test(sandbox): address PR #250 round-4 review — SSRF accept-path tests, MCP structuredContent (#243)

Mandatory (test-coverage):
- internal-file-urls.test: pin the SSRF/traversal ACCEPT path of
  resolveInternalFilePath (the sole guard for content-controlled `src`): an
  absolute/protocol-relative URL has its foreign host dropped and only an
  /api/files/ pathname survives (http://evil.com/api/files/x/y.png -> /files/x/y.png),
  while a host-dropped path that escapes /api/files/ (https://evil.com/api/auth/whoami)
  or a backslash-traversal (/api/files\..\auth\whoami) is rejected. Locks the
  behavior so a future prefix-only refactor cannot silently open a bypass.

Suggestions:
- index.ts: the stash_page MCP tool now returns structuredContent
  { uri, sha256, size, images } alongside the resource_link, so the MCP output
  matches the documented shape (clients get the blob's sha256/ETag and the
  mirror counts, not just the link). No outputSchema registered. Rebuilt build/.
- new stash-page-mcp-result.test: server round-trip via InMemoryTransport asserts
  both the resource_link and the structuredContent mirror.
- internal-file-urls.test: cover the new URL parse-failure catch branch
  (http://[ -> "Invalid internal file src").
- environment.service.spec: assert getPositiveIntEnv warns once per key and
  independently across keys (the invalidPositiveIntWarned dedup).

Tests: packages/mcp 383 pass; apps/server sandbox/environment/mcp 235 pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.env.example

@@ -124,6 +124,26 @@ MCP_DOCMOST_PASSWORD=
 # MCP_TOKEN=
 # MCP_SESSION_IDLE_MS=1800000
 #
+# BLOB SANDBOX (stash_page). An in-RAM, process-local store that hands large page
+# content + images to an external consumer WITHOUT bloating the model context or
+# requiring Docmost auth. The stash_page tool serializes a page, mirrors its
+# internal images into the store, and returns ONLY a short anonymous URL; the
+# consumer fetches blobs via `GET /api/sb/<uuid>` (no token — the capability is
+# the unguessable UUID + short TTL + TLS). Blobs are RAM-only and cleared on
+# restart. ETag = the blob's sha256 (integrity check).
+# SANDBOX_PUBLIC_URL is the base used to build those URLs; it MUST be reachable
+# by the consumer (do NOT use a loopback address if the consumer is remote).
+# Defaults to APP_URL when unset.
+# NOTE: the store is process-local — blobs live only on the instance that
+# created them. Behind a multi-replica load balancer WITHOUT sticky sessions a
+# consumer may hit a different instance and get a 404 (indistinguishable from an
+# expired blob). Single-host deployments are unaffected.
+# SANDBOX_PUBLIC_URL=https://docs.example.com
+# SANDBOX_TTL_MS=3600000
+# SANDBOX_MAX_BYTES=8388608
+# SANDBOX_MAX_IMAGE_BYTES=20971520
+# SANDBOX_MAX_TOTAL_BYTES=134217728
+#
 # AI-AGENT ATTRIBUTION (comments/pages written via MCP are badged as "AI"):
 # attribution is driven by a per-user `is_agent` flag on the users row. There is
 # NO admin UI/API for it — set it out-of-band with SQL. Use a DEDICATED service

AGENTS.md

@@ -241,7 +241,7 @@ Migration files live in `apps/server/src/database/migrations/` and are named `YY
 - **API server** — `dist/main` (`apps/server/src/main.ts`), the Fastify HTTP app (`AppModule`).
 - **Collaboration server** — `dist/collaboration/server/collab-main` (`pnpm collab`), a Hocuspocus/Yjs WebSocket server (`apps/server/src/collaboration/`) handling real-time document editing, persistence, and page-history snapshots. It listens on `COLLAB_PORT` (default `3001`), separate from the API server's `PORT` (default `3000`), and shares state with the API server through Redis.
 
-The API server is a Fastify app with a global `/api` prefix (`main.ts` excludes `robots.txt`, public share pages, and `mcp` from the prefix). A `preHandler` hook enforces that a resolved `workspaceId` exists for most `/api` routes (multi-tenant by hostname/subdomain via `DomainMiddleware`). Auth is JWT (cookie + bearer); authorization is **CASL** (`core/casl`) — every data access is scoped to the user's abilities.
+The API server is a Fastify app with a global `/api` prefix (`main.ts` excludes `robots.txt`, public share pages, and `mcp` from the prefix). A `preHandler` hook enforces that a resolved `workspaceId` exists for most `/api` routes (multi-tenant by hostname/subdomain via `DomainMiddleware`). `GET /api/sb/:id` (the anonymous blob-sandbox read route) is listed in that preHandler's `excludedPaths`, so it is exempt from workspace resolution and carries no session auth at all (its capability is the unguessable UUID + TTL + TLS) — unlike `/api/files/public/...`, which still resolves a workspace and requires a workspace-bound attachment JWT. Auth is JWT (cookie + bearer); authorization is **CASL** (`core/casl`) — every data access is scoped to the user's abilities.
 
 ### Module structure (server)
 `AppModule` wires integration modules (`integrations/*`: storage [local/S3/Azure], mail, queue [BullMQ on Redis], security, telemetry, throttle, `mcp`, `ai`) plus `CoreModule`, `DatabaseModule`, and `CollaborationModule`. `CoreModule` (`core/*`) holds the domain modules: `page`, `space`, `comment`, `workspace`, `user`, `auth`, `group`, `attachment`, `search`, `share`, `ai-chat`, etc. Each domain module follows NestJS controller → service → repo layering; DB repos live under `database/repos` and are injected app-wide from the global `DatabaseModule`.
@@ -254,7 +254,7 @@ The API server is a Fastify app with a global `/api` prefix (`main.ts` excludes
 - **Redis** backs caching, the BullMQ queues, the WebSocket Socket.IO adapter, and collaboration sync.
 
 ### The two AI subsystems (the main fork additions)
-1. **Embedded MCP server** (`integrations/mcp/` + `packages/mcp`). The standalone `@docmost/mcp` server (39 agent-native tools: per-block patch/insert/delete by id, scripted `(doc)=>doc` transforms with dry-run diff, table editing, version diff/restore, comments, images, shares) is bundled and served over HTTP at `/mcp`. It writes through Docmost's real-time-collaboration layer so concurrent human edits aren't clobbered. Each request authenticates **per-user** via the `Authorization` header — either HTTP Basic (`base64(email:password)`, the user's own Docmost login, validated through `AuthService`) or a Bearer access JWT (the user's `authToken`) — and the session acts under that user's permissions. `MCP_DOCMOST_EMAIL` / `MCP_DOCMOST_PASSWORD` are an **optional service-account fallback**, used only when a request carries neither Basic nor Bearer credentials (back-compat for CI/scripts). An admin enables MCP with a workspace toggle (Workspace settings → AI). Optionally protected by a shared `MCP_TOKEN`: when set, every `/mcp` request must carry a matching `X-MCP-Token` header (its own header, separate from `Authorization`, which now carries the per-user Basic/Bearer credentials). Note: this changed from the older `Authorization: Bearer <MCP_TOKEN>` scheme — see `.env.example` and the CHANGELOG Breaking Changes entry.
+1. **Embedded MCP server** (`integrations/mcp/` + `packages/mcp`). The standalone `@docmost/mcp` server (40 agent-native tools: per-block patch/insert/delete by id, scripted `(doc)=>doc` transforms with dry-run diff, table editing, version diff/restore, comments, images, shares) is bundled and served over HTTP at `/mcp`. It writes through Docmost's real-time-collaboration layer so concurrent human edits aren't clobbered. Each request authenticates **per-user** via the `Authorization` header — either HTTP Basic (`base64(email:password)`, the user's own Docmost login, validated through `AuthService`) or a Bearer access JWT (the user's `authToken`) — and the session acts under that user's permissions. `MCP_DOCMOST_EMAIL` / `MCP_DOCMOST_PASSWORD` are an **optional service-account fallback**, used only when a request carries neither Basic nor Bearer credentials (back-compat for CI/scripts). An admin enables MCP with a workspace toggle (Workspace settings → AI). Optionally protected by a shared `MCP_TOKEN`: when set, every `/mcp` request must carry a matching `X-MCP-Token` header (its own header, separate from `Authorization`, which now carries the per-user Basic/Bearer credentials). Note: this changed from the older `Authorization: Bearer <MCP_TOKEN>` scheme — see `.env.example` and the CHANGELOG Breaking Changes entry.
 2. **AI agent chat** (`core/ai-chat/` server + `apps/client/src/features/ai-chat/` client). A built-in agent over the wiki using the Vercel **AI SDK** (`ai`, `@ai-sdk/*`) against any OpenAI-compatible provider configured per workspace (`integrations/ai/` — credentials encrypted at rest via `integrations/crypto`, stored in `ai_provider_credentials`). Key pieces:
    - `core/ai-chat/tools/` — the agent's ~40 read+write tools. Every tool runs under the **calling user's** CASL permissions via a per-user loopback access token (`docmost-client.loader.ts`), so the agent can never exceed what the user could do. Only **reversible** operations are exposed (page history + trash; no permanent delete). Agent edits get an "AI agent" provenance badge in page history (`20260616T130000-agent-provenance` migration).
    - `core/ai-chat/embedding/` — RAG indexer + a BullMQ consumer on `AI_QUEUE` that embeds pages into `page_embeddings` (vector search), complementing Postgres full-text search. Pages are (re)indexed on edit; `AI_EMBEDDING_TIMEOUT_MS` bounds a hung embeddings endpoint.

CHANGELOG.md

@@ -58,6 +58,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   append/prepend fragments, nor to COMMENT bodies — a comment may legitimately
   contain a standalone footnote definition, which canonicalization would drop.
   (#228)
+- **Out-of-band page transfer via an in-RAM blob sandbox (`stash_page`).** A
+  new MCP tool serializes a whole page (its full ProseMirror JSON, with every
+  internal image/file mirrored) into an ephemeral in-RAM blob and returns only
+  a short anonymous URL, so a large page can be handed to an external consumer
+  without flooding the model context. Blobs are served by unguessable UUID over
+  a new anonymous `GET /api/sb/:id` route (strong sha256 ETag, short TTL,
+  `nosniff` + restrictive CSP + attachment disposition for non-image mimes) and
+  are RAM-only, bound to the instance that created them. Tunable via five
+  `SANDBOX_*` env vars (see `.env.example`). (#243)
 
 ### Changed
 

README.md

@@ -34,7 +34,7 @@ The goal of the fork is a **100% open, AGPL-only build with no Enterprise-Editio
 | --- | --- |
 | **EE code removed** | Stripped all client and server Enterprise-Edition code; ships as a clean community/AGPL build with no license checks. |
 | **Comment resolution** | Re-implemented from scratch as a community feature (resolve / re-open with Open/Resolved tabs). No EE code reused, available to anyone who can comment. |
-| **Embedded MCP server** | A community MCP server (`@docmost/mcp`, 39 tools) is served over HTTP at `/mcp` — no enterprise license required. Replaces the removed license-gated EE MCP. |
+| **Embedded MCP server** | A community MCP server (`@docmost/mcp`, 40 tools) is served over HTTP at `/mcp` — no enterprise license required. Replaces the removed license-gated EE MCP. |
 | **AI agent chat** | Built-in AI agent chat over your wiki, written from scratch as a community feature — no enterprise license. The agent reads and edits pages on your behalf (scoped to your permissions), with full-text + vector (RAG) search and optional web access via external MCP servers. |
 | **Rebranding** | App logo / name changed from *Docmost* to *Gitmost*. |
 | **Compact page tree** | Default page-tree indentation reduced from 16px to 8px per nesting level. |
@@ -44,7 +44,7 @@ The goal of the fork is a **100% open, AGPL-only build with no Enterprise-Editio
 ### Embedded MCP server
 
 Gitmost has **our own MCP server** — [docmost-mcp](https://github.com/vvzvlad/docmost-mcp),
-which we wrote — **built directly into the app** and served at `/mcp`. It exposes **39
+which we wrote — **built directly into the app** and served at `/mcp`. It exposes **40
 agent-native tools**: surgical per-block edits (patch / insert / delete by id),
 structure-preserving find/replace, scripted `(doc) => doc` transforms with a dry-run diff,
 structured table editing, version history with diff / restore, comments, images and share
@@ -60,7 +60,7 @@ every little fix. And it needs no enterprise license.
 | | **Gitmost `/mcp` (our docmost-mcp)** | Docmost's built-in MCP |
 | --- | :---: | :---: |
 | **Enterprise license** | Not required | Required |
-| **Tools** | 39, agent-native | Coarse (read Markdown, page CRUD, replace whole page) |
+| **Tools** | 40, agent-native | Coarse (read Markdown, page CRUD, replace whole page) |
 | **Per-block edits / find-replace / scripted transforms** | ✅ | — |
 | **Structured table editing, version diff / restore** | ✅ | — |
 | **Comments, images, share links** | ✅ | — |

README.ru.md

@@ -33,7 +33,7 @@
 | --- | --- |
 | **Удалён EE-код** | Вырезан весь код Enterprise-редакции на клиенте и сервере; это чистая community/AGPL-сборка без лицензионных проверок. |
 | **Резолв комментариев** | Переписан с нуля как community-функция (резолв / переоткрытие с вкладками «Открытые» / «Решённые»). EE-код не используется, доступно любому, кто может комментировать. |
-| **Встроенный MCP-сервер** | Community MCP-сервер (`@docmost/mcp`, 39 инструментов) отдаётся по HTTP на `/mcp` — без enterprise-лицензии. Заменяет удалённый лицензируемый EE MCP. |
+| **Встроенный MCP-сервер** | Community MCP-сервер (`@docmost/mcp`, 40 инструментов) отдаётся по HTTP на `/mcp` — без enterprise-лицензии. Заменяет удалённый лицензируемый EE MCP. |
 | **Чат с AI-агентом** | Встроенный чат с AI-агентом по содержимому вики, написанный с нуля как community-функция — без enterprise-лицензии. Агент читает и редактирует страницы от вашего имени (в рамках ваших прав), с полнотекстовым + векторным (RAG) поиском и опциональным доступом в интернет через внешние MCP-серверы. |
 | **Ребрендинг** | Логотип / название приложения изменены с *Docmost* на *Gitmost*. |
 | **Компактное дерево страниц** | Отступ дерева страниц по умолчанию уменьшен с 16px до 8px на уровень вложенности. |
@@ -44,7 +44,7 @@
 
 В Gitmost есть **наш собственный MCP-сервер** — [docmost-mcp](https://github.com/vvzvlad/docmost-mcp),
 который мы написали сами, — **встроенный прямо в приложение** и доступный на `/mcp`. Он даёт
-**39 agent-native инструментов**: точечное редактирование по блокам (patch / insert / delete
+**40 agent-native инструментов**: точечное редактирование по блокам (patch / insert / delete
 по id), find/replace с сохранением структуры, скриптовые трансформации `(doc) => doc` с
 предпросмотром диффа, структурное редактирование таблиц, история версий с диффом /
 восстановлением, комментарии, изображения и ссылки на шаринг — всё применяется через слой
@@ -60,7 +60,7 @@ real-time-коллаборации Docmost, поэтому запись нико
 | | **`/mcp` в Gitmost (наш docmost-mcp)** | Родной MCP у Docmost |
 | --- | :---: | :---: |
 | **Enterprise-лицензия** | Не нужна | Нужна |
-| **Инструменты** | 39, agent-native | Примитивные (Markdown, CRUD страниц, замена целиком) |
+| **Инструменты** | 40, agent-native | Примитивные (Markdown, CRUD страниц, замена целиком) |
 | **Правки по блокам / find-replace / скриптовые трансформации** | ✅ | — |
 | **Структурное редактирование таблиц, дифф / восстановление версий** | ✅ | — |
 | **Комментарии, изображения, ссылки на шаринг** | ✅ | — |

apps/server/src/app.module.ts

@@ -28,6 +28,7 @@ import { ClsModule } from 'nestjs-cls';
 import { NoopAuditModule } from './integrations/audit/audit.module';
 import { ThrottleModule } from './integrations/throttle/throttle.module';
 import { McpModule } from './integrations/mcp/mcp.module';
+import { SandboxModule } from './integrations/sandbox/sandbox.module';
 import { AiModule } from './integrations/ai/ai.module';
 import { AiChatModule } from './core/ai-chat/ai-chat.module';
 
@@ -89,6 +90,7 @@ try {
     TelemetryModule,
     ThrottleModule,
     McpModule,
+    SandboxModule,
     AiModule,
     AiChatModule,
     ...enterpriseModules,

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

@@ -63,6 +63,9 @@ describe('AiChatToolsService deletePage guardrail (H4)', () => {
       {} as never,
       {} as never,
       {} as never,
+      // sandboxStore (only used by the stash tool closure, which these tests do
+      // not execute).
+      {} as never,
     );
   });
 
@@ -175,6 +178,9 @@ describe('AiChatToolsService expanded toolset guardrails', () => {
       {} as never,
       {} as never,
       {} as never,
+      // sandboxStore (only used by the stash tool closure, which these tests do
+      // not execute).
+      {} as never,
     );
   });
 
@@ -290,6 +296,9 @@ describe('AiChatToolsService node-arg JSON-string coercion', () => {
       {} as never,
       {} as never,
       {} as never,
+      // sandboxStore (only used by the stash tool closure, which these tests do
+      // not execute).
+      {} as never,
     );
   });
 
@@ -440,6 +449,9 @@ describe('AiChatToolsService model-friendly input validation (#190)', () => {
       {} as never,
       {} as never,
       {} as never,
+      // sandboxStore (only used by the stash tool closure, which these tests do
+      // not execute).
+      {} as never,
     );
   });
 

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

@@ -16,6 +16,7 @@ import {
 import { resolveCurrentPageResult } from './current-page.util';
 import { parseNodeArg } from './parse-node-arg';
 import { modelFriendlyInput } from './model-friendly-input';
+import { SandboxStore } from '../../../integrations/sandbox/sandbox.store';
 
 /**
  * Per-user, per-request adapter that exposes Docmost READ operations to the
@@ -41,6 +42,8 @@ export class AiChatToolsService {
     private readonly pageEmbeddingRepo: PageEmbeddingRepo,
     private readonly spaceMemberRepo: SpaceMemberRepo,
     private readonly pagePermissionRepo: PagePermissionRepo,
+    // Shared singleton in-RAM blob store backing the stash tool.
+    private readonly sandboxStore: SandboxStore,
   ) {}
 
   async forUser(
@@ -86,11 +89,17 @@ export class AiChatToolsService {
         aiChatId,
       });
 
+    // Bind the stash tool to the shared in-RAM SandboxStore. The store owns the
+    // anonymous-URL composition (putAndLink) and the live/evict probes the MCP
+    // package needs to keep its mirror counts honest under FIFO eviction (the
+    // package never touches env or the store). asSink() centralizes the uri↔id
+    // mapping next to putAndLink, shared with the embedded-MCP wiring site.
     const { DocmostClient, sharedToolSpecs } = await loadDocmostMcp();
     const client: DocmostClientLike = new DocmostClient({
       apiUrl,
       getToken,
       getCollabToken,
+      sandbox: this.sandboxStore.asSink(),
     });
 
     // Build an ai-SDK tool from a shared, zod-agnostic spec. The spec owns the
@@ -625,6 +634,14 @@ export class AiChatToolsService {
         async ({ pageId, edits }) => await client.editPageText(pageId, edits),
       ),
 
+      // Returns ONLY the short link object — never the document body — so a
+      // large page can be handed to an external consumer without bloating
+      // context.
+      stashPage: sharedTool(
+        sharedToolSpecs.stashPage,
+        async ({ pageId }) => await client.stashPage(pageId),
+      ),
+
       patchNode: tool({
         description:
           'Replace a single content block (by id) with a new ProseMirror ' +

apps/server/src/core/ai-chat/tools/docmost-client.loader.ts

@@ -154,6 +154,14 @@ export interface DocmostClientLike {
     commentId: string,
     resolved: boolean,
   ): Promise<Record<string, unknown>>;
+  // Serialize a page + mirror its internal images into the blob sandbox; returns
+  // ONLY a short anonymous URL (the body never enters the model context).
+  stashPage(pageId: string): Promise<{
+    uri: string;
+    sha256: string;
+    size: number;
+    images: { mirrored: number; failed: number };
+  }>;
 }
 
 export type DocmostClientConfig = {
@@ -161,6 +169,18 @@ export type DocmostClientConfig = {
   getToken: () => Promise<string>;
   // Provenance collab-token provider for content mutations (signed agent claim).
   getCollabToken?: () => Promise<string>;
+  // Optional blob-sandbox sink for the stash tool. `put` stores a blob in the
+  // host's in-RAM SandboxStore and returns the anonymous read URL + integrity.
+  // The optional `has`/`evict` probes let stashPage keep its mirror counts
+  // honest under the store's FIFO eviction (mirror of the package's sink type).
+  sandbox?: {
+    put: (
+      buf: Buffer,
+      mime: string,
+    ) => { uri: string; sha256: string; size: number };
+    has?: (uri: string) => boolean;
+    evict?: (uri: string) => void;
+  };
 };
 
 export interface DocmostClientCtor {

apps/server/src/integrations/environment/environment.service.spec.ts

@@ -14,4 +14,148 @@ describe('EnvironmentService', () => {
   it('should be defined', () => {
     expect(service).toBeDefined();
   });
+
+  describe('getSandboxTtlMs', () => {
+    // ConfigService stub: get(key, def) returns the configured value for the key
+    // (falling back to def), matching the @nestjs/config contract the service
+    // calls with (key, default).
+    const build = (sandboxTtl?: string) =>
+      new EnvironmentService({
+        get: (key: string, def?: string) =>
+          key === 'SANDBOX_TTL_MS' ? (sandboxTtl ?? def) : def,
+      } as any);
+
+    it.each(['0', '-5', 'abc'])(
+      'falls back to the 3600000 default for invalid value %s',
+      (value) => {
+        expect(build(value).getSandboxTtlMs()).toBe(3_600_000);
+      },
+    );
+
+    it('returns the parsed value for a valid positive integer', () => {
+      expect(build('120000').getSandboxTtlMs()).toBe(120_000);
+    });
+
+    it('uses the 3600000 default when SANDBOX_TTL_MS is unset', () => {
+      expect(build(undefined).getSandboxTtlMs()).toBe(3_600_000);
+    });
+  });
+
+  // The three byte caps share the same getPositiveIntEnv() helper as the TTL,
+  // so a non-integer / non-positive value ('0'/'-5'/'abc') falls back to the
+  // documented default and a valid positive integer is returned parsed. Note
+  // parseInt truncates '1.5' -> 1 (a valid positive integer), so that value is
+  // accepted, not rejected — same as the pre-existing TTL getter.
+  describe.each([
+    {
+      name: 'getSandboxMaxBytes',
+      key: 'SANDBOX_MAX_BYTES',
+      def: 8_388_608,
+      getter: (s: EnvironmentService) => s.getSandboxMaxBytes(),
+    },
+    {
+      name: 'getSandboxMaxImageBytes',
+      key: 'SANDBOX_MAX_IMAGE_BYTES',
+      def: 20_971_520,
+      getter: (s: EnvironmentService) => s.getSandboxMaxImageBytes(),
+    },
+    {
+      name: 'getSandboxMaxTotalBytes',
+      key: 'SANDBOX_MAX_TOTAL_BYTES',
+      def: 134_217_728,
+      getter: (s: EnvironmentService) => s.getSandboxMaxTotalBytes(),
+    },
+  ])('$name', ({ key, def, getter }) => {
+    // ConfigService stub: get(k, d) returns the configured value for THIS cap's
+    // key (falling back to d), and the default for every other key.
+    const build = (value?: string) =>
+      new EnvironmentService({
+        get: (k: string, d?: string) =>
+          k === key ? (value ?? d) : d,
+      } as any);
+
+    it.each(['0', '-5', 'abc'])(
+      `falls back to the ${def} default for invalid value %s`,
+      (value) => {
+        expect(getter(build(value))).toBe(def);
+      },
+    );
+
+    it('returns the parsed value for a valid positive integer', () => {
+      expect(getter(build('4096'))).toBe(4096);
+    });
+
+    it('truncates a non-integer like "1.5" to 1 via parseInt (not rejected)', () => {
+      expect(getter(build('1.5'))).toBe(1);
+    });
+
+    it(`uses the ${def} default when the env is unset`, () => {
+      expect(getter(build(undefined))).toBe(def);
+    });
+  });
+
+  // getPositiveIntEnv keeps a one-shot `invalidPositiveIntWarned` set so a bad
+  // value is logged ONCE per key (not on every getter call, which the sandbox
+  // hits per-put). These tests pin that dedup so a regression to per-call logging
+  // would fail loudly.
+  describe('invalid-value warn dedup', () => {
+    it('warns only once per key across repeated getter calls', () => {
+      const service = new EnvironmentService({
+        get: (k: string, d?: string) =>
+          k === 'SANDBOX_MAX_TOTAL_BYTES' ? '-5' : d,
+      } as any);
+      const warnSpy = jest
+        .spyOn((service as any).logger, 'warn')
+        .mockImplementation(() => undefined);
+
+      service.getSandboxMaxTotalBytes();
+      service.getSandboxMaxTotalBytes();
+
+      expect(warnSpy).toHaveBeenCalledTimes(1);
+    });
+
+    it('warns independently per key (dedup is per-key, not global)', () => {
+      // Two DIFFERENT SANDBOX_* keys are both invalid -> each warns once, so two
+      // warns total. This proves the dedup set is keyed, not a single global flag.
+      const service = new EnvironmentService({
+        get: (k: string, d?: string) =>
+          k === 'SANDBOX_MAX_BYTES' || k === 'SANDBOX_MAX_TOTAL_BYTES'
+            ? '-5'
+            : d,
+      } as any);
+      const warnSpy = jest
+        .spyOn((service as any).logger, 'warn')
+        .mockImplementation(() => undefined);
+
+      service.getSandboxMaxBytes();
+      service.getSandboxMaxTotalBytes();
+
+      expect(warnSpy).toHaveBeenCalledTimes(2);
+    });
+  });
+
+  describe('getSandboxPublicUrl', () => {
+    // Stub that resolves BOTH keys the public-url logic consults.
+    const build = (vals: { sandboxUrl?: string; appUrl?: string }) =>
+      new EnvironmentService({
+        get: (key: string, def?: string) =>
+          key === 'SANDBOX_PUBLIC_URL'
+            ? (vals.sandboxUrl ?? def)
+            : key === 'APP_URL'
+              ? (vals.appUrl ?? def)
+              : def,
+      } as any);
+
+    it('uses SANDBOX_PUBLIC_URL and trims a trailing slash', () => {
+      expect(
+        build({ sandboxUrl: 'https://docs.example.com/' }).getSandboxPublicUrl(),
+      ).toBe('https://docs.example.com');
+    });
+
+    it('falls back to APP_URL (origin) when SANDBOX_PUBLIC_URL is unset', () => {
+      expect(
+        build({ appUrl: 'https://app.example.com' }).getSandboxPublicUrl(),
+      ).toBe('https://app.example.com');
+    });
+  });
 });

apps/server/src/integrations/environment/environment.service.ts

@@ -1,9 +1,15 @@
-import { Injectable } from '@nestjs/common';
+import { Injectable, Logger } from '@nestjs/common';
 import { ConfigService } from '@nestjs/config';
 import ms, { StringValue } from 'ms';
 
 @Injectable()
 export class EnvironmentService {
+  private readonly logger = new Logger(EnvironmentService.name);
+  // Env keys already warned about for an invalid value (one-shot per key, so a
+  // bad SANDBOX_* value is not logged on every blob put). Mirrors the original
+  // sandboxTtlWarned guard, generalized across the TTL + the three byte caps.
+  private readonly invalidPositiveIntWarned = new Set<string>();
+
   constructor(private configService: ConfigService) {}
 
   getNodeEnv(): string {
@@ -332,4 +338,63 @@ export class EnvironmentService {
       .map((o) => o.trim())
       .filter(Boolean);
   }
+
+  // --- Blob sandbox (in-RAM ephemeral blob transfer; see SandboxModule) ---
+
+  // Base URL the sandbox `uri` is built from. It MUST be reachable over the
+  // network by the external consumer that fetches the blobs (not a loopback
+  // address if that consumer is remote). Falls back to APP_URL when unset so a
+  // single-host deployment works out of the box; set it explicitly when the
+  // consumer lives on another host.
+  getSandboxPublicUrl(): string {
+    const raw =
+      this.configService.get<string>('SANDBOX_PUBLIC_URL') || this.getAppUrl();
+    // Drop any trailing slash so `${base}/api/sb/${id}` never doubles up.
+    return raw.replace(/\/+$/, '');
+  }
+
+  // Parse a REQUIRED positive-integer env (TTL in ms or a byte cap). A
+  // non-integer or <= 0 value would break the sandbox silently (instant expiry,
+  // or every put failing against a 0-byte cap), so warn once and fall back to
+  // the default instead. Blob bodies are never logged.
+  private getPositiveIntEnv(key: string, def: number): number {
+    const parsed = parseInt(
+      this.configService.get<string>(key, String(def)),
+      10,
+    );
+    if (!Number.isInteger(parsed) || parsed <= 0) {
+      if (!this.invalidPositiveIntWarned.has(key)) {
+        this.invalidPositiveIntWarned.add(key);
+        this.logger.warn(
+          `Invalid ${key} (must be a positive integer); falling back to the ${def} default`,
+        );
+      }
+      return def;
+    }
+    return parsed;
+  }
+
+  // Blob time-to-live. Default 1h. The unguessable UUID + this short TTL + TLS
+  // are the whole capability model (no tokens). A non-positive or non-integer
+  // value would make every blob expire instantly (silent 404s), so reject it and
+  // fall back to the 1h default (warned about once to avoid per-put log spam).
+  getSandboxTtlMs(): number {
+    return this.getPositiveIntEnv('SANDBOX_TTL_MS', 3_600_000);
+  }
+
+  // Per-blob cap for non-image blobs (the serialized document). Default 8 MiB.
+  getSandboxMaxBytes(): number {
+    return this.getPositiveIntEnv('SANDBOX_MAX_BYTES', 8_388_608);
+  }
+
+  // Per-blob cap for mirrored image blobs. Default 20 MiB.
+  getSandboxMaxImageBytes(): number {
+    return this.getPositiveIntEnv('SANDBOX_MAX_IMAGE_BYTES', 20_971_520);
+  }
+
+  // RAM guard: total bytes the whole store may hold. Default 128 MiB. On
+  // overflow the store evicts oldest entries to make room.
+  getSandboxMaxTotalBytes(): number {
+    return this.getPositiveIntEnv('SANDBOX_MAX_TOTAL_BYTES', 134_217_728);
+  }
 }

apps/server/src/integrations/environment/environment.validation.ts

@@ -2,6 +2,7 @@ import {
   IsIn,
   IsNotEmpty,
   IsNotIn,
+  IsNumberString,
   IsOptional,
   IsString,
   IsUrl,
@@ -170,6 +171,35 @@ export class EnvironmentVariables {
     },
   )
   CLICKHOUSE_URL: string;
+
+  // --- Blob sandbox (in-RAM ephemeral blob transfer; see SandboxModule) ---
+
+  @IsOptional()
+  @ValidateIf((obj) => obj.SANDBOX_PUBLIC_URL != '' && obj.SANDBOX_PUBLIC_URL != null)
+  @IsUrl(
+    { protocols: ['http', 'https'], require_tld: false },
+    {
+      message:
+        'SANDBOX_PUBLIC_URL must be a valid http(s) URL reachable by the external blob consumer',
+    },
+  )
+  SANDBOX_PUBLIC_URL: string;
+
+  @IsOptional()
+  @IsNumberString({}, { message: 'SANDBOX_TTL_MS must be an integer (milliseconds)' })
+  SANDBOX_TTL_MS: string;
+
+  @IsOptional()
+  @IsNumberString({}, { message: 'SANDBOX_MAX_BYTES must be an integer (bytes)' })
+  SANDBOX_MAX_BYTES: string;
+
+  @IsOptional()
+  @IsNumberString({}, { message: 'SANDBOX_MAX_IMAGE_BYTES must be an integer (bytes)' })
+  SANDBOX_MAX_IMAGE_BYTES: string;
+
+  @IsOptional()
+  @IsNumberString({}, { message: 'SANDBOX_MAX_TOTAL_BYTES must be an integer (bytes)' })
+  SANDBOX_MAX_TOTAL_BYTES: string;
 }
 
 export function validate(config: Record<string, any>) {

apps/server/src/integrations/mcp/mcp-auth.helpers.ts

@@ -131,10 +131,25 @@ export class FailedLoginLimiter {
 }
 
 // The per-session DocmostMcpConfig shape understood by @docmost/mcp: either the
-// service-account credentials variant OR the per-user getToken variant.
+// service-account credentials variant OR the per-user getToken variant. The
-export type DocmostMcpConfig =
+// optional `sandbox` sink (blob store for the stash tool) is common to both and
+// injected by McpService after the auth decision.
+export type DocmostMcpConfig = (
   | { apiUrl: string; email: string; password: string }
-  | { apiUrl: string; getToken: () => Promise<string> };
+  | { apiUrl: string; getToken: () => Promise<string> }
+) & {
+  sandbox?: {
+    put: (
+      buf: Buffer,
+      mime: string,
+    ) => { uri: string; sha256: string; size: number };
+    // Optional live/evict probes the package uses to keep stash_page's mirror
+    // counts honest under the store's FIFO eviction (mirror of the package's
+    // sink type); older bindings omit them.
+    has?: (uri: string) => boolean;
+    evict?: (uri: string) => void;
+  };
+};
 
 export interface ResolvedMcpAuth {
   config: DocmostMcpConfig;

apps/server/src/integrations/mcp/mcp-basic-login-gate.spec.ts

@@ -109,13 +109,13 @@ function makeService(opts: {
   };
 
   const service = new McpService(
-    undefined as never, // environmentService
     undefined as never, // workspaceRepo
     undefined as never, // authService
     undefined as never, // tokenService
     undefined as never, // userRepo
     undefined as never, // userSessionRepo
     moduleRef as never, // moduleRef (read by the MFA branch)
+    undefined as never, // sandboxStore (unused by the login-gate path)
   );
   // Stop the constructor's unref'd sweep timer leaking across tests.
   service.onModuleDestroy();

apps/server/src/integrations/mcp/mcp.module.ts

@@ -2,17 +2,15 @@ import { Module } from '@nestjs/common';
 import { McpController } from './mcp.controller';
 import { McpService } from './mcp.service';
 import { DatabaseModule } from '@docmost/db/database.module';
-import { EnvironmentModule } from '../environment/environment.module';
 import { AuthModule } from '../../core/auth/auth.module';
 import { TokenModule } from '../../core/auth/token.module';
 
 // Community MCP feature: the server itself serves the Model Context Protocol
-// over HTTP at /mcp. DatabaseModule (global) provides WorkspaceRepo and
+// over HTTP at /mcp. DatabaseModule (global) provides WorkspaceRepo. AuthModule
-// EnvironmentModule (global) provides EnvironmentService. AuthModule supplies
+// supplies AuthService (per-user HTTP-Basic login validation) and TokenModule
-// AuthService (per-user HTTP-Basic login validation) and TokenModule supplies
+// supplies TokenService (Bearer access-JWT verification for the token fallback).
-// TokenService (Bearer access-JWT verification for the token fallback).
 @Module({
-  imports: [DatabaseModule, EnvironmentModule, AuthModule, TokenModule],
+  imports: [DatabaseModule, AuthModule, TokenModule],
   controllers: [McpController],
   providers: [McpService],
 })

apps/server/src/integrations/mcp/mcp.service.ts

@@ -8,7 +8,6 @@ import { ModuleRef } from '@nestjs/core';
 import { pathToFileURL } from 'node:url';
 import { IncomingMessage } from 'node:http';
 import { FastifyReply, FastifyRequest } from 'fastify';
-import { EnvironmentService } from '../environment/environment.service';
 import { WorkspaceRepo } from '@docmost/db/repos/workspace/workspace.repo';
 import { UserRepo } from '@docmost/db/repos/user/user.repo';
 import { UserSessionRepo } from '@docmost/db/repos/session/user-session.repo';
@@ -30,6 +29,7 @@ import {
   DocmostMcpConfig,
   ResolvedMcpAuth,
 } from './mcp-auth.helpers';
+import { SandboxStore } from '../sandbox/sandbox.store';
 
 // Minimal shape of the embedded MCP HTTP handler exported by @docmost/mcp/http.
 interface McpHttpHandler {
@@ -92,13 +92,14 @@ export class McpService implements OnModuleDestroy {
   private readonly sweepTimer: NodeJS.Timeout;
 
   constructor(
-    private readonly environmentService: EnvironmentService,
     private readonly workspaceRepo: WorkspaceRepo,
     private readonly authService: AuthService,
     private readonly tokenService: TokenService,
     private readonly userRepo: UserRepo,
     private readonly userSessionRepo: UserSessionRepo,
     private readonly moduleRef: ModuleRef,
+    // Shared singleton in-RAM blob store backing the stash tool.
+    private readonly sandboxStore: SandboxStore,
   ) {
     this.sweepTimer = setInterval(() => {
       try {
@@ -326,7 +327,11 @@ export class McpService implements OnModuleDestroy {
               // Should never happen: handle() always stashes before delegating.
               throw new UnauthorizedException('MCP authentication missing.');
             }
-            return resolved.config;
+            // Inject the blob-sandbox sink after the auth decision so stash_page
+            // can store blobs in the shared in-RAM store regardless of which
+            // credential variant resolved. The sink (put/has/evict + uri↔id
+            // mapping) is owned by SandboxStore.asSink().
+            return { ...resolved.config, sandbox: this.sandboxStore.asSink() };
           },
           {
             identify: (req: IncomingMessage) => {

apps/server/src/integrations/sandbox/sandbox.constants.ts

@@ -0,0 +1,6 @@
+// Single source of truth for the anonymous blob-sandbox route. The controller
+// is mounted under the global `/api` prefix, so its decorator uses the bare
+// segment while the public URL and the workspace-gate exclusion need the full
+// path — derive the latter from the former so the two never drift.
+export const SANDBOX_ROUTE_SEGMENT = 'sb';
+export const SANDBOX_API_PATH = `/api/${SANDBOX_ROUTE_SEGMENT}`;

apps/server/src/integrations/sandbox/sandbox.controller.spec.ts

@@ -0,0 +1,265 @@
+import { SandboxController } from './sandbox.controller';
+import { SandboxEntry } from './sandbox.store';
+
+// Capturing fake of the FastifyReply surface the controller uses:
+// status()/header()/headers()/send(), all chainable.
+function makeRes() {
+  const sent: { status: number; headers: Record<string, any>; body: any } = {
+    status: 200,
+    headers: {},
+    body: undefined,
+  };
+  const res: any = {
+    status(code: number) {
+      sent.status = code;
+      return res;
+    },
+    header(key: string, value: any) {
+      sent.headers[key.toLowerCase()] = value;
+      return res;
+    },
+    headers(obj: Record<string, any>) {
+      for (const k of Object.keys(obj)) sent.headers[k.toLowerCase()] = obj[k];
+      return res;
+    },
+    send(body?: any) {
+      sent.body = body;
+      return res;
+    },
+    _sent: sent,
+  };
+  return res;
+}
+
+function makeReq(headers: Record<string, any> = {}) {
+  return { headers } as any;
+}
+
+// A syntactically valid v4 UUID (version nibble 4, variant nibble 8). The
+// shared `uuid` validator is stricter than a bare hex-shape regex, so the id
+// must carry a real version/variant.
+const VALID_ID = 'aaaaaaaa-bbbb-4ccc-8ddd-eeeeeeeeeeee';
+
+function entry(buf: Buffer, mime: string, sha256: string): SandboxEntry {
+  return { buf, mime, sha256, expiresAt: Date.now() + 60_000 };
+}
+
+describe('SandboxController', () => {
+  it('serves 200 with body, Content-Type, Content-Length and sha256 ETag', async () => {
+    const buf = Buffer.from('{"ok":true}', 'utf8');
+    const sha = 'a'.repeat(64);
+    const store = { get: jest.fn().mockReturnValue(entry(buf, 'application/json', sha)) };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq(), res);
+
+    expect(store.get).toHaveBeenCalledWith(VALID_ID);
+    expect(res._sent.status).toBe(200);
+    expect(res._sent.headers['content-type']).toBe('application/json');
+    expect(res._sent.headers['content-length']).toBe(buf.length);
+    expect(res._sent.headers['etag']).toBe(`"${sha}"`);
+    expect(res._sent.body).toBe(buf);
+  });
+
+  it('returns 404 for a missing/expired blob', async () => {
+    const store = { get: jest.fn().mockReturnValue(undefined) };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq(), res);
+
+    expect(res._sent.status).toBe(404);
+    expect(res._sent.body).toBeUndefined();
+  });
+
+  it('returns 404 for a non-UUID id WITHOUT touching the store (anti-traversal)', async () => {
+    const store = { get: jest.fn() };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get('../../etc/passwd', makeReq(), res);
+
+    expect(store.get).not.toHaveBeenCalled();
+    expect(res._sent.status).toBe(404);
+  });
+
+  it('returns 304 (no body) when If-None-Match matches the ETag', async () => {
+    const sha = 'b'.repeat(64);
+    const store = {
+      get: jest.fn().mockReturnValue(entry(Buffer.from('x'), 'application/json', sha)),
+    };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq({ 'if-none-match': `"${sha}"` }), res);
+
+    expect(res._sent.status).toBe(304);
+    expect(res._sent.body).toBeUndefined();
+    expect(res._sent.headers['etag']).toBe(`"${sha}"`);
+  });
+
+  it('accepts a bare (unquoted) sha256 in If-None-Match too', async () => {
+    const sha = 'c'.repeat(64);
+    const store = {
+      get: jest.fn().mockReturnValue(entry(Buffer.from('x'), 'application/json', sha)),
+    };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq({ 'if-none-match': sha }), res);
+
+    expect(res._sent.status).toBe(304);
+  });
+
+  it('serves 200 when If-None-Match does NOT match', async () => {
+    const sha = 'd'.repeat(64);
+    const store = {
+      get: jest.fn().mockReturnValue(entry(Buffer.from('x'), 'application/json', sha)),
+    };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq({ 'if-none-match': '"stale"' }), res);
+
+    expect(res._sent.status).toBe(200);
+  });
+
+  it('returns 304 for a wildcard "*" If-None-Match', async () => {
+    const sha = 'e'.repeat(64);
+    const store = {
+      get: jest.fn().mockReturnValue(entry(Buffer.from('x'), 'application/json', sha)),
+    };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq({ 'if-none-match': '*' }), res);
+
+    expect(res._sent.status).toBe(304);
+  });
+
+  it('returns 304 for a weak validator W/"<sha>"', async () => {
+    const sha = 'f'.repeat(64);
+    const store = {
+      get: jest.fn().mockReturnValue(entry(Buffer.from('x'), 'application/json', sha)),
+    };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq({ 'if-none-match': `W/"${sha}"` }), res);
+
+    expect(res._sent.status).toBe(304);
+  });
+
+  it('returns 304 when a comma-separated If-None-Match list contains the sha', async () => {
+    const sha = '1'.repeat(64);
+    const store = {
+      get: jest.fn().mockReturnValue(entry(Buffer.from('x'), 'application/json', sha)),
+    };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(
+      VALID_ID,
+      makeReq({ 'if-none-match': `"other", "${sha}"` }),
+      res,
+    );
+
+    expect(res._sent.status).toBe(304);
+  });
+
+  it('sets a private, immutable Cache-Control with a max-age within the TTL on 200', async () => {
+    const sha = '2'.repeat(64);
+    // Known TTL: ~30s out, so the floored max-age must land within [0, 60].
+    const e: SandboxEntry = {
+      buf: Buffer.from('x'),
+      mime: 'application/json',
+      sha256: sha,
+      expiresAt: Date.now() + 30_000,
+    };
+    const store = { get: jest.fn().mockReturnValue(e) };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq(), res);
+
+    expect(res._sent.status).toBe(200);
+    const cc = res._sent.headers['cache-control'] as string;
+    expect(cc).toMatch(/^private, max-age=\d+, immutable$/);
+    const maxAge = Number(cc.match(/max-age=(\d+)/)![1]);
+    expect(maxAge).toBeGreaterThanOrEqual(0);
+    expect(maxAge).toBeLessThanOrEqual(60);
+  });
+
+  it('emits Cache-Control alongside ETag on the 304 branch', async () => {
+    const sha = '3'.repeat(64);
+    const store = {
+      get: jest.fn().mockReturnValue(entry(Buffer.from('x'), 'application/json', sha)),
+    };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq({ 'if-none-match': `"${sha}"` }), res);
+
+    expect(res._sent.status).toBe(304);
+    expect(res._sent.headers['cache-control']).toMatch(
+      /^private, max-age=\d+, immutable$/,
+    );
+  });
+
+  it('sets nosniff + restrictive CSP and serves an allowlisted image inline', async () => {
+    const sha = '4'.repeat(64);
+    const store = {
+      get: jest.fn().mockReturnValue(entry(Buffer.from('x'), 'image/png', sha)),
+    };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq(), res);
+
+    expect(res._sent.status).toBe(200);
+    expect(res._sent.headers['x-content-type-options']).toBe('nosniff');
+    expect(res._sent.headers['content-security-policy']).toBe(
+      "base-uri 'none'; object-src 'self'; default-src 'self';",
+    );
+    expect(res._sent.headers['content-disposition']).toBe('inline');
+  });
+
+  it('forces an SVG to download (attachment) while keeping nosniff + CSP', async () => {
+    const sha = '5'.repeat(64);
+    const store = {
+      get: jest.fn().mockReturnValue(entry(Buffer.from('<svg/>'), 'image/svg+xml', sha)),
+    };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq(), res);
+
+    expect(res._sent.status).toBe(200);
+    expect(res._sent.headers['content-disposition']).toBe('attachment');
+    expect(res._sent.headers['x-content-type-options']).toBe('nosniff');
+    expect(res._sent.headers['content-security-policy']).toBe(
+      "base-uri 'none'; object-src 'self'; default-src 'self';",
+    );
+  });
+
+  it('forces text/html to download (attachment) while keeping nosniff + CSP', async () => {
+    const sha = '6'.repeat(64);
+    const store = {
+      get: jest
+        .fn()
+        .mockReturnValue(entry(Buffer.from('<h1>x</h1>'), 'text/html', sha)),
+    };
+    const controller = new SandboxController(store as any);
+    const res = makeRes();
+
+    await controller.get(VALID_ID, makeReq(), res);
+
+    expect(res._sent.status).toBe(200);
+    expect(res._sent.headers['content-disposition']).toBe('attachment');
+    expect(res._sent.headers['x-content-type-options']).toBe('nosniff');
+    expect(res._sent.headers['content-security-policy']).toBe(
+      "base-uri 'none'; object-src 'self'; default-src 'self';",
+    );
+  });
+});

apps/server/src/integrations/sandbox/sandbox.controller.ts

@@ -0,0 +1,130 @@
+import { Controller, Get, Param, Req, Res } from '@nestjs/common';
+import { FastifyReply, FastifyRequest } from 'fastify';
+import { validate as isValidUUID } from 'uuid';
+import { SandboxStore } from './sandbox.store';
+import { SANDBOX_ROUTE_SEGMENT } from './sandbox.constants';
+
+// MIME types safe to render inline in a browser. SVG is deliberately EXCLUDED
+// (it can carry script), as are text/html and the JSON document blob — anything
+// not on this list is served as an attachment so an attacker-controlled mime can
+// never execute script on this origin (the route is anonymous + same-origin).
+const INLINE_SAFE_MIME = new Set([
+  'image/png',
+  'image/jpeg',
+  'image/gif',
+  'image/webp',
+  'image/avif',
+]);
+
+/**
+ * Anonymous read endpoint for the in-RAM blob sandbox.
+ *
+ * Mounted under the global `/api` prefix as `GET /api/sb/:id`. It carries NO
+ * `@UseGuards(JwtAuthGuard)`, so — exactly like the public attachment route
+ * `GET /api/files/public/...` — it is exempt from Docmost session auth. The
+ * route is ALSO listed in the workspace-resolution preHandler's excludedPaths
+ * in main.ts so a request from a remote consumer (which carries no workspace
+ * host) is not rejected with "Workspace not found".
+ *
+ * It only ever serves blobs looked up from the SandboxStore by a validated
+ * UUID; `:id` is never used as a filesystem path, so there is no traversal
+ * surface. Never returns tokens, never 401s.
+ *
+ * Anti-XSS hardening mirrors the public attachment route: every response sets
+ * `X-Content-Type-Options: nosniff` and a restrictive CSP, and serves any mime
+ * NOT on the inline-safe allowlist (svg/html/the JSON document blob) as an
+ * attachment, so an attacker-controlled `entry.mime` can never execute script
+ * on this same-origin anonymous route.
+ */
+@Controller(SANDBOX_ROUTE_SEGMENT)
+export class SandboxController {
+  constructor(private readonly store: SandboxStore) {}
+
+  @Get(':id')
+  async get(
+    @Param('id') id: string,
+    @Req() req: FastifyRequest,
+    @Res() res: FastifyReply,
+  ): Promise<void> {
+    // Validate `:id` as a real UUID via the shared `uuid` validator (same as the
+    // attachment routes). This is anti-traversal / input hygiene (so `:id` can
+    // never be a path like `../...`), NOT authorization — the capability is the
+    // unguessable id itself plus the short TTL plus TLS. A non-UUID id (including
+    // any traversal attempt) → 404 before touching the store; no stack trace
+    // leaks out.
+    if (!isValidUUID(id)) {
+      res.status(404).send();
+      return;
+    }
+
+    const entry = this.store.get(id);
+    if (!entry) {
+      // Missing or expired — indistinguishable to the caller, by design.
+      res.status(404).send();
+      return;
+    }
+
+    // Strong validator: quoted sha256, no W/ weak prefix. Same value computed
+    // at put() time, so an external consumer can detect a truncated/corrupted
+    // body — the original bug this whole channel exists to fix.
+    const etag = `"${entry.sha256}"`;
+
+    // Compute freshness BEFORE the conditional check: a 304 conditional
+    // revalidation must not lose the Cache-Control freshness directives, or a
+    // revalidating client would forget how long the blob stays fresh.
+    const ttlSeconds = Math.max(
+      0,
+      Math.floor((entry.expiresAt - Date.now()) / 1000),
+    );
+    // Capability URL — keep it out of shared caches; immutable for its TTL.
+    const cacheControl = `private, max-age=${ttlSeconds}, immutable`;
+
+    // Conditional request: an exact ETag match → 304 with no body. The blob is
+    // immutable, so the validator is stable for the blob's whole lifetime.
+    if (this.ifNoneMatchMatches(req.headers['if-none-match'], entry.sha256)) {
+      res
+        .status(304)
+        .header('ETag', etag)
+        .header('Cache-Control', cacheControl)
+        .send();
+      return;
+    }
+
+    // Non-allowlisted mimes (svg/html/the JSON blob) are forced to download so
+    // an attacker-controlled mime can never run script inline on this origin.
+    const disposition = INLINE_SAFE_MIME.has(entry.mime)
+      ? 'inline'
+      : 'attachment';
+
+    // Use @Res() + res.send(Buffer) with an explicit Content-Type so the binary
+    // body bypasses the global JSON response transform/serializer.
+    res
+      .status(200)
+      .headers({
+        'Content-Type': entry.mime,
+        'Content-Length': entry.buf.length,
+        ETag: etag,
+        'Cache-Control': cacheControl,
+        'X-Content-Type-Options': 'nosniff',
+        'Content-Security-Policy':
+          "base-uri 'none'; object-src 'self'; default-src 'self';",
+        'Content-Disposition': disposition,
+      })
+      .send(entry.buf);
+  }
+
+  // Accept the consumer's If-None-Match whether it sends the quoted ETag, a bare
+  // sha256, a weak "W/"-prefixed validator, or a comma-separated list.
+  private ifNoneMatchMatches(
+    header: string | string[] | undefined,
+    sha256: string,
+  ): boolean {
+    if (!header) return false;
+    const raw = Array.isArray(header) ? header.join(',') : header;
+    if (raw.trim() === '*') return true;
+    return raw
+      .split(',')
+      .map((t) => t.trim().replace(/^W\//, '').replace(/^"|"$/g, ''))
+      .some((t) => t === sha256);
+  }
+}

apps/server/src/integrations/sandbox/sandbox.module.ts

@@ -0,0 +1,19 @@
+import { Global, Module } from '@nestjs/common';
+import { SandboxController } from './sandbox.controller';
+import { SandboxStore } from './sandbox.store';
+
+/**
+ * In-RAM blob sandbox: a SINGLE shared SandboxStore (the @Injectable singleton)
+ * is written to by the stash tool (via McpService / AiChatToolsService) and read
+ * back by the anonymous SandboxController. Marked @Global so the same store
+ * instance is injectable everywhere without import churn — put() and get() MUST
+ * hit the same Map. EnvironmentService (caps/TTL/public URL) is provided by the
+ * global EnvironmentModule.
+ */
+@Global()
+@Module({
+  controllers: [SandboxController],
+  providers: [SandboxStore],
+  exports: [SandboxStore],
+})
+export class SandboxModule {}

apps/server/src/integrations/sandbox/sandbox.store.spec.ts

@@ -0,0 +1,163 @@
+import { createHash } from 'node:crypto';
+import { validate as isValidUUID } from 'uuid';
+import { SandboxStore } from './sandbox.store';
+
+// Build a minimal EnvironmentService stub with overridable caps/TTL.
+function makeEnv(
+  overrides: Partial<{
+    ttlMs: number;
+    maxBytes: number;
+    maxImageBytes: number;
+    maxTotalBytes: number;
+  }> = {},
+) {
+  const cfg = {
+    ttlMs: 3_600_000,
+    maxBytes: 8_388_608,
+    maxImageBytes: 20_971_520,
+    maxTotalBytes: 134_217_728,
+    ...overrides,
+  };
+  return {
+    getSandboxTtlMs: () => cfg.ttlMs,
+    getSandboxMaxBytes: () => cfg.maxBytes,
+    getSandboxMaxImageBytes: () => cfg.maxImageBytes,
+    getSandboxMaxTotalBytes: () => cfg.maxTotalBytes,
+    getSandboxPublicUrl: () => 'https://example.test',
+  } as any;
+}
+
+describe('SandboxStore', () => {
+  let store: SandboxStore;
+
+  afterEach(() => {
+    // Clear the unref'd sweep interval so it never leaks across tests.
+    store?.onModuleDestroy();
+    jest.useRealTimers();
+  });
+
+  it('put/get round-trips the exact bytes + mime and returns a UUID id', () => {
+    store = new SandboxStore(makeEnv());
+    const buf = Buffer.from('{"type":"doc","content":[]}', 'utf8');
+
+    const res = store.put(buf, 'application/json');
+    expect(isValidUUID(res.id)).toBe(true);
+    expect(res.size).toBe(buf.length);
+
+    const entry = store.get(res.id);
+    expect(entry).toBeDefined();
+    expect(entry!.buf.equals(buf)).toBe(true);
+    expect(entry!.mime).toBe('application/json');
+  });
+
+  it('computes sha256 over the body (matches a manual digest)', () => {
+    store = new SandboxStore(makeEnv());
+    const buf = Buffer.from('hello sandbox', 'utf8');
+    const expected = createHash('sha256').update(buf).digest('hex');
+
+    const res = store.put(buf, 'text/plain');
+    expect(res.sha256).toBe(expected);
+    expect(store.get(res.id)!.sha256).toBe(expected);
+  });
+
+  it('returns undefined for a missing id', () => {
+    store = new SandboxStore(makeEnv());
+    expect(store.get('11111111-1111-1111-1111-111111111111')).toBeUndefined();
+  });
+
+  it('lazily expires entries past the TTL (get returns undefined)', () => {
+    jest.useFakeTimers();
+    jest.setSystemTime(new Date('2026-01-01T00:00:00Z'));
+    store = new SandboxStore(makeEnv({ ttlMs: 1000 }));
+    const res = store.put(Buffer.from('x'), 'text/plain');
+
+    expect(store.get(res.id)).toBeDefined();
+    jest.setSystemTime(new Date('2026-01-01T00:00:02Z')); // +2s > 1s TTL
+    expect(store.get(res.id)).toBeUndefined();
+    // Eviction also frees the byte accounting.
+    expect(store.bytes).toBe(0);
+  });
+
+  it('background sweep drops expired entries without a get()', () => {
+    jest.useFakeTimers();
+    jest.setSystemTime(new Date('2026-01-01T00:00:00Z'));
+    store = new SandboxStore(makeEnv({ ttlMs: 1000 }));
+    store.put(Buffer.from('x'), 'text/plain');
+    expect(store.size).toBe(1);
+
+    jest.setSystemTime(new Date('2026-01-01T00:01:30Z')); // past TTL
+    jest.advanceTimersByTime(60_000); // fire the sweep interval
+    expect(store.size).toBe(0);
+  });
+
+  it('rejects a non-image blob over SANDBOX_MAX_BYTES', () => {
+    store = new SandboxStore(makeEnv({ maxBytes: 16 }));
+    expect(() => store.put(Buffer.alloc(17), 'application/json')).toThrow(
+      /per-blob cap/,
+    );
+  });
+
+  it('uses the larger image cap for image/* blobs', () => {
+    // 100 bytes exceeds the doc cap (16) but fits the image cap (1024).
+    store = new SandboxStore(makeEnv({ maxBytes: 16, maxImageBytes: 1024 }));
+    expect(() => store.put(Buffer.alloc(100), 'image/png')).not.toThrow();
+    // SVG counts as an image too.
+    expect(() => store.put(Buffer.alloc(100), 'image/svg+xml')).not.toThrow();
+  });
+
+  it('evicts oldest entries when the total cap would be exceeded', () => {
+    // Total cap 250 bytes; each blob 100 bytes -> only 2 fit at a time.
+    store = new SandboxStore(
+      makeEnv({ maxTotalBytes: 250, maxBytes: 1024 }),
+    );
+    const a = store.put(Buffer.alloc(100), 'application/json');
+    const b = store.put(Buffer.alloc(100), 'application/json');
+    const c = store.put(Buffer.alloc(100), 'application/json'); // evicts a
+
+    expect(store.get(a.id)).toBeUndefined(); // oldest evicted
+    expect(store.get(b.id)).toBeDefined();
+    expect(store.get(c.id)).toBeDefined();
+    expect(store.bytes).toBeLessThanOrEqual(250);
+  });
+
+  it('rejects a single blob larger than the whole total cap', () => {
+    store = new SandboxStore(
+      makeEnv({ maxTotalBytes: 50, maxBytes: 1024 }),
+    );
+    expect(() => store.put(Buffer.alloc(100), 'application/json')).toThrow(
+      /total store cap/,
+    );
+  });
+
+  it('putAndLink composes the anonymous /api/sb/<id> url with matching integrity', () => {
+    store = new SandboxStore(makeEnv());
+    const buf = Buffer.from('hello link', 'utf8');
+    const expected = createHash('sha256').update(buf).digest('hex');
+
+    const res = store.putAndLink(buf, 'image/png');
+    expect(res.uri).toMatch(/^https:\/\/example\.test\/api\/sb\/[0-9a-f-]{36}$/);
+    expect(res.sha256).toBe(expected);
+    expect(res.size).toBe(buf.length);
+  });
+
+  it('has()/remove() report and free a blob by id', () => {
+    store = new SandboxStore(makeEnv());
+    const { id } = store.put(Buffer.from('x'), 'text/plain');
+
+    expect(store.has(id)).toBe(true);
+    store.remove(id);
+    expect(store.has(id)).toBe(false);
+    expect(store.bytes).toBe(0);
+  });
+
+  it('asSink() round-trips put/has/evict through the anonymous uri', () => {
+    store = new SandboxStore(makeEnv());
+    const sink = store.asSink();
+    const buf = Buffer.from('sink bytes', 'utf8');
+
+    const r = sink.put(buf, 'image/png');
+    expect(sink.has(r.uri)).toBe(true);
+    sink.evict(r.uri);
+    expect(sink.has(r.uri)).toBe(false);
+  });
+});

apps/server/src/integrations/sandbox/sandbox.store.ts

@@ -0,0 +1,178 @@
+import { Injectable, Logger, OnModuleDestroy } from '@nestjs/common';
+import { createHash, randomUUID } from 'node:crypto';
+import { EnvironmentService } from '../environment/environment.service';
+import { SANDBOX_API_PATH } from './sandbox.constants';
+
+// In-RAM, process-local blob store. No disk, no DB. Ephemeral by design: a
+// restart empties it. A blob is addressed by an unguessable randomUUID() which
+// IS the read capability — there are NO tokens. Each blob is immutable (its id
+// never maps to changing content), so its sha256 is a perfect strong ETag.
+export interface SandboxEntry {
+  buf: Buffer;
+  mime: string;
+  sha256: string;
+  expiresAt: number;
+}
+
+export interface SandboxPutResult {
+  id: string;
+  sha256: string;
+  size: number;
+}
+
+@Injectable()
+export class SandboxStore implements OnModuleDestroy {
+  private readonly logger = new Logger(SandboxStore.name);
+  // Map preserves insertion order, so the first key is the oldest entry — used
+  // for FIFO eviction when the total-bytes RAM guard is exceeded.
+  private readonly map = new Map<string, SandboxEntry>();
+  private totalBytes = 0;
+
+  // Background sweep clears expired entries so never-fetched blobs do not linger
+  // until the next get(). unref()'d so it never holds the event loop open;
+  // cleared on module destroy. Mirrors the sweepTimer pattern in
+  // integrations/mcp/mcp.service.ts and packages/mcp/src/http.ts.
+  private readonly sweepIntervalMs = 60_000;
+  private readonly sweepTimer: NodeJS.Timeout;
+
+  constructor(private readonly environmentService: EnvironmentService) {
+    this.sweepTimer = setInterval(() => {
+      try {
+        this.sweep();
+      } catch (err) {
+        this.logger.error('Sandbox sweep failed', err as Error);
+      }
+    }, this.sweepIntervalMs);
+    this.sweepTimer.unref?.();
+  }
+
+  onModuleDestroy(): void {
+    clearInterval(this.sweepTimer);
+  }
+
+  /**
+   * Store a blob and return its read capability id + integrity metadata. The
+   * per-blob cap is chosen by mime (images get the larger image cap), and the
+   * total-store RAM guard evicts oldest entries to make room. Throws a clear
+   * error when a single blob cannot fit even after eviction. Blob bodies are
+   * never logged.
+   */
+  put(buf: Buffer, mime: string): SandboxPutResult {
+    const perBlobCap = mime.startsWith('image/')
+      ? this.environmentService.getSandboxMaxImageBytes()
+      : this.environmentService.getSandboxMaxBytes();
+    if (buf.length > perBlobCap) {
+      throw new Error(
+        `Sandbox blob of ${buf.length} bytes exceeds the ${perBlobCap}-byte per-blob cap`,
+      );
+    }
+
+    const maxTotal = this.environmentService.getSandboxMaxTotalBytes();
+    if (buf.length > maxTotal) {
+      throw new Error(
+        `Sandbox blob of ${buf.length} bytes exceeds the total store cap of ${maxTotal} bytes`,
+      );
+    }
+
+    // Drop expired entries first, then evict oldest until the new blob fits.
+    this.sweep();
+    while (this.totalBytes + buf.length > maxTotal && this.map.size > 0) {
+      const oldest = this.map.keys().next().value as string;
+      this.evict(oldest);
+    }
+
+    const id = randomUUID();
+    const sha256 = createHash('sha256').update(buf).digest('hex');
+    const expiresAt = Date.now() + this.environmentService.getSandboxTtlMs();
+    this.map.set(id, { buf, mime, sha256, expiresAt });
+    this.totalBytes += buf.length;
+    return { id, sha256, size: buf.length };
+  }
+
+  /**
+   * Store a blob and return its anonymous read URL plus integrity metadata.
+   * Owns the single sandbox-URL composition (`${publicBase}${SANDBOX_API_PATH}/
+   * <id>`) so callers never hand-build the route; the raw put() stays public for
+   * tests/low-level callers. sha256 is also the blob's strong ETag.
+   */
+  putAndLink(
+    buf: Buffer,
+    mime: string,
+  ): { uri: string; sha256: string; size: number } {
+    const stored = this.put(buf, mime);
+    const base = this.environmentService.getSandboxPublicUrl();
+    return {
+      uri: `${base}${SANDBOX_API_PATH}/${stored.id}`,
+      sha256: stored.sha256,
+      size: stored.size,
+    };
+  }
+
+  /**
+   * Adapter to the package's blob-sandbox sink contract `{ put, has, evict }`.
+   * The sink speaks anonymous `uri`s while the store is keyed by `id`, so this is
+   * the ONE place that maps a sandbox uri back to its id (the last path segment).
+   * Both wiring sites (embedded MCP + in-app agent tools) use this so the uri↔id
+   * mapping and URL composition live next to putAndLink, not copy-pasted.
+   */
+  asSink(): {
+    put: (buf: Buffer, mime: string) => { uri: string; sha256: string; size: number };
+    has: (uri: string) => boolean;
+    evict: (uri: string) => void;
+  } {
+    const idOf = (uri: string) => uri.substring(uri.lastIndexOf('/') + 1);
+    return {
+      put: (buf, mime) => this.putAndLink(buf, mime),
+      has: (uri) => this.has(idOf(uri)),
+      evict: (uri) => this.remove(idOf(uri)),
+    };
+  }
+
+  /** True if the blob is still live (not evicted/expired). */
+  has(id: string): boolean {
+    return this.get(id) !== undefined;
+  }
+
+  /** Drop a blob by id (public wrapper over the private FIFO evict). */
+  remove(id: string): void {
+    this.evict(id);
+  }
+
+  /** Returns the entry, or undefined if missing OR expired (lazy expiry). */
+  get(id: string): SandboxEntry | undefined {
+    const entry = this.map.get(id);
+    if (!entry) return undefined;
+    if (entry.expiresAt <= Date.now()) {
+      this.evict(id);
+      return undefined;
+    }
+    return entry;
+  }
+
+  /** Current number of live entries (test/diagnostic helper). */
+  get size(): number {
+    return this.map.size;
+  }
+
+  /** Current total bytes held (test/diagnostic helper). */
+  get bytes(): number {
+    return this.totalBytes;
+  }
+
+  private evict(id: string): void {
+    const entry = this.map.get(id);
+    if (entry) {
+      this.totalBytes -= entry.buf.length;
+      this.map.delete(id);
+    }
+  }
+
+  private sweep(): void {
+    const now = Date.now();
+    for (const [id, entry] of this.map) {
+      if (entry.expiresAt <= now) {
+        this.evict(id);
+      }
+    }
+  }
+}

apps/server/src/main.ts

@@ -13,6 +13,7 @@ import fastifyCookie from '@fastify/cookie';
 import fastifyIp from 'fastify-ip';
 import { InternalLogFilter } from './common/logger/internal-log-filter';
 import { EnvironmentService } from './integrations/environment/environment.service';
+import { SANDBOX_API_PATH } from './integrations/sandbox/sandbox.constants';
 import { resolveFrameHeader } from './common/helpers';
 import { resolveTrustProxy } from './integrations/environment/trust-proxy.util';
 
@@ -126,6 +127,10 @@ async function bootstrap() {
         '/api/workspace/create',
         '/api/workspace/joined',
         '/api/workspace/find-by-email',
+        // Anonymous in-RAM blob sandbox: a remote consumer fetches blobs by an
+        // unguessable UUID without any workspace host context, so the
+        // workspace-resolution gate must not apply.
+        SANDBOX_API_PATH,
       ];
 
       if (

packages/mcp/README.md

@@ -16,7 +16,7 @@ license.
 > that interface. Other Docmost MCPs are human-shaped — they expose "open the page" and
 > "replace the page"; this one exposes the editing primitives a model is good at.
 
-It exposes **38 tools** built around three ideas that the other Docmost MCPs do not
+It exposes **40 tools** built around three ideas that the other Docmost MCPs do not
 combine:
 
 1. **Surgical, token-cheap edits.** Address a single block by id and patch it, or run
@@ -106,7 +106,7 @@ There are several Docmost MCPs. Here is a capability-by-capability comparison.
 
 ## Tools
 
-All 38 tools, grouped by what you'd reach for them.
+All 40 tools, grouped by what you'd reach for them.
 
 ### Exploration & retrieval
 
@@ -203,6 +203,14 @@ All 38 tools, grouped by what you'd reach for them.
   node referencing the old attachment (recursively, including callouts/tables) via the
   live document, preserving comments, alignment and alt text. (In-place overwrite is
   deliberately avoided — some Docmost versions corrupt the attachment on overwrite.)
+- **`stash_page`** — Serialize a whole page (its full ProseMirror JSON) into an ephemeral
+  in-RAM blob and return ONLY a short anonymous URL — the body never enters the model
+  context, so it is the way to hand a large page (and its images) to an external consumer
+  without truncation. Every internal file/image attachment is mirrored into the same
+  sandbox and its `src` rewritten to a sandbox URL; external http(s) images are left
+  untouched. Returns `{ uri, size, sha256, images:{ mirrored, failed } }` (`sha256` is also
+  the blob's ETag). Blobs are RAM-only, expire after a short TTL (~1h) and are bound to the
+  server instance that created them.
 
 ### Comments
 

packages/mcp/README.ru.md

@@ -17,7 +17,7 @@
 > «открыть страницу» и «заменить страницу»; этот даёт примитивы редактирования, в которых
 > модель сильна.
 
-Сервер предоставляет **38 инструментов**, построенных вокруг трёх идей, которые другие
+Сервер предоставляет **40 инструментов**, построенных вокруг трёх идей, которые другие
 Docmost-MCP не сочетают:
 
 1. **Точечные, экономичные по токенам правки.** Адресуйте отдельный блок по id и патчите
@@ -109,7 +109,7 @@ Docmost-MCP не сочетают:
 
 ## Инструменты
 
-Все 38 инструментов, сгруппированы по задачам, для которых вы их возьмёте.
+Все 40 инструментов, сгруппированы по задачам, для которых вы их возьмёте.
 
 ### Чтение и поиск
 
@@ -209,6 +209,15 @@ Docmost-MCP не сочетают:
   коллауты/таблицы), через живой документ, сохраняя комментарии, выравнивание и alt-текст.
   (Перезапись «по месту» намеренно не используется — некоторые версии Docmost портят
   вложение при перезаписи.)
+- **`stash_page`** — Сериализовать страницу целиком (её полный ProseMirror JSON) в
+  эфемерный blob в оперативной памяти и вернуть ТОЛЬКО короткий анонимный URL — тело
+  никогда не попадает в контекст модели, поэтому это способ передать большую страницу
+  (вместе с её изображениями) внешнему потребителю без усечения. Каждое внутреннее
+  файловое/графическое вложение зеркалируется в тот же sandbox, а его `src` переписывается
+  на URL sandbox; внешние http(s)-изображения остаются нетронутыми. Возвращает
+  `{ uri, size, sha256, images:{ mirrored, failed } }` (`sha256` — это также ETag blob'а).
+  Blob'ы хранятся только в оперативной памяти, истекают через короткий TTL (~1 ч) и
+  привязаны к тому экземпляру сервера, который их создал.
 
 ### Комментарии
 

packages/mcp/build/client.js

@@ -7,6 +7,7 @@ import { TiptapTransformer } from "@hocuspocus/transformer";
 import * as Y from "yjs";
 import WebSocket from "ws";
 import { convertProseMirrorToMarkdown } from "./lib/markdown-converter.js";
+import { collectInternalFileNodes, normalizeFileUrl, resolveInternalFilePath, } from "./lib/internal-file-urls.js";
 import { updatePageContentRealtime, replacePageContent, markdownToProseMirror, markdownToProseMirrorCanonical, mutatePageContent, buildCollabWsUrl, assertYjsEncodable, applyDocToFragment, } from "./lib/collaboration.js";
 import { footnoteWarningsField } from "./lib/footnote-analyze.js";
 import { buildPageTree } from "./lib/tree.js";
@@ -51,6 +52,13 @@ export class DocmostClient {
     // its token instead of calling POST /auth/collab-token; on a 401/403 it is
     // re-invoked once. Used by the internal agent to carry signed provenance.
     getCollabTokenFn = null;
+    // Optional blob-sandbox sink for the stash tool. Null when not configured.
+    sandboxPut = null;
+    // Optional probes paired with the sink. `has` lets stashPage detect a blob
+    // FIFO-evicted by a LATER put in the same stash; `evict` lets it free this
+    // op's image blobs if the final doc put throws. Null when the sink omits them.
+    sandboxHas = null;
+    sandboxEvict = null;
     // In-flight login dedup: when the token expires, the 401 interceptor,
     // ensureAuthenticated, getCollabTokenWithReauth and the two multipart retries
     // can all call login() at once. Memoizing a single promise collapses that
@@ -77,6 +85,11 @@ export class DocmostClient {
         if (config.getCollabToken) {
             this.getCollabTokenFn = config.getCollabToken;
         }
+        if (config.sandbox) {
+            this.sandboxPut = config.sandbox.put;
+            this.sandboxHas = config.sandbox.has ?? null;
+            this.sandboxEvict = config.sandbox.evict ?? null;
+        }
         this.client = axios.create({
             baseURL: this.apiUrl,
             // Default request timeout so a hung connection cannot wedge a per-page
@@ -605,6 +618,181 @@ export class DocmostClient {
             content: data.content || { type: "doc", content: [] },
         };
     }
+    /**
+     * Fetch an INTERNAL Docmost file (authed loopback) for sandbox mirroring.
+     * `src` is normalized to `/api/files/<id>/<file>`; `this.client.baseURL`
+     * already ends in `/api`, so we strip the leading `/api` and request the
+     * relative path with the client's Authorization header. Returns the raw bytes
+     * and the response Content-Type (mime), defaulting to octet-stream.
+     *
+     * The fetch is size-bounded (hard 64 MiB ceiling) purely to protect memory;
+     * the authoritative per-blob cap is enforced by the sandbox `put`. The path is
+     * resolved via resolveInternalFilePath, which REJECTS (throws) any traversal
+     * or percent-encoded src that would let an attacker-controlled `attrs.src`
+     * escape `/api/files/` and reach another internal endpoint (SSRF). That throw
+     * happens before this.client.get, so a malicious src is counted as a failed
+     * mirror — it never reaches the network.
+     */
+    async fetchInternalFile(src) {
+        const HARD_CEILING = 64 * 1024 * 1024; // 64 MiB memory guard
+        const relPath = resolveInternalFilePath(src);
+        const response = await this.client.get(relPath, {
+            responseType: "arraybuffer",
+            timeout: 30000,
+            maxContentLength: HARD_CEILING,
+            maxBodyLength: HARD_CEILING,
+        });
+        const buffer = Buffer.from(response.data);
+        if (buffer.length === 0) {
+            throw new Error(`Empty file response from "${src}"`);
+        }
+        const rawCt = response.headers?.["content-type"];
+        const mime = typeof rawCt === "string" && rawCt.length > 0
+            ? rawCt.split(";")[0].trim().toLowerCase()
+            : "application/octet-stream";
+        return { buffer, mime };
+    }
+    /**
+     * Stash a page's full content into the in-RAM blob sandbox and return ONLY a
+     * short anonymous URL — the body never enters the model context (this is the
+     * whole point: ~30KB+ ProseMirror docs blow the model context if passed as a
+     * tool argument). Every INTERNAL file/image src (the type-agnostic criterion,
+     * so drawio/excalidraw/video/file nodes are covered too) is mirrored into the
+     * sandbox and its `src` rewritten to the sandbox URL, so an external consumer
+     * can fetch the images anonymously. External http(s) srcs are left untouched.
+     *
+     * Blobs live in RAM with a short TTL and are cleared on restart — consume the
+     * URLs within the TTL and one uptime. A failed image fetch never aborts the
+     * doc: the original src is kept and the failure counted.
+     *
+     * Returns { uri, sha256, size, images:{mirrored, failed} }. `uri` and `sha256`
+     * are for the document blob; `sha256` is also the blob's ETag (integrity).
+     */
+    async stashPage(pageId) {
+        if (!this.sandboxPut) {
+            throw new Error("stash_page is unavailable: the blob sandbox is not configured on this server");
+        }
+        await this.ensureAuthenticated();
+        // Stash the SAME shape get_page_json returns (id/title/.../content), with a
+        // deep clone so the rewrite never mutates anything shared.
+        const pageJson = await this.getPageJson(pageId);
+        const cloned = structuredClone(pageJson);
+        // Group internal-file nodes by normalized src so each unique resource is
+        // fetched + stored ONCE (dedup), and every node sharing that src points at
+        // the one sandbox blob. Capture each node's ORIGINAL raw src per-node:
+        // dedup groups nodes whose normalized src is equal even when their raw srcs
+        // differ (e.g. `/api/files/...` vs the bare `/files/...`), so on a revert we
+        // must restore each node's own original value, not the group key.
+        const bySrc = new Map();
+        for (const node of collectInternalFileNodes(cloned.content)) {
+            const origSrc = String(node.attrs.src);
+            const src = normalizeFileUrl(origSrc);
+            const entry = { node, origSrc };
+            const group = bySrc.get(src);
+            if (group)
+                group.push(entry);
+            else
+                bySrc.set(src, [entry]);
+        }
+        let mirrored = 0;
+        let failed = 0;
+        // Record every successful mirror so it can be (a) reverted if its blob gets
+        // FIFO-evicted by a LATER put in this same stash, and (b) freed if the final
+        // doc put throws.
+        const mirrors = [];
+        const MAX_CONCURRENCY = 5;
+        const groups = [...bySrc.entries()];
+        for (let i = 0; i < groups.length; i += MAX_CONCURRENCY) {
+            const batch = groups.slice(i, i + MAX_CONCURRENCY);
+            await Promise.all(batch.map(async ([src, entries]) => {
+                try {
+                    const { buffer, mime } = await this.fetchInternalFile(src);
+                    // put may throw if the blob exceeds the per-blob/total caps.
+                    const stored = this.sandboxPut(buffer, mime);
+                    for (const entry of entries)
+                        entry.node.attrs.src = stored.uri;
+                    mirrors.push({ uri: stored.uri, entries });
+                    mirrored++;
+                }
+                catch (err) {
+                    // One bad/oversized image (or a rejected traversal src) must not
+                    // abort the document. Logged unconditionally (never the blob body),
+                    // matching the package's ungated console.warn convention.
+                    failed++;
+                    console.warn(`stash_page: failed to mirror "${src}": ${err instanceof Error ? err.message : String(err)}`);
+                }
+            }));
+        }
+        // Revert one mirror's nodes to their original internal srcs and re-count it
+        // as failed (its blob was FIFO-evicted before the doc could reference it
+        // safely).
+        const revertMirror = (mirror) => {
+            for (const entry of mirror.entries)
+                entry.node.attrs.src = entry.origSrc;
+            mirrored--;
+            failed++;
+            console.warn(`stash_page: mirrored blob ${mirror.uri} was evicted before the doc ` +
+                `could safely reference it; reverted its src and counted it as failed`);
+        };
+        // Pre-put reconciliation: an image put earlier in THIS stash can FIFO-evict
+        // an even-earlier image of the same stash. Drop those from the live set
+        // first so the first serialized doc is already mostly correct.
+        let liveMirrors = mirrors;
+        if (this.sandboxHas) {
+            liveMirrors = [];
+            for (const mirror of mirrors) {
+                if (this.sandboxHas(mirror.uri))
+                    liveMirrors.push(mirror);
+                else
+                    revertMirror(mirror);
+            }
+        }
+        // Put the document, then reconcile against eviction caused by the doc put
+        // ITSELF (the doc is newest, FIFO drops oldest = this stash's images). Each
+        // iteration reverts >=1 mirror, so the loop terminates (worst case: all
+        // images reverted and the doc references no sandbox image URLs).
+        let stored;
+        for (;;) {
+            const docBuf = Buffer.from(JSON.stringify(cloned), "utf8");
+            let docStored;
+            try {
+                docStored = this.sandboxPut(docBuf, "application/json");
+            }
+            catch (err) {
+                // The doc put failed (e.g. doc exceeds the cap). Free this op's image
+                // blobs instead of leaking them in RAM for the whole TTL, then
+                // re-throw.
+                if (this.sandboxEvict) {
+                    for (const mirror of liveMirrors)
+                        this.sandboxEvict(mirror.uri);
+                }
+                throw err;
+            }
+            if (!this.sandboxHas) {
+                stored = docStored;
+                break;
+            }
+            const evictedNow = liveMirrors.filter((m) => !this.sandboxHas(m.uri));
+            if (evictedNow.length === 0) {
+                stored = docStored;
+                break;
+            }
+            // The doc we just stored references now-dead blobs. Revert those nodes,
+            // drop the stale doc blob, and loop to re-serialize + re-put the
+            // corrected doc.
+            for (const mirror of evictedNow)
+                revertMirror(mirror);
+            liveMirrors = liveMirrors.filter((m) => this.sandboxHas(m.uri));
+            if (this.sandboxEvict)
+                this.sandboxEvict(docStored.uri);
+        }
+        return {
+            uri: stored.uri,
+            sha256: stored.sha256,
+            size: stored.size,
+            images: { mirrored, failed },
+        };
+    }
     /**
      * Compact outline of a page's top-level blocks (no full document body).
      * Cheap way to locate sections/tables and grab block ids before drilling in

packages/mcp/build/index.js

@@ -285,6 +285,38 @@ export function createDocmostMcpServer(config) {
         const result = await docmostClient.editPageText(pageId, edits);
         return jsonContent(result);
     });
+    // Tool: stash_page — returns a resource_link (NOT embedded text) so the doc
+    // body never enters the model context. Registered directly (not via
+    // registerShared) because that helper only emits text content. Also returns
+    // `structuredContent` carrying the full documented `{uri, sha256, size, images}`
+    // shape alongside the resource_link, so MCP clients receive the blob's sha256
+    // (its ETag, for integrity) and mirror counts, not just the link.
+    server.registerTool(SHARED_TOOL_SPECS.stashPage.mcpName, {
+        description: SHARED_TOOL_SPECS.stashPage.description,
+        inputSchema: SHARED_TOOL_SPECS.stashPage.buildShape(z),
+    }, async ({ pageId }) => {
+        const result = await docmostClient.stashPage(pageId);
+        return {
+            content: [
+                {
+                    type: "resource_link",
+                    uri: result.uri,
+                    name: "page.json",
+                    mimeType: "application/json",
+                    size: result.size,
+                },
+            ],
+            // Mirror the full documented result shape ({ uri, size, sha256, images })
+            // as structuredContent so MCP clients get the blob's sha256 (its ETag, for
+            // integrity) and the mirror counts, not just the resource_link.
+            structuredContent: {
+                uri: result.uri,
+                sha256: result.sha256,
+                size: result.size,
+                images: result.images,
+            },
+        };
+    });
     // Tool: patch_node
     server.registerTool("patch_node", {
         description: "Replaces a single block identified by its attrs.id WITHOUT resending the " +

packages/mcp/build/lib/internal-file-urls.js

@@ -0,0 +1,110 @@
+// Detection + collection of INTERNAL Docmost file URLs inside a ProseMirror doc.
+//
+// An internal file URL is a relative path served by Docmost's authenticated
+// attachment route (`GET /api/files/:fileId/:fileName`). It is useless to an
+// external consumer (relative + needs a Docmost session), so the stash tool
+// mirrors every such resource into the blob sandbox and rewrites its `src`.
+//
+// The criterion is "internal file URL", NOT the node TYPE: image, drawio,
+// excalidraw, video and file nodes all carry such a `src`, so a type-agnostic
+// walker covers them all. External http(s) srcs (CDNs) are left untouched.
+//
+// Mirrors editor-ext's isInternalFileUrl / normalizeFileUrl (kept as a local
+// dup so the ESM mcp package does not depend on the editor-ext build).
+function isInternalFileUrl(url) {
+    if (typeof url !== "string")
+        return false;
+    const normalized = url.trim();
+    return (normalized.startsWith("/api/files/") || normalized.startsWith("/files/"));
+}
+/** Normalize a bare `/files/...` src to the canonical `/api/files/...` form. */
+export function normalizeFileUrl(src) {
+    const trimmed = src.trim();
+    if (trimmed.startsWith("/files/"))
+        return "/api" + trimmed;
+    return trimmed;
+}
+/**
+ * Resolve a page-content `src` into the safe, `/api`-relative path the stash
+ * tool may fetch over the authenticated loopback client — or THROW.
+ *
+ * SECURITY (SSRF / path-traversal): `src` comes from page content and is fully
+ * attacker-controllable. The mirroring fetch runs through the AUTHENTICATED
+ * loopback axios client whose baseURL ends in `/api`, so a naive
+ * `src.replace(/^\/api/, "")` lets a crafted value like
+ * `/api/files/../auth/whoami` collapse (via axios/WHATWG URL `..` resolution)
+ * into an ARBITRARY internal GET endpoint, whose authed response would then be
+ * stored in the anonymous sandbox (SSRF + data exfiltration). A prefix-only
+ * `startsWith("/api/files/")` check does NOT defend against this because the
+ * `..` segments are still present in the raw string and resolved later.
+ *
+ * This function defeats that by resolving the canonical pathname FIRST and only
+ * then asserting it still lives under `/api/files/`:
+ *  - it rejects any percent-encoded dot/slash (`%2e` / `%2f`): the WHATWG URL
+ *    parser collapses LITERAL `../` but does NOT decode `%2f` separators, so a
+ *    content-controlled src must never be allowed to smuggle those past the
+ *    canonicalization;
+ *  - it resolves `new URL(trimmed, "http://internal.invalid").pathname`, which
+ *    normalizes `..`/`.` segments (e.g. `/api/files/../auth/whoami` →
+ *    `/api/auth/whoami`);
+ *  - it then requires the canonical pathname to start with `/api/files/`, so a
+ *    traversal that escaped that subtree is rejected.
+ *
+ * Returns the path RELATIVE to the `/api` base (e.g. `/files/<id>/<name>`),
+ * ready to hand to the loopback client. The throw happens BEFORE any network
+ * call, so a rejected src is counted as a failed mirror and its original src is
+ * kept (the per-image try/catch in stashPage never aborts the whole document).
+ */
+export function resolveInternalFilePath(src) {
+    const trimmed = src.trim();
+    // Percent-encoded dot/slash must never reach the URL canonicalizer: the
+    // WHATWG parser does NOT decode `%2f` into a path separator, so an encoded
+    // `..%2fauth` would survive canonicalization and still escape /api/files/.
+    if (/%2e|%2f/i.test(trimmed)) {
+        throw new Error(`Refusing internal file src with percent-encoded path segment: "${src}"`);
+    }
+    let pathname;
+    try {
+        // The base host is irrelevant (never contacted); it only lets the parser
+        // resolve a relative `src` and normalize `..`/`.` segments.
+        pathname = new URL(trimmed, "http://internal.invalid").pathname;
+    }
+    catch {
+        throw new Error(`Invalid internal file src: "${src}"`);
+    }
+    if (!pathname.startsWith("/api/files/")) {
+        throw new Error(`Refusing internal file src that escapes /api/files/: "${src}"`);
+    }
+    // Strip the `/api` base prefix; the loopback client's baseURL already ends
+    // in `/api`, so it expects the path relative to that (e.g. /files/<id>/<f>).
+    return pathname.replace(/^\/api/, "");
+}
+/**
+ * Recursively collect every node whose `attrs.src` is an internal file URL.
+ * Returns references to the live nodes (so the caller can rewrite `attrs.src`
+ * in place on its clone). Descends `content` arrays, covering callouts, tables,
+ * details and any other nested container.
+ */
+export function collectInternalFileNodes(doc) {
+    const out = [];
+    const visit = (node) => {
+        if (!node)
+            return;
+        if (Array.isArray(node)) {
+            for (const child of node)
+                visit(child);
+            return;
+        }
+        if (typeof node !== "object")
+            return;
+        if (node.attrs && isInternalFileUrl(node.attrs.src)) {
+            out.push(node);
+        }
+        if (Array.isArray(node.content)) {
+            for (const child of node.content)
+                visit(child);
+        }
+    };
+    visit(doc);
+    return out;
+}

packages/mcp/build/tool-specs.js

@@ -209,4 +209,27 @@ export const SHARED_TOOL_SPECS = {
                 .describe('List of find/replace operations, applied in order'),
         }),
     },
+    // --- hand a large page to an external consumer without bloating context ---
+    stashPage: {
+        mcpName: 'stash_page',
+        inAppKey: 'stashPage',
+        description: 'Serialize a whole page (the full ProseMirror JSON, as get_page_json ' +
+            'returns) into an ephemeral in-memory blob and return ONLY a short ' +
+            'anonymous URL to it — the body NEVER enters the model context, so this ' +
+            'is the way to hand a large page (or its images) to an external consumer ' +
+            'without truncation. Every internal file/image attachment is mirrored ' +
+            'into the same sandbox and its src rewritten to a sandbox URL, so the ' +
+            'consumer can fetch the images anonymously too; external http(s) images ' +
+            'are left untouched. Returns { uri, size, sha256, images:{mirrored, ' +
+            'failed} }. Integrity: the blob is served with ETag = its sha256, so a ' +
+            'truncated/corrupted fetch is detectable. Blobs are RAM-only: they expire ' +
+            'after a short TTL (~1h) and are cleared on restart — consume the URL ' +
+            'within the TTL and one uptime, or re-stash. A blob is bound to the ' +
+            'server instance that created it: in a multi-replica deployment without ' +
+            'sticky sessions a blob stored on one instance is not retrievable via the ' +
+            'sandbox URL on another (it 404s like an expired one).',
+        buildShape: (z) => ({
+            pageId: z.string().min(1),
+        }),
+    },
 };

packages/mcp/src/client.ts

@@ -13,6 +13,11 @@ import { TiptapTransformer } from "@hocuspocus/transformer";
 import * as Y from "yjs";
 import WebSocket from "ws";
 import { convertProseMirrorToMarkdown } from "./lib/markdown-converter.js";
+import {
+  collectInternalFileNodes,
+  normalizeFileUrl,
+  resolveInternalFilePath,
+} from "./lib/internal-file-urls.js";
 import {
   updatePageContentRealtime,
   replacePageContent,
@@ -102,6 +107,14 @@ const MIME_TO_EXT: Record<string, string> = {
  * Housed here (not in index.ts) so client.ts has no type dependency on index.ts;
  * index.ts re-exports it for the package's public surface.
  */
+// Sink the stash tool writes blobs into. The host app binds this to its in-RAM
+// SandboxStore and composes the public `uri` (the package never sees the store
+// or any env). `put` returns the anonymous read URL plus integrity metadata.
+export type SandboxPut = (
+  buf: Buffer,
+  mime: string,
+) => { uri: string; sha256: string; size: number };
+
 export type DocmostMcpConfig = { apiUrl: string } & (
   | { email: string; password: string }
   | { getToken: () => Promise<string> } // returns a BARE JWT; the client adds "Bearer "
@@ -109,6 +122,15 @@ export type DocmostMcpConfig = { apiUrl: string } & (
     // Optional collab-token provider (returns a ready collab JWT). Common to
     // both branches; see the type doc above.
     getCollabToken?: () => Promise<string>;
+    // Optional blob sandbox sink. Present only where the stash tool is wired;
+    // when absent, stash_page throws a clear "not configured" error. The
+    // optional `has`/`evict` probes let stashPage keep its mirror counts honest
+    // under the store's FIFO eviction (see stashPage); older sinks omit them.
+    sandbox?: {
+      put: SandboxPut;
+      has?: (uri: string) => boolean;
+      evict?: (uri: string) => void;
+    };
   };
 
 export class DocmostClient {
@@ -126,6 +148,13 @@ export class DocmostClient {
   // its token instead of calling POST /auth/collab-token; on a 401/403 it is
   // re-invoked once. Used by the internal agent to carry signed provenance.
   private getCollabTokenFn: (() => Promise<string>) | null = null;
+  // Optional blob-sandbox sink for the stash tool. Null when not configured.
+  private sandboxPut: SandboxPut | null = null;
+  // Optional probes paired with the sink. `has` lets stashPage detect a blob
+  // FIFO-evicted by a LATER put in the same stash; `evict` lets it free this
+  // op's image blobs if the final doc put throws. Null when the sink omits them.
+  private sandboxHas: ((uri: string) => boolean) | null = null;
+  private sandboxEvict: ((uri: string) => void) | null = null;
   // In-flight login dedup: when the token expires, the 401 interceptor,
   // ensureAuthenticated, getCollabTokenWithReauth and the two multipart retries
   // can all call login() at once. Memoizing a single promise collapses that
@@ -165,6 +194,11 @@ export class DocmostClient {
     if (config.getCollabToken) {
       this.getCollabTokenFn = config.getCollabToken;
     }
+    if (config.sandbox) {
+      this.sandboxPut = config.sandbox.put;
+      this.sandboxHas = config.sandbox.has ?? null;
+      this.sandboxEvict = config.sandbox.evict ?? null;
+    }
     this.client = axios.create({
       baseURL: this.apiUrl,
       // Default request timeout so a hung connection cannot wedge a per-page
@@ -767,6 +801,203 @@ export class DocmostClient {
     };
   }
 
+  /**
+   * Fetch an INTERNAL Docmost file (authed loopback) for sandbox mirroring.
+   * `src` is normalized to `/api/files/<id>/<file>`; `this.client.baseURL`
+   * already ends in `/api`, so we strip the leading `/api` and request the
+   * relative path with the client's Authorization header. Returns the raw bytes
+   * and the response Content-Type (mime), defaulting to octet-stream.
+   *
+   * The fetch is size-bounded (hard 64 MiB ceiling) purely to protect memory;
+   * the authoritative per-blob cap is enforced by the sandbox `put`. The path is
+   * resolved via resolveInternalFilePath, which REJECTS (throws) any traversal
+   * or percent-encoded src that would let an attacker-controlled `attrs.src`
+   * escape `/api/files/` and reach another internal endpoint (SSRF). That throw
+   * happens before this.client.get, so a malicious src is counted as a failed
+   * mirror — it never reaches the network.
+   */
+  private async fetchInternalFile(
+    src: string,
+  ): Promise<{ buffer: Buffer; mime: string }> {
+    const HARD_CEILING = 64 * 1024 * 1024; // 64 MiB memory guard
+    const relPath = resolveInternalFilePath(src);
+    const response = await this.client.get(relPath, {
+      responseType: "arraybuffer",
+      timeout: 30000,
+      maxContentLength: HARD_CEILING,
+      maxBodyLength: HARD_CEILING,
+    });
+    const buffer = Buffer.from(response.data);
+    if (buffer.length === 0) {
+      throw new Error(`Empty file response from "${src}"`);
+    }
+    const rawCt = response.headers?.["content-type"];
+    const mime =
+      typeof rawCt === "string" && rawCt.length > 0
+        ? rawCt.split(";")[0].trim().toLowerCase()
+        : "application/octet-stream";
+    return { buffer, mime };
+  }
+
+  /**
+   * Stash a page's full content into the in-RAM blob sandbox and return ONLY a
+   * short anonymous URL — the body never enters the model context (this is the
+   * whole point: ~30KB+ ProseMirror docs blow the model context if passed as a
+   * tool argument). Every INTERNAL file/image src (the type-agnostic criterion,
+   * so drawio/excalidraw/video/file nodes are covered too) is mirrored into the
+   * sandbox and its `src` rewritten to the sandbox URL, so an external consumer
+   * can fetch the images anonymously. External http(s) srcs are left untouched.
+   *
+   * Blobs live in RAM with a short TTL and are cleared on restart — consume the
+   * URLs within the TTL and one uptime. A failed image fetch never aborts the
+   * doc: the original src is kept and the failure counted.
+   *
+   * Returns { uri, sha256, size, images:{mirrored, failed} }. `uri` and `sha256`
+   * are for the document blob; `sha256` is also the blob's ETag (integrity).
+   */
+  async stashPage(pageId: string): Promise<{
+    uri: string;
+    sha256: string;
+    size: number;
+    images: { mirrored: number; failed: number };
+  }> {
+    if (!this.sandboxPut) {
+      throw new Error(
+        "stash_page is unavailable: the blob sandbox is not configured on this server",
+      );
+    }
+    await this.ensureAuthenticated();
+
+    // Stash the SAME shape get_page_json returns (id/title/.../content), with a
+    // deep clone so the rewrite never mutates anything shared.
+    const pageJson = await this.getPageJson(pageId);
+    const cloned: any = structuredClone(pageJson);
+
+    // Group internal-file nodes by normalized src so each unique resource is
+    // fetched + stored ONCE (dedup), and every node sharing that src points at
+    // the one sandbox blob. Capture each node's ORIGINAL raw src per-node:
+    // dedup groups nodes whose normalized src is equal even when their raw srcs
+    // differ (e.g. `/api/files/...` vs the bare `/files/...`), so on a revert we
+    // must restore each node's own original value, not the group key.
+    const bySrc = new Map<string, Array<{ node: any; origSrc: string }>>();
+    for (const node of collectInternalFileNodes(cloned.content)) {
+      const origSrc = String(node.attrs.src);
+      const src = normalizeFileUrl(origSrc);
+      const entry = { node, origSrc };
+      const group = bySrc.get(src);
+      if (group) group.push(entry);
+      else bySrc.set(src, [entry]);
+    }
+
+    let mirrored = 0;
+    let failed = 0;
+    // Record every successful mirror so it can be (a) reverted if its blob gets
+    // FIFO-evicted by a LATER put in this same stash, and (b) freed if the final
+    // doc put throws.
+    const mirrors: Array<{
+      uri: string;
+      entries: Array<{ node: any; origSrc: string }>;
+    }> = [];
+    const MAX_CONCURRENCY = 5;
+    const groups = [...bySrc.entries()];
+    for (let i = 0; i < groups.length; i += MAX_CONCURRENCY) {
+      const batch = groups.slice(i, i + MAX_CONCURRENCY);
+      await Promise.all(
+        batch.map(async ([src, entries]) => {
+          try {
+            const { buffer, mime } = await this.fetchInternalFile(src);
+            // put may throw if the blob exceeds the per-blob/total caps.
+            const stored = this.sandboxPut!(buffer, mime);
+            for (const entry of entries) entry.node.attrs.src = stored.uri;
+            mirrors.push({ uri: stored.uri, entries });
+            mirrored++;
+          } catch (err) {
+            // One bad/oversized image (or a rejected traversal src) must not
+            // abort the document. Logged unconditionally (never the blob body),
+            // matching the package's ungated console.warn convention.
+            failed++;
+            console.warn(
+              `stash_page: failed to mirror "${src}": ${
+                err instanceof Error ? err.message : String(err)
+              }`,
+            );
+          }
+        }),
+      );
+    }
+
+    // Revert one mirror's nodes to their original internal srcs and re-count it
+    // as failed (its blob was FIFO-evicted before the doc could reference it
+    // safely).
+    const revertMirror = (mirror: {
+      uri: string;
+      entries: Array<{ node: any; origSrc: string }>;
+    }) => {
+      for (const entry of mirror.entries) entry.node.attrs.src = entry.origSrc;
+      mirrored--;
+      failed++;
+      console.warn(
+        `stash_page: mirrored blob ${mirror.uri} was evicted before the doc ` +
+          `could safely reference it; reverted its src and counted it as failed`,
+      );
+    };
+
+    // Pre-put reconciliation: an image put earlier in THIS stash can FIFO-evict
+    // an even-earlier image of the same stash. Drop those from the live set
+    // first so the first serialized doc is already mostly correct.
+    let liveMirrors = mirrors;
+    if (this.sandboxHas) {
+      liveMirrors = [];
+      for (const mirror of mirrors) {
+        if (this.sandboxHas(mirror.uri)) liveMirrors.push(mirror);
+        else revertMirror(mirror);
+      }
+    }
+
+    // Put the document, then reconcile against eviction caused by the doc put
+    // ITSELF (the doc is newest, FIFO drops oldest = this stash's images). Each
+    // iteration reverts >=1 mirror, so the loop terminates (worst case: all
+    // images reverted and the doc references no sandbox image URLs).
+    let stored: { uri: string; sha256: string; size: number };
+    for (;;) {
+      const docBuf = Buffer.from(JSON.stringify(cloned), "utf8");
+      let docStored: { uri: string; sha256: string; size: number };
+      try {
+        docStored = this.sandboxPut(docBuf, "application/json");
+      } catch (err) {
+        // The doc put failed (e.g. doc exceeds the cap). Free this op's image
+        // blobs instead of leaking them in RAM for the whole TTL, then
+        // re-throw.
+        if (this.sandboxEvict) {
+          for (const mirror of liveMirrors) this.sandboxEvict(mirror.uri);
+        }
+        throw err;
+      }
+
+      if (!this.sandboxHas) {
+        stored = docStored;
+        break;
+      }
+      const evictedNow = liveMirrors.filter((m) => !this.sandboxHas!(m.uri));
+      if (evictedNow.length === 0) {
+        stored = docStored;
+        break;
+      }
+      // The doc we just stored references now-dead blobs. Revert those nodes,
+      // drop the stale doc blob, and loop to re-serialize + re-put the
+      // corrected doc.
+      for (const mirror of evictedNow) revertMirror(mirror);
+      liveMirrors = liveMirrors.filter((m) => this.sandboxHas!(m.uri));
+      if (this.sandboxEvict) this.sandboxEvict(docStored.uri);
+    }
+    return {
+      uri: stored.uri,
+      sha256: stored.sha256,
+      size: stored.size,
+      images: { mirrored, failed },
+    };
+  }
+
   /**
    * Compact outline of a page's top-level blocks (no full document body).
    * Cheap way to locate sections/tables and grab block ids before drilling in

packages/mcp/src/index.ts

@@ -408,6 +408,43 @@ registerShared(SHARED_TOOL_SPECS.editPageText, async ({ pageId, edits }) => {
   return jsonContent(result);
 });
 
+// Tool: stash_page — returns a resource_link (NOT embedded text) so the doc
+// body never enters the model context. Registered directly (not via
+// registerShared) because that helper only emits text content. Also returns
+// `structuredContent` carrying the full documented `{uri, sha256, size, images}`
+// shape alongside the resource_link, so MCP clients receive the blob's sha256
+// (its ETag, for integrity) and mirror counts, not just the link.
+server.registerTool(
+  SHARED_TOOL_SPECS.stashPage.mcpName,
+  {
+    description: SHARED_TOOL_SPECS.stashPage.description,
+    inputSchema: SHARED_TOOL_SPECS.stashPage.buildShape!(z),
+  },
+  async ({ pageId }: { pageId: string }) => {
+    const result = await docmostClient.stashPage(pageId);
+    return {
+      content: [
+        {
+          type: "resource_link" as const,
+          uri: result.uri,
+          name: "page.json",
+          mimeType: "application/json",
+          size: result.size,
+        },
+      ],
+      // Mirror the full documented result shape ({ uri, size, sha256, images })
+      // as structuredContent so MCP clients get the blob's sha256 (its ETag, for
+      // integrity) and the mirror counts, not just the resource_link.
+      structuredContent: {
+        uri: result.uri,
+        sha256: result.sha256,
+        size: result.size,
+        images: result.images,
+      },
+    };
+  },
+);
+
 // Tool: patch_node
 server.registerTool(
   "patch_node",

packages/mcp/src/lib/internal-file-urls.ts

@@ -0,0 +1,113 @@
+// Detection + collection of INTERNAL Docmost file URLs inside a ProseMirror doc.
+//
+// An internal file URL is a relative path served by Docmost's authenticated
+// attachment route (`GET /api/files/:fileId/:fileName`). It is useless to an
+// external consumer (relative + needs a Docmost session), so the stash tool
+// mirrors every such resource into the blob sandbox and rewrites its `src`.
+//
+// The criterion is "internal file URL", NOT the node TYPE: image, drawio,
+// excalidraw, video and file nodes all carry such a `src`, so a type-agnostic
+// walker covers them all. External http(s) srcs (CDNs) are left untouched.
+//
+// Mirrors editor-ext's isInternalFileUrl / normalizeFileUrl (kept as a local
+// dup so the ESM mcp package does not depend on the editor-ext build).
+
+function isInternalFileUrl(url: unknown): boolean {
+  if (typeof url !== "string") return false;
+  const normalized = url.trim();
+  return (
+    normalized.startsWith("/api/files/") || normalized.startsWith("/files/")
+  );
+}
+
+/** Normalize a bare `/files/...` src to the canonical `/api/files/...` form. */
+export function normalizeFileUrl(src: string): string {
+  const trimmed = src.trim();
+  if (trimmed.startsWith("/files/")) return "/api" + trimmed;
+  return trimmed;
+}
+
+/**
+ * Resolve a page-content `src` into the safe, `/api`-relative path the stash
+ * tool may fetch over the authenticated loopback client — or THROW.
+ *
+ * SECURITY (SSRF / path-traversal): `src` comes from page content and is fully
+ * attacker-controllable. The mirroring fetch runs through the AUTHENTICATED
+ * loopback axios client whose baseURL ends in `/api`, so a naive
+ * `src.replace(/^\/api/, "")` lets a crafted value like
+ * `/api/files/../auth/whoami` collapse (via axios/WHATWG URL `..` resolution)
+ * into an ARBITRARY internal GET endpoint, whose authed response would then be
+ * stored in the anonymous sandbox (SSRF + data exfiltration). A prefix-only
+ * `startsWith("/api/files/")` check does NOT defend against this because the
+ * `..` segments are still present in the raw string and resolved later.
+ *
+ * This function defeats that by resolving the canonical pathname FIRST and only
+ * then asserting it still lives under `/api/files/`:
+ *  - it rejects any percent-encoded dot/slash (`%2e` / `%2f`): the WHATWG URL
+ *    parser collapses LITERAL `../` but does NOT decode `%2f` separators, so a
+ *    content-controlled src must never be allowed to smuggle those past the
+ *    canonicalization;
+ *  - it resolves `new URL(trimmed, "http://internal.invalid").pathname`, which
+ *    normalizes `..`/`.` segments (e.g. `/api/files/../auth/whoami` →
+ *    `/api/auth/whoami`);
+ *  - it then requires the canonical pathname to start with `/api/files/`, so a
+ *    traversal that escaped that subtree is rejected.
+ *
+ * Returns the path RELATIVE to the `/api` base (e.g. `/files/<id>/<name>`),
+ * ready to hand to the loopback client. The throw happens BEFORE any network
+ * call, so a rejected src is counted as a failed mirror and its original src is
+ * kept (the per-image try/catch in stashPage never aborts the whole document).
+ */
+export function resolveInternalFilePath(src: string): string {
+  const trimmed = src.trim();
+  // Percent-encoded dot/slash must never reach the URL canonicalizer: the
+  // WHATWG parser does NOT decode `%2f` into a path separator, so an encoded
+  // `..%2fauth` would survive canonicalization and still escape /api/files/.
+  if (/%2e|%2f/i.test(trimmed)) {
+    throw new Error(
+      `Refusing internal file src with percent-encoded path segment: "${src}"`,
+    );
+  }
+  let pathname: string;
+  try {
+    // The base host is irrelevant (never contacted); it only lets the parser
+    // resolve a relative `src` and normalize `..`/`.` segments.
+    pathname = new URL(trimmed, "http://internal.invalid").pathname;
+  } catch {
+    throw new Error(`Invalid internal file src: "${src}"`);
+  }
+  if (!pathname.startsWith("/api/files/")) {
+    throw new Error(
+      `Refusing internal file src that escapes /api/files/: "${src}"`,
+    );
+  }
+  // Strip the `/api` base prefix; the loopback client's baseURL already ends
+  // in `/api`, so it expects the path relative to that (e.g. /files/<id>/<f>).
+  return pathname.replace(/^\/api/, "");
+}
+
+/**
+ * Recursively collect every node whose `attrs.src` is an internal file URL.
+ * Returns references to the live nodes (so the caller can rewrite `attrs.src`
+ * in place on its clone). Descends `content` arrays, covering callouts, tables,
+ * details and any other nested container.
+ */
+export function collectInternalFileNodes(doc: unknown): any[] {
+  const out: any[] = [];
+  const visit = (node: any): void => {
+    if (!node) return;
+    if (Array.isArray(node)) {
+      for (const child of node) visit(child);
+      return;
+    }
+    if (typeof node !== "object") return;
+    if (node.attrs && isInternalFileUrl(node.attrs.src)) {
+      out.push(node);
+    }
+    if (Array.isArray(node.content)) {
+      for (const child of node.content) visit(child);
+    }
+  };
+  visit(doc);
+  return out;
+}

packages/mcp/src/tool-specs.ts

@@ -266,4 +266,29 @@ export const SHARED_TOOL_SPECS = {
         .describe('List of find/replace operations, applied in order'),
     }),
   },
+
+  // --- hand a large page to an external consumer without bloating context ---
+  stashPage: {
+    mcpName: 'stash_page',
+    inAppKey: 'stashPage',
+    description:
+      'Serialize a whole page (the full ProseMirror JSON, as get_page_json ' +
+      'returns) into an ephemeral in-memory blob and return ONLY a short ' +
+      'anonymous URL to it — the body NEVER enters the model context, so this ' +
+      'is the way to hand a large page (or its images) to an external consumer ' +
+      'without truncation. Every internal file/image attachment is mirrored ' +
+      'into the same sandbox and its src rewritten to a sandbox URL, so the ' +
+      'consumer can fetch the images anonymously too; external http(s) images ' +
+      'are left untouched. Returns { uri, size, sha256, images:{mirrored, ' +
+      'failed} }. Integrity: the blob is served with ETag = its sha256, so a ' +
+      'truncated/corrupted fetch is detectable. Blobs are RAM-only: they expire ' +
+      'after a short TTL (~1h) and are cleared on restart — consume the URL ' +
+      'within the TTL and one uptime, or re-stash. A blob is bound to the ' +
+      'server instance that created it: in a multi-replica deployment without ' +
+      'sticky sessions a blob stored on one instance is not retrievable via the ' +
+      'sandbox URL on another (it 404s like an expired one).',
+    buildShape: (z) => ({
+      pageId: z.string().min(1),
+    }),
+  },
 } satisfies Record<string, SharedToolSpec>;

packages/mcp/test/mock/stash-page-mcp-result.test.mjs

@@ -0,0 +1,155 @@
+// Server round-trip test for the stash_page MCP tool result shape. The in-app
+// path returns the full documented `{ uri, size, sha256, images }` object, but
+// the MCP transport must deliver the SAME shape: a resource_link (primary
+// payload) PLUS a `structuredContent` mirror carrying sha256 + image counts.
+// This connects a real MCP Client to the server over a linked in-memory
+// transport pair and asserts both halves of the result, end to end.
+import { test, after } from "node:test";
+import assert from "node:assert/strict";
+import http from "node:http";
+import { createHash } from "node:crypto";
+import { createDocmostMcpServer } from "../../build/index.js";
+import { Client } from "@modelcontextprotocol/sdk/client/index.js";
+import { InMemoryTransport } from "@modelcontextprotocol/sdk/inMemory.js";
+
+function readBody(req) {
+  return new Promise((resolve) => {
+    let raw = "";
+    req.on("data", (c) => (raw += c));
+    req.on("end", () => resolve(raw));
+  });
+}
+
+function startServer(handler) {
+  return new Promise((resolve) => {
+    const server = http.createServer(handler);
+    server.listen(0, "127.0.0.1", () => {
+      const { port } = server.address();
+      resolve({ server, baseURL: `http://127.0.0.1:${port}/api` });
+    });
+  });
+}
+
+const openServers = [];
+async function spawn(handler) {
+  const { server, baseURL } = await startServer(handler);
+  openServers.push(server);
+  return baseURL;
+}
+after(async () => {
+  await Promise.all(openServers.map((s) => new Promise((r) => s.close(r))));
+});
+
+// Minimal in-memory sandbox sink: store the blob and return a uri + sha256 +
+// size, with has/evict probes the client's reconciliation may call.
+function makeSandbox() {
+  const live = new Map();
+  const idOf = (uri) => uri.substring(uri.lastIndexOf("/") + 1);
+  let n = 0;
+  return {
+    put(buf) {
+      const sha256 = createHash("sha256").update(buf).digest("hex");
+      const id = `id-${n++}`;
+      live.set(id, buf.length);
+      return { uri: `https://sb.test/api/sb/${id}`, sha256, size: buf.length };
+    },
+    has(uri) {
+      return live.has(idOf(uri));
+    },
+    evict(uri) {
+      live.delete(idOf(uri));
+    },
+  };
+}
+
+const IMAGE_BYTES = Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a]);
+
+// One internal image (so images.mirrored === 1) inside a normal page doc.
+function pageDoc() {
+  return {
+    type: "doc",
+    content: [
+      {
+        type: "image",
+        attrs: { src: "/api/files/att-1/pic.png", attachmentId: "att-1" },
+      },
+    ],
+  };
+}
+
+// Mock Docmost: login, page info, internal file bytes — same pattern as
+// stash-page.test.mjs.
+async function buildBaseURL() {
+  return spawn(async (req, res) => {
+    await readBody(req);
+    if (req.url === "/api/auth/login") {
+      res.writeHead(200, {
+        "Content-Type": "application/json",
+        "Set-Cookie": "authToken=tok; HttpOnly",
+      });
+      res.end(JSON.stringify({ token: "tok" }));
+      return;
+    }
+    if (req.url === "/api/pages/info") {
+      res.writeHead(200, { "Content-Type": "application/json" });
+      res.end(
+        JSON.stringify({ data: { id: "page-1", title: "T", content: pageDoc() } }),
+      );
+      return;
+    }
+    if (req.url.startsWith("/api/files/")) {
+      res.writeHead(200, { "Content-Type": "image/png" });
+      res.end(IMAGE_BYTES);
+      return;
+    }
+    res.writeHead(404);
+    res.end();
+  });
+}
+
+test("stash_page MCP tool returns a resource_link AND a structuredContent mirror", async () => {
+  const baseURL = await buildBaseURL();
+  const sandbox = makeSandbox();
+  const server = createDocmostMcpServer({
+    apiUrl: baseURL,
+    email: "u@example.com",
+    password: "pw",
+    sandbox,
+  });
+
+  const client = new Client({ name: "test-client", version: "0.0.0" });
+  const [a, b] = InMemoryTransport.createLinkedPair();
+  await server.connect(b);
+  await client.connect(a);
+
+  try {
+    const res = await client.callTool({
+      name: "stash_page",
+      arguments: { pageId: "page-1" },
+    });
+
+    // Primary payload: a resource_link pointing at the sandbox doc blob.
+    const link = res.content[0];
+    assert.equal(link.type, "resource_link");
+    assert.match(link.uri, /^https:\/\/sb\.test\/api\/sb\//);
+
+    // structuredContent mirrors the full documented shape.
+    const sc = res.structuredContent;
+    assert.equal(typeof sc, "object");
+    assert.equal(sc.uri, link.uri); // same blob as the link
+    assert.match(sc.sha256, /^[0-9a-f]{64}$/); // 64-hex ETag
+    assert.equal(typeof sc.size, "number");
+    assert.deepEqual(sc.images, { mirrored: 1, failed: 0 });
+
+    // Deep-equal the whole structured payload against what the mock implies.
+    assert.deepEqual(sc, {
+      uri: link.uri,
+      sha256: sc.sha256,
+      size: sc.size,
+      images: { mirrored: 1, failed: 0 },
+    });
+  } finally {
+    await client.close();
+    await server.close();
+  }
+});

packages/mcp/test/mock/stash-page.test.mjs

@@ -0,0 +1,378 @@
+// Mock-HTTP test for DocmostClient.stashPage: a local http server stands in for
+// Docmost so the whole flow stays deterministic and offline. Asserts the tool
+// (1) serializes the page into the sandbox and returns ONLY a link (uri + sha256
+// + size), never the body; (2) mirrors INTERNAL image srcs into the sandbox and
+// rewrites them to the sandbox uri; (3) leaves EXTERNAL http(s) srcs untouched;
+// (4) de-duplicates a repeated internal src to a single blob; (5) counts a
+// failed image fetch without aborting the document.
+import { test, after } from "node:test";
+import assert from "node:assert/strict";
+import http from "node:http";
+import { createHash } from "node:crypto";
+import { DocmostClient } from "../../build/client.js";
+
+function readBody(req) {
+  return new Promise((resolve) => {
+    let raw = "";
+    req.on("data", (c) => (raw += c));
+    req.on("end", () => resolve(raw));
+  });
+}
+
+function startServer(handler) {
+  return new Promise((resolve) => {
+    const server = http.createServer(handler);
+    server.listen(0, "127.0.0.1", () => {
+      const { port } = server.address();
+      resolve({ server, baseURL: `http://127.0.0.1:${port}/api` });
+    });
+  });
+}
+
+const openServers = [];
+async function spawn(handler) {
+  const { server, baseURL } = await startServer(handler);
+  openServers.push(server);
+  return baseURL;
+}
+after(async () => {
+  await Promise.all(openServers.map((s) => new Promise((r) => s.close(r))));
+});
+
+// In-memory sandbox sink mirroring the host binding: store the blob, return a
+// uri + sha256 + size. Records every put so the test can inspect what was
+// stashed (and verify the doc body never leaves via the return value). Models
+// the real store's FIFO eviction + cap + the has/evict probes so B1 (self-
+// eviction reconciliation and doc-put-throw cleanup) is testable. Default
+// maxTotal is effectively unlimited so the happy-path tests behave as before.
+//
+// `throwOnJson` forces the final document put to throw, standing in for "doc
+// exceeds the cap".
+function makeSandbox({ maxTotal = Infinity, throwOnJson = false } = {}) {
+  const puts = [];
+  const evicted = [];
+  // id -> size, in insertion order (Map preserves it) so the oldest is first.
+  const live = new Map();
+  let total = 0;
+  const idOf = (uri) => uri.substring(uri.lastIndexOf("/") + 1);
+  return {
+    puts,
+    evicted,
+    put(buf, mime) {
+      if (throwOnJson && mime === "application/json") {
+        throw new Error("doc blob exceeds the sandbox cap");
+      }
+      const sha256 = createHash("sha256").update(buf).digest("hex");
+      const id = `id-${puts.length}`;
+      puts.push({ buf, mime, sha256, id });
+      live.set(id, buf.length);
+      total += buf.length;
+      // FIFO-evict the oldest live blobs until this put fits under the cap.
+      while (total > maxTotal && live.size > 0) {
+        const oldest = live.keys().next().value;
+        if (oldest === id) break; // never evict the blob we just stored
+        total -= live.get(oldest);
+        live.delete(oldest);
+        evicted.push(oldest);
+      }
+      return { uri: `https://sb.test/api/sb/${id}`, sha256, size: buf.length };
+    },
+    has(uri) {
+      return live.has(idOf(uri));
+    },
+    evict(uri) {
+      const id = idOf(uri);
+      if (live.has(id)) {
+        total -= live.get(id);
+        live.delete(id);
+      }
+      evicted.push(id);
+    },
+  };
+}
+
+const IMAGE_BYTES = Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a]); // "PNG" header-ish
+
+function pageDoc() {
+  return {
+    type: "doc",
+    content: [
+      {
+        type: "image",
+        attrs: { src: "/api/files/att-1/pic.png", attachmentId: "att-1", width: 100 },
+      },
+      // Same internal src again -> must dedup to ONE blob, both rewritten.
+      {
+        type: "image",
+        attrs: { src: "/api/files/att-1/pic.png", attachmentId: "att-1", width: 50 },
+      },
+      // External CDN image -> must be left untouched.
+      {
+        type: "image",
+        attrs: { src: "https://cdn.example.com/remote.png" },
+      },
+    ],
+  };
+}
+
+// Build a client wired to a server that logs in, serves the page, and serves the
+// internal file bytes. `fileStatus` lets a test force the file fetch to fail;
+// `doc` overrides the served page; `fileBytes`/`fileHeaders` shape the file
+// response (used by the empty-body / missing-Content-Type branch tests).
+async function buildClient(
+  sandbox,
+  {
+    fileStatus = 200,
+    doc = pageDoc(),
+    fileBytes = IMAGE_BYTES,
+    fileHeaders = { "Content-Type": "image/png" },
+  } = {},
+) {
+  const baseURL = await spawn(async (req, res) => {
+    await readBody(req);
+    if (req.url === "/api/auth/login") {
+      res.writeHead(200, {
+        "Content-Type": "application/json",
+        "Set-Cookie": "authToken=tok; HttpOnly",
+      });
+      res.end(JSON.stringify({ token: "tok" }));
+      return;
+    }
+    if (req.url === "/api/pages/info") {
+      res.writeHead(200, { "Content-Type": "application/json" });
+      res.end(JSON.stringify({ data: { id: "page-1", title: "T", content: doc } }));
+      return;
+    }
+    if (req.url.startsWith("/api/files/")) {
+      if (fileStatus !== 200) {
+        res.writeHead(fileStatus);
+        res.end();
+        return;
+      }
+      res.writeHead(200, fileHeaders);
+      res.end(fileBytes);
+      return;
+    }
+    res.writeHead(404);
+    res.end();
+  });
+  return new DocmostClient({
+    apiUrl: baseURL,
+    email: "u@example.com",
+    password: "pw",
+    sandbox: {
+      put: (buf, mime) => sandbox.put(buf, mime),
+      has: (uri) => sandbox.has(uri),
+      evict: (uri) => sandbox.evict(uri),
+    },
+  });
+}
+
+// A page with several DISTINCT internal images (each a unique attachment id) so
+// each is its own sandbox blob — needed to exercise FIFO self-eviction.
+function multiImageDoc(n) {
+  return {
+    type: "doc",
+    content: Array.from({ length: n }, (_, i) => ({
+      type: "image",
+      attrs: { src: `/api/files/att-${i}/pic.png`, attachmentId: `att-${i}` },
+    })),
+  };
+}
+
+test("stashPage stores the doc + mirrors/rewrites internal images, returns only a link", async () => {
+  const sandbox = makeSandbox();
+  const client = await buildClient(sandbox);
+
+  const result = await client.stashPage("page-1");
+
+  // Returns ONLY a link shape — never the document body.
+  assert.equal(typeof result.uri, "string");
+  assert.match(result.uri, /^https:\/\/sb\.test\/api\/sb\//);
+  assert.equal(typeof result.sha256, "string");
+  assert.equal(typeof result.size, "number");
+  assert.ok(!("doc" in result) && !("content" in result) && !("body" in result));
+  assert.deepEqual(result.images, { mirrored: 1, failed: 0 });
+
+  // One image blob (dedup) + one doc blob = 2 puts.
+  assert.equal(sandbox.puts.length, 2);
+  const imagePut = sandbox.puts[0];
+  const docPut = sandbox.puts[1];
+  assert.equal(imagePut.mime, "image/png");
+  assert.ok(imagePut.buf.equals(IMAGE_BYTES));
+  assert.equal(docPut.mime, "application/json");
+
+  // The returned uri/sha256 are the DOCUMENT blob's.
+  assert.equal(result.sha256, docPut.sha256);
+
+  // Inspect the stashed document: internal srcs rewritten, external untouched.
+  const stashed = JSON.parse(docPut.buf.toString("utf8"));
+  const imgs = stashed.content.content.filter((n) => n.type === "image");
+  assert.equal(imgs[0].attrs.src, "https://sb.test/api/sb/id-0");
+  assert.equal(imgs[1].attrs.src, "https://sb.test/api/sb/id-0"); // same blob (dedup)
+  assert.equal(imgs[2].attrs.src, "https://cdn.example.com/remote.png"); // external kept
+});
+
+test("stashPage counts a failed image fetch without aborting the document", async () => {
+  const sandbox = makeSandbox();
+  const client = await buildClient(sandbox, { fileStatus: 500 });
+
+  const result = await client.stashPage("page-1");
+
+  assert.deepEqual(result.images, { mirrored: 0, failed: 1 });
+  // Only the doc blob was stored (image fetch failed).
+  assert.equal(sandbox.puts.length, 1);
+  assert.equal(sandbox.puts[0].mime, "application/json");
+
+  // The failed internal src is LEFT as-is so nothing is silently dropped.
+  const stashed = JSON.parse(sandbox.puts[0].buf.toString("utf8"));
+  const imgs = stashed.content.content.filter((n) => n.type === "image");
+  assert.equal(imgs[0].attrs.src, "/api/files/att-1/pic.png");
+});
+
+test("stashPage throws a clear error when no sandbox is configured", async () => {
+  const baseURL = await spawn(async (req, res) => {
+    await readBody(req);
+    res.writeHead(200, { "Content-Type": "application/json" });
+    res.end(JSON.stringify({}));
+  });
+  const client = new DocmostClient({
+    apiUrl: baseURL,
+    email: "u@example.com",
+    password: "pw",
+  });
+  await assert.rejects(() => client.stashPage("page-1"), /not configured/);
+});
+
+test("stashPage reverts a FIFO-evicted image and counts it as failed (B1)", async () => {
+  // 3 distinct images of S=4000 bytes each; doc JSON is far smaller than one
+  // image. With a cap of 4500: storing img1 evicts img0, storing img2 evicts
+  // img1 — so only img2 survives the loop (img0 + img1 reverted). The doc
+  // (4000 + a few hundred bytes <= 4500) then fits alongside the survivor, so it
+  // does NOT trigger further eviction. The stored doc must therefore reference
+  // exactly one live blob and revert the other two to their internal srcs.
+  const BIG = Buffer.alloc(4000, 0x41);
+  const sandbox = makeSandbox({ maxTotal: 4500 });
+  const client = await buildClient(sandbox, {
+    doc: multiImageDoc(3),
+    fileBytes: BIG,
+  });
+
+  const result = await client.stashPage("page-1");
+
+  // Two images were evicted before the doc was stored -> counted as failed.
+  assert.deepEqual(result.images, { mirrored: 1, failed: 2 });
+
+  // Inspect the stashed doc: no node may point at an evicted (now-dead) blob,
+  // and every reverted node carries its ORIGINAL internal src again.
+  const docPut = sandbox.puts.find((p) => p.mime === "application/json");
+  const stashed = JSON.parse(docPut.buf.toString("utf8"));
+  const imgs = stashed.content.content.filter((n) => n.type === "image");
+  let live = 0;
+  let reverted = 0;
+  for (const img of imgs) {
+    const src = img.attrs.src;
+    if (src.startsWith("https://sb.test/api/sb/")) {
+      assert.ok(sandbox.has(src), `doc references evicted blob ${src}`);
+      live++;
+    } else {
+      // Reverted to the original internal src.
+      assert.match(src, /^\/api\/files\/att-\d+\/pic\.png$/);
+      reverted++;
+    }
+  }
+  assert.equal(live, 1);
+  assert.equal(reverted, 2);
+});
+
+test("stashPage reverts an image evicted by the DOC put itself (after-put reconcile, B1)", async () => {
+  // Both images (1000 bytes each) survive the image phase: total 2000 <= cap
+  // 2500. The doc, however, serializes large (a node with a ~700-byte string
+  // attr), so putting it (newest) tips total over the cap and FIFO-evicts the
+  // OLDEST image (img0) — an eviction caused by the doc put itself, which only
+  // the after-put reconciliation can catch. The loop then reverts img0, drops
+  // the stale doc blob, and re-puts the corrected doc (now total = img1 +
+  // docSize <= cap, so img1 survives).
+  const BIG = Buffer.alloc(1000, 0x41);
+  const sandbox = makeSandbox({ maxTotal: 2500 });
+  const doc = {
+    type: "doc",
+    content: [
+      { type: "image", attrs: { src: "/api/files/att-0/pic.png", attachmentId: "att-0" } },
+      { type: "image", attrs: { src: "/api/files/att-1/pic.png", attachmentId: "att-1" } },
+      // Bulk the doc JSON up so the doc put crosses the cap on its own. Stays in
+      // the doc across reverts, so each re-serialization is similarly large.
+      { type: "paragraph", attrs: { filler: "x".repeat(700) }, content: [] },
+    ],
+  };
+  const client = await buildClient(sandbox, { doc, fileBytes: BIG });
+
+  const result = await client.stashPage("page-1");
+
+  // The doc put evicted exactly one image -> reverted + counted as failed.
+  assert.deepEqual(result.images, { mirrored: 1, failed: 1 });
+
+  // Use the LAST json put: the first (stale) doc referenced the now-dead blob
+  // and was itself evicted; the corrected re-put is the one that stands.
+  const docPut = sandbox.puts.filter((p) => p.mime === "application/json").at(-1);
+  const stashed = JSON.parse(docPut.buf.toString("utf8"));
+  const imgs = stashed.content.content.filter((n) => n.type === "image");
+  let live = 0;
+  let reverted = 0;
+  for (const img of imgs) {
+    const src = img.attrs.src;
+    if (src.startsWith("https://sb.test/api/sb/")) {
+      assert.ok(sandbox.has(src), `final doc references evicted blob ${src}`);
+      live++;
+    } else {
+      assert.match(src, /^\/api\/files\/att-\d+\/pic\.png$/);
+      reverted++;
+    }
+  }
+  assert.equal(live, 1);
+  assert.equal(reverted, 1);
+});
+
+test("stashPage frees image blobs when the doc put throws (B1)", async () => {
+  // Two distinct images mirror fine; the final JSON doc put throws (doc exceeds
+  // cap). stashPage must reject AND evict every image blob it stored this op.
+  const sandbox = makeSandbox({ throwOnJson: true });
+  const client = await buildClient(sandbox, { doc: multiImageDoc(2) });
+
+  await assert.rejects(() => client.stashPage("page-1"));
+
+  // Both image blobs were stored, then evicted on the doc-put failure.
+  const imagePuts = sandbox.puts.filter((p) => p.mime === "image/png");
+  assert.equal(imagePuts.length, 2);
+  for (const p of imagePuts) {
+    assert.ok(sandbox.evicted.includes(p.id), `image ${p.id} was not freed`);
+  }
+});
+
+test("stashPage counts an empty file response as failed (B1/fetchInternalFile)", async () => {
+  const sandbox = makeSandbox();
+  const client = await buildClient(sandbox, {
+    fileBytes: Buffer.alloc(0),
+    fileHeaders: { "Content-Type": "image/png", "Content-Length": "0" },
+  });
+
+  const result = await client.stashPage("page-1");
+
+  // The single internal image (deduped) yielded an empty body -> failed.
+  assert.deepEqual(result.images, { mirrored: 0, failed: 1 });
+  // Only the doc blob was stored.
+  assert.equal(sandbox.puts.filter((p) => p.mime === "image/png").length, 0);
+});
+
+test("stashPage mirrors a file with no Content-Type as octet-stream (fetchInternalFile)", async () => {
+  const sandbox = makeSandbox();
+  // No Content-Type header at all -> fetchInternalFile defaults to octet-stream.
+  const client = await buildClient(sandbox, { fileHeaders: {} });
+
+  const result = await client.stashPage("page-1");
+
+  assert.equal(result.images.mirrored, 1);
+  const imagePut = sandbox.puts.find((p) => p.mime !== "application/json");
+  assert.ok(imagePut, "expected an image put");
+  assert.equal(imagePut.mime, "application/octet-stream");
+});

packages/mcp/test/unit/internal-file-urls.test.mjs

@@ -0,0 +1,101 @@
+// Unit tests for the internal-file URL helpers the stash tool relies on. The
+// critical case is resolveInternalFilePath, whose whole job is to REJECT a
+// content-controlled `src` that tries to escape /api/files/ (SSRF / traversal)
+// before it ever reaches the authenticated loopback client.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import {
+  resolveInternalFilePath,
+  normalizeFileUrl,
+  collectInternalFileNodes,
+} from "../../build/lib/internal-file-urls.js";
+
+test("resolveInternalFilePath accepts a normal internal src", () => {
+  assert.equal(
+    resolveInternalFilePath("/api/files/att-1/pic.png"),
+    "/files/att-1/pic.png",
+  );
+});
+
+test("resolveInternalFilePath rejects traversal / encoded variants (SSRF guard)", () => {
+  // `..` collapses to /api/auth/whoami -> outside /api/files/ -> rejected.
+  assert.throws(() => resolveInternalFilePath("/api/files/../auth/whoami"));
+  // Escapes the /api base entirely.
+  assert.throws(() => resolveInternalFilePath("/api/files/../../internal"));
+  // Percent-encoded dot -> rejected before canonicalization.
+  assert.throws(() => resolveInternalFilePath("/api/files/%2e%2e/x"));
+  // Percent-encoded slash separator -> rejected before canonicalization.
+  assert.throws(() => resolveInternalFilePath("/api/files/..%2fauth"));
+});
+
+test("resolveInternalFilePath drops a foreign host and keeps only the /api/files/ pathname (SSRF accept-path)", () => {
+  // ACCEPT path: an absolute URL has its host dropped; only the canonical
+  // pathname survives, and it must still start with /api/files/. This is SAFE
+  // because the loopback axios client ignores any host in `src` and uses its own
+  // /api baseURL — so a foreign host like evil.com is never contacted. This is
+  // the SOLE SSRF/traversal guard for content-controlled `src`, so it must be
+  // pinned: a future refactor to a prefix-only check would silently open a
+  // bypass with no failing test.
+  assert.equal(
+    resolveInternalFilePath("http://evil.com/api/files/x/y.png"),
+    "/files/x/y.png",
+  );
+  // Protocol-relative URL: host likewise dropped, pathname kept.
+  assert.equal(
+    resolveInternalFilePath("//evil.com/api/files/x/y.png"),
+    "/files/x/y.png",
+  );
+});
+
+test("resolveInternalFilePath rejects a foreign-host src whose pathname escapes /api/files/", () => {
+  // Even though the host is dropped, the canonical pathname /api/auth/whoami
+  // does NOT start with /api/files/, so it is rejected.
+  assert.throws(() =>
+    resolveInternalFilePath("https://evil.com/api/auth/whoami"),
+  );
+  // The WHATWG URL parser converts backslashes to `/` for http(s), so this
+  // collapses to /api/auth/whoami and escapes the /api/files/ subtree.
+  assert.throws(() => resolveInternalFilePath("/api/files\\..\\auth\\whoami"));
+});
+
+test("resolveInternalFilePath wraps a new URL parse failure in a clear error", () => {
+  // `http://[` has no %2e/%2f so it passes the first guard, then fails the
+  // `new URL(...)` parse — exercising the catch branch that re-throws with a
+  // clear message.
+  assert.throws(
+    () => resolveInternalFilePath("http://["),
+    /Invalid internal file src/,
+  );
+});
+
+test("normalizeFileUrl rewrites the bare /files/ branch and leaves /api/files/ alone", () => {
+  assert.equal(
+    normalizeFileUrl("/files/att-1/pic.png"),
+    "/api/files/att-1/pic.png",
+  );
+  assert.equal(
+    normalizeFileUrl("/api/files/att-1/pic.png"),
+    "/api/files/att-1/pic.png",
+  );
+});
+
+test("collectInternalFileNodes recurses into nested content containers", () => {
+  // The internal image is buried inside a callout's content array, so a
+  // regression on the recursion (e.g. a shallow .filter()) would miss it.
+  const nested = {
+    type: "image",
+    attrs: { src: "/api/files/att-9/deep.png", attachmentId: "att-9" },
+  };
+  const doc = {
+    type: "doc",
+    content: [
+      {
+        type: "callout",
+        content: [{ type: "paragraph", content: [nested] }],
+      },
+    ],
+  };
+  const found = collectInternalFileNodes(doc);
+  assert.equal(found.length, 1);
+  assert.equal(found[0], nested);
+});