refactor(review): address PR #186 re-review (approve-with-comments)

Approve-with-comments re-review; no blockers. All 7 actionable points (8 is a
forward-looking architecture note — recommendation A, keep as-is):

1. chat-markdown.util spec: restore parity coverage of the removed client spec —
   tool error state (+ errorText), unknown-tool fallback (`Ran tool <name>` en /
   `Выполнил инструмент <name>` ru), and the circular-output stringify catch.
2. findAllByChat row cap is now testable (injectable limit) + an int-spec proves
   truncation on a modest volume.
3. Stability: the per-step durability updates are SERIALIZED via a promise chain
   (stepUpdateChain) so they commit in step order — onlyIfStreaming already
   closed the finalize race, this closes inter-step ordering.
4. findAllByChat keeps the NEWEST messages on truncation (order DESC + reverse,
   like findRecent) and logs a warning with chatId, instead of silently dropping
   the newest tail.
5. The LABELS parity comment already references the real path (tool-parts.tsx /
   toolLabelKey) — confirmed accurate.
6. Removed the redundant 'off-by-one boundary' test (strict subset of the two
   adjacent prepareAgentStep cases).
7. Extracted the terminal-finalize dispatch into a shared `applyFinalize`, used
   by BOTH the service's finalizeAssistant and its test — the test now exercises
   the real path, not a copy, so a production drift fails it.

Verified: server build + 325 ai-chat unit + 6 integration; prettier clean.

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

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

@@ -231,4 +231,40 @@ describe('AiChatMessageRepo.update + sweepStreaming [integration]', () => {
     // ...while the stale one alongside it was swept to 'aborted'.
     expect(byId.get(stale.id)!.status).toBe('aborted');
   });
+
+  it('findAllByChat caps the result, keeping the NEWEST messages in order (#183 review)', async () => {
+    // A dedicated chat so the cap test is independent of the rows above.
+    const cappedChat = (
+      await createChat(db, { workspaceId, creatorId: userId })
+    ).id;
+    const base = Date.now();
+    // Three messages at strictly increasing timestamps.
+    await createMessage(db, {
+      workspaceId,
+      chatId: cappedChat,
+      content: 'm1-oldest',
+      createdAt: new Date(base),
+    });
+    await createMessage(db, {
+      workspaceId,
+      chatId: cappedChat,
+      content: 'm2',
+      createdAt: new Date(base + 1000),
+    });
+    await createMessage(db, {
+      workspaceId,
+      chatId: cappedChat,
+      content: 'm3-newest',
+      createdAt: new Date(base + 2000),
+    });
+
+    // Cap of 2 -> the OLDEST message is dropped; the newest two stay, in
+    // chronological order (oldest -> newest).
+    const capped = await repo.findAllByChat(cappedChat, workspaceId, 2);
+    expect(capped.map((r) => r.content)).toEqual(['m2', 'm3-newest']);
+
+    // Without a cap (well above the row count) all three come back in order.
+    const all = await repo.findAllByChat(cappedChat, workspaceId, 100);
+    expect(all.map((r) => r.content)).toEqual(['m1-oldest', 'm2', 'm3-newest']);
+  });
 });