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/src/database/repos/ai-chat/ai-chat-message.repo.ts

@@ -1,4 +1,4 @@
-import { Injectable } from '@nestjs/common';
+import { Injectable, Logger } from '@nestjs/common';
 import { InjectKysely } from 'nestjs-kysely';
 import { KyselyDB, KyselyTransaction } from '../../types/kysely.types';
 import { dbOrTx } from '../../utils';
@@ -25,6 +25,8 @@ const FIND_ALL_BY_CHAT_LIMIT = 5000;
 
 @Injectable()
 export class AiChatMessageRepo {
+  private readonly logger = new Logger(AiChatMessageRepo.name);
+
   constructor(@InjectKysely() private readonly db: KyselyDB) {}
 
   // The `tsv` column is a trigger-maintained tsvector used only for
@@ -87,17 +89,32 @@ export class AiChatMessageRepo {
   async findAllByChat(
     chatId: string,
     workspaceId: string,
+    // Injectable for tests so truncation can be exercised on a modest volume.
+    limit: number = FIND_ALL_BY_CHAT_LIMIT,
   ): Promise<AiChatMessage[]> {
-    return this.db
+    // Fetch newest-first (+1 to DETECT truncation), so on overflow we keep the
+    // NEWEST `limit` messages — the recent conversation matters most for an
+    // export — rather than silently dropping the tail (#183 review). Reverse back
+    // to chronological for rendering, like findRecent.
+    const rows = await this.db
       .selectFrom('aiChatMessages')
       .select(this.baseFields)
       .where('chatId', '=', chatId)
       .where('workspaceId', '=', workspaceId)
       .where('deletedAt', 'is', null)
-      .orderBy('createdAt', 'asc')
-      .orderBy('id', 'asc')
-      .limit(FIND_ALL_BY_CHAT_LIMIT)
+      .orderBy('createdAt', 'desc')
+      .orderBy('id', 'desc')
+      .limit(limit + 1)
       .execute();
+
+    if (rows.length > limit) {
+      rows.length = limit; // keep the newest `limit` (rows are newest-first here)
+      this.logger.warn(
+        `Chat ${chatId} export truncated to the newest ${limit} messages ` +
+          `(older messages omitted).`,
+      );
+    }
+    return rows.reverse();
   }
 
   // Load the most RECENT `limit` messages for a chat and return them in