diff --git a/src/arts/timer/fake-clock.ts b/src/arts/timer/fake-clock.ts
new file mode 100644
index 0000000..16e980c
--- /dev/null
+++ b/src/arts/timer/fake-clock.ts
@@ -0,0 +1,100 @@
+import type { TimerClock, TimerNativeHandle } from '$libs/timer';
+
+interface FakeClockEntry {
+	id: number;
+	dueAt: number;
+	fn: () => void;
+	cancelled: boolean;
+}
+
+/**
+ * Test-only TimerClock with manual time advancement. Same shape that
+ * `createEngineTimers({ clock })` and the format/storage `clock`
+ * options accept, so any artifact under test can be wired against this
+ * deterministic source without touching `vi.useFakeTimers()`.
+ *
+ * Methods:
+ * - `advanceBy(ms)` — fires every entry whose `dueAt` is reached during
+ *   the advancement, in due-order, with microtask flushes between each
+ *   so awaited promises inside callbacks resolve before time moves on.
+ * - `advanceTo(ms)` — convenience over `advanceBy`.
+ * - `pendingCount()` — for tests that want to assert teardown is clean.
+ */
+export interface FakeTimerClock extends TimerClock {
+	advanceBy(ms: number): Promise<void>;
+	advanceTo(ms: number): Promise<void>;
+	pendingCount(): number;
+}
+
+/**
+ * Build a fake `TimerClock` with manual time advancement. Use in tests
+ * for any artifact that accepts a `clock` injection (storage, format,
+ * logger, http, session auto-refresh, …).
+ *
+ * @example
+ * const clock = createFakeTimerClock(0);
+ * const timers = createEngineTimers({ clock });
+ * timers.schedule('demo', 100, () => fired = true);
+ * await clock.advanceBy(150);
+ * expect(fired).toBe(true);
+ */
+export function createFakeTimerClock(start = 0): FakeTimerClock {
+	let now = start;
+	const queue = new Map<number, FakeClockEntry>();
+	let nextId = 1;
+
+	function fire(entry: FakeClockEntry): void {
+		if (entry.cancelled) return;
+		queue.delete(entry.id);
+		entry.fn();
+	}
+
+	async function flushMicrotasks(): Promise<void> {
+		// Yield to the microtask queue so any awaited promises inside
+		// scheduled callbacks resolve before we advance further.
+		for (let i = 0; i < 10; i++) await Promise.resolve();
+	}
+
+	const clock: FakeTimerClock = {
+		now: () => now,
+		setTimeout: (fn: () => void, delayMs: number): TimerNativeHandle => {
+			const entry: FakeClockEntry = {
+				id: nextId++,
+				dueAt: now + delayMs,
+				fn,
+				cancelled: false
+			};
+			queue.set(entry.id, entry);
+			return entry.id;
+		},
+		clearTimeout: (handle: TimerNativeHandle): void => {
+			const entry = queue.get(handle as number);
+			if (entry !== undefined) {
+				entry.cancelled = true;
+				queue.delete(entry.id);
+			}
+		},
+		async advanceBy(ms: number): Promise<void> {
+			const target = now + ms;
+			while (true) {
+				let next: FakeClockEntry | undefined;
+				for (const e of queue.values()) {
+					if (e.dueAt > target) continue;
+					if (next === undefined || e.dueAt < next.dueAt) next = e;
+				}
+				if (next === undefined) break;
+				now = next.dueAt;
+				fire(next);
+				await flushMicrotasks();
+			}
+			now = target;
+			await flushMicrotasks();
+		},
+		async advanceTo(target: number): Promise<void> {
+			if (target <= now) return;
+			await clock.advanceBy(target - now);
+		},
+		pendingCount: () => queue.size
+	};
+	return clock;
+}
diff --git a/src/arts/timer/index.ts b/src/arts/timer/index.ts
index 119e0ab..ae2fc02 100644
--- a/src/arts/timer/index.ts
+++ b/src/arts/timer/index.ts
@@ -5,6 +5,7 @@
 export { createEngineTimers } from './engine-timers.ts';
 export { createActiveTimers, type ActiveTimers } from './active-timers.svelte.ts';
 export { createSystemTimerClock } from './clock.ts';
+export { createFakeTimerClock, type FakeTimerClock } from './fake-clock.ts';
 export { computeBackoffDelay } from './backoff.ts';
 export { createTimerDiagnostics, emitTimerDiagnostic } from './diagnostics.ts';
 
diff --git a/src/arts/timer/test/fake-clock.test.ts b/src/arts/timer/test/fake-clock.test.ts
new file mode 100644
index 0000000..a7e9c2c
--- /dev/null
+++ b/src/arts/timer/test/fake-clock.test.ts
@@ -0,0 +1,45 @@
+import { describe, expect, it } from 'vitest';
+import { createFakeTimerClock } from '../fake-clock.ts';
+
+describe('createFakeTimerClock', () => {
+	it('starts at the configured time and advances on demand', async () => {
+		const clock = createFakeTimerClock(1000);
+		expect(clock.now()).toBe(1000);
+
+		await clock.advanceBy(500);
+		expect(clock.now()).toBe(1500);
+
+		await clock.advanceTo(2000);
+		expect(clock.now()).toBe(2000);
+	});
+
+	it('fires scheduled timeouts in due-order on advanceBy', async () => {
+		const clock = createFakeTimerClock(0);
+		const events: string[] = [];
+
+		clock.setTimeout(() => events.push('B-200'), 200);
+		clock.setTimeout(() => events.push('A-100'), 100);
+		clock.setTimeout(() => events.push('C-300'), 300);
+
+		await clock.advanceBy(250);
+		expect(events).toEqual(['A-100', 'B-200']);
+
+		await clock.advanceBy(100);
+		expect(events).toEqual(['A-100', 'B-200', 'C-300']);
+		expect(clock.pendingCount()).toBe(0);
+	});
+
+	it('cancels timeouts via clearTimeout', async () => {
+		const clock = createFakeTimerClock(0);
+		let fired = false;
+
+		const handle = clock.setTimeout(() => {
+			fired = true;
+		}, 100);
+		clock.clearTimeout(handle);
+
+		await clock.advanceBy(200);
+		expect(fired).toBe(false);
+		expect(clock.pendingCount()).toBe(0);
+	});
+});