diff --git a/clients/cli/src/commands/chat-writeback.ts b/clients/cli/src/commands/chat-writeback.ts
index 91dedf1..3dc80c9 100644
--- a/clients/cli/src/commands/chat-writeback.ts
+++ b/clients/cli/src/commands/chat-writeback.ts
@@ -8,11 +8,12 @@
  *        official, no exec   → POST Host /chat/completions (CLI-owned; omit usage)
  *        byo                 → --chat-complete-url | --chat-complete-exec
  *   2) mints a short-lived ACN agent JWT via POST /oauth/token (acn_* API key)
- *   3) POSTs { content, reply_to_id?, usage? } to Chat Gateway agent-messages
- *      with Bearer JWT
+ *   3) POSTs { content, reply_to_id?, usage?, attachments? } to Chat Gateway
+ *      agent-messages with Bearer JWT
  *
  * Hosts return {"content":"..."} and optionally usage (in/out billed;
- * extras stored). See skills/acn/references/INTERFAZE.md.
+ * extras stored) and mailbox ``attachments`` (``mbx:{id}`` only).
+ * See skills/acn/references/INTERFAZE.md.
  * They do not call Gateway themselves.
  */
 
@@ -156,6 +157,8 @@ export type ChatCompleteResult = {
   usage?: ChatTokenUsage;
   /** Top-level complete.model_id when no token usage is present. */
   modelId?: string;
+  /** Mailbox refs only (``mbx:{id}``). Hotlinks are dropped. */
+  attachments?: string[];
 };
 
 /**
@@ -289,6 +292,26 @@ export function extractUsage(payload: unknown): ChatTokenUsage | undefined {
   return out;
 }
 
+const MAILBOX_REF = /^mbx:[A-Za-z0-9._-]+$/;
+
+/** Complete JSON ``attachments`` — only mailbox ids; never forward http(s). */
+export function extractMailboxAttachments(payload: unknown): string[] | undefined {
+  const rec = asRecord(payload);
+  if (!rec || !Array.isArray(rec.attachments) || rec.attachments.length === 0) {
+    return undefined;
+  }
+  const out: string[] = [];
+  const seen = new Set<string>();
+  for (const item of rec.attachments) {
+    if (typeof item !== 'string') continue;
+    const t = item.trim();
+    if (!MAILBOX_REF.test(t) || seen.has(t)) continue;
+    seen.add(t);
+    out.push(t);
+  }
+  return out.length ? out : undefined;
+}
+
 function parseCompletePayload(
   payload: unknown
 ): { ok: true; result: ChatCompleteResult } | { ok: false; reason: string } {
@@ -296,9 +319,11 @@ function parseCompletePayload(
   if (!content) return { ok: false, reason: 'complete_missing_content' };
   const usage = extractUsage(payload);
   const modelId = extractModelId(payload);
+  const attachments = extractMailboxAttachments(payload);
   const result: ChatCompleteResult = { content };
   if (usage) result.usage = usage;
   else if (modelId) result.modelId = modelId;
+  if (attachments) result.attachments = attachments;
   return { ok: true, result };
 }
 
@@ -811,6 +836,9 @@ async function postWriteback(
     // model_id only — do not invent zero token counts; Host defaults tokens to 0.
     body.usage = { model_id: complete.modelId };
   }
+  if (complete.attachments?.length) {
+    body.attachments = complete.attachments;
+  }
 
   const postOnce = async (
     token: string
diff --git a/clients/cli/tests/chat-writeback.test.ts b/clients/cli/tests/chat-writeback.test.ts
index 3209542..67a502b 100644
--- a/clients/cli/tests/chat-writeback.test.ts
+++ b/clients/cli/tests/chat-writeback.test.ts
@@ -13,6 +13,7 @@ import {
   extractContent,
   extractModelId,
   extractUsage,
+  extractMailboxAttachments,
   handleChatWriteback,
   officialCompleteFailureContent,
   officialV0SupportsModel,
@@ -321,6 +322,25 @@ describe('extractUsage', () => {
   });
 });
 
+describe('extractMailboxAttachments', () => {
+  it('keeps mbx refs and drops hotlinks', () => {
+    expect(
+      extractMailboxAttachments({
+        content: 'duck',
+        attachments: [
+          'mbx:att-1',
+          'https://cdn.example/x.png',
+          'mbx:att-1',
+          'mbx:att-2',
+        ],
+      })
+    ).toEqual(['mbx:att-1', 'mbx:att-2']);
+    expect(
+      extractMailboxAttachments({ content: 'hi', attachments: ['https://x'] })
+    ).toBeUndefined();
+  });
+});
+
 describe('validateChatWritebackOptions', () => {
   it('allows disabled', () => {
     expect(validateChatWritebackOptions({})).toBeNull();
@@ -431,6 +451,54 @@ describe('handleChatWriteback', () => {
     expect(hdrs['X-Internal-Token']).toBeUndefined();
   });
 
+  it('forwards mailbox attachments from complete JSON', async () => {
+    clearAgentJwtCache();
+    const calls: Array<{ url: string; body: string }> = [];
+    const fetchFn = vi.fn(async (url: string | URL, init?: RequestInit) => {
+      const u = String(url);
+      calls.push({ url: u, body: String(init?.body ?? '') });
+      if (u.includes('/complete')) {
+        return mockOkResponse(
+          JSON.stringify({
+            content: 'here is a duck',
+            attachments: ['mbx:att-1', 'https://cdn.example/x.png'],
+          })
+        );
+      }
+      if (u.includes('/oauth/token')) {
+        return mockOkResponse(
+          JSON.stringify({ access_token: 'jwt-from-acn', expires_in: 1800 })
+        );
+      }
+      return mockOkResponse(JSON.stringify({ id: 'm1' }), 201);
+    });
+
+    const event = normalizeEvent(
+      (parseJsonRpcBody(chatMessageBody()) as { ok: true; body: Record<string, unknown> })
+        .body
+    );
+    const opts = buildChatWritebackOptions({
+      chatWriteback: true,
+      chatApiBase: 'http://gw:8000',
+      acnBaseUrl: 'https://api.acnlabs.dev',
+      apiKey: 'acn_secret',
+      chatCompleteUrl: 'http://127.0.0.1:9/complete',
+      agentId: 'agent-1',
+    })!;
+
+    const result = await handleChatWriteback(event, opts, {
+      fetchFn: fetchFn as unknown as typeof fetch,
+      logFn: () => {},
+    });
+    expect(result).toEqual({ ok: true, httpStatus: 201 });
+    const writeback = calls.find((c) => c.url.includes('/agent-messages'));
+    expect(JSON.parse(writeback?.body ?? '{}')).toEqual({
+      content: 'here is a duck',
+      reply_to_id: 'user-msg-1',
+      attachments: ['mbx:att-1'],
+    });
+  });
+
   it('injects official hop env for complete-exec and headers for complete-url', async () => {
     clearAgentJwtCache();
     const event = normalizeEvent(
diff --git a/skills/acn/references/INTERFAZE.md b/skills/acn/references/INTERFAZE.md
index 08c3239..2a3ea5b 100644
--- a/skills/acn/references/INTERFAZE.md
+++ b/skills/acn/references/INTERFAZE.md
@@ -119,11 +119,14 @@ Content-Type: application/json
     "total_tokens": 1540,
     "duration_ms": 3711,
     "provider": "tencenttokenplan"
-  }
+  },
+  "attachments": ["mbx:<attachment_id>"]
 }
 ```
 
-`acn listen --chat-writeback`：complete 返回 `{"content"}` 即可；若附带 `usage`，CLI **1.0.3+** 会一并 POST（并自动填 `reply_to_id`）。Host 开了 `CHAT_BILLING_ENABLED` 且要求 usage 时，缺 usage 则本跳不扣费。
+有图或视频：先 `POST /api/chats/{chat_id}/files`（multipart `file`：图或 mp4/webm）拿到 `ref`，再写进 `attachments`。只认本会话 `mbx:`；http(s) 热链会被 Host 拒。没有 `metadata.agentplanet.chat_id` 不要打 `/api/chats`。另一场开聊看不见这场的件。
+
+`acn listen --chat-writeback`：complete 返回 `{"content"}` 即可；若附带 `usage`，CLI **1.0.3+** 会一并 POST（并自动填 `reply_to_id`）。`attachments` 里的 `mbx:` 会转发，外链会被丢掉。Host 开了 `CHAT_BILLING_ENABLED` 且要求 usage 时，缺 usage 则本跳不扣费。 CLI 不会代传文件，宿主必须自己先 POST files。
 
 #### Owner 改默认模型