fix(ai-chat): guard step-update vs finalize race with WHERE status='streaming' (#183 review)

Review caught a real race: onStepFinish fires `updateStreaming()` fire-and-
forget (not awaited), so the FINAL step's streaming UPDATE and the terminal
`finalizeAssistant` UPDATE run as two concurrent statements on different pool
connections — commit order is not guaranteed. If the late streaming update
lands AFTER finalize, the completed row is clobbered back to status='streaming'
with no usage/finishReason, and the next startup sweep then mis-marks the
finished turn 'aborted'. Green unit/integration tests don't reproduce a
cross-connection race.

Fix: scope the per-step update with `onlyIfStreaming` → SQL `WHERE
status='streaming'`. Once finalize has set a terminal status the late update
matches zero rows and no-ops, regardless of commit order; finalize runs
unguarded so it always wins. A cheap `if (finalized) return` short-circuit
avoids most wasted queries, but the SQL guard is the authoritative fix (the
flag can be set after a query is already in flight).

Integration test: finalize to 'completed', then a late onlyIfStreaming update
is a no-op — status/content/usage preserved.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/server/test/integration/ai-chat-message-status.int-spec.ts

@@ -73,6 +73,40 @@ describe('AiChatMessageRepo.update + sweepStreaming [integration]', () => {
     );
   });
 
+  it('onlyIfStreaming update is a NO-OP once the row is finalized (race guard)', async () => {
+    // Reproduce the step-update-vs-finalize race (#183 review): the row is
+    // finalized to 'completed', then a LATE per-step 'streaming' update lands.
+    // With `onlyIfStreaming` it must match nothing and leave the finalized row
+    // untouched (no clobber back to 'streaming', no lost usage).
+    const seeded = await repo.insert({
+      chatId,
+      workspaceId,
+      userId,
+      role: 'assistant',
+      content: 'partial',
+      status: 'streaming',
+    });
+    // Terminal finalize (unguarded) wins.
+    await repo.update(seeded.id, workspaceId, {
+      content: 'final answer',
+      status: 'completed',
+      metadata: { usage: { totalTokens: 42 } } as never,
+    });
+    // A straggler per-step update arrives AFTER finalize.
+    const late = await repo.update(
+      seeded.id,
+      workspaceId,
+      { content: 'partial', status: 'streaming', metadata: {} as never },
+      { onlyIfStreaming: true },
+    );
+    expect(late).toBeUndefined(); // matched no 'streaming' row -> no-op
+    const rows = await repo.findAllByChat(chatId, workspaceId);
+    const row = rows.find((r) => r.id === seeded.id)!;
+    expect(row.status).toBe('completed'); // NOT clobbered back to streaming
+    expect(row.content).toBe('final answer');
+    expect((row.metadata as any).usage.totalTokens).toBe(42); // usage preserved
+  });
+
   it('update is workspace-scoped: a foreign workspace id matches nothing', async () => {
     const seeded = await repo.insert({
       chatId,