Show persistent timestamps for operation and teacher messages

tests/unit/pi-event-projector.test.ts

@@ -58,6 +58,19 @@ function apply(
 }
 
 describe('Pi event projector', () => {
+  it.each(['stop', 'error', 'aborted'])('uses send time and terminal time for %s, never the assistant start time', async stopReason => {
+    let now = 2000;
+    const projector = new PiEventProjector({ createId: () => 'live-message', now: () => now });
+    let snapshot = emptySnapshot();
+    snapshot = apply(snapshot, await projector.project(snapshot, { type: 'message_start', message: { role: 'user', timestamp: 1000, content: [{ type: 'text', text: '你好' }] } }));
+    expect(snapshot.nodes[0]).toMatchObject({ role: 'user', timestamp: 1000 });
+    snapshot = apply(snapshot, await projector.project(snapshot, { type: 'message_start', message: { role: 'assistant', timestamp: 2000, content: [] } }));
+    expect(snapshot.nodes.at(-1)).not.toHaveProperty('timestamp');
+    now = 9000;
+    snapshot = apply(snapshot, await projector.project(snapshot, { type: 'message_end', message: { role: 'assistant', timestamp: 2000, stopReason, content: [{ type: 'text', text: '你好呀' }] } }));
+    expect(snapshot.nodes.at(-1)).toMatchObject({ role: 'assistant', timestamp: 9000 });
+  });
+
   it('projects only subagent.v1 details and never exposes unknown raw details', async () => {
     const projector = new PiEventProjector({ createId: () => 'unused' });
     let snapshot = emptySnapshot();
@@ -157,6 +170,7 @@ describe('Pi event projector', () => {
   it('keeps one assistant UI identity while content-index deltas become an authoritative message', async () => {
     const projector = new PiEventProjector({
       createId: () => 'assistant-ui-a',
+      now: () => 9000,
     });
     let snapshot = emptySnapshot();
     const initialAssistant = {
@@ -217,6 +231,7 @@ describe('Pi event projector', () => {
       kind: 'message',
       id: 'assistant-ui-a',
       role: 'assistant',
+      timestamp: 9000,
       status: 'complete',
       blocks: [{
         kind: 'text',
@@ -624,6 +639,7 @@ describe('Pi event projector', () => {
       kind: 'message',
       id: 'user-ui-a',
       clientRequestId: 'request-a',
+      timestamp: 20,
       role: 'user',
       status: 'complete',
       blocks: [