fix(coding): keep optimistic identity across snapshots

tests/unit/coding-conversations-store.test.tsx

@@ -337,6 +337,43 @@ describe('coding Conversation store', () => {
     expect(store.getState().requestsByConversationId['conversation-a']).toEqual({});
   });
 
+  it('preserves the optimistic UI id when a reconnect snapshot is already durable', async () => {
+    const store = createCodingConversationStore({
+      getSnapshot: vi.fn(),
+      openEvents: vi.fn(),
+      submitPrompt: vi.fn(async (input) => acceptance(
+        input.conversationId,
+        input.clientRequestId,
+      )),
+      createId: ids(),
+    });
+    store.getState().applySnapshotEvent(snapshotEvent(snapshot('conversation-a')));
+    store.getState().setDraft('conversation-a', 'Already durable');
+    await store.getState().submitPrompt({ conversationId: 'conversation-a', mode: 'prompt' });
+    const durable = snapshot('conversation-a', 1, 1);
+    store.getState().applySnapshotEvent(snapshotEvent({
+      ...durable,
+      nodes: [{
+        kind: 'message',
+        id: 'durable-user-1',
+        sourceEntryId: 'entry-user-1',
+        clientRequestId: 'request-1',
+        role: 'user',
+        status: 'complete',
+        blocks: [{ kind: 'text', id: 'durable-text-1', text: 'Already durable', status: 'complete' }],
+      }],
+    }));
+
+    expect(selectCodingConversationSnapshot('conversation-a')(store.getState())?.nodes[0])
+      .toMatchObject({
+        id: 'node-1',
+        sourceEntryId: 'entry-user-1',
+        clientRequestId: 'request-1',
+        status: 'complete',
+      });
+    expect(store.getState().requestsByConversationId['conversation-a']).toEqual({});
+  });
+
   it('restores draft attachments and marks the optimistic node on definite rejection', async () => {
     const submitPrompt = vi.fn(async () => {
       throw new AppError('RUNTIME', 'Model unavailable', undefined, {