perf(mcp): checkNewComments — параллелизм с капом (#490)

checkNewComments делал O(N) последовательных REST-вызовов listComments по страницам
working set — большой space линеен по round-trip'ам. Теперь per-page фетчи идут с
ограниченным параллелизмом (cap 6, середина полосы 5–8): независимые чтения не ждут
друг друга, но и не заваливают сервер/сокеты.

mapWithConcurrency — крошечный пул без зависимости от p-limit: N воркеров тянут
следующий индекс с общего курсора. Порядок результатов сохраняется (по входному
порядку страниц), поэтому вывод детерминирован независимо от того, какой фетч
завершился первым. Серверный batch-эндпоинт «comments updated since T по space» —
опционально, отдельным заходом.

Тест (mock-HTTP): 13 страниц, задержанный /api/comments — maxInFlight > 1 и <= 6
(последовательная реализация дала бы 1), порядок результатов = порядок обхода.

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

.gitignore

@@ -29,6 +29,10 @@ packages/mcp/build/
 # is a build artifact like build/ — never committed, always fresh.
 packages/mcp/src/registry-stamp.generated.ts
 
+# token-estimate compiled output (#490; built in CI/Docker via `pnpm build` /
+# the server `pretest`, never committed, so src/ and prod can never diverge).
+packages/token-estimate/dist/
+
 # Logs
 logs
 *.log

apps/client/package.json

@@ -22,6 +22,7 @@
     "@casl/react": "5.0.1",
     "@docmost/editor-ext": "workspace:*",
     "@docmost/prosemirror-markdown": "workspace:*",
+    "@docmost/token-estimate": "workspace:*",
     "@excalidraw/excalidraw": "0.18.0-3a5ef40",
     "@mantine/core": "8.3.18",
     "@mantine/dates": "8.3.18",

apps/client/src/features/ai-chat/utils/count-stream-tokens.test.ts

@@ -6,10 +6,13 @@ describe("estimateTokens", () => {
     expect(estimateTokens("")).toBe(0);
   });
 
-  it("ceils chars/4 so any non-empty text is at least 1 token", () => {
+  // #490: migrated onto the shared @docmost/token-estimate module (chars/2.5, up
+  // from the old client-only chars/4) so the client counter and the server replay
+  // budgeter can never diverge.
+  it("ceils chars/2.5 so any non-empty text is at least 1 token", () => {
     expect(estimateTokens("a")).toBe(1);
-    expect(estimateTokens("abcd")).toBe(1);
-    expect(estimateTokens("abcde")).toBe(2);
-    expect(estimateTokens("12345678")).toBe(2);
+    expect(estimateTokens("ab")).toBe(1);
+    expect(estimateTokens("abcde")).toBe(2); // 5 / 2.5 = 2
+    expect(estimateTokens("x".repeat(10))).toBe(4); // 10 / 2.5 = 4
   });
 });

apps/client/src/features/ai-chat/utils/count-stream-tokens.ts

@@ -2,18 +2,10 @@
  * Rough client-side token estimation for AI-chat UI affordances.
  *
  * No provider streams exact per-token usage mid-stream, so any in-flight figure
- * is a CLIENT ESTIMATE (chars/≈4 heuristic). Pure + unit-testable: it never runs
- * a real BPE tokenizer (that would be O(n²) on the hot path, bloat the bundle,
- * and be wrong for Gemini/Ollama anyway). Used by the in-body reasoning counter
- * ("Thinking · N tokens").
+ * is a CLIENT ESTIMATE. This re-exports the SHARED estimator from
+ * `@docmost/token-estimate` (chars/2.5) so the in-body counter and the server's
+ * replay budgeter use the SAME heuristic — two divergent estimators would mean
+ * "the badge shows 60%" while "the budgeter already trimmed" (#490). Used by the
+ * in-body reasoning counter ("Thinking · N tokens").
  */
-
-/**
- * Rough token estimate for a piece of text using the standard chars/≈4 heuristic.
- * Returns 0 for empty/whitespace-free-of-content input, and ceils so any
- * non-empty text counts as at least one token.
- */
-export function estimateTokens(text: string): number {
-  if (!text) return 0;
-  return Math.ceil(text.length / 4);
-}
+export { estimateTokens } from "@docmost/token-estimate";

apps/server/package.json

@@ -23,7 +23,7 @@
     "migration:reset": "tsx src/database/migrate.ts down-to NO_MIGRATIONS",
     "migration:codegen": "kysely-codegen --dialect=postgres --camel-case --env-file=../../.env --out-file=./src/database/types/db.d.ts",
     "lint": "eslint \"{src,apps,libs,test}/**/*.ts\" --fix",
-    "pretest": "pnpm --filter @docmost/editor-ext build && pnpm --filter @docmost/prosemirror-markdown build",
+    "pretest": "pnpm --filter @docmost/editor-ext build && pnpm --filter @docmost/prosemirror-markdown build && pnpm --filter @docmost/token-estimate build",
     "test": "jest",
     "test:int": "jest --config test/jest-integration.json",
     "test:watch": "jest --watch",
@@ -44,6 +44,7 @@
     "@docmost/mcp": "workspace:*",
     "@docmost/pdf-inspector": "1.9.6",
     "@docmost/prosemirror-markdown": "workspace:*",
+    "@docmost/token-estimate": "workspace:*",
     "@fastify/compress": "^9.0.0",
     "@fastify/cookie": "^11.0.2",
     "@fastify/multipart": "^10.0.0",
@@ -206,6 +207,7 @@
       "^@docmost/db/(.*)$": "<rootDir>/database/$1",
       "^@docmost/transactional/(.*)$": "<rootDir>/integrations/transactional/$1",
       "^@docmost/ee/(.*)$": "<rootDir>/ee/$1",
+      "^@docmost/token-estimate$": "<rootDir>/../../../packages/token-estimate/src/index.ts",
       "^src/(.*)$": "<rootDir>/$1",
       "^@tiptap/react$": "<rootDir>/../test/stubs/tiptap-react.js"
     }

apps/server/src/core/ai-chat/ai-chat.service.run-race.spec.ts

@@ -181,7 +181,7 @@ describe('AiChatService.stream — abortSignal wiring (#184 F3)', () => {
       {} as never, // pageAccess
       { isAiChatDeferredToolsEnabled: () => false, isAiChatFinalStepLockdownEnabled: () => false } as never, // environment
     );
-    return { svc };
+    return { svc, aiChatMessageRepo };
   }
 
   const body = {
@@ -287,7 +287,7 @@ describe('AiChatService.stream — abortSignal wiring (#184 F3)', () => {
   // Drive stream() to the point streamText is called, capturing the options object
   // (which carries onStepFinish/onFinish/onError/onAbort) and the run hooks.
   async function captureStreamCallbacks() {
-    const { svc } = makeService();
+    const { svc, aiChatMessageRepo } = makeService();
     let capturedOpts: any;
     streamTextMock.mockImplementation((opts: any) => {
       capturedOpts = opts;
@@ -314,7 +314,7 @@ describe('AiChatService.stream — abortSignal wiring (#184 F3)', () => {
       runHooks: runHooks as never,
     });
     expect(capturedOpts).toBeDefined();
-    return { capturedOpts, runHooks };
+    return { capturedOpts, runHooks, aiChatMessageRepo };
   }
 
   it('F9: onStepFinish bumps the run step count, onFinish settles the run "completed" (the dominant autonomous-run path)', async () => {
@@ -369,6 +369,51 @@ describe('AiChatService.stream — abortSignal wiring (#184 F3)', () => {
       expect.stringContaining('provider exploded'),
     );
   });
+
+  // #490 reactive branch: a provider CONTEXT-OVERFLOW 400 in onError is classified,
+  // records a distinguishable cause, and stamps metadata.replayOverflow so the NEXT
+  // turn's budgeter trims aggressively (the recovery that un-bricks the chat).
+  it('#490: a context-overflow 400 stamps replayOverflow on the finalized row', async () => {
+    jest
+      .spyOn(Logger.prototype, 'error')
+      .mockImplementation(() => undefined as never);
+    jest
+      .spyOn(Logger.prototype, 'warn')
+      .mockImplementation(() => undefined as never);
+    const { capturedOpts, aiChatMessageRepo } = await captureStreamCallbacks();
+
+    const overflow = Object.assign(new Error('too large'), {
+      statusCode: 400,
+      message:
+        "This model's maximum context length is 128000 tokens. However, your messages resulted in 214000 tokens. Please reduce the length.",
+    });
+    await capturedOpts.onError({ error: overflow });
+
+    // The seed row exists (finalizeOwner is the owner-write path).
+    expect(aiChatMessageRepo.finalizeOwner).toHaveBeenCalled();
+    const calls = aiChatMessageRepo.finalizeOwner.mock.calls as any[][];
+    const patch = calls[calls.length - 1][2] as {
+      status: string;
+      metadata: Record<string, unknown>;
+    };
+    expect(patch.status).toBe('error');
+    expect(patch.metadata.replayOverflow).toBe(true);
+    expect(patch.metadata.error).toContain('контекстное окно');
+  });
+
+  it('#490: a non-overflow error does NOT stamp replayOverflow', async () => {
+    jest
+      .spyOn(Logger.prototype, 'error')
+      .mockImplementation(() => undefined as never);
+    const { capturedOpts, aiChatMessageRepo } = await captureStreamCallbacks();
+    await capturedOpts.onError({ error: new Error('network reset') });
+    const calls = aiChatMessageRepo.finalizeOwner.mock.calls as any[][];
+    const patch = calls[calls.length - 1][2] as {
+      status: string;
+      metadata: Record<string, unknown>;
+    };
+    expect('replayOverflow' in patch.metadata).toBe(false);
+  });
 });
 
 /**

apps/server/src/core/ai-chat/ai-chat.service.spec.ts

@@ -13,6 +13,7 @@ import {
   compactToolOutput,
   assistantParts,
   serializeSteps,
+  type StepPartsCache,
   rowToUiMessage,
   prepareAgentStep,
   stepBudgetWarning,
@@ -28,6 +29,9 @@ import {
   FINAL_STEP_NUDGE,
   STEP_LIMIT_NO_ANSWER_MARKER,
   OUTPUT_DEGENERATION_ERROR,
+  lastAssistantContextTokens,
+  lastAssistantReplayOverflow,
+  seedActivatedTools,
 } from './ai-chat.service';
 import type { AiChatMessage, Workspace } from '@docmost/db/types/entity.types';
 import { buildSystemPrompt } from './ai-chat.prompt';
@@ -114,6 +118,54 @@ describe('compactToolOutput', () => {
 describe('assistantParts', () => {
   type AnyPart = Record<string, unknown>;
 
+  // #490 memoization: assistantParts builds each step's parts once and caches
+  // them by the step OBJECT's identity, so a mid-stream flush does not
+  // re-stringify every prior step's (large) output. Observable property: with a
+  // shared cache, the second call over the SAME step object returns the cached
+  // (identical) part array even if the step's underlying output was swapped —
+  // proving the work was memoized, not redone.
+  it('memoizes a step by identity (shared cache => one build per step)', () => {
+    const cache: StepPartsCache = new WeakMap();
+    const step = {
+      text: 'x',
+      toolCalls: [{ toolCallId: 'c1', toolName: 'getPage', input: {} }],
+      toolResults: [{ toolCallId: 'c1', toolName: 'getPage', output: { v: 1 } }],
+    };
+    const first = assistantParts([step], '', cache) as AnyPart[];
+    expect((first.find((p) => p.type === 'tool-getPage')!.output as any).v).toBe(
+      1,
+    );
+    // Swap the output for a NEW value; a re-build would pick it up, a cache hit
+    // keeps the first result.
+    step.toolResults[0] = {
+      toolCallId: 'c1',
+      toolName: 'getPage',
+      output: { v: 2 },
+    };
+    const second = assistantParts([step], '', cache) as AnyPart[];
+    expect((second.find((p) => p.type === 'tool-getPage')!.output as any).v).toBe(
+      1,
+    );
+    // Same cached part objects are reused.
+    expect(second.find((p) => p.type === 'tool-getPage')).toBe(
+      first.find((p) => p.type === 'tool-getPage'),
+    );
+  });
+
+  it('without a cache, each call rebuilds (no stale memo)', () => {
+    const step = {
+      text: 'x',
+      toolCalls: [{ toolCallId: 'c1', toolName: 'getPage', input: {} }],
+      toolResults: [{ toolCallId: 'c1', toolName: 'getPage', output: { v: 1 } }],
+    };
+    const first = assistantParts([step], '') as AnyPart[];
+    step.toolResults[0].output = { v: 2 };
+    const second = assistantParts([step], '') as AnyPart[];
+    expect((second.find((p) => p.type === 'tool-getPage')!.output as any).v).toBe(
+      2,
+    );
+  });
+
   it('emits output-available for a tool-call WITH a paired result', () => {
     const steps = [
       {
@@ -231,61 +283,299 @@ describe('assistantParts', () => {
   });
 });
 
-describe('serializeSteps', () => {
+// #490 trace format v2: per call the trace stores { input } for the call and an
+// OUTCOME element — { ok: true } on success, { error, kind: 'thrown' } on a
+// thrown tool-error, { error, kind: 'interrupted' } on a mid-step abort. The tool
+// OUTPUT is no longer duplicated here (it lives once in metadata.parts).
+describe('serializeSteps (trace v2)', () => {
   it('returns null when there are no calls or results', () => {
     expect(serializeSteps([])).toBeNull();
   });
 
-  it('flattens calls and results into a compact trace', () => {
+  it('pairs a successful call with an { ok: true } outcome and NO output', () => {
     const trace = serializeSteps([
       {
-        toolCalls: [{ toolName: 'getPage', input: { id: 'p1' } }],
-        toolResults: [{ toolName: 'getPage', output: { title: 'T' } }],
+        toolCalls: [{ toolCallId: 'c1', toolName: 'getPage', input: { id: 'p1' } }],
+        toolResults: [{ toolCallId: 'c1', toolName: 'getPage' }],
       },
     ]) as Array<Record<string, unknown>>;
     expect(trace).toHaveLength(2);
     expect(trace[0]).toEqual({ toolName: 'getPage', input: { id: 'p1' } });
-    expect(trace[1]).toEqual({ toolName: 'getPage', output: { title: 'T' } });
+    expect(trace[1]).toEqual({ toolName: 'getPage', ok: true });
+    // The output is NOT stored in the trace any more (dedup: it lives in parts).
+    expect(trace.some((e) => 'output' in e)).toBe(false);
   });
 
-  it('records a THROWN tool failure (tool-error part) with its error message', () => {
+  it('records a THROWN failure with { error, kind: "thrown" }', () => {
     const trace = serializeSteps([
       {
-        toolCalls: [{ toolName: 'editPageText', input: { id: 'p1' } }],
+        toolCalls: [
+          { toolCallId: 'c1', toolName: 'editPageText', input: { id: 'p1' } },
+        ],
         toolResults: [],
         content: [
           {
             type: 'tool-error',
+            toolCallId: 'c1',
             toolName: 'editPageText',
             error: new Error('page is locked'),
           },
         ],
       },
     ]) as Array<Record<string, unknown>>;
-    // The call element is followed by a paired error element (mirroring how a
-    // successful result is appended), so the failure survives in the trace.
     expect(trace).toHaveLength(2);
     expect(trace[0]).toEqual({ toolName: 'editPageText', input: { id: 'p1' } });
     expect(trace[1]).toEqual({
       toolName: 'editPageText',
       error: 'page is locked',
+      kind: 'thrown',
     });
   });
 
-  it('truncates a very long tool-error message to the tool-output limit', () => {
+  it('marks an interrupted call (no result, no throw) with kind "interrupted"', () => {
+    const trace = serializeSteps([
+      {
+        toolCalls: [
+          { toolCallId: 'c1', toolName: 'createComment', input: { x: 1 } },
+        ],
+        toolResults: [],
+        content: [],
+      },
+    ]) as Array<Record<string, unknown>>;
+    expect(trace).toHaveLength(2);
+    expect(trace[1]).toEqual({
+      toolName: 'createComment',
+      error: 'Tool call did not complete.',
+      kind: 'interrupted',
+    });
+    // Structurally distinct from a thrown hard-fail so it never inflates an
+    // error-rate scan.
+    expect((trace[1] as { kind: string }).kind).not.toBe('thrown');
+  });
+
+  it('truncates a very long thrown-error message to the tool-output limit', () => {
     const long = 'x'.repeat(5000);
     const trace = serializeSteps([
       {
-        toolCalls: [{ toolName: 'editPageText', input: {} }],
+        toolCalls: [{ toolCallId: 'c1', toolName: 'editPageText', input: {} }],
         toolResults: [],
-        content: [{ type: 'tool-error', toolName: 'editPageText', error: long }],
+        content: [
+          {
+            type: 'tool-error',
+            toolCallId: 'c1',
+            toolName: 'editPageText',
+            error: long,
+          },
+        ],
       },
     ]) as Array<Record<string, unknown>>;
     const errorText = trace[1].error as string;
-    // Truncated (not the full 5000 chars) and carries the omission marker.
     expect(errorText.length).toBeLessThan(long.length);
     expect(errorText).toContain('chars omitted');
   });
+
+  it('pairs parallel calls in one step with their outcomes by id', () => {
+    const trace = serializeSteps([
+      {
+        toolCalls: [
+          { toolCallId: 'a', toolName: 'getPage', input: {} },
+          { toolCallId: 'b', toolName: 'searchPages', input: {} },
+        ],
+        toolResults: [{ toolCallId: 'b', toolName: 'searchPages' }],
+        content: [
+          { type: 'tool-error', toolCallId: 'a', toolName: 'getPage', error: 'nope' },
+        ],
+      },
+    ]) as Array<Record<string, unknown>>;
+    // call a, outcome a (thrown), call b, outcome b (ok)
+    expect(trace).toHaveLength(4);
+    expect(trace[1]).toEqual({ toolName: 'getPage', error: 'nope', kind: 'thrown' });
+    expect(trace[3]).toEqual({ toolName: 'searchPages', ok: true });
+  });
+});
+
+// #490: every assistant row flushAssistant writes carries the v2 era marker so a
+// dual-shape diagnostic query can branch on the trace shape without inspecting it.
+describe('toolTraceVersion era marker (#490)', () => {
+  it('stamps metadata.toolTraceVersion = 2 on every flushed row', () => {
+    const seed = flushAssistant([], '', 'streaming');
+    expect(seed.metadata.toolTraceVersion).toBe(2);
+    const done = flushAssistant(
+      [
+        {
+          text: 'ok',
+          toolCalls: [{ toolCallId: 'c1', toolName: 'getPage', input: {} }],
+          toolResults: [{ toolCallId: 'c1', toolName: 'getPage' }],
+        },
+      ],
+      '',
+      'completed',
+      { finishReason: 'stop' },
+    );
+    expect(done.metadata.toolTraceVersion).toBe(2);
+  });
+});
+
+// #490 replay-budget signal helpers over persisted history.
+describe('lastAssistantContextTokens', () => {
+  const row = (
+    role: string,
+    metadata: Record<string, unknown> | null,
+  ): AiChatMessage => ({ role, metadata }) as unknown as AiChatMessage;
+
+  it('reads the most recent assistant turn contextTokens (provider fact)', () => {
+    const hist = [
+      row('user', null),
+      row('assistant', { contextTokens: 12000 }),
+      row('user', null),
+      row('assistant', { contextTokens: 41000 }),
+    ];
+    expect(lastAssistantContextTokens(hist)).toBe(41000);
+  });
+
+  it('returns undefined when the last assistant turn recorded no usage', () => {
+    const hist = [row('assistant', { error: 'boom' }), row('user', null)];
+    expect(lastAssistantContextTokens(hist)).toBeUndefined();
+    expect(lastAssistantContextTokens([])).toBeUndefined();
+  });
+});
+
+// #490 snapshotOpenPage fast-path: skip the full Markdown export + upsert when a
+// snapshot already exists at the page's CURRENT version (same updated_at instant).
+describe('snapshotOpenPage fast-path (#490)', () => {
+  function makeSvc(existingSnapshot: unknown, pageUpdatedAt: Date) {
+    const exportPageMarkdown = jest.fn(async () => '# md');
+    const upsert = jest.fn(async () => undefined);
+    const findByChatPage = jest.fn(async () => existingSnapshot);
+    const pageRepo = {
+      findById: jest.fn(async () => ({
+        id: 'p1',
+        workspaceId: 'ws1',
+        updatedAt: pageUpdatedAt,
+      })),
+    };
+    const svc = new AiChatService(
+      {} as never, // ai
+      {} as never, // aiChatRepo
+      {} as never, // aiChatMessageRepo
+      { findByChatPage, upsert } as never, // aiChatPageSnapshotRepo
+      {} as never, // aiSettings
+      { exportPageMarkdown } as never, // tools
+      {} as never, // mcpClients
+      {} as never, // aiAgentRoleRepo
+      pageRepo as never, // pageRepo
+      {} as never, // pageAccess
+      {} as never, // environment
+    );
+    return { svc, exportPageMarkdown, upsert, findByChatPage };
+  }
+
+  const args = () =>
+    [
+      'chat1',
+      'p1',
+      { id: 'ws1' } as never,
+      { id: 'u1' } as never,
+      'sess',
+    ] as const;
+
+  it('skips export + upsert when the snapshot is already at this page version', async () => {
+    const t = new Date('2026-07-07T10:00:00Z');
+    const { svc, exportPageMarkdown, upsert } = makeSvc(
+      { pageUpdatedAt: t, contentMd: '# md' },
+      t,
+    );
+    await (svc as unknown as { snapshotOpenPage: (...a: unknown[]) => Promise<void> })
+      .snapshotOpenPage(...args());
+    expect(exportPageMarkdown).not.toHaveBeenCalled();
+    expect(upsert).not.toHaveBeenCalled();
+  });
+
+  it('exports + upserts when the page advanced since the snapshot', async () => {
+    const { svc, exportPageMarkdown, upsert } = makeSvc(
+      { pageUpdatedAt: new Date('2026-07-07T10:00:00Z'), contentMd: 'old' },
+      new Date('2026-07-07T11:00:00Z'),
+    );
+    await (svc as unknown as { snapshotOpenPage: (...a: unknown[]) => Promise<void> })
+      .snapshotOpenPage(...args());
+    expect(exportPageMarkdown).toHaveBeenCalledTimes(1);
+    expect(upsert).toHaveBeenCalledTimes(1);
+  });
+
+  it('seeds (exports + upserts) on the first turn (no snapshot yet)', async () => {
+    const { svc, exportPageMarkdown, upsert } = makeSvc(
+      undefined,
+      new Date('2026-07-07T10:00:00Z'),
+    );
+    await (svc as unknown as { snapshotOpenPage: (...a: unknown[]) => Promise<void> })
+      .snapshotOpenPage(...args());
+    expect(exportPageMarkdown).toHaveBeenCalledTimes(1);
+    expect(upsert).toHaveBeenCalledTimes(1);
+  });
+});
+
+// #490 deferred-tool activation persisted across turns.
+describe('seedActivatedTools', () => {
+  const valid = new Set(['Search_web', 'getPageJson', 'diffPageVersions']);
+
+  it('seeds from persisted metadata, intersected with current valid names', () => {
+    expect(
+      seedActivatedTools(
+        { activatedTools: ['Search_web', 'getPageJson'] },
+        valid,
+      ),
+    ).toEqual(['Search_web', 'getPageJson']);
+  });
+
+  it('drops a stored tool that is no longer valid (allowlist/role changed)', () => {
+    // 'Habr_publish' was activated before but is not in the current allowlist.
+    expect(
+      seedActivatedTools({ activatedTools: ['Search_web', 'Habr_publish'] }, valid),
+    ).toEqual(['Search_web']);
+  });
+
+  it('is empty/robust for missing, non-array, or unknown-shaped metadata', () => {
+    expect(seedActivatedTools(undefined, valid)).toEqual([]);
+    expect(seedActivatedTools({}, valid)).toEqual([]);
+    expect(seedActivatedTools({ activatedTools: 'nope' }, valid)).toEqual([]);
+    expect(
+      seedActivatedTools({ activatedTools: [1, 'getPageJson', null] }, valid),
+    ).toEqual(['getPageJson']);
+  });
+
+  it('de-duplicates stored names', () => {
+    expect(
+      seedActivatedTools(
+        { activatedTools: ['getPageJson', 'getPageJson'] },
+        valid,
+      ),
+    ).toEqual(['getPageJson']);
+  });
+});
+
+describe('lastAssistantReplayOverflow', () => {
+  const row = (
+    role: string,
+    metadata: Record<string, unknown> | null,
+  ): AiChatMessage => ({ role, metadata }) as unknown as AiChatMessage;
+
+  it('is true only when the LAST assistant turn overflowed', () => {
+    expect(
+      lastAssistantReplayOverflow([
+        row('assistant', { replayOverflow: true }),
+        row('user', null),
+      ]),
+    ).toBe(true);
+    // A recovered (later, non-overflow) assistant turn clears it.
+    expect(
+      lastAssistantReplayOverflow([
+        row('assistant', { replayOverflow: true }),
+        row('user', null),
+        row('assistant', { contextTokens: 5 }),
+      ]),
+    ).toBe(false);
+    expect(lastAssistantReplayOverflow([])).toBe(false);
+  });
 });
 
 describe('rowToUiMessage', () => {
@@ -618,6 +908,23 @@ describe('flushAssistant', () => {
     expect(flushed.metadata.error).toBe('boom');
   });
 
+  // #490 observability: the replay budgeter's decision is stamped on the turn.
+  it('records replayTrimmedToTokens + replayOverflow when provided', () => {
+    const f = flushAssistant([], '', 'error', {
+      error: 'ctx',
+      replayTrimmedToTokens: 42_000,
+      replayOverflow: true,
+    });
+    expect(f.metadata.replayTrimmedToTokens).toBe(42_000);
+    expect(f.metadata.replayOverflow).toBe(true);
+  });
+
+  it('omits the replay metadata when not provided', () => {
+    const f = flushAssistant([], '', 'completed', { finishReason: 'stop' });
+    expect('replayTrimmedToTokens' in f.metadata).toBe(false);
+    expect('replayOverflow' in f.metadata).toBe(false);
+  });
+
   // #274 observability: the page-change diff the agent saw this turn is persisted
   // to metadata.pageChanged when a non-empty diff was injected, and omitted when
   // the diff is empty/whitespace or the arg is not supplied.

apps/server/src/core/ai-chat/ai-chat.service.ts

@@ -55,6 +55,12 @@ import {
   type SelectionContext,
 } from './tools/current-page.util';
 import { roleModelOverride } from './roles/role-model-config';
+import {
+  resolveReplayBudget,
+  isContextOverflowError,
+  trimHistoryForReplay,
+  REPLAY_AGGRESSIVE_FRACTION,
+} from './history-budget';
 import {
   startSseHeartbeat,
   stripStreamingHopByHopHeaders,
@@ -127,6 +133,15 @@ const STEP_LIMIT_NO_ANSWER_MARKER =
 const OUTPUT_DEGENERATION_ERROR =
   'Output degeneration detected (repeated token loop)';
 
+// Prefix recorded on the assistant row when the provider rejected the turn for
+// CONTEXT OVERFLOW (#490): the replayed history exceeded the model's window. The
+// row is ALSO stamped `metadata.replayOverflow` so the NEXT turn's budgeter trims
+// aggressively (the reactive recovery — the overflowing turn had no usage signal
+// to trigger preventive trimming, so the classified 400 is what un-bricks it).
+export const CONTEXT_OVERFLOW_ERROR_PREFIX =
+  'Диалог превысил контекстное окно модели; история будет агрессивно ' +
+  'сокращена на следующем ходу.';
+
 /**
  * Compute the step-budget warning text (#444), or '' when this step is outside
  * the warning band. The warning fires on steps
@@ -882,6 +897,21 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
       const freshPage = await this.pageRepo.findById(pageId);
       // Page deleted during the turn (or somehow foreign) => don't write.
       if (!freshPage || freshPage.workspaceId !== workspace.id) return;
+      // Fast-path (#490): if a snapshot already exists at THIS page version
+      // (same updated_at instant), its content is already current — skip the full
+      // Markdown export + upsert entirely. A turn that did NOT touch the open page
+      // (the common case) thus does no snapshot work. This mirrors the read-side
+      // fast path in detectPageChange (sameInstant): both trust that a page edit
+      // bumps updated_at. When the agent (or a human) DID edit the page this turn,
+      // updated_at advanced, so this does not match and we re-export as before.
+      const existing = await this.aiChatPageSnapshotRepo.findByChatPage(
+        chatId,
+        pageId,
+        workspace.id,
+      );
+      if (existing && sameInstant(existing.pageUpdatedAt, freshPage.updatedAt)) {
+        return;
+      }
       const currentMd = await this.tools.exportPageMarkdown(
         user,
         sessionId,
@@ -921,10 +951,17 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
     // supplied or the supplied one does not belong to this workspace.
     let isNewChat = false;
     let chatId = body.chatId;
+    // Persisted chat-level metadata bag (#490): read once here so the deferred-tool
+    // activation set can be seeded from the previous turn. Undefined for a new chat.
+    let chatMetadata: Record<string, unknown> | undefined;
     if (chatId) {
       const existing = await this.aiChatRepo.findById(chatId, workspace.id);
       if (!existing) {
         chatId = undefined;
+      } else {
+        chatMetadata = (existing.metadata ?? undefined) as
+          | Record<string, unknown>
+          | undefined;
       }
     }
     // The open page the client sent is attacker-controllable — BOTH its id and
@@ -1086,7 +1123,7 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
       // per-row conversion and degraded to plain text with a "[tool context
       // omitted]" marker rather than 500-ing the whole turn (silent loss of tool
       // context is not acceptable — the model must see the truncation).
-      const messages = await convertHistoryResilient(uiMessages, (index, err) =>
+      let messages = await convertHistoryResilient(uiMessages, (index, err) =>
         this.logger.warn(
           `Degraded unconvertible history row ${index} on chat ${chatId} to text: ${
             err instanceof Error ? err.message : 'unknown error'
@@ -1135,6 +1172,58 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
       // Here we only need the admin-configured system prompt.
       const resolved = await this.aiSettings.resolve(workspace.id);
 
+      // History-replay token budget (#490). The full conversation is replayed to
+      // the provider every turn, so a long chat eventually 400s on the context
+      // window — forever. Bound the REPLAYED history (never the persisted rows).
+      // PRIMARY signal is the provider's own fact: the last turn's contextTokens.
+      const replayBudget = resolveReplayBudget(resolved?.chatContextWindowRaw);
+      if (replayBudget.usedDefault) {
+        // The default fires precisely for installs with NO configured window —
+        // the ones that hit terminal overflow. Warn so it is observable.
+        this.logger.warn(
+          `AI chat (chat ${chatId}): no chatContextWindow configured; ` +
+            `applying the default replay budget (${replayBudget.thresholdTokens} tokens).`,
+        );
+      }
+      // Last turn's provider-reported context size (authoritative when present).
+      const priorContextTokens = lastAssistantContextTokens(oldHistory);
+      // Reactive recovery (#490): if the LAST turn was rejected for context
+      // overflow (stamped by onError), trim AGGRESSIVELY this turn — the
+      // overflowing turn produced no usage signal, so a normal-threshold trim may
+      // not shrink enough to fit. This is what un-bricks a chat that just 400'd.
+      const priorOverflowed = lastAssistantReplayOverflow(oldHistory);
+      const effectiveThreshold =
+        priorOverflowed && replayBudget.thresholdTokens != null
+          ? Math.floor(
+              replayBudget.thresholdTokens * REPLAY_AGGRESSIVE_FRACTION,
+            )
+          : replayBudget.thresholdTokens;
+      if (priorOverflowed) {
+        this.logger.warn(
+          `AI chat (chat ${chatId}): previous turn hit context overflow; ` +
+            `applying aggressive replay budget (${effectiveThreshold} tokens).`,
+        );
+      }
+      const preTrim = trimHistoryForReplay(
+        messages,
+        effectiveThreshold,
+        // A prior OVERFLOW means the provider count is stale/absent — force the
+        // char-estimate path by ignoring priorContextTokens on recovery.
+        priorOverflowed ? undefined : priorContextTokens,
+      );
+      messages = preTrim.messages;
+      // Observability (#490): record the budgeter's decision on the turn so the UI
+      // can surface "replay truncated at N tokens". Threaded into flushAssistant.
+      let replayTrimmedToTokens: number | undefined = preTrim.trimmed
+        ? preTrim.estimatedTokens
+        : undefined;
+      if (preTrim.trimmed) {
+        this.logger.log(
+          `AI chat (chat ${chatId}): replay history trimmed to ~${preTrim.estimatedTokens} ` +
+            `tokens (budget ${replayBudget.thresholdTokens}).`,
+        );
+      }
+
       // Build the external MCP toolset FIRST so the system prompt can carry each
       // connected server's admin-authored guidance (#180). Merge in admin-
       // configured external MCP tools (web search, etc.; §6.8). A down/slow
@@ -1326,10 +1415,19 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
       //    tools + ALL external MCP tools), computed from the ACTUAL toolset so an
       //    external tool is loadable by its namespaced name. loadTools rejects any
       //    name outside this set.
-      const activatedTools = new Set<string>();
       const validDeferredNames = new Set<string>(
         Object.keys(baseTools).filter((k) => !CORE_TOOL_SET.has(k)),
       );
+      // #490: seed the activation set from the chat's PERSISTED set so the model
+      // does not re-run loadTools every turn to re-activate the same tools. Only
+      // when deferred loading is enabled, and ALWAYS intersected with the CURRENT
+      // valid deferred names — an allowlist/role change must never resurrect a tool
+      // that no longer exists (prepareAgentStep would get a phantom active name).
+      const activatedTools = new Set<string>(
+        deferredEnabled
+          ? seedActivatedTools(chatMetadata, validDeferredNames)
+          : [],
+      );
       // Add the loadTools meta-tool ONLY when the feature is enabled; when off the
       // toolset and behavior are exactly as before.
       const tools = deferredEnabled
@@ -1339,6 +1437,39 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
           }
         : baseTools;
 
+      // #490: persist the (deterministically ordered) activation set back onto the
+      // chat metadata at turn end, so the NEXT turn seeds from it. Once-guarded and
+      // skipped when nothing new was activated (the set equals its seed) so an
+      // ordinary turn adds no extra write. Preserves other metadata keys.
+      let activatedToolsPersisted = false;
+      const persistActivatedTools = async (): Promise<void> => {
+        if (!deferredEnabled || activatedToolsPersisted || !chatId) return;
+        activatedToolsPersisted = true;
+        const current = [...activatedTools].sort();
+        const seeded = seedActivatedTools(chatMetadata, validDeferredNames).sort();
+        if (current.length === 0 || current.join('') === seeded.join('')) {
+          return; // nothing new activated -> no write
+        }
+        try {
+          await this.aiChatRepo.update(
+            chatId,
+            {
+              metadata: {
+                ...(chatMetadata ?? {}),
+                activatedTools: current,
+              },
+            } as never,
+            workspace.id,
+          );
+        } catch (err) {
+          this.logger.warn(
+            `Failed to persist activated tools (chat ${chatId}): ${
+              err instanceof Error ? err.message : 'unknown error'
+            }`,
+          );
+        }
+      };
+
       // Accumulate the turn's streamed output so a provider error / disconnect can
       // persist the PARTIAL answer the user already saw — the SDK's onError/onAbort
       // callbacks don't hand us the in-progress text. `capturedSteps` holds finished
@@ -1347,6 +1478,11 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
       const capturedSteps: StepLike[] = [];
       let inProgressText = '';
 
+      // Per-turn step->parts memo (#490): shared across every flushAssistant call
+      // this turn so each finished step's (large) output is JSON-stringified ONCE,
+      // not re-stringified on every subsequent onStepFinish flush (was O(N²)).
+      const partsCache: StepPartsCache = new WeakMap();
+
       // Token-degeneration guard (#444). When the final-step lockdown is OFF, a
       // runaway repetition loop (the 255KB "loadTools." incident) is aborted via
       // this internal controller, unioned with the run/socket signal below. The
@@ -1416,7 +1552,10 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
           await this.aiChatMessageRepo.update(
             assistantId,
             workspace.id,
-            flushAssistant(capturedSteps, '', 'streaming', { pageChanged }),
+            flushAssistant(capturedSteps, '', 'streaming', {
+              pageChanged,
+              partsCache,
+            }),
             { onlyIfStreaming: true },
           );
         } catch (err) {
@@ -1649,6 +1788,8 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
                 // closure scope here). Omitted/0 = no limit.
                 maxContextTokens: resolved?.chatContextWindow,
                 pageChanged,
+                partsCache,
+                replayTrimmedToTokens,
               }),
             );
             // #184/#487: the RUN is finalized ALWAYS (never gated on the message).
@@ -1673,6 +1814,8 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
             // own edits are baked in — and this also SEEDS the snapshot on the first
             // turn. Runs once across every terminal path (see snapshotTurnEnd).
             await snapshotTurnEnd();
+            // #490: persist the deferred-tool activation set for the next turn.
+            await persistActivatedTools();
 
             // Generate the chat title for a freshly created chat AFTER the stream's
             // provider call has completed — NOT concurrently with it. The z.ai coding
@@ -1696,7 +1839,16 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
             // object, so the actual provider cause is clearly logged. Reuse the
             // shared formatter so provider error formatting stays unified.
             const e = error as { stack?: string };
-            const errorText = describeProviderError(error, String(error));
+            // #490 reactive branch: classify a CONTEXT-OVERFLOW rejection (the
+            // replayed history exceeded the model window). The overflowing turn had
+            // no prior usage to trigger preventive trimming, so we record a clear,
+            // distinguishable cause AND stamp the row so the NEXT turn's budgeter
+            // trims aggressively — the reactive recovery that un-bricks the chat.
+            const overflow = isContextOverflowError(error);
+            const providerError = describeProviderError(error, String(error));
+            const errorText = overflow
+              ? `${CONTEXT_OVERFLOW_ERROR_PREFIX} (${providerError})`
+              : providerError;
             this.logger.error(`AI chat stream error: ${errorText}`, e?.stack);
             // DIAGNOSTIC (Safari stream-drop investigation) — temporary: timing of
             // an error-terminated stream.
@@ -1714,6 +1866,9 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
               flushAssistant(capturedSteps, inProgressText, 'error', {
                 error: errorText,
                 pageChanged,
+                partsCache,
+                replayTrimmedToTokens,
+                replayOverflow: overflow || undefined,
               }),
             );
             // #184: settle the RUN as failed, carrying the provider/transport cause.
@@ -1723,6 +1878,8 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
             // committed before the error must be baked into the snapshot, or the
             // next turn would mis-report it as a user edit.
             await snapshotTurnEnd();
+            // #490: persist the deferred-tool activation set for the next turn.
+            await persistActivatedTools();
           },
           onAbort: async ({ steps }) => {
             // #444: distinguish a degeneration abort (our internal controller) from
@@ -1737,6 +1894,7 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
                 flushAssistant(capturedSteps, truncated, 'error', {
                   error: OUTPUT_DEGENERATION_ERROR,
                   pageChanged,
+                  partsCache,
                 }),
               );
               if (runId)
@@ -1747,6 +1905,8 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
                 );
               await closeExternalClients();
               await snapshotTurnEnd();
+              // #490: persist the deferred-tool activation set for the next turn.
+              await persistActivatedTools();
               return;
             }
             const partialChars =
@@ -1771,6 +1931,7 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
             await finalizeAssistant(
               flushAssistant(capturedSteps, inProgressText, 'aborted', {
                 pageChanged,
+                partsCache,
               }),
             );
             // #184: settle the RUN as aborted (an explicit user stop reached the
@@ -1781,6 +1942,8 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
             // committed before the client disconnect / stop() must be baked into the
             // snapshot, or the next turn would mis-report it as a user edit.
             await snapshotTurnEnd();
+            // #490: persist the deferred-tool activation set for the next turn.
+            await persistActivatedTools();
           },
         });
 
@@ -2091,6 +2254,70 @@ export function chatStreamMetadata(
   return undefined;
 }
 
+/**
+ * The provider-reported context size of the most recent assistant turn, read from
+ * its persisted `metadata.contextTokens` (#490 replay budgeter's PRIMARY signal —
+ * the provider's own fact, not an estimate). Returns undefined for a chat with no
+ * assistant turn yet, or one whose last turn recorded no usage (e.g. it errored),
+ * in which case the budgeter falls back to the char-estimate.
+ */
+export function lastAssistantContextTokens(
+  history: ReadonlyArray<AiChatMessage>,
+): number | undefined {
+  for (let i = history.length - 1; i >= 0; i--) {
+    const row = history[i];
+    if (row.role !== 'assistant') continue;
+    const meta = (row.metadata ?? {}) as { contextTokens?: unknown };
+    const n = meta.contextTokens;
+    return typeof n === 'number' && Number.isFinite(n) && n > 0 ? n : undefined;
+  }
+  return undefined;
+}
+
+/**
+ * Seed the per-turn deferred-tool activation set from a chat's persisted metadata
+ * (#490), INTERSECTED with the current valid deferred names. Persisting the set
+ * across turns saves the model re-running loadTools every turn to re-activate the
+ * same tools; intersecting on load means a changed allowlist / role can never
+ * resurrect a tool that no longer exists (which would hand prepareAgentStep a
+ * phantom active name). Tolerant of any stored shape — a non-array is ignored.
+ */
+export function seedActivatedTools(
+  metadata: Record<string, unknown> | undefined,
+  validDeferredNames: ReadonlySet<string>,
+): string[] {
+  const stored = metadata?.activatedTools;
+  if (!Array.isArray(stored)) return [];
+  const seen = new Set<string>();
+  const out: string[] = [];
+  for (const name of stored) {
+    if (typeof name === 'string' && validDeferredNames.has(name) && !seen.has(name)) {
+      seen.add(name);
+      out.push(name);
+    }
+  }
+  return out;
+}
+
+/**
+ * Whether the most recent assistant turn was rejected for CONTEXT OVERFLOW
+ * (#490): its row carries `metadata.replayOverflow` (stamped by the stream's
+ * onError). The next turn's budgeter reads this to trim aggressively — the
+ * reactive recovery. Only the LAST assistant turn matters (an older overflow was
+ * already recovered), so we stop at the first assistant row scanning backwards.
+ */
+export function lastAssistantReplayOverflow(
+  history: ReadonlyArray<AiChatMessage>,
+): boolean {
+  for (let i = history.length - 1; i >= 0; i--) {
+    const row = history[i];
+    if (row.role !== 'assistant') continue;
+    const meta = (row.metadata ?? {}) as { replayOverflow?: unknown };
+    return meta.replayOverflow === true;
+  }
+  return false;
+}
+
 /** The last message with role 'user' from a useChat payload, if any. */
 function lastUserMessage(
   messages: UIMessage[] | undefined,
@@ -2152,6 +2379,15 @@ export function sanitizeUserParts(
 /** Marker for a history row whose tool parts could not be replayed (#489). */
 export const TOOL_CONTEXT_OMITTED_MARKER = '[tool context omitted]';
 
+/**
+ * Synthetic error text for a tool call that neither returned a result nor threw
+ * a `tool-error` — i.e. it was interrupted mid-step (an abort / server restart).
+ * Shared by `assistantParts` (the replayed `output-error` part) and
+ * `serializeSteps` (the `{ kind: 'interrupted' }` trace element) so the replay
+ * text and the trace stay in lockstep (#490).
+ */
+export const TOOL_CALL_INCOMPLETE_TEXT = 'Tool call did not complete.';
+
 /**
  * Convert persisted UI history to model messages, tolerating a single poisoned
  * row (#489). `convertToModelMessages` over the WHOLE array throws if ANY row is
@@ -2359,71 +2595,97 @@ function normalizeToolError(error: unknown): string {
  */
 // Exported only so the unit tests can import these pure helpers; exporting
 // them does not change runtime behavior.
+/**
+ * Per-turn memo for {@link assistantParts}: a step's rebuilt parts keyed by the
+ * step OBJECT's identity (#490). A finished step in `capturedSteps` keeps a stable
+ * reference across every mid-stream flush, and `compactToolOutput` inside it does a
+ * `JSON.stringify` of the whole (often 50–200 KB) output — so without a memo each
+ * `onStepFinish` re-stringifies EVERY prior step's output (O(N²) stringify over a
+ * turn). Keyed by step identity => one stringify per step per turn. WeakMap so a
+ * turn's steps are GC'd with the turn.
+ */
+export type StepPartsCache = WeakMap<object, Array<Record<string, unknown>>>;
+
+/** Build the parts for ONE step (text + a part per tool call). Pure. */
+function buildStepParts(step: StepLike): Array<Record<string, unknown>> {
+  const parts: Array<Record<string, unknown>> = [];
+  if (step.text) {
+    parts.push({ type: 'text', text: step.text });
+  }
+  // Index this step's results by tool call id to pair calls with outputs.
+  const resultsById = new Map<string, unknown>();
+  for (const r of step.toolResults ?? []) {
+    if (r.toolCallId) resultsById.set(r.toolCallId, r.output);
+  }
+  // Index this step's THROWN tool failures (ai@6 `tool-error` content parts)
+  // by tool call id, so a call that failed replays with its real error text.
+  const errorsById = new Map<string, unknown>();
+  for (const part of step.content ?? []) {
+    if (part.type === 'tool-error' && part.toolCallId) {
+      errorsById.set(part.toolCallId, part.error);
+    }
+  }
+  for (const call of step.toolCalls ?? []) {
+    if (!call.toolName || !call.toolCallId) continue;
+    const hasResult = resultsById.has(call.toolCallId);
+    if (hasResult) {
+      // output-available: the tool returned; the next turn replays its result.
+      parts.push({
+        type: `tool-${call.toolName}`,
+        toolCallId: call.toolCallId,
+        state: 'output-available',
+        input: call.input,
+        output: compactToolOutput(resultsById.get(call.toolCallId)),
+      });
+    } else if (errorsById.has(call.toolCallId)) {
+      // The tool THREW: replay the REAL error so the model on the next turn
+      // knows WHY the call failed (and does not blindly repeat it). An
+      // output-error round-trips through convertToModelMessages as a balanced
+      // tool-call + tool-result, keeping the rebuilt history valid.
+      parts.push({
+        type: `tool-${call.toolName}`,
+        toolCallId: call.toolCallId,
+        state: 'output-error',
+        input: call.input,
+        errorText: normalizeToolError(errorsById.get(call.toolCallId)),
+      });
+    } else {
+      // No paired result AND no tool-error (e.g. aborted mid-step). Persisting
+      // a bare tool-call (input-available) would replay as an unpaired call and
+      // throw MissingToolResultsError on the next turn (convertToModelMessages
+      // emits no tool-result for it). Emit a SYNTHETIC paired result instead:
+      // an output-error round-trips through convertToModelMessages as a
+      // balanced tool-call + tool-result, keeping the rebuilt history valid.
+      parts.push({
+        type: `tool-${call.toolName}`,
+        toolCallId: call.toolCallId,
+        state: 'output-error',
+        input: call.input,
+        errorText: TOOL_CALL_INCOMPLETE_TEXT,
+      });
+    }
+  }
+  return parts;
+}
+
 export function assistantParts(
   steps: ReadonlyArray<StepLike> | undefined,
   fallbackText: string,
+  cache?: StepPartsCache,
 ): UIMessage['parts'] {
   const parts: Array<Record<string, unknown>> = [];
-  let sawText = false;
   for (const step of steps ?? []) {
-    if (step.text) {
-      parts.push({ type: 'text', text: step.text });
-      sawText = true;
-    }
-    // Index this step's results by tool call id to pair calls with outputs.
-    const resultsById = new Map<string, unknown>();
-    for (const r of step.toolResults ?? []) {
-      if (r.toolCallId) resultsById.set(r.toolCallId, r.output);
-    }
-    // Index this step's THROWN tool failures (ai@6 `tool-error` content parts)
-    // by tool call id, so a call that failed replays with its real error text.
-    const errorsById = new Map<string, unknown>();
-    for (const part of step.content ?? []) {
-      if (part.type === 'tool-error' && part.toolCallId) {
-        errorsById.set(part.toolCallId, part.error);
-      }
-    }
-    for (const call of step.toolCalls ?? []) {
-      if (!call.toolName || !call.toolCallId) continue;
-      const hasResult = resultsById.has(call.toolCallId);
-      if (hasResult) {
-        // output-available: the tool returned; the next turn replays its result.
-        parts.push({
-          type: `tool-${call.toolName}`,
-          toolCallId: call.toolCallId,
-          state: 'output-available',
-          input: call.input,
-          output: compactToolOutput(resultsById.get(call.toolCallId)),
-        });
-      } else if (errorsById.has(call.toolCallId)) {
-        // The tool THREW: replay the REAL error so the model on the next turn
-        // knows WHY the call failed (and does not blindly repeat it). An
-        // output-error round-trips through convertToModelMessages as a balanced
-        // tool-call + tool-result, keeping the rebuilt history valid.
-        parts.push({
-          type: `tool-${call.toolName}`,
-          toolCallId: call.toolCallId,
-          state: 'output-error',
-          input: call.input,
-          errorText: normalizeToolError(errorsById.get(call.toolCallId)),
-        });
-      } else {
-        // No paired result AND no tool-error (e.g. aborted mid-step). Persisting
-        // a bare tool-call (input-available) would replay as an unpaired call and
-        // throw MissingToolResultsError on the next turn (convertToModelMessages
-        // emits no tool-result for it). Emit a SYNTHETIC paired result instead:
-        // an output-error round-trips through convertToModelMessages as a
-        // balanced tool-call + tool-result, keeping the rebuilt history valid.
-        parts.push({
-          type: `tool-${call.toolName}`,
-          toolCallId: call.toolCallId,
-          state: 'output-error',
-          input: call.input,
-          errorText: 'Tool call did not complete.',
-        });
-      }
+    // Memoize per step object (#490): a finished step is immutable and keeps its
+    // reference across flushes, so its parts (and the costly output stringify) are
+    // built exactly once per turn. A cache miss (or no cache) just rebuilds.
+    let stepParts = cache?.get(step as object);
+    if (!stepParts) {
+      stepParts = buildStepParts(step);
+      cache?.set(step as object, stepParts);
     }
+    parts.push(...stepParts);
   }
+  const sawText = parts.some((p) => p.type === 'text');
   if (!sawText && fallbackText) {
     // No per-step text (e.g. a single final block): append the final text after
     // any tool parts so the natural call -> result -> answer order is preserved.
@@ -2586,6 +2848,16 @@ export function flushAssistant(
     maxContextTokens?: number;
     error?: string;
     pageChanged?: { title: string; diff: string } | null;
+    // Per-turn step->parts memo (#490): pass the SAME cache on every flush of a
+    // turn so each finished step's output is stringified once, not once per flush.
+    partsCache?: StepPartsCache;
+    // #490 observability: when the replay budgeter trimmed this turn's history,
+    // the (estimated) token size it trimmed to — the UI can show "replay truncated
+    // at N tokens". Omitted when nothing was trimmed.
+    replayTrimmedToTokens?: number;
+    // #490 reactive branch: set when the provider rejected this turn for context
+    // overflow. Stamped into metadata so the NEXT turn's budgeter trims aggressively.
+    replayOverflow?: boolean;
   },
 ): AssistantFlush {
   const finished = capturedSteps ?? [];
@@ -2595,13 +2867,20 @@ export function flushAssistant(
   // in-progress step's text (the partial answer cut off by an error/abort, or
   // simply not yet flushed mid-stream) as the last text part so the persisted
   // parts match what streamed to the client.
-  const parts = assistantParts(finished, '') as unknown as Array<
-    Record<string, unknown>
-  >;
+  const parts = assistantParts(
+    finished,
+    '',
+    extra?.partsCache,
+  ) as unknown as Array<Record<string, unknown>>;
   if (trailing) parts.push({ type: 'text', text: trailing });
 
   const metadata: Record<string, unknown> = {
     parts: parts as unknown as UIMessage['parts'],
+    // Era marker for the `tool_calls` trace shape (#490): v2 stores outcome flags
+    // ({ ok } / { error, kind }) and NO tool output (the output lives once in
+    // `parts`). Old rows have no marker and the legacy { output } shape; a
+    // dual-shape query branches on this. Old rows are deliberately NOT migrated.
+    toolTraceVersion: 2,
   };
   // finishReason: prefer an explicit one; else derive a sensible value from the
   // terminal status (so onError/onAbort records keep their historical reason).
@@ -2617,6 +2896,9 @@ export function flushAssistant(
   if (extra?.contextTokens) metadata.contextTokens = extra.contextTokens;
   if (extra?.maxContextTokens)
     metadata.maxContextTokens = extra.maxContextTokens;
+  if (extra?.replayTrimmedToTokens)
+    metadata.replayTrimmedToTokens = extra.replayTrimmedToTokens;
+  if (extra?.replayOverflow) metadata.replayOverflow = true;
   if (extra?.error) metadata.error = extra.error;
   // Persist the page-change diff the agent saw this turn (#274 observability),
   // so history / the Markdown export can show what the user changed. Only when
@@ -2642,42 +2924,85 @@ export function flushAssistant(
 
 /**
  * Reduce SDK step objects to a compact, JSON-serializable trace for the
- * `tool_calls` column. Stores only what the UI action-log and history need —
- * never raw provider payloads or keys.
+ * `tool_calls` column — trace format **v2** (#490).
+ *
+ * v2 stores, per call, ONLY the metadata a queryable trace needs — never the
+ * tool OUTPUT. Before #490 each output was persisted TWICE: once here (compacted)
+ * and once in `metadata.parts` (via `assistantParts`), so a 50-step run with
+ * 50–200 KB outputs wrote hundreds of MB per turn (each `onStepFinish` rewrote
+ * the whole row). The parts copy is the one the model replays and the UI/Markdown
+ * export render, so the trace copy of the output was pure duplication. v2 keeps
+ * the output ONLY in parts and reduces the trace to outcome flags.
+ *
+ * Element shapes (paired per call, in order):
+ *  - `{ toolName, input }`                       — the call
+ *  - `{ toolName, ok: true }`                     — it returned a result (success)
+ *  - `{ toolName, error, kind: 'thrown' }`        — it threw a `tool-error`
+ *  - `{ toolName, error, kind: 'interrupted' }`   — no result and no throw (an
+ *      abort / server restart mid-step). `kind` is MANDATORY: without it a
+ *      synthetic "Tool call did not complete." is indistinguishable from a real
+ *      hard-fail and pollutes any error-rate scan. The distinction is STRUCTURAL
+ *      (an `errorsById` hit vs the synthetic fallback branch), NOT a per-tool
+ *      classifier — soft failures stay OUT of the trace (they live in
+ *      `metadata.parts` outputs; a per-tool mirror would persist its own bugs).
+ *
+ * Rows carry `metadata.toolTraceVersion: 2` (set by {@link flushAssistant}) so a
+ * dual-shape query can branch on the era. Old rows are NOT migrated (rewriting
+ * giant jsonb is the very WAL churn this removes); see docs/reading-ai-logs.md.
  */
 export function serializeSteps(
   steps: ReadonlyArray<{
-    toolCalls?: ReadonlyArray<{ toolName?: string; input?: unknown }>;
-    toolResults?: ReadonlyArray<{ toolName?: string; output?: unknown }>;
+    toolCalls?: ReadonlyArray<{
+      toolCallId?: string;
+      toolName?: string;
+      input?: unknown;
+    }>;
+    toolResults?: ReadonlyArray<{ toolCallId?: string; toolName?: string }>;
     content?: ReadonlyArray<{
       type?: string;
+      toolCallId?: string;
       toolName?: string;
       error?: unknown;
     }>;
   }>,
 ): unknown {
-  const calls: Array<{
-    toolName?: string;
-    input?: unknown;
-    output?: unknown;
-    error?: string;
-  }> = [];
+  const calls: Array<
+    | { toolName?: string; input?: unknown }
+    | { toolName?: string; ok: true }
+    | { toolName?: string; error: string; kind: 'thrown' | 'interrupted' }
+  > = [];
   for (const step of steps ?? []) {
+    // Index this step's results + thrown errors by tool call id, so each call is
+    // paired with its outcome (mirrors assistantParts' pairing exactly).
+    const resultIds = new Set<string>();
+    for (const r of step.toolResults ?? []) {
+      if (r.toolCallId) resultIds.add(r.toolCallId);
+    }
+    const errorsById = new Map<string, unknown>();
+    for (const part of step.content ?? []) {
+      if (part.type === 'tool-error' && part.toolCallId) {
+        errorsById.set(part.toolCallId, part.error);
+      }
+    }
     for (const call of step.toolCalls ?? []) {
       calls.push({ toolName: call.toolName, input: call.input });
-    }
-    for (const r of step.toolResults ?? []) {
-      calls.push({ toolName: r.toolName, output: compactToolOutput(r.output) });
-    }
-    // ai@6 surfaces a THROWN tool failure as a `tool-error` content part, NOT as
-    // a `toolResults` entry. Record it as its own paired element (mirroring how a
-    // successful result is appended) so the failure and its reason survive in the
-    // trace instead of leaving an orphaned call with no result.
-    for (const part of step.content ?? []) {
-      if (part.type === 'tool-error') {
+      if (call.toolCallId && resultIds.has(call.toolCallId)) {
+        // Success: the output itself lives in metadata.parts, not here.
+        calls.push({ toolName: call.toolName, ok: true });
+      } else if (call.toolCallId && errorsById.has(call.toolCallId)) {
+        // Hard fail: the tool threw. Persist the real (bounded) reason.
         calls.push({
-          toolName: part.toolName,
-          error: normalizeToolError(part.error),
+          toolName: call.toolName,
+          error: normalizeToolError(errorsById.get(call.toolCallId)),
+          kind: 'thrown',
+        });
+      } else {
+        // Neither a result nor a throw: interrupted mid-step (abort/restart).
+        // Marked structurally so it never inflates a thrown-error count.
+        calls.push({
+          toolName: call.toolName,
+          error: TOOL_CALL_INCOMPLETE_TEXT,
+          kind: 'interrupted',
         });
       }
     }

apps/server/src/core/ai-chat/ai-chat.write-volume.spec.ts

@@ -0,0 +1,209 @@
+import { randomBytes } from 'crypto';
+import { Client } from 'pg';
+import { flushAssistant, serializeSteps } from './ai-chat.service';
+
+/**
+ * #490 write-volume regression — an OBSERVABLE-PROPERTY test on a LIVE Postgres,
+ * not "bytes through a mock repo" (a mock measures exactly the thing that does not
+ * hurt). It drives a realistic 50-step run where each step returns a ~100 KB tool
+ * output and, at every `onStepFinish`, UPDATEs the assistant row the way the
+ * service does — then reads the REAL write volume via the `pg_current_wal_lsn()`
+ * delta around the run.
+ *
+ * The property proven: v2 stores each tool OUTPUT only in `metadata.parts`, no
+ * longer ALSO in the `tool_calls` trace. So:
+ *   1. the trace (`tool_calls`) column's write volume is now O(Σ steps) — tiny,
+ *      linear outcome flags — vs the pre-#490 O(N²) that re-persisted every prior
+ *      output on every step; and
+ *   2. the FULL-row write volume drops sharply (the duplicated output copy is gone).
+ *
+ * Connects to the local gitmost test Postgres (docker `gitmost-test-pg` on :5432);
+ * SKIPS cleanly when that DB is not reachable so it never breaks a DB-less CI.
+ */
+const CONN =
+  process.env.WAL_TEST_DATABASE_URL ??
+  'postgresql://docmost:docmost_dev_pw@localhost:5432/docmost';
+
+// A step whose tool output is ~100 KB (a page read), in the SDK StepLike shape.
+// The body is INCOMPRESSIBLE random text — a `'x'.repeat()` filler would TOAST-
+// compress to nothing and hide the real write volume (a page body does not).
+function makeStep(i: number, outputBytes = 100_000) {
+  const body = randomBytes(Math.ceil(outputBytes * 0.75)).toString('base64');
+  return {
+    text: `step ${i} reasoning`,
+    toolCalls: [{ toolCallId: `c${i}`, toolName: 'getPage', input: { id: `p${i}` } }],
+    toolResults: [
+      {
+        toolCallId: `c${i}`,
+        toolName: 'getPage',
+        output: { id: `p${i}`, title: `Page ${i}`, body },
+      },
+    ],
+  };
+}
+
+// The pre-#490 (v1) trace: outputs stored a SECOND time in `tool_calls`
+// (the duplication #490 removed). Mirrors the OLD serializeSteps shape.
+function v1Trace(steps: ReturnType<typeof makeStep>[]): unknown {
+  const calls: unknown[] = [];
+  for (const s of steps) {
+    for (const c of s.toolCalls) calls.push({ toolName: c.toolName, input: c.input });
+    for (const r of s.toolResults)
+      calls.push({ toolName: r.toolName, output: r.output });
+  }
+  return calls;
+}
+
+async function walDelta(
+  client: Client,
+  fn: () => Promise<void>,
+): Promise<number> {
+  const before = (await client.query('SELECT pg_current_wal_lsn() AS l')).rows[0]
+    .l as string;
+  await fn();
+  // NOTE: do NOT pg_switch_wal() here — a segment switch pads the LSN to the next
+  // 16 MB boundary and would swamp the actual write delta. The raw LSN advances by
+  // the bytes of WAL emitted, which is exactly what we want to measure.
+  const after = (await client.query('SELECT pg_current_wal_lsn() AS l')).rows[0]
+    .l as string;
+  return Number(
+    (await client.query('SELECT pg_wal_lsn_diff($1,$2) AS d', [after, before]))
+      .rows[0].d,
+  );
+}
+
+describe('#490 write-volume on a live Postgres (pg_current_wal_lsn delta)', () => {
+  let client: Client | undefined;
+  let available = false;
+
+  beforeAll(async () => {
+    try {
+      client = new Client(CONN);
+      await client.connect();
+      await client.query('SELECT pg_current_wal_lsn()');
+      available = true;
+    } catch {
+      available = false;
+      client = undefined;
+    }
+  });
+
+  afterAll(async () => {
+    await client?.end().catch(() => undefined);
+  });
+
+  const STEPS = 50;
+
+  it('v2 trace write volume is O(Σ steps) — a tiny fraction of the v1 duplicate', async () => {
+    if (!available || !client) {
+      console.warn('SKIP: gitmost-test-pg not reachable; skipping WAL test.');
+      return;
+    }
+    const c = client;
+    // Isolated table so we measure only the tool_calls (trace) column's writes.
+    await c.query('DROP TABLE IF EXISTS _wal_trace');
+    await c.query('CREATE TABLE _wal_trace(id int primary key, tool_calls jsonb)');
+    await c.query("INSERT INTO _wal_trace VALUES (1, '[]'::jsonb)");
+
+    const steps: ReturnType<typeof makeStep>[] = [];
+
+    // v1: each step re-persists ALL prior outputs into the trace (the O(N²) churn).
+    const v1 = await walDelta(c, async () => {
+      const acc: ReturnType<typeof makeStep>[] = [];
+      for (let i = 0; i < STEPS; i++) {
+        acc.push(makeStep(i));
+        await c.query('UPDATE _wal_trace SET tool_calls=$1 WHERE id=1', [
+          JSON.stringify(v1Trace(acc)),
+        ]);
+      }
+      steps.push(...acc);
+    });
+
+    await c.query("UPDATE _wal_trace SET tool_calls='[]'::jsonb WHERE id=1");
+
+    // v2: the REAL serializeSteps — outcome flags only, NO outputs.
+    const v2 = await walDelta(c, async () => {
+      const acc: ReturnType<typeof makeStep>[] = [];
+      for (let i = 0; i < STEPS; i++) {
+        acc.push(makeStep(i));
+        await c.query('UPDATE _wal_trace SET tool_calls=$1 WHERE id=1', [
+          JSON.stringify(serializeSteps(acc)),
+        ]);
+      }
+    });
+
+    await c.query('DROP TABLE IF EXISTS _wal_trace');
+
+    // eslint-disable-next-line no-console
+    console.log(
+      `[#490 WAL] trace column over ${STEPS} steps: v1=${(v1 / 1e6).toFixed(1)}MB ` +
+        `v2=${(v2 / 1e6).toFixed(2)}MB (${(v1 / v2).toFixed(0)}x smaller)`,
+    );
+
+    // The trace no longer carries outputs: v2 is a tiny fraction of v1's WAL.
+    expect(v2).toBeLessThan(v1 * 0.1);
+    // And v2's trace WAL is small in absolute terms — O(Σ steps) of flags, not
+    // O(N² × output). 50 steps of ~40-byte flags is well under a few MB of WAL.
+    expect(v2).toBeLessThan(5_000_000);
+    // v1's duplicate alone is huge (≈ the 100 KB output re-written N² times).
+    expect(v1).toBeGreaterThan(50_000_000);
+  }, 120_000);
+
+  it('the full assistant row write drops sharply once the duplicate is gone', async () => {
+    if (!available || !client) return;
+    const c = client;
+    await c.query('DROP TABLE IF EXISTS _wal_full');
+    await c.query(
+      'CREATE TABLE _wal_full(id int primary key, content text, tool_calls jsonb, metadata jsonb, status text)',
+    );
+    await c.query("INSERT INTO _wal_full VALUES (1, '', '[]'::jsonb, '{}'::jsonb, 'streaming')");
+
+    const writeRow = async (patch: {
+      content: string;
+      toolCalls: unknown;
+      metadata: unknown;
+      status: string;
+    }) =>
+      c.query(
+        'UPDATE _wal_full SET content=$1, tool_calls=$2, metadata=$3, status=$4 WHERE id=1',
+        [
+          patch.content,
+          JSON.stringify(patch.toolCalls ?? null),
+          JSON.stringify(patch.metadata),
+          patch.status,
+        ],
+      );
+
+    // v2 (real flushAssistant): outputs live once, in metadata.parts.
+    const v2 = await walDelta(c, async () => {
+      const acc: ReturnType<typeof makeStep>[] = [];
+      for (let i = 0; i < STEPS; i++) {
+        acc.push(makeStep(i));
+        await writeRow(flushAssistant(acc as never, '', 'streaming'));
+      }
+    });
+
+    await c.query("UPDATE _wal_full SET content='', tool_calls='[]'::jsonb, metadata='{}'::jsonb WHERE id=1");
+
+    // v1: same row PLUS the duplicated outputs in the trace column.
+    const v1 = await walDelta(c, async () => {
+      const acc: ReturnType<typeof makeStep>[] = [];
+      for (let i = 0; i < STEPS; i++) {
+        acc.push(makeStep(i));
+        const f = flushAssistant(acc as never, '', 'streaming');
+        await writeRow({ ...f, toolCalls: v1Trace(acc) });
+      }
+    });
+
+    await c.query('DROP TABLE IF EXISTS _wal_full');
+
+    // eslint-disable-next-line no-console
+    console.log(
+      `[#490 WAL] full row over ${STEPS} steps: v1=${(v1 / 1e6).toFixed(1)}MB ` +
+        `v2=${(v2 / 1e6).toFixed(1)}MB (saved ${((1 - v2 / v1) * 100).toFixed(0)}%)`,
+    );
+
+    // Removing the duplicated trace copy is a large, real write-volume reduction.
+    expect(v2).toBeLessThan(v1 * 0.75);
+  }, 120_000);
+});

apps/server/src/core/ai-chat/history-budget.spec.ts

@@ -0,0 +1,266 @@
+import type { ModelMessage } from 'ai';
+import {
+  resolveReplayBudget,
+  isContextOverflowError,
+  estimateMessagesTokens,
+  trimHistoryForReplay,
+  REPLAY_BUDGET_DEFAULT_TOKENS,
+  REPLAY_TRUNCATION_MARKER,
+  REPLAY_TURN_COLLAPSED_MARKER,
+} from './history-budget';
+
+describe('resolveReplayBudget', () => {
+  it('uses min(default, 0.7 x window) for a configured window', () => {
+    // 0.7 x 60k = 42k < 100k
+    expect(resolveReplayBudget(60_000)).toEqual({
+      thresholdTokens: 42_000,
+      usedDefault: false,
+    });
+    // 0.7 x 1M = 700k, capped to the 100k default
+    expect(resolveReplayBudget(1_000_000)).toEqual({
+      thresholdTokens: REPLAY_BUDGET_DEFAULT_TOKENS,
+      usedDefault: false,
+    });
+  });
+
+  it('accepts the raw ::text stored form', () => {
+    expect(resolveReplayBudget('60000').thresholdTokens).toBe(42_000);
+  });
+
+  // The crux (#490): a chat with NO context window configured must STILL be
+  // budgeted — those are exactly the installs that hit terminal overflow.
+  it('applies the flat default when the window is unset/empty', () => {
+    expect(resolveReplayBudget(undefined)).toEqual({
+      thresholdTokens: REPLAY_BUDGET_DEFAULT_TOKENS,
+      usedDefault: true,
+    });
+    expect(resolveReplayBudget('')).toEqual({
+      thresholdTokens: REPLAY_BUDGET_DEFAULT_TOKENS,
+      usedDefault: true,
+    });
+    expect(resolveReplayBudget('   ')).toEqual({
+      thresholdTokens: REPLAY_BUDGET_DEFAULT_TOKENS,
+      usedDefault: true,
+    });
+  });
+
+  it('treats an explicit 0 as the off-switch (distinct from unset)', () => {
+    expect(resolveReplayBudget(0)).toEqual({
+      thresholdTokens: null,
+      usedDefault: false,
+    });
+    expect(resolveReplayBudget('0')).toEqual({
+      thresholdTokens: null,
+      usedDefault: false,
+    });
+  });
+
+  it('falls back to the default on a negative/garbage value', () => {
+    expect(resolveReplayBudget(-5).usedDefault).toBe(true);
+    expect(resolveReplayBudget('abc').usedDefault).toBe(true);
+  });
+});
+
+describe('isContextOverflowError', () => {
+  it('classifies a real provider 400 context-overflow shape', () => {
+    // OpenAI-compatible shape.
+    expect(
+      isContextOverflowError({
+        statusCode: 400,
+        message:
+          "This model's maximum context length is 128000 tokens. However, your messages resulted in 214000 tokens. Please reduce the length of the messages.",
+      }),
+    ).toBe(true);
+    // Anthropic-style wording.
+    expect(
+      isContextOverflowError({
+        status: 400,
+        message: 'prompt is too long: 250000 tokens > 200000 maximum',
+      }),
+    ).toBe(true);
+    // Nested body + string status.
+    expect(
+      isContextOverflowError({
+        response: { status: '400' },
+        message: 'input is too long for the requested model',
+      }),
+    ).toBe(true);
+    // Error instance with the cause carrying the body.
+    const e = new Error('Bad request');
+    (e as any).statusCode = 400;
+    (e as any).cause = new Error('maximum context window exceeded');
+    expect(isContextOverflowError(e)).toBe(true);
+  });
+
+  it('does NOT classify unrelated 400s or auth/rate-limit errors', () => {
+    expect(
+      isContextOverflowError({ statusCode: 400, message: 'invalid tool schema' }),
+    ).toBe(false);
+    expect(
+      isContextOverflowError({
+        statusCode: 429,
+        message: 'context length exceeded but rate limited',
+      }),
+    ).toBe(false);
+    expect(isContextOverflowError({ statusCode: 500, message: 'server error' })).toBe(
+      false,
+    );
+    expect(isContextOverflowError(undefined)).toBe(false);
+    expect(isContextOverflowError('some random string')).toBe(false);
+  });
+});
+
+// Helpers to build ModelMessage fixtures in the ai@6 shape.
+const userMsg = (text: string): ModelMessage =>
+  ({ role: 'user', content: [{ type: 'text', text }] }) as ModelMessage;
+const assistantMsg = (
+  text: string,
+  toolCallId?: string,
+  toolName?: string,
+): ModelMessage =>
+  ({
+    role: 'assistant',
+    content: [
+      { type: 'text', text },
+      ...(toolCallId
+        ? [{ type: 'tool-call', toolCallId, toolName, input: {} }]
+        : []),
+    ],
+  }) as ModelMessage;
+const toolMsg = (
+  toolCallId: string,
+  toolName: string,
+  value: unknown,
+): ModelMessage =>
+  ({
+    role: 'tool',
+    content: [
+      { type: 'tool-result', toolCallId, toolName, output: { type: 'json', value } },
+    ],
+  }) as ModelMessage;
+
+describe('trimHistoryForReplay', () => {
+  it('null budget disables trimming (returns the same reference)', () => {
+    const msgs = [userMsg('hi'), assistantMsg('yo')];
+    const r = trimHistoryForReplay(msgs, null);
+    expect(r.trimmed).toBe(false);
+    expect(r.messages).toBe(msgs);
+  });
+
+  it('leaves history under budget untouched (same reference)', () => {
+    const msgs = [userMsg('hi'), assistantMsg('a short answer')];
+    const r = trimHistoryForReplay(msgs, 100_000);
+    expect(r.trimmed).toBe(false);
+    expect(r.messages).toBe(msgs);
+  });
+
+  it('truncates OLD tool outputs but keeps recent turns full', () => {
+    const big = 'X'.repeat(40_000); // ~16k tokens on its own
+    const msgs: ModelMessage[] = [];
+    // 6 OLD turns (indices 0..5), each with a huge tool output.
+    for (let i = 0; i < 6; i++) {
+      msgs.push(userMsg(`old q${i}`));
+      msgs.push(assistantMsg('looking', `c${i}`, 'getPage'));
+      msgs.push(toolMsg(`c${i}`, 'getPage', { body: big }));
+      msgs.push(assistantMsg(`old a${i}`));
+    }
+    // 3 small recent turns, then the CURRENT turn with its own huge tool output.
+    // With REPLAY_KEEP_RECENT_TURNS=4 the last 4 user-turns stay full, so only
+    // these small recent turns + the current big one are kept full; the 6 old
+    // turns above fall in the trim region.
+    for (let i = 0; i < 3; i++) {
+      msgs.push(userMsg(`recent q${i}`));
+      msgs.push(assistantMsg(`recent a${i}`));
+    }
+    msgs.push(userMsg('current q'));
+    msgs.push(assistantMsg('looking', 'cR', 'getPage'));
+    msgs.push(toolMsg('cR', 'getPage', { body: big }));
+    msgs.push(assistantMsg('current a'));
+
+    // Budget large enough that phase-1 tool truncation alone brings it under.
+    const r = trimHistoryForReplay(msgs, 30_000);
+    expect(r.trimmed).toBe(true);
+    const flat = JSON.stringify(r.messages);
+    // The CURRENT turn's tool output survives in full.
+    expect(flat).toContain(big);
+    // Old outputs were truncated with the marker.
+    expect(flat).toContain(REPLAY_TRUNCATION_MARKER);
+    // Phase 1 sufficed: the oldest turns were NOT collapsed.
+    expect(flat).not.toContain(REPLAY_TURN_COLLAPSED_MARKER);
+    expect(estimateMessagesTokens(r.messages)).toBeLessThan(
+      estimateMessagesTokens(msgs),
+    );
+  });
+
+  it('collapses the oldest turns when tool truncation is not enough', () => {
+    // Many turns with LARGE assistant TEXT (not tool output) so phase 1 can't help.
+    const bigText = 'слово '.repeat(8_000); // large Cyrillic text per turn
+    const msgs: ModelMessage[] = [];
+    for (let i = 0; i < 12; i++) {
+      msgs.push(userMsg(`q${i}`));
+      msgs.push(assistantMsg(bigText));
+    }
+    const r = trimHistoryForReplay(msgs, 30_000);
+    expect(r.trimmed).toBe(true);
+    // Oldest turns collapsed; result fits (best-effort) and is much smaller.
+    expect(estimateMessagesTokens(r.messages)).toBeLessThan(
+      estimateMessagesTokens(msgs),
+    );
+    // The LAST turn's text is preserved in full (recent turns stay full).
+    expect(JSON.stringify(r.messages[r.messages.length - 1])).toContain(bigText);
+  });
+
+  it('is deterministic / byte-stable for identical inputs', () => {
+    const big = 'Y'.repeat(30_000);
+    const build = (): ModelMessage[] => {
+      const m: ModelMessage[] = [];
+      for (let i = 0; i < 10; i++) {
+        m.push(userMsg(`q${i}`));
+        m.push(assistantMsg('t', `c${i}`, 'getPage'));
+        m.push(toolMsg(`c${i}`, 'getPage', { body: big }));
+      }
+      return m;
+    };
+    const a = trimHistoryForReplay(build(), 15_000);
+    const b = trimHistoryForReplay(build(), 15_000);
+    expect(JSON.stringify(a.messages)).toBe(JSON.stringify(b.messages));
+  });
+
+  it('never leaves an unpaired tool-call after collapsing (balanced history)', () => {
+    const big = 'Z'.repeat(40_000);
+    const msgs: ModelMessage[] = [];
+    for (let i = 0; i < 10; i++) {
+      msgs.push(userMsg(`q${i}`));
+      msgs.push(assistantMsg('t', `c${i}`, 'getPage'));
+      msgs.push(toolMsg(`c${i}`, 'getPage', { body: big }));
+    }
+    const r = trimHistoryForReplay(msgs, 8_000);
+    // Count tool-call vs tool-result parts in the trimmed output.
+    let calls = 0;
+    let results = 0;
+    for (const m of r.messages) {
+      if (!Array.isArray(m.content)) continue;
+      for (const p of m.content as Array<{ type?: string }>) {
+        if (p.type === 'tool-call') calls++;
+        if (p.type === 'tool-result' || p.type === 'tool-error') results++;
+      }
+    }
+    // Every surviving tool-call has a surviving result (collapsing drops BOTH).
+    expect(calls).toBe(results);
+    // Collapsed turns carry the marker.
+    expect(JSON.stringify(r.messages)).toContain(REPLAY_TURN_COLLAPSED_MARKER);
+  });
+
+  it('respects the provider fact: under-budget contextTokens skips trimming', () => {
+    const big = 'W'.repeat(60_000);
+    const msgs = [
+      userMsg('q'),
+      assistantMsg('t', 'c1', 'getPage'),
+      toolMsg('c1', 'getPage', { body: big }),
+    ];
+    // char-estimate is high, but the provider says we are well under budget.
+    const r = trimHistoryForReplay(msgs, 100_000, 5_000);
+    expect(r.trimmed).toBe(false);
+    expect(r.messages).toBe(msgs);
+  });
+});

apps/server/src/core/ai-chat/history-budget.ts

@@ -0,0 +1,356 @@
+/**
+ * History-replay token budget (#490).
+ *
+ * The whole persisted conversation is replayed to the provider on EVERY turn, so
+ * a long chat eventually exceeds the model's context window and the provider 400s
+ * on every turn — terminally (the chat "bricks"). This module bounds the replayed
+ * history at REPLAY TIME only: it never mutates what is persisted (the DB stays
+ * the full record), and its output is a deterministic, byte-stable function of its
+ * input so the trimmed prefix is identical turn to turn (provider prompt-cache
+ * friendliness — real money on long chats).
+ *
+ * The PRIMARY signal is the provider's own fact: `metadata.contextTokens` from the
+ * last turn. The chars-based {@link estimateTokens} (shared with the client) is
+ * used only for the DELTA of not-yet-sent messages, to decide WHAT to trim, and as
+ * the fallback for chats with no usage yet.
+ */
+import type { ModelMessage } from 'ai';
+import { estimateTokens } from '@docmost/token-estimate';
+
+/** Flat default budget when no context window is configured (tokens). */
+export const REPLAY_BUDGET_DEFAULT_TOKENS = 100_000;
+/** Fraction of a configured context window used as the budget. */
+export const REPLAY_BUDGET_WINDOW_FRACTION = 0.7;
+/**
+ * Fraction of the normal budget used for the REACTIVE re-trim after a provider
+ * context-overflow 400 — the preventive estimate under-counted, so cut harder.
+ */
+export const REPLAY_AGGRESSIVE_FRACTION = 0.5;
+/**
+ * Turns (a user message + its assistant/tool replies) kept FULL at the tail,
+ * including the current one — never trimmed. Older turns are compacted first.
+ */
+export const REPLAY_KEEP_RECENT_TURNS = 4;
+/** Leading chars kept from a truncated old tool output. */
+export const REPLAY_TOOL_OUTPUT_HEAD = 800;
+/** Trailing chars kept from a truncated old tool output. */
+export const REPLAY_TOOL_OUTPUT_TAIL = 300;
+/** Marker inserted where an old tool output was truncated for replay. */
+export const REPLAY_TRUNCATION_MARKER =
+  '[…truncated for replay; call the tool again to read the full output]';
+/** Marker for a whole old turn collapsed to its text. */
+export const REPLAY_TURN_COLLAPSED_MARKER =
+  '[earlier tool activity omitted for replay]';
+
+export interface ReplayBudget {
+  /** Token threshold above which replay history is trimmed; `null` = OFF. */
+  thresholdTokens: number | null;
+  /** True when the flat default was used (no context window configured). */
+  usedDefault: boolean;
+}
+
+/**
+ * Resolve the replay budget from the RAW stored `chatContextWindow` (text/number).
+ *  - a positive value  -> `min(default, floor(fraction × window))`
+ *  - explicit `0`       -> OFF (admin opt-out; `null` threshold)
+ *  - unset/empty/invalid-> the flat default (still protects — the installations
+ *    that hit terminal overflow are exactly the ones that never set a window)
+ *
+ * Note the raw value is needed because the parsed `chatContextWindow` collapses
+ * both `0` and unset to `undefined`, which would erase the explicit off-switch.
+ */
+export function resolveReplayBudget(rawContextWindow: unknown): ReplayBudget {
+  let n: number | undefined;
+  if (typeof rawContextWindow === 'number') {
+    n = rawContextWindow;
+  } else if (typeof rawContextWindow === 'string') {
+    const t = rawContextWindow.trim();
+    n = t === '' ? undefined : Number(t);
+  }
+  // Unset / empty / non-numeric / negative -> flat default (the protective case).
+  if (n === undefined || !Number.isFinite(n) || n < 0) {
+    return { thresholdTokens: REPLAY_BUDGET_DEFAULT_TOKENS, usedDefault: true };
+  }
+  // Explicit 0 -> off-switch.
+  if (n === 0) {
+    return { thresholdTokens: null, usedDefault: false };
+  }
+  return {
+    thresholdTokens: Math.min(
+      REPLAY_BUDGET_DEFAULT_TOKENS,
+      Math.floor(REPLAY_BUDGET_WINDOW_FRACTION * n),
+    ),
+    usedDefault: false,
+  };
+}
+
+/**
+ * True when a provider error is a CONTEXT-OVERFLOW rejection (the prompt exceeds
+ * the model's window). Providers surface this as an HTTP 400 with a recognizable
+ * message; match both the status and the message patterns robustly across
+ * OpenAI-compatible / Anthropic / Gemini wordings, since the exact shape varies.
+ */
+export function isContextOverflowError(error: unknown): boolean {
+  const status = extractStatus(error);
+  const msg = extractMessage(error).toLowerCase();
+  // Message patterns seen across providers for "prompt too long".
+  const overflowPattern =
+    /context (?:length|window)|maximum context|too many tokens|too large for|reduce the length|prompt is too long|input (?:is )?too long|exceeds? the (?:maximum )?(?:context|token)|maximum.*tokens|string too long/;
+  if (!overflowPattern.test(msg)) return false;
+  // A 400/413 with an overflow-shaped message is an overflow. Some providers
+  // omit/rewrite the status, so accept the message match when the status is
+  // unknown, but reject it for auth/rate-limit statuses that never mean overflow.
+  if (status === 400 || status === 413) return true;
+  if (status === 401 || status === 403 || status === 429) return false;
+  return true;
+}
+
+function extractStatus(error: unknown): number | undefined {
+  if (!error || typeof error !== 'object') return undefined;
+  const e = error as Record<string, unknown>;
+  for (const k of ['statusCode', 'status']) {
+    const v = e[k];
+    if (typeof v === 'number') return v;
+    if (typeof v === 'string' && /^\d+$/.test(v)) return Number(v);
+  }
+  // Nested (e.g. { response: { status } } / { cause: { statusCode } }).
+  for (const k of ['response', 'cause', 'data']) {
+    const nested = e[k];
+    if (nested && typeof nested === 'object') {
+      const s = extractStatus(nested);
+      if (s !== undefined) return s;
+    }
+  }
+  return undefined;
+}
+
+function extractMessage(error: unknown): string {
+  if (error == null) return '';
+  if (typeof error === 'string') return error;
+  if (error instanceof Error) {
+    // Include nested causes (provider libs wrap the real body in `cause`).
+    const cause = (error as { cause?: unknown }).cause;
+    return `${error.message} ${cause ? extractMessage(cause) : ''}`;
+  }
+  if (typeof error === 'object') {
+    const e = error as Record<string, unknown>;
+    const parts: string[] = [];
+    for (const k of ['message', 'error', 'body', 'responseBody', 'data']) {
+      const v = e[k];
+      if (typeof v === 'string') parts.push(v);
+      else if (v && typeof v === 'object') parts.push(extractMessage(v));
+    }
+    return parts.join(' ');
+  }
+  return String(error);
+}
+
+/** Rough token size of a ModelMessage array via the shared chars estimator. */
+export function estimateMessagesTokens(
+  messages: ReadonlyArray<ModelMessage>,
+): number {
+  let total = 0;
+  for (const m of messages) {
+    total += estimateTokens(serializeContent(m.content));
+  }
+  return total;
+}
+
+function serializeContent(content: unknown): string {
+  if (typeof content === 'string') return content;
+  try {
+    return JSON.stringify(content) ?? '';
+  } catch {
+    return '';
+  }
+}
+
+/** Deep JSON string of an arbitrary value, bounded so estimation never throws. */
+function stringifyValue(value: unknown): string {
+  if (typeof value === 'string') return value;
+  try {
+    return JSON.stringify(value) ?? String(value);
+  } catch {
+    return String(value);
+  }
+}
+
+export interface TrimResult {
+  messages: ModelMessage[];
+  /** Whether any trimming was applied. */
+  trimmed: boolean;
+  /** Estimated tokens of the returned messages (chars-based). */
+  estimatedTokens: number;
+}
+
+/**
+ * Bound the replayed history to `budgetTokens`, deterministically. Returns the
+ * SAME array reference (no copy) when nothing needs trimming, so the common case
+ * is free and byte-identical. Trimming order (spec #490):
+ *   1. truncate OLD turns' tool outputs (head+tail + marker) — the bulk of the size
+ *   2. mechanically collapse the OLDEST turns to their text (concatenation, no LLM)
+ *   3. the current + last {@link REPLAY_KEEP_RECENT_TURNS} turns stay FULL
+ *
+ * `budgetTokens === null` disables trimming. `priorContextTokens` (the provider's
+ * fact from last turn) short-circuits the decision: when it is known and already
+ * under budget we skip trimming even if the char-estimate is higher (the provider
+ * count is authoritative). The char-estimate drives WHAT to cut.
+ */
+export function trimHistoryForReplay(
+  messages: ModelMessage[],
+  budgetTokens: number | null,
+  priorContextTokens?: number,
+): TrimResult {
+  if (budgetTokens == null) {
+    return { messages, trimmed: false, estimatedTokens: 0 };
+  }
+  const estimated = estimateMessagesTokens(messages);
+  // Decision signal: prefer the provider's fact (last turn's contextTokens) plus
+  // the estimated delta of the messages appended since; fall back to the pure
+  // char-estimate for a chat with no usage yet.
+  const projected =
+    priorContextTokens != null
+      ? Math.max(priorContextTokens, estimated)
+      : estimated;
+  if (projected <= budgetTokens) {
+    return { messages, trimmed: false, estimatedTokens: estimated };
+  }
+
+  // The tail we always keep full: from the Nth-from-last user message onward.
+  const boundary = recentBoundaryIndex(messages, REPLAY_KEEP_RECENT_TURNS);
+  const tail = messages.slice(boundary);
+  let head = messages.slice(0, boundary).map(cloneMessage);
+
+  // Phase 1: truncate old tool outputs.
+  for (const m of head) {
+    if (m.role === 'tool') truncateToolMessage(m);
+  }
+  let out = [...head, ...tail];
+  let est = estimateMessagesTokens(out);
+  if (est <= budgetTokens) {
+    return { messages: out, trimmed: true, estimatedTokens: est };
+  }
+
+  // Phase 2: collapse the oldest turns (in `head`) to their text, one at a time,
+  // from the oldest, until we fit or the whole head is collapsed.
+  const turns = splitTurns(head);
+  const collapsed: ModelMessage[] = [];
+  let i = 0;
+  for (; i < turns.length; i++) {
+    if (est <= budgetTokens) break;
+    collapsed.push(...collapseTurn(turns[i]));
+    // Re-estimate the whole prospective output.
+    const remaining = turns.slice(i + 1).flat();
+    out = [...collapsed, ...remaining, ...tail];
+    est = estimateMessagesTokens(out);
+  }
+  // Include any turns we didn't need to collapse.
+  const remaining = turns.slice(i).flat();
+  out = [...collapsed, ...remaining, ...tail];
+  est = estimateMessagesTokens(out);
+  return { messages: out, trimmed: true, estimatedTokens: est };
+}
+
+/** Index of the first message of the Nth-from-last user turn (0 if fewer). */
+function recentBoundaryIndex(
+  messages: ReadonlyArray<ModelMessage>,
+  keepTurns: number,
+): number {
+  const userIdx: number[] = [];
+  for (let i = 0; i < messages.length; i++) {
+    if (messages[i].role === 'user') userIdx.push(i);
+  }
+  if (userIdx.length <= keepTurns) return 0;
+  return userIdx[userIdx.length - keepTurns];
+}
+
+/** Split a message list into turns; each turn starts at a `user` message. */
+function splitTurns(messages: ModelMessage[]): ModelMessage[][] {
+  const turns: ModelMessage[][] = [];
+  for (const m of messages) {
+    if (m.role === 'user' || turns.length === 0) turns.push([m]);
+    else turns[turns.length - 1].push(m);
+  }
+  return turns;
+}
+
+/**
+ * Collapse a whole turn to its plain text (mechanical concatenation, not an LLM
+ * summary). Keeps the user message; replaces the assistant/tool messages with a
+ * single assistant text message = the assistant's concatenated text + a marker
+ * when tool activity was dropped. Dropping BOTH the tool-call and tool-result
+ * parts together keeps the rebuilt history balanced (no unpaired calls).
+ */
+function collapseTurn(turn: ModelMessage[]): ModelMessage[] {
+  const out: ModelMessage[] = [];
+  let assistantText = '';
+  let hadTools = false;
+  for (const m of turn) {
+    if (m.role === 'user') {
+      out.push(m);
+    } else if (m.role === 'assistant') {
+      const { text, tools } = extractAssistantText(m.content);
+      assistantText += text;
+      hadTools = hadTools || tools;
+    } else if (m.role === 'tool') {
+      hadTools = true;
+    } else {
+      out.push(m);
+    }
+  }
+  const note =
+    (assistantText ? assistantText.trimEnd() : '') +
+    (hadTools
+      ? `${assistantText ? '\n\n' : ''}${REPLAY_TURN_COLLAPSED_MARKER}`
+      : '');
+  if (note) out.push({ role: 'assistant', content: note } as ModelMessage);
+  return out;
+}
+
+function extractAssistantText(content: unknown): {
+  text: string;
+  tools: boolean;
+} {
+  if (typeof content === 'string') return { text: content, tools: false };
+  if (!Array.isArray(content)) return { text: '', tools: false };
+  let text = '';
+  let tools = false;
+  for (const part of content) {
+    const type = (part as { type?: string })?.type;
+    if (type === 'text') text += (part as { text?: string }).text ?? '';
+    else if (type === 'tool-call') tools = true;
+  }
+  return { text, tools };
+}
+
+/** Truncate every tool-result output in a `tool` message to head+tail+marker. */
+function truncateToolMessage(message: ModelMessage): void {
+  const content = message.content;
+  if (!Array.isArray(content)) return;
+  for (const part of content) {
+    const p = part as { type?: string; output?: { type?: string; value?: unknown } };
+    if (p.type !== 'tool-result' && p.type !== 'tool-error') continue;
+    if (!p.output) continue;
+    const raw = stringifyValue(p.output.value);
+    const budget = REPLAY_TOOL_OUTPUT_HEAD + REPLAY_TOOL_OUTPUT_TAIL;
+    if (raw.length <= budget + REPLAY_TRUNCATION_MARKER.length) continue;
+    const truncated =
+      raw.slice(0, REPLAY_TOOL_OUTPUT_HEAD) +
+      `\n${REPLAY_TRUNCATION_MARKER}\n` +
+      raw.slice(raw.length - REPLAY_TOOL_OUTPUT_TAIL);
+    // Represent the shrunk output as a text output (a valid tool-result output).
+    p.output = { type: 'text', value: truncated };
+  }
+}
+
+/** Shallow-ish clone so trimming never mutates the caller's (persisted-derived)
+ *  message objects — only the OLD region is cloned before it is edited. */
+function cloneMessage(m: ModelMessage): ModelMessage {
+  if (typeof m.content === 'string') return { ...m };
+  return {
+    ...m,
+    content: (m.content as unknown[]).map((p) =>
+      p && typeof p === 'object' ? { ...(p as object) } : p,
+    ),
+  } as ModelMessage;
+}

apps/server/src/database/migrations/20260707T120000-ai-chat-metadata.ts

@@ -0,0 +1,24 @@
+import { type Kysely, sql } from 'kysely';
+
+export async function up(db: Kysely<any>): Promise<void> {
+  // Chat-level metadata bag (#490). First use: the deferred-tool ACTIVATION set
+  // (`activatedTools`) is persisted here so it survives across turns — previously
+  // the set was reset every turn, forcing the model to re-run loadTools and pay a
+  // fresh round-trip to re-activate the same tools each turn. On load the stored
+  // set is intersected with the current valid deferred names, so an allowlist /
+  // role change can never inject a now-nonexistent tool.
+  //
+  // jsonb, defaulted to '{}' so every row (incl. pre-migration ones, backfilled
+  // by the default) is a readable object — the app never has to null-guard the
+  // bag itself, only individual keys.
+  await db.schema
+    .alterTable('ai_chats')
+    .addColumn('metadata', 'jsonb', (col) =>
+      col.notNull().defaultTo(sql`'{}'::jsonb`),
+    )
+    .execute();
+}
+
+export async function down(db: Kysely<any>): Promise<void> {
+  await db.schema.alterTable('ai_chats').dropColumn('metadata').execute();
+}

apps/server/src/database/types/db.d.ts

@@ -606,6 +606,9 @@ export interface AiChats {
   // The document the chat was created in (open page at first message). NULL =>
   // started outside any document. ON DELETE SET NULL on the page FK.
   pageId: string | null;
+  // Chat-level metadata bag (#490). jsonb, defaulted to '{}'. First key:
+  // `activatedTools` — the deferred-tool activation set persisted across turns.
+  metadata: Generated<Json>;
   createdAt: Generated<Timestamp>;
   updatedAt: Generated<Timestamp>;
   deletedAt: Timestamp | null;

apps/server/src/integrations/ai/ai-settings.service.ts

@@ -245,6 +245,9 @@ export class AiSettingsService {
       // Max context window for the chat header badge denominator. Stored as
       // ::text; 0/unset/invalid = no limit (undefined).
       chatContextWindow: parsePositiveInt(provider.chatContextWindow),
+      // RAW stored value (#490): the replay budgeter reads this to distinguish an
+      // explicit `0` (off-switch) from unset, which parsePositiveInt cannot.
+      chatContextWindowRaw: provider.chatContextWindow,
       // Plain passthrough; getChatModel defaults unset to 'openai-compatible'.
       chatApiStyle: provider.chatApiStyle,
       // Cheap model id for the anonymous public-share assistant; reuses the chat

apps/server/src/integrations/ai/ai.types.ts

@@ -105,6 +105,10 @@ export interface ResolvedAiConfig extends Partial<AiProviderSettings> {
   // Max context window in tokens; surfaced to the chat header badge as the
   // "current / max" denominator. 0/unset = no limit.
   chatContextWindow?: number;
+  // RAW stored context window (::text), BEFORE parsePositiveInt collapses `0` and
+  // unset to `undefined`. The #490 replay budgeter needs the raw value to honor an
+  // explicit `0` off-switch distinctly from "unset -> flat default".
+  chatContextWindowRaw?: string | number;
   // Cheap model id for the public-share assistant; reuses the chat creds.
   publicShareChatModel?: string;
   // Agent-role id whose persona the public-share assistant adopts (empty/unset

docs/reading-ai-logs.md

@@ -8,19 +8,35 @@ real pain (a "which tools fail most?" analysis that confidently answered
 
 Read the **Gotchas** section before you trust any error count.
 
+> **TWO ERAS — check the marker first.** The `tool_calls` shape changed in **#490
+> (trace v2)**. A row written by v2 carries `metadata.toolTraceVersion = 2`; older
+> rows have no such key. The two shapes store DIFFERENT things (v2 dropped the tool
+> OUTPUT from the trace), so **every query below is dual-shape** — branch on the
+> marker. **Never compare an aggregate or trend across the era boundary**: a metric
+> jump on the cut-over week is an artifact of the shape change, not a behavior
+> change.
+
 ## TL;DR
 
 - Agent chats live in Postgres, DB `docmost`, tables `ai_chat_*`.
-- Each tool invocation is stored as **two** array elements (a `tool-call` part and
-  a `tool-result` part), so naive counting double-counts.
-- **A tool that *throws* writes no result part.** Since the #407 fix its error is
-  persisted as a dedicated `{toolName, error}` element in `tool_calls` (queryable +
-  replayed to the model). **Rows written before #407 still drop it** — the error is
-  nowhere in the DB and shows only in the live UI. So `isError` / `success=false`
-  scans under-report by design, and pre-#407 thrown errors are invisible.
-- To find where agents fail: (1) soft-failure markers in `tool_calls`, (2) the new
-  `error` field for thrown errors (new rows) / the orphan-gap proxy (old rows),
-  (3) server logs / the live UI for full stack traces beyond the truncated message.
+- **Era marker:** `metadata.toolTraceVersion = 2` ⇒ v2 (#490) row; absent ⇒ legacy row.
+- Each tool invocation is stored as **two** consecutive array elements — a
+  `tool-call` part then an OUTCOME part — so naive counting double-counts.
+  - **v2 (#490):** outcome is `{toolName, ok: true}` on success, or
+    `{toolName, error, kind: 'thrown'|'interrupted'}` on failure. The tool **OUTPUT
+    is NOT in `tool_calls`** any more — it lives once in `metadata.parts` (this
+    removed a hundreds-of-MB-per-run write duplication). Soft-failure analysis
+    therefore reads `metadata.parts`, not `tool_calls`.
+  - **legacy:** outcome is `{toolName, output}` on success; a **thrown** failure is
+    a `{toolName, error}` element **only on rows after #407**, and is dropped
+    entirely (silent orphan) on pre-#407 rows.
+- **A tool that *throws* writes no result part.** In v2 it is a
+  `{error, kind:'thrown'}` element; an interrupted/aborted call is a distinct
+  `{error, kind:'interrupted'}`. `isError`/`success=false` scans read the *output*
+  and so under-report thrown failures in every era.
+- To find where agents fail: (1) soft-failure markers in `metadata.parts` outputs
+  (v2) / `tool_calls` outputs (legacy), (2) the `error`/`kind` fields for thrown
+  failures (v2 + post-#407), (3) server logs / the live UI for full stack traces.
 
 ## Where the data lives
 
@@ -53,33 +69,67 @@ are rows in `workspaces`, not separate deployments.
 separate `tool` role), `content` (text), `tool_calls` (jsonb array), `metadata`
 (jsonb, holds run `error` + rendered `parts`), `status`, `tsv` (full-text index).
 
+## Era marker — check this before every query
+
+```sql
+-- how many rows are in each era?
+SELECT COALESCE((metadata->>'toolTraceVersion'), 'legacy') AS era, count(*)
+FROM ai_chat_messages
+WHERE role = 'assistant' AND jsonb_typeof(tool_calls) = 'array'
+GROUP BY 1 ORDER BY 2 DESC;
+```
+
+- `toolTraceVersion = '2'` → **v2** (#490): outcome flags, **no output in the trace**.
+- `NULL` (`'legacy'`) → pre-#490: outcome carries the tool `output` inline.
+
+**Do not trend a metric across the cut-over.** The shape change alone shifts counts
+(e.g. "elements with `output`" collapses to zero for v2), so a week that straddles
+the boundary shows an artifact, not a behavior change. Segment by era, or restrict to
+one era, before comparing.
+
 ## How tool calls are stored — READ THIS
 
 Tool calls are **not** one-object-per-call. Each logical invocation is split into
-two consecutive elements of the `tool_calls` array:
+two consecutive elements of the `tool_calls` array — a **call** then an **outcome**.
+The outcome shape is era-dependent:
 
 ```text
-index 0: { "toolName": "getPage",  "input":  { "pageId": "…" } }   ← tool-call   (has input, NO output)
-index 1: { "toolName": "getPage",  "output": { … } }                ← tool-result (has output, NO input)
+# v2 (#490) — metadata.toolTraceVersion = 2
+index 0: { "toolName":"getPage", "input":{...} }                       ← call     (has input)
+index 1: { "toolName":"getPage", "ok":true }                          ← success  (NO output here)
+   or  : { "toolName":"getPage", "error":"…", "kind":"thrown" }       ← threw
+   or  : { "toolName":"getPage", "error":"…", "kind":"interrupted" }  ← aborted mid-step
+
+# legacy — no toolTraceVersion
+index 0: { "toolName":"getPage", "input":{...} }                       ← call     (has input, NO output)
+index 1: { "toolName":"getPage", "output":{...} }                     ← success  (has output)
+   or  : { "toolName":"getPage", "error":"…" }                        ← threw (post-#407 only)
 ```
 
-The keys that appear on an element are `toolName`, `input`, `output`, and — for a
-**thrown** failure on rows written after the #407 fix — `error` (the tool's error
-message; see the "Hard failures" section below). There is no `state`, no `errorText`,
-no `type`. On pre-#407 rows a thrown failure has NO paired result element at all
-(silent orphan). Consequences:
+The keys that can appear: `toolName`, `input` (call), and on the outcome — **v2:**
+`ok` **or** `error`+`kind`; **legacy:** `output` **or** (post-#407) `error`. There is
+no `state`, no `errorText`, no `type` in `tool_calls` (those live on `metadata.parts`).
+Consequences:
 
-1. **Real invocation count = elements that have `output` or `error`.** Counting every
-   element double-counts (you get ~2× and a spurious "~50% of every tool has no output").
-2. **Pairing:** a call = a `tool-call` part followed by its result part. A success
-   carries `output`; a thrown failure (post-#407) carries `error` instead. Both carry
-   `toolName`, so you can group by tool on either.
+1. **Real invocation count** — count the OUTCOME elements, not every element (else you
+   double-count): **v2** = elements with `ok` or `error`; **legacy** = elements with
+   `output` or `error`.
+2. **Pairing:** a call (`input`) is followed by its outcome. `toolName` is on both, so
+   you can group by tool on either. In v2 the `kind` field separates a real hard-fail
+   (`thrown`) from an aborted call (`interrupted`) — a distinction legacy rows cannot
+   make (both are orphans; see below).
+3. **The tool OUTPUT is only in `metadata.parts` on v2 rows.** To inspect what a tool
+   returned (soft-error markers, page bodies) on a v2 row, read the parts
+   (`part->>'type' LIKE 'tool-%'`, `part->>'state' = 'output-available'`, `part->'output'`),
+   not `tool_calls`.
 
 ## The two classes of failure (and which the DB can see)
 
 ### 1. Soft failures — tool RAN and returned an error-shaped result → PERSISTED ✅
 
-These are visible in the `tool-result` `output`. The marker differs per tool:
+These are visible in the tool `output` — **on v2 rows in `metadata.parts`** (the
+`output-available` part's `output`), on **legacy rows in the `tool_calls` outcome
+element's `output`**. The marker differs per tool:
 
 | Tool(s) | Error marker in `output` |
 | --- | --- |
@@ -91,37 +141,32 @@ These are visible in the `tool-result` `output`. The marker differs per tool:
 Note `editPageText` returns `failed: []` on success — filtering on the *presence*
 of the key gives false positives; filter on **non-empty**.
 
-### 2. Hard failures — tool THREW → NOW PERSISTED ✅ (since the #407 fix)
+### 2. Hard failures — tool THREW → PERSISTED ✅
 
 When a tool throws (the classic one is `patchNode` / `insertNode` / `tableUpdateCell`
 → `Failed to encode document to Yjs (fromJSON): Unknown node type: undefined`), the
-runtime still writes **no `tool-result` part** — the failure is an ai@6 `tool-error`
-content part instead. **Since the #407 fix, that error is persisted**: `serializeSteps`
-appends a dedicated element `{toolName, error: "<message>"}` right after the failed
-call, mirroring how a successful `{toolName, output}` element is appended. So a thrown
-error now leaves a queryable `error` field carrying its (truncated) reason, and the
-same real text is replayed to the model on the next turn (an `output-error` part with
-the real `errorText`, no longer the `'Tool call did not complete.'` placeholder).
+runtime writes **no `tool-result` part** — the failure is an ai@6 `tool-error` content
+part. How that lands in `tool_calls` depends on the era:
 
-**Cutover caveat — old rows keep the old blind shape.** Rows written **before** this
-change have the two-part shape (`call` + `output` only) and simply **drop** thrown
-errors, leaving a silent **orphan** (a `call` with no `output` *and* no `error`). Rows
-written **after** the fix additionally carry the `error` element. So:
+- **v2 (#490):** a `{toolName, error, kind:'thrown'}` outcome element. An interrupted /
+  aborted mid-step call is a **distinct** `{toolName, error:'Tool call did not
+  complete.', kind:'interrupted'}` element — so you can tell a real hard-fail from an
+  abort **directly, without the orphan heuristic**. Query `kind = 'thrown'`.
+- **post-#407 legacy:** a `{toolName, error}` element (no `kind`) right after the call.
+- **pre-#407 legacy:** the error is **dropped** — a silent **orphan** (a `call` with no
+  `output` *and* no `error`).
 
-- **New rows:** query the `error` field directly (see the hard-error query below) — no
-  orphan heuristic needed for thrown failures.
-- **Old rows (pre-#407):** the only DB-side proxy is still an **orphan**: a `tool-call`
-  part with no matching `tool-result` *and* no `error`. Orphans also appear when a run
-  is **aborted** mid-flight (server restart), so a high-volume tool (`createComment`,
-  `searchInPage`, `Search_web_search`) shows orphans from aborts, not real errors on
-  old rows. Treat the orphan gap as an *upper bound*, and cross-check the tool: a gap on
-  a structural editor (`patchNode`, `insertNode`, `updatePageJson`, `transformPage`) is
-  almost certainly a thrown Yjs-encode error; a gap on `createComment` is mostly aborts.
+The same real error text is replayed to the model on the next turn (an `output-error`
+part with the real `errorText`, from `metadata.parts`), in every era.
 
-A note on the aborted-call fallback: a call with **neither** a result **nor** a
-`tool-error` (genuinely interrupted mid-step) still replays with the
-`'Tool call did not complete.'` placeholder and persists as an orphan — that path is
-unchanged, and is distinct from a real thrown error, which now carries `error`.
+**Cutover caveat.** Only pre-#407 legacy rows need the orphan proxy: an orphan is a
+`tool-call` with no matching outcome. Orphans there also appear when a run is **aborted**
+mid-flight (server restart), so a high-volume tool (`createComment`, `searchInPage`,
+`Search_web_search`) shows orphans from aborts, not real errors. Treat the orphan gap as
+an *upper bound* and cross-check the tool: a gap on a structural editor (`patchNode`,
+`insertNode`, `updatePageJson`, `transformPage`) is almost certainly a thrown Yjs-encode
+error; a gap on `createComment` is mostly aborts. **On v2 rows this ambiguity is gone**
+— `kind` labels each outcome.
 
 ### 3. Run-level failures → `ai_chat_runs`
 
@@ -134,22 +179,34 @@ the wild: `Run interrupted by a server restart.` (aborts) and
 
 Run all of these via `docker exec gitmost-postgresql psql -U docmost -d docmost -P pager=off -c "…"`.
 
-**Real invocation count per tool** (result parts only — the correct denominator):
+**Real invocation count per tool** (outcome parts only — the correct denominator).
+Dual-shape: a v2 outcome has `ok` or `error`; a legacy outcome has `output` or `error`:
 
 ```sql
 SELECT elem->>'toolName' AS tool, count(*) AS calls
 FROM ai_chat_messages m, jsonb_array_elements(m.tool_calls) elem
-WHERE jsonb_typeof(m.tool_calls) = 'array' AND elem ? 'output'
+WHERE jsonb_typeof(m.tool_calls) = 'array'
+  AND (elem ? 'ok' OR elem ? 'output' OR elem ? 'error')
 GROUP BY 1 ORDER BY 2 DESC;
 ```
 
-**Soft errors per tool** (everything the DB can honestly see):
+**Soft errors per tool.** The soft-error marker lives in the tool OUTPUT — which on
+**v2 rows is in `metadata.parts`**, on **legacy rows is in the `tool_calls` outcome
+element**. This query UNIONs both eras, projecting each output as `o`:
 
 ```sql
 WITH res AS (
+  -- v2 (#490): output is in metadata.parts (output-available tool parts)
+  SELECT part->>'type' AS tool, part->'output' AS o
+  FROM ai_chat_messages m, jsonb_array_elements(m.metadata->'parts') part
+  WHERE (m.metadata->>'toolTraceVersion') = '2'
+    AND part->>'type' LIKE 'tool-%' AND part->>'state' = 'output-available'
+  UNION ALL
+  -- legacy: output is inline in the tool_calls outcome element
   SELECT elem->>'toolName' AS tool, elem->'output' AS o
   FROM ai_chat_messages m, jsonb_array_elements(m.tool_calls) elem
-  WHERE jsonb_typeof(m.tool_calls) = 'array' AND elem ? 'output'
+  WHERE (m.metadata->>'toolTraceVersion') IS NULL
+    AND jsonb_typeof(m.tool_calls) = 'array' AND elem ? 'output'
 )
 SELECT tool, count(*) AS calls,
        sum(COALESCE(
@@ -167,13 +224,23 @@ FROM res GROUP BY tool HAVING sum(COALESCE(
 ORDER BY soft_errors DESC;
 ```
 
-**`editPageText` failure reasons** (the most common real agent mistake — bad `find`):
+Note the v2 `tool` label is the part type (`tool-editPageText`); strip the `tool-`
+prefix if you join it against the legacy `toolName`.
+
+**`editPageText` failure reasons** (the most common real agent mistake — bad `find`).
+Same dual-shape output source:
 
 ```sql
 WITH res AS (
+  SELECT part->'output' AS o
+  FROM ai_chat_messages m, jsonb_array_elements(m.metadata->'parts') part
+  WHERE (m.metadata->>'toolTraceVersion') = '2'
+    AND part->>'type' = 'tool-editPageText' AND part->>'state' = 'output-available'
+  UNION ALL
   SELECT elem->'output' AS o
   FROM ai_chat_messages m, jsonb_array_elements(m.tool_calls) elem
-  WHERE jsonb_typeof(m.tool_calls) = 'array'
+  WHERE (m.metadata->>'toolTraceVersion') IS NULL
+    AND jsonb_typeof(m.tool_calls) = 'array'
     AND elem->>'toolName' = 'editPageText' AND elem ? 'output'
 )
 SELECT f->>'reason' AS reason, count(*)
@@ -182,30 +249,43 @@ WHERE jsonb_typeof(o->'failed') = 'array'
 GROUP BY 1 ORDER BY 2 DESC;
 ```
 
-**Hard errors — persisted `error` field per tool (NEW rows, since #407)** — thrown
-tool failures now carry their real reason, so query them directly:
+**Hard errors — persisted `error` field per tool (v2 + post-#407 rows)** — thrown tool
+failures carry their real reason, so query them directly. On **v2** rows exclude the
+`interrupted` kind so an aborted call is not counted as a hard-fail:
 
 ```sql
 SELECT elem->>'toolName' AS tool, count(*) AS thrown_errors,
        min(elem->>'error') AS sample_error
 FROM ai_chat_messages m, jsonb_array_elements(m.tool_calls) elem
 WHERE jsonb_typeof(m.tool_calls) = 'array' AND elem ? 'error'
+  -- v2 rows label the kind; a legacy error element has no kind (count it).
+  AND COALESCE(elem->>'kind', 'thrown') = 'thrown'
+GROUP BY 1 ORDER BY 2 DESC;
+```
+
+Aborted mid-step calls on v2 rows are a distinct, directly countable population:
+
+```sql
+SELECT elem->>'toolName' AS tool, count(*) AS interrupted
+FROM ai_chat_messages m, jsonb_array_elements(m.tool_calls) elem
+WHERE jsonb_typeof(m.tool_calls) = 'array' AND elem->>'kind' = 'interrupted'
 GROUP BY 1 ORDER BY 2 DESC;
 ```
 
 **Hard-error proxy for OLD rows (pre-#407) — orphan gap per tool, WITH a spread column**
-(call parts minus result parts, plus how many distinct chats the gap is spread across).
-This covers rows written before thrown errors were persisted; on new rows a thrown
-failure now has its own `error` element (use the query above) and an orphan means only
-a genuinely aborted mid-step call:
+(call parts minus outcome parts, plus how many distinct chats the gap is spread across).
+This is needed ONLY for pre-#407 legacy rows (v2 and post-#407 rows carry the error /
+`kind` directly — use the queries above). The `WHERE` restricts to the legacy era so v2
+rows (where an `ok` outcome is not an `output`) never produce phantom orphans:
 
 ```sql
 WITH parts AS (
   SELECT m.chat_id, elem->>'toolName' AS tool,
-         (elem ? 'input' AND NOT (elem ? 'output')) AS is_call,
-         (elem ? 'output' OR elem ? 'error')        AS is_result
+         (elem ? 'input' AND NOT (elem ? 'output') AND NOT (elem ? 'ok')) AS is_call,
+         (elem ? 'output' OR elem ? 'error' OR elem ? 'ok')               AS is_result
   FROM ai_chat_messages m, jsonb_array_elements(m.tool_calls) elem
   WHERE jsonb_typeof(m.tool_calls) = 'array' AND m.role = 'assistant'
+    AND (m.metadata->>'toolTraceVersion') IS NULL
 ),
 per_chat AS (
   SELECT tool, chat_id, sum(is_call::int) - sum(is_result::int) AS gap
@@ -261,11 +341,21 @@ WHERE tsv @@ websearch_to_tsquery('english', 'some phrase') LIMIT 20;
 
 ## Don't blow up your context
 
-A single `tool_calls` row can be **300–400 KB** (results embed full page content and
-search payloads). Never `SELECT tool_calls` (or `jsonb_pretty(tool_calls)`) raw.
-Always project just the keys you need and truncate:
+Tool outputs embed full page content and search payloads (hundreds of KB per row).
+On **legacy** rows they are in `tool_calls`; on **v2** rows they moved to
+`metadata->'parts'` (the `tool_calls` trace itself is now small). Never `SELECT
+tool_calls` / `metadata` (or `jsonb_pretty(...)`) raw — project just the keys you need
+and truncate:
 
 ```sql
+-- v2: outputs live in metadata.parts
+SELECT part->>'type',
+       left(regexp_replace((part->'output')::text, '\s+', ' ', 'g'), 200)
+FROM ai_chat_messages m, jsonb_array_elements(m.metadata->'parts') part
+WHERE (m.metadata->>'toolTraceVersion') = '2'
+  AND part->>'state' = 'output-available' LIMIT 5;
+
+-- legacy: outputs live in tool_calls
 SELECT elem->>'toolName',
        left(regexp_replace((elem->'output')::text, '\s+', ' ', 'g'), 200)
 FROM ai_chat_messages m, jsonb_array_elements(m.tool_calls) elem
@@ -280,26 +370,32 @@ docker compose -p gitmost logs -f --tail=100 # whole stack
 ```
 
 Logging is `json-file`, `max-size=10m max-file=5` → ~50 MB retained, then rotated,
-and **wiped on container recreate**. Since the #407 fix, thrown-tool error text is
-**persisted in the `error` field** of `tool_calls` (see the hard-error query above), so
-you no longer depend on live logs for it. Logs/live UI remain useful for **pre-#407
-rows** (whose thrown errors were dropped) and for full stack traces beyond the
-truncated stored message. A per-tool `tool_calls_total{tool,status}` metric to
-VictoriaMetrics is still a possible future add for aggregate dashboards.
+and **wiped on container recreate**. Thrown-tool error text is **persisted** — in the
+`error` field of `tool_calls` (v2 `kind:'thrown'` / post-#407 legacy) — so you no longer
+depend on live logs for it. Logs/live UI remain useful for **pre-#407 rows** (whose
+thrown errors were dropped) and for full stack traces beyond the truncated stored
+message. A per-tool `tool_calls_total{tool,status}` metric to VictoriaMetrics is still a
+possible future add for aggregate dashboards.
 
 ## Gotchas checklist
 
-- [ ] Counting every `tool_calls` element → **overcount**. Count `output` elements; add `error` elements for thrown failures (new rows), but don't count both as invocations.
-- [ ] `isError` / `success=false` ≈ 0 does **not** mean "no errors" — thrown errors are a separate `error` element (new rows) or dropped entirely (pre-#407 rows).
-- [ ] Thrown errors persist only on rows written **after the #407 fix** — pre-#407 rows still drop them (orphan only). Mind the cutover when trending over time.
+- [ ] **Check `metadata.toolTraceVersion` first.** v2 (`= 2`) has no output in `tool_calls`; legacy has it inline. Never trend a metric across the era boundary.
+- [ ] Counting every `tool_calls` element → **overcount**. Count OUTCOME elements — v2: `ok` or `error`; legacy: `output` or `error` — never both call+outcome as invocations.
+- [ ] `isError` / `success=false` ≈ 0 does **not** mean "no errors" — thrown errors are an `error` element (v2 `kind:'thrown'` / post-#407), not in the output.
+- [ ] **v2:** soft-error markers (the tool output) are in `metadata.parts`, NOT `tool_calls`. Legacy: they are in the `tool_calls` outcome `output`.
+- [ ] **v2:** `kind` splits a real hard-fail (`thrown`) from an aborted call (`interrupted`) directly — no orphan heuristic needed. The orphan gap is a pre-#407-legacy-only proxy.
 - [ ] `editPageText.failed` is `[]` on success — test for **non-empty**, not presence.
-- [ ] Orphan gap on OLD rows mixes thrown errors **and** aborted runs — split by tool. On NEW rows a thrown error is its own `error` element, so a gap ≈ aborted call.
 - [ ] `aborted` runs = server restarts, `failed` runs = provider overload — not agent mistakes.
-- [ ] Never dump a raw `tool_calls` cell — it can be hundreds of KB.
-- [ ] Logs are ephemeral (≤50 MB, wiped on recreate) — grab hard-error text live.
+- [ ] Never dump a raw `tool_calls` **or** `metadata.parts` cell — outputs are hundreds of KB.
+- [ ] Logs are ephemeral (≤50 MB, wiped on recreate) — grab pre-#407 hard-error text live.
 
 ## Snapshot (2026-07-07, illustrative — rerun the queries for current numbers)
 
+> All rows in this snapshot predate #490, so they are **legacy-era** (outputs inline in
+> `tool_calls`, orphan proxy for thrown errors). Do not trend these numbers against v2
+> rows — segment by `toolTraceVersion` first.
+
+
 - 226 chats, 732 messages, 46 runs; ~4 400 real tool invocations.
 - Soft errors (persisted): `editPageText` 4/79 (bad/non-unique `find`) + 9 markdown-in-`find` warnings; `semanticSearch` 3/4 (`unavailable`); `Habr_update_draft_from_docmost` 1/2 (`doc` sent as object, not string).
 - Missing-result proxy, read WITH the spread column:

packages/mcp/src/client/comments.ts

@@ -59,6 +59,39 @@ import {
   mergeFootnoteDefinitions,
 } from "../lib/transforms.js";
 
+// Max concurrent per-page comment fetches in checkNewComments (#490). The scan is
+// O(N) independent REST reads over the working set; running them one-at-a-time made
+// a large space linear in round-trips. A small cap parallelizes without hammering
+// the server (or exhausting sockets). 6 is a conservative middle of the 5–8 band.
+const COMMENT_SCAN_CONCURRENCY = 6;
+
+/**
+ * Map `items` through `fn` with at most `limit` in flight, preserving INPUT ORDER
+ * in the returned array. A tiny bounded pool (no p-limit dependency): `limit`
+ * workers pull the next index off a shared cursor until the list is drained.
+ */
+async function mapWithConcurrency<T, R>(
+  items: readonly T[],
+  limit: number,
+  fn: (item: T, index: number) => Promise<R>,
+): Promise<R[]> {
+  const results = new Array<R>(items.length);
+  let cursor = 0;
+  const worker = async (): Promise<void> => {
+    for (;;) {
+      const i = cursor++;
+      if (i >= items.length) return;
+      results[i] = await fn(items[i], i);
+    }
+  };
+  const workers = Array.from(
+    { length: Math.max(1, Math.min(limit, items.length)) },
+    () => worker(),
+  );
+  await Promise.all(workers);
+  return results;
+}
+
 // Public method surface of CommentsMixin (issue #450) — a NAMED type so the factory
 // return type is expressible in the emitted .d.ts (the anonymous mixin class
 // carries the base's protected shared state, which would otherwise trip TS4094).
@@ -655,27 +688,32 @@ export function CommentsMixin<TBase extends GConstructor<DocmostClientContext>>(
       parentPageId,
     );
 
-    // 2. Fetch comments for each page, keep ones created after since
-    const results: any[] = [];
-    for (const page of pagesInScope) {
-      try {
-        // Full feed (incl. resolved): a "new comments since" scan reports all
-        // recent activity; the active-only filter is scoped to listComments.
-        const comments = (await this.listComments(page.id, true)).items;
-        const newComments = comments.filter(
-          (c: any) => new Date(c.createdAt) > sinceDate,
-        );
-        if (newComments.length > 0) {
-          results.push({
-            pageId: page.id,
-            pageTitle: page.title,
-            comments: newComments,
-          });
+    // 2. Fetch comments for each page, keep ones created after since. Runs with
+    // bounded concurrency (#490) instead of one-at-a-time — the per-page reads are
+    // independent, so a large working set no longer costs O(N) serial round-trips.
+    // Order is preserved (mapWithConcurrency keeps input order), so the output is
+    // deterministic regardless of which fetch finishes first.
+    const perPage = await mapWithConcurrency(
+      pagesInScope,
+      COMMENT_SCAN_CONCURRENCY,
+      async (page: any) => {
+        try {
+          // Full feed (incl. resolved): a "new comments since" scan reports all
+          // recent activity; the active-only filter is scoped to listComments.
+          const comments = (await this.listComments(page.id, true)).items;
+          const newComments = comments.filter(
+            (c: any) => new Date(c.createdAt) > sinceDate,
+          );
+          return newComments.length > 0
+            ? { pageId: page.id, pageTitle: page.title, comments: newComments }
+            : null;
+        } catch (e: any) {
+          // Skip pages with errors (e.g. deleted between calls)
+          return null;
         }
-      } catch (e: any) {
-        // Skip pages with errors (e.g. deleted between calls)
-      }
-    }
+      },
+    );
+    const results: any[] = perPage.filter((r): r is any => r !== null);
 
     const totalNewComments = results.reduce(
       (sum, r) => sum + r.comments.length,

packages/mcp/test/mock/pagination-cursor.test.mjs

@@ -442,3 +442,71 @@ test("checkNewComments subtree includes the root without a separate getPageRaw",
   assert.equal(result.checkedPages, 2, "root + one descendant scanned");
   assert.equal(result.totalNewComments, 1, "the root's fresh comment found");
 });
+
+// -----------------------------------------------------------------------------
+// 6) checkNewComments parallelism (#490): the per-page comment fetches run with
+//    bounded concurrency (not one-at-a-time), and the results still preserve the
+//    page order deterministically regardless of which fetch finishes first.
+// -----------------------------------------------------------------------------
+test("checkNewComments fetches pages concurrently (bounded) and preserves order", async () => {
+  // A subtree with 12 descendants so the scan has plenty to parallelize.
+  const NODES = [{ id: "parent", title: "Parent", parentPageId: null, hasChildren: true }];
+  for (let i = 0; i < 12; i++) {
+    NODES.push({ id: `k${i}`, title: `Kid ${i}`, parentPageId: "parent", hasChildren: false });
+  }
+
+  let inFlight = 0;
+  let maxInFlight = 0;
+
+  const { baseURL } = await spawn(async (req, res) => {
+    const raw = await readBody(req);
+    if (handleLogin(req, res)) return;
+    if (req.url === "/api/pages/tree") {
+      sendJson(res, 200, { success: true, data: { items: NODES } });
+      return;
+    }
+    if (req.url === "/api/comments") {
+      const body = JSON.parse(raw || "{}");
+      inFlight++;
+      maxInFlight = Math.max(maxInFlight, inFlight);
+      // Hold the response briefly so concurrent fetches actually overlap.
+      setTimeout(() => {
+        inFlight--;
+        // Every page carries one fresh comment so ordering is observable.
+        sendJson(res, 200, {
+          success: true,
+          data: {
+            items: [
+              { id: `c-${body.pageId}`, createdAt: "2030-01-01T00:00:00.000Z", content: null },
+            ],
+            meta: { nextCursor: null },
+          },
+        });
+      }, 25);
+      return;
+    }
+    sendJson(res, 404, {});
+  });
+
+  const client = new DocmostClient(baseURL, "user@example.com", "pw");
+  const result = await client.checkNewComments(
+    "space-1",
+    "2020-01-01T00:00:00.000Z",
+    "parent",
+  );
+
+  // 13 pages (parent + 12 kids) were scanned; each had a fresh comment.
+  assert.equal(result.checkedPages, 13, "all pages scanned");
+  assert.equal(result.totalNewComments, 13, "one fresh comment per page");
+  // Parallelism: more than one request was in flight at once, but never above the
+  // cap (6). A serial implementation would show maxInFlight === 1.
+  assert.ok(maxInFlight > 1, `expected concurrent fetches, saw max ${maxInFlight}`);
+  assert.ok(maxInFlight <= 6, `concurrency must be bounded, saw ${maxInFlight}`);
+  // Deterministic order: results follow the page-enumeration order (parent first).
+  assert.equal(result.comments[0].pageId, "parent", "results preserve page order");
+  assert.deepEqual(
+    result.comments.map((r) => r.pageId),
+    ["parent", ...Array.from({ length: 12 }, (_, i) => `k${i}`)],
+    "result order matches the enumeration order regardless of finish order",
+  );
+});

packages/token-estimate/package.json

@@ -0,0 +1,19 @@
+{
+  "name": "@docmost/token-estimate",
+  "version": "0.1.0",
+  "description": "Shared, provider-agnostic token estimator (chars/2.5) used by the AI-chat client counter and the server history-replay budgeter, so the two never diverge.",
+  "private": true,
+  "main": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "scripts": {
+    "build": "tsc",
+    "watch": "tsc --watch",
+    "test": "vitest run",
+    "test:watch": "vitest"
+  },
+  "license": "MIT",
+  "devDependencies": {
+    "typescript": "^5.0.0",
+    "vitest": "4.1.6"
+  }
+}

packages/token-estimate/src/index.test.ts

@@ -0,0 +1,31 @@
+import { describe, it, expect } from 'vitest';
+import { estimateTokens, CHARS_PER_TOKEN } from './index';
+
+describe('estimateTokens (shared chars/2.5)', () => {
+  it('returns 0 for empty / nullish input', () => {
+    expect(estimateTokens('')).toBe(0);
+    expect(estimateTokens(null)).toBe(0);
+    expect(estimateTokens(undefined)).toBe(0);
+  });
+
+  it('uses the chars/2.5 ratio, ceiled', () => {
+    expect(CHARS_PER_TOKEN).toBe(2.5);
+    // 5 chars / 2.5 = 2
+    expect(estimateTokens('abcde')).toBe(2);
+    // any non-empty string is at least 1 token (ceil)
+    expect(estimateTokens('a')).toBe(1);
+    // 100 chars / 2.5 = 40
+    expect(estimateTokens('x'.repeat(100))).toBe(40);
+  });
+
+  it('counts Cyrillic ~2x higher than the old chars/4 rule (no undercount)', () => {
+    const cyr = 'привет мир как дела'; // 19 chars
+    expect(estimateTokens(cyr)).toBe(Math.ceil(19 / 2.5)); // 8
+    expect(estimateTokens(cyr)).toBeGreaterThan(Math.ceil(19 / 4)); // > 5
+  });
+
+  it('is deterministic / byte-stable (same input => same output)', () => {
+    const s = 'the quick brown fox';
+    expect(estimateTokens(s)).toBe(estimateTokens(s));
+  });
+});

packages/token-estimate/src/index.ts

@@ -0,0 +1,35 @@
+/**
+ * Shared, provider-agnostic token estimator (#490).
+ *
+ * No provider exposes an exact tokenizer we can afford to run on the hot path (a
+ * real BPE pass is O(n²)-ish, bloats the client bundle, and is wrong for
+ * Gemini/Ollama anyway), so both the client's in-body counter AND the server's
+ * history-replay budgeter use this ONE cheap chars-based heuristic. Keeping it in
+ * a single shared module is deliberate: two independent estimators drift, and then
+ * "the badge shows 60%" while "the budgeter already trimmed" — the exact confusion
+ * this package prevents.
+ *
+ * Ratio: **chars / 2.5**. Most content here is Cyrillic, where a token is ~2.5
+ * characters; the common English `chars/4` rule of thumb UNDER-counts Cyrillic by
+ * ~2×, which for a budget check is the dangerous direction (it lets the context
+ * overflow). 2.5 slightly over-estimates pure English/code, which is the SAFE
+ * direction for a budget. This is an estimate, never an exact count — the
+ * authoritative figure is always the provider's reported usage; the estimate is
+ * for UI affordances, the delta of not-yet-sent messages, and deciding what to
+ * trim.
+ */
+
+/** Characters per token for the shared estimate. See the module comment. */
+export const CHARS_PER_TOKEN = 2.5;
+
+/**
+ * Rough token estimate for a piece of text (chars / {@link CHARS_PER_TOKEN}).
+ * Returns 0 for empty/nullish input, and ceils so any non-empty text counts as at
+ * least one token. Pure and deterministic (byte-stable), so the same text always
+ * yields the same estimate — which the server budgeter relies on to keep replay
+ * trimming stable turn to turn (provider prompt-cache friendliness).
+ */
+export function estimateTokens(text: string | null | undefined): number {
+  if (!text) return 0;
+  return Math.ceil(text.length / CHARS_PER_TOKEN);
+}

packages/token-estimate/tsconfig.json

@@ -0,0 +1,16 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "CommonJS",
+    "moduleResolution": "Node",
+    "outDir": "./dist",
+    "rootDir": "./src",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "declaration": true
+  },
+  "include": ["src/**/*"],
+  "exclude": ["src/**/*.test.ts"]
+}

pnpm-lock.yaml

@@ -287,6 +287,9 @@ importers:
       '@docmost/prosemirror-markdown':
         specifier: workspace:*
         version: link:../../packages/prosemirror-markdown
+      '@docmost/token-estimate':
+        specifier: workspace:*
+        version: link:../../packages/token-estimate
       '@excalidraw/excalidraw':
         specifier: 0.18.0-3a5ef40
         version: 0.18.0-3a5ef40(@types/react-dom@18.3.1)(@types/react@18.3.12)(react-dom@18.3.1(react@18.3.1))(react@18.3.1)
@@ -561,6 +564,9 @@ importers:
       '@docmost/prosemirror-markdown':
         specifier: workspace:*
         version: link:../../packages/prosemirror-markdown
+      '@docmost/token-estimate':
+        specifier: workspace:*
+        version: link:../../packages/token-estimate
       '@fastify/compress':
         specifier: ^9.0.0
         version: 9.0.0
@@ -1148,6 +1154,15 @@ importers:
         specifier: 4.1.6
         version: 4.1.6(@opentelemetry/api@1.9.0)(@types/node@20.19.43)(@vitest/coverage-v8@4.1.6)(happy-dom@20.8.9)(jsdom@25.0.0)(vite@8.0.5(@types/node@20.19.43)(esbuild@0.28.0)(jiti@2.4.2)(less@4.2.0)(sugarss@5.0.1(postcss@8.5.14))(terser@5.39.0)(tsx@4.21.0)(yaml@2.8.3))
 
+  packages/token-estimate:
+    devDependencies:
+      typescript:
+        specifier: ^5.0.0
+        version: 5.9.3
+      vitest:
+        specifier: 4.1.6
+        version: 4.1.6(@opentelemetry/api@1.9.0)(@types/node@25.5.0)(@vitest/coverage-v8@4.1.6)(happy-dom@20.8.9)(jsdom@27.4.0(@noble/hashes@2.0.1))(vite@8.0.5(@types/node@25.5.0)(esbuild@0.28.0)(jiti@2.4.2)(less@4.2.0)(sugarss@5.0.1(postcss@8.5.14))(terser@5.39.0)(tsx@4.21.0)(yaml@2.8.3))
+
 packages:
 
   '@aashutoshrathi/word-wrap@1.2.6':