fix: preserve Pi projection continuity

tests/unit/pi-conversation-runtime.test.ts

@@ -203,6 +203,12 @@ describe('Pi Conversation runtime', () => {
       },
     });
     await Promise.all(inputs.slice(0, 2).map((input) => runtime.prepare(input)));
+    const leftGenerationOneSeqs: number[] = [];
+    const unsubscribe = runtime.subscribe((envelope) => {
+      if (envelope.conversationId === left.id && envelope.workerGeneration === 1) {
+        leftGenerationOneSeqs.push(envelope.seq);
+      }
+    });
 
     const releasePromptAcceptance = workers.get(left.id)!.holdNext('prompt');
     let acceptanceResolved = false;
@@ -280,6 +286,8 @@ describe('Pi Conversation runtime', () => {
     expect((await runtime.getSnapshot(left.id)).run.status).toBe('idle');
     const settledNodes = (await runtime.getSnapshot(left.id)).nodes;
     expect(settledNodes).toEqual(checkpoint.nodes);
+    expect(leftGenerationOneSeqs).toEqual(leftGenerationOneSeqs.map((_, index) => index + 1));
+    expect((await runtime.getSnapshot(left.id)).cursor.seq).toBe(leftGenerationOneSeqs.at(-1));
 
     const changed = await runtime.setModel({
       conversationId: left.id,
@@ -452,5 +460,6 @@ describe('Pi Conversation runtime', () => {
     await expect(runtime.getSnapshot(forkTarget.id)).rejects.toMatchObject({
       publicError: { code: 'CODING_CONVERSATION_NOT_FOUND' },
     });
+    unsubscribe();
   });
 });