diff --git a/services/api/src/events/__tests__/bus.test.ts b/services/api/src/events/__tests__/bus.test.ts
index 571355e..d9e6660 100644
--- a/services/api/src/events/__tests__/bus.test.ts
+++ b/services/api/src/events/__tests__/bus.test.ts
@@ -56,7 +56,7 @@ describe('EventBus — delivery', () => {
   it('does not throw when publishing with no subscribers', () => {
     const b = makeBus();
     expect(() =>
-      b.publish('signals.task.synced', { userId: 'u', count: 3, syncedAt: '' }),
+      b.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 3, syncedAt: '' }),
     ).not.toThrow();
   });
 
@@ -101,7 +101,7 @@ describe('EventBus — ring buffer / tail()', () => {
   it('tail() filters by subject prefix', () => {
     const b = makeBus();
     b.publish('signals.tip.served', { userId: 'u', tipId: 't', policy: 'p', servedAt: '' });
-    b.publish('signals.task.synced', { userId: 'u', count: 1, syncedAt: '' });
+    b.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 1, syncedAt: '' });
 
     const tipEvents = b.tail({ subject: 'signals.tip' });
     expect(tipEvents.every((e) => e.subject.startsWith('signals.tip'))).toBe(true);
@@ -178,7 +178,7 @@ describe('EventBus — onPublish hook (NATS bridge contract)', () => {
     const hook = vi.fn();
     b.onPublish(hook);
 
-    const payload = { userId: 'u', count: 2, syncedAt: 'now' };
+    const payload = { userId: 'u', source: 'todoist', count: 2, syncedAt: 'now' };
     b.publish('signals.task.synced', payload);
 
     expect(hook).toHaveBeenCalledOnce();
@@ -191,7 +191,7 @@ describe('EventBus — onPublish hook (NATS bridge contract)', () => {
     b.onPublish(() => calls.push('a'));
     b.onPublish(() => calls.push('b'));
 
-    b.publish('signals.task.synced', { userId: 'u', count: 0, syncedAt: '' });
+    b.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 0, syncedAt: '' });
     expect(calls).toEqual(['a', 'b']);
   });
 
@@ -202,7 +202,7 @@ describe('EventBus — onPublish hook (NATS bridge contract)', () => {
     b.onPublish(hook);
     b.subscribe('signals.task.synced', sub);
 
-    b.publish('signals.task.synced', { userId: 'u', count: 1, syncedAt: '' });
+    b.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 1, syncedAt: '' });
     expect(hook).toHaveBeenCalledOnce();
     expect(sub).toHaveBeenCalledOnce();
   });
@@ -215,7 +215,7 @@ describe('EventBus — onPublish hook (NATS bridge contract)', () => {
       throw new Error('boom');
     });
     expect(() =>
-      b.publish('signals.task.synced', { userId: 'u', count: 0, syncedAt: '' }),
+      b.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 0, syncedAt: '' }),
     ).toThrow('boom');
   });
 });
diff --git a/services/api/src/events/__tests__/nats.test.ts b/services/api/src/events/__tests__/nats.test.ts
index 6f411fb..0b287b2 100644
--- a/services/api/src/events/__tests__/nats.test.ts
+++ b/services/api/src/events/__tests__/nats.test.ts
@@ -106,7 +106,7 @@ describe('connectNats — bridge bus → JetStream', () => {
 
     await connectNats('nats://test:4222');
 
-    const payload = { userId: 'u1', count: 7, syncedAt: '2026-01-01T00:00:00Z' };
+    const payload = { userId: 'u1', source: 'todoist', count: 7, syncedAt: '2026-01-01T00:00:00Z' };
     bus.publish('signals.task.synced', payload);
 
     // Allow the queued microtask in the hook to flush.
@@ -130,7 +130,7 @@ describe('connectNats — bridge bus → JetStream', () => {
     const errSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
 
     expect(() =>
-      bus.publish('signals.task.synced', { userId: 'u', count: 0, syncedAt: '' }),
+      bus.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 0, syncedAt: '' }),
     ).not.toThrow();
 
     // Wait a tick for the rejected promise's catch to run.
@@ -156,7 +156,7 @@ describe('Bus.onPublish contract — used by NATS bridge', () => {
     const b = new Bus();
     const hook = vi.fn();
     b.onPublish(hook);
-    b.publish('signals.task.synced', { userId: 'u', count: 0, syncedAt: '' });
+    b.publish('signals.task.synced', { userId: 'u', source: 'todoist', count: 0, syncedAt: '' });
     expect(hook).toHaveBeenCalledOnce();
   });
 });
diff --git a/services/api/src/events/bus.ts b/services/api/src/events/bus.ts
index 3693212..798fd26 100644
--- a/services/api/src/events/bus.ts
+++ b/services/api/src/events/bus.ts
@@ -45,6 +45,7 @@ export type RewardDeliveryFailedEvent = {
 
 export type TaskSyncedEvent = {
   userId: string;
+  source: string;   // e.g. 'todoist'
   count: number;
   syncedAt: string;
 };
diff --git a/services/api/src/signals/todoist.ts b/services/api/src/signals/todoist.ts
index 16d7f6c..1b76437 100644
--- a/services/api/src/signals/todoist.ts
+++ b/services/api/src/signals/todoist.ts
@@ -88,7 +88,7 @@ export class TodoistSignalSource implements SignalSource {
     });
 
     this.cache.set(userId, { signals, fetchedAt: Date.now() });
-    bus.publish('signals.task.synced', { userId, count: signals.length, syncedAt: now });
+    bus.publish('signals.task.synced', { userId, source: 'todoist', count: signals.length, syncedAt: now });
 
     return signals;
   }