +1,6 @@
-import { contextValue, type Context } from "@aris/core"
+import type { FeedSource } from "@aris/core"
+
+import { Context } from "@aris/core"
 import { LocationKey } from "@aris/source-location"
 import { describe, expect, test } from "bun:test"
 
@@ -6,7 +8,7 @@ import type { WeatherKitClient, WeatherKitResponse } from "./weatherkit"
 
 import fixture from "../fixtures/san-francisco.json"
 import { WeatherFeedItemType } from "./feed-items"
-import { WeatherKey } from "./weather-context"
+import { WeatherKey, type Weather } from "./weather-context"
 import { WeatherSource, Units } from "./weather-source"
 
 const mockCredentials = {
@@ -23,9 +25,9 @@ function createMockClient(response: WeatherKitResponse): WeatherKitClient {
 }
 
 function createMockContext(location?: { lat: number; lng: number }): Context {
-	const ctx: Context = { time: new Date("2026-01-17T00:00:00Z") }
+	const ctx = new Context(new Date("2026-01-17T00:00:00Z"))
 	if (location) {
-		ctx[LocationKey] = { ...location, accuracy: 10, timestamp: new Date() }
+		ctx.set([[LocationKey, { ...location, accuracy: 10, timestamp: new Date() }]])
 	}
 	return ctx
 }
@@ -63,18 +65,19 @@ describe("WeatherSource", () => {
 			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)
+			const entries = await source.fetchContext(context)
+			expect(entries).not.toBeNull()
+			expect(entries).toHaveLength(1)
 
-			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")
+			const [key, weather] = entries![0]! as [typeof WeatherKey, Weather]
+			expect(key).toEqual(WeatherKey)
+			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 () => {
@@ -84,12 +87,12 @@ describe("WeatherSource", () => {
 			})
 			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)
+			const entries = await source.fetchContext(context)
+			expect(entries).not.toBeNull()
 
+			const [, weather] = entries![0]! as [typeof WeatherKey, Weather]
 			// Fixture has temperature around 10°C, imperial should be around 50°F
-			expect(weather!.temperature).toBeGreaterThan(40)
+			expect(weather.temperature).toBeGreaterThan(40)
 		})
 	})
 
@@ -177,12 +180,12 @@ describe("WeatherSource", () => {
 
 	describe("no reactive methods", () => {
 		test("does not implement onContextUpdate", () => {
-			const source = new WeatherSource({ credentials: mockCredentials })
+			const source: FeedSource = new WeatherSource({ credentials: mockCredentials })
 			expect(source.onContextUpdate).toBeUndefined()
 		})
 
 		test("does not implement onItemsUpdate", () => {
-			const source = new WeatherSource({ credentials: mockCredentials })
+			const source: FeedSource = new WeatherSource({ credentials: mockCredentials })
 			expect(source.onItemsUpdate).toBeUndefined()
 		})
 	})
diff --git a/packages/aris-source-weatherkit/src/weather-source.ts b/packages/aris-source-weatherkit/src/weather-source.ts
index 9247fcd..92df059 100644
--- a/packages/aris-source-weatherkit/src/weather-source.ts
+++ b/packages/aris-source-weatherkit/src/weather-source.ts
@@ -1,6 +1,6 @@
-import type { ActionDefinition, Context, FeedItemSignals, FeedSource } from "@aris/core"
+import type { ActionDefinition, ContextEntry, FeedItemSignals, FeedSource } from "@aris/core"
 
-import { TimeRelevance, UnknownActionError, contextValue } from "@aris/core"
+import { Context, TimeRelevance, UnknownActionError } from "@aris/core"
 import { LocationKey } from "@aris/source-location"
 
 import { WeatherFeedItemType, type WeatherFeedItem } from "./feed-items"
@@ -86,7 +86,7 @@ const MODERATE_CONDITIONS = new Set<ConditionCode>([
  * })
  *
  * // Access weather context in downstream sources
- * const weather = contextValue(context, WeatherKey)
+ * const weather = context.get(WeatherKey)
  * if (weather?.condition === "Rain") {
  *   // suggest umbrella
  * }
@@ -119,8 +119,8 @@ export class WeatherSource implements FeedSource<WeatherFeedItem> {
 		throw new UnknownActionError(actionId)
 	}
 
-	async fetchContext(context: Context): Promise<Partial<Context> | null> {
-		const location = contextValue(context, LocationKey)
+	async fetchContext(context: Context): Promise<readonly ContextEntry[] | null> {
+		const location = context.get(LocationKey)
 		if (!location) {
 			return null
 		}
@@ -147,11 +147,11 @@ export class WeatherSource implements FeedSource<WeatherFeedItem> {
 			daylight: response.currentWeather.daylight,
 		}
 
-		return { [WeatherKey]: weather }
+		return [[WeatherKey, weather]]
 	}
 
 	async fetchItems(context: Context): Promise<WeatherFeedItem[]> {
-		const location = contextValue(context, LocationKey)
+		const location = context.get(LocationKey)
 		if (!location) {
 			return []
 		}