diff --git a/src/gateway/chat-attachments.test.ts b/src/gateway/chat-attachments.test.ts
index ff68480b2c2..7f30da554fa 100644
--- a/src/gateway/chat-attachments.test.ts
+++ b/src/gateway/chat-attachments.test.ts
@@ -18,10 +18,14 @@ vi.mock("../media/store.js", async (importOriginal) => {
     deleteMediaBuffer: deleteMediaBufferMock,
   };
 });
+
+import type { OpenClawConfig } from "../config/types.openclaw.js";
 import {
   buildMessageWithAttachments,
   type ChatAttachment,
+  DEFAULT_CHAT_ATTACHMENT_MAX_MB,
   parseMessageWithAttachments,
+  resolveChatAttachmentMaxBytes,
   UnsupportedAttachmentError,
 } from "./chat-attachments.js";
 
@@ -411,6 +415,32 @@ describe("parseMessageWithAttachments validation errors", () => {
   });
 });
 
+describe("resolveChatAttachmentMaxBytes", () => {
+  const MB = 1024 * 1024;
+  const DEFAULT_BYTES = DEFAULT_CHAT_ATTACHMENT_MAX_MB * MB;
+
+  const cfgWithMediaMaxMb = (value: unknown): OpenClawConfig =>
+    ({ agents: { defaults: { mediaMaxMb: value } } }) as unknown as OpenClawConfig;
+
+  it("honours a configured agents.defaults.mediaMaxMb", () => {
+    expect(resolveChatAttachmentMaxBytes(cfgWithMediaMaxMb(10))).toBe(10 * MB);
+    expect(resolveChatAttachmentMaxBytes(cfgWithMediaMaxMb(50))).toBe(50 * MB);
+  });
+
+  it("falls back to DEFAULT_CHAT_ATTACHMENT_MAX_MB when unset", () => {
+    expect(resolveChatAttachmentMaxBytes({} as OpenClawConfig)).toBe(DEFAULT_BYTES);
+    expect(resolveChatAttachmentMaxBytes({ agents: {} } as unknown as OpenClawConfig)).toBe(
+      DEFAULT_BYTES,
+    );
+  });
+
+  it("rejects non-positive, non-finite, or non-number values", () => {
+    for (const bad of [0, -5, Number.NaN, Number.POSITIVE_INFINITY, "50", null, undefined]) {
+      expect(resolveChatAttachmentMaxBytes(cfgWithMediaMaxMb(bad))).toBe(DEFAULT_BYTES);
+    }
+  });
+});
+
 describe("shared attachment validation", () => {
   it("rejects invalid base64 content for both builder and parser", async () => {
     const bad: ChatAttachment = {
diff --git a/src/gateway/chat-attachments.ts b/src/gateway/chat-attachments.ts
index 6f2df3f70d1..7f61e02d5b2 100644
--- a/src/gateway/chat-attachments.ts
+++ b/src/gateway/chat-attachments.ts
@@ -257,6 +257,11 @@ export async function parseMessageWithAttachments(
       const providedMime = normalizeMime(mime);
       const sniffedMime = normalizeMime(await sniffMimeFromBase64(b64));
       const labelMime = normalizeMime(mimeTypeFromFilePath(label));
+
+      // Prefer specific MIME signals over generic container types. OOXML
+      // documents (docx/xlsx/pptx) sniff as application/zip; without this
+      // priority the agent would receive a `.zip` instead of the specific
+      // Office document the caller declared.
       const finalMime =
         (sniffedMime && !isGenericContainerMime(sniffedMime) && sniffedMime) ||
         (providedMime && !isGenericContainerMime(providedMime) && providedMime) ||
diff --git a/src/gateway/server-methods/agent.ts b/src/gateway/server-methods/agent.ts
index 52c49075a63..640df493eb4 100644
--- a/src/gateway/server-methods/agent.ts
+++ b/src/gateway/server-methods/agent.ts
@@ -79,7 +79,11 @@ import {
 } from "../../utils/message-channel.js";
 import { resolveAssistantIdentity } from "../assistant-identity.js";
 import { registerChatAbortController, resolveAgentRunExpiresAtMs } from "../chat-abort.js";
-import { MediaOffloadError, parseMessageWithAttachments } from "../chat-attachments.js";
+import {
+  MediaOffloadError,
+  parseMessageWithAttachments,
+  resolveChatAttachmentMaxBytes,
+} from "../chat-attachments.js";
 import { resolveAssistantAvatarUrl } from "../control-ui-shared.js";
 import { ADMIN_SCOPE } from "../method-scopes.js";
 import { GATEWAY_CLIENT_CAPS, hasGatewayClientCap } from "../protocol/client-info.js";
@@ -506,7 +510,7 @@ export const agentHandlers: GatewayRequestHandlers = {
 
       try {
         const parsed = await parseMessageWithAttachments(message, normalizedAttachments, {
-          maxBytes: 5_000_000,
+          maxBytes: resolveChatAttachmentMaxBytes(cfg),
           log: context.logGateway,
           supportsInlineImages,
           // agent.run does not yet wire a ctx.MediaPaths stage path, so reject
diff --git a/src/gateway/server-methods/chat.directive-tags.test.ts b/src/gateway/server-methods/chat.directive-tags.test.ts
index f845dd3284a..fb1f6f0a302 100644
--- a/src/gateway/server-methods/chat.directive-tags.test.ts
+++ b/src/gateway/server-methods/chat.directive-tags.test.ts
@@ -66,6 +66,10 @@ const mockState = vi.hoisted(() => ({
   saveMediaWait: null as Promise<void> | null,
   activeSaveMediaCalls: 0,
   maxActiveSaveMediaCalls: 0,
+  sandboxWorkspace: null as { workspaceDir: string; containerWorkdir?: string } | null,
+  stageSandboxMediaError: null as Error | null,
+  stagedRelativePaths: null as string[] | null,
+  deleteMediaBufferCalls: [] as Array<{ id: string; subdir?: string }>,
 }));
 
 const bindingMocks = vi.hoisted(() => ({
@@ -216,11 +220,38 @@ vi.mock("../../sessions/transcript-events.js", () => ({
   ),
 }));
 
+vi.mock("../../agents/sandbox/context.js", async () => {
+  const original = await vi.importActual<typeof import("../../agents/sandbox/context.js")>(
+    "../../agents/sandbox/context.js",
+  );
+  return {
+    ...original,
+    ensureSandboxWorkspaceForSession: vi.fn(async () => mockState.sandboxWorkspace),
+  };
+});
+
+vi.mock("../../auto-reply/reply/stage-sandbox-media.js", () => ({
+  stageSandboxMedia: vi.fn(
+    async (params: { ctx: { MediaPaths?: string[]; MediaPath?: string } }) => {
+      if (mockState.stageSandboxMediaError) {
+        throw mockState.stageSandboxMediaError;
+      }
+      if (mockState.stagedRelativePaths) {
+        params.ctx.MediaPaths = [...mockState.stagedRelativePaths];
+        params.ctx.MediaPath = mockState.stagedRelativePaths[0];
+      }
+    },
+  ),
+}));
+
 vi.mock("../../media/store.js", async () => {
   const original =
     await vi.importActual<typeof import("../../media/store.js")>("../../media/store.js");
   return {
     ...original,
+    deleteMediaBuffer: vi.fn(async (id: string, subdir?: string) => {
+      mockState.deleteMediaBufferCalls.push({ id, subdir });
+    }),
     saveMediaBuffer: vi.fn(async (buffer: Buffer, contentType?: string, subdir?: string) => {
       mockState.activeSaveMediaCalls += 1;
       mockState.maxActiveSaveMediaCalls = Math.max(
@@ -465,6 +496,10 @@ describe("chat directive tag stripping for non-streaming final payloads", () =>
     mockState.maxActiveSaveMediaCalls = 0;
     bindingMocks.resolveByConversation.mockReset();
     bindingMocks.resolveByConversation.mockReturnValue(null);
+    mockState.sandboxWorkspace = null;
+    mockState.stageSandboxMediaError = null;
+    mockState.stagedRelativePaths = null;
+    mockState.deleteMediaBufferCalls = [];
   });
 
   it("registers tool-event recipients for clients advertising tool-events capability", async () => {
@@ -2522,6 +2557,119 @@ describe("chat directive tag stripping for non-streaming final payloads", () =>
     expect(mockState.lastDispatchCtx?.MediaStaged).toBe(true);
   });
 
+  it("absolutizes sandbox-relative MediaPaths so media-understanding can resolve them", async () => {
+    createTranscriptFixture("openclaw-chat-send-non-image-absolutize-");
+    mockState.finalText = "ok";
+    mockState.sessionEntry = {
+      modelProvider: "test-provider",
+      model: "vision-model",
+    };
+    mockState.modelCatalog = [
+      {
+        provider: "test-provider",
+        id: "vision-model",
+        name: "Vision model",
+        input: ["text", "image"],
+      },
+    ];
+    mockState.savedMediaResults = [
+      { path: "/home/user/.openclaw/media/inbound/report.pdf", contentType: "application/pdf" },
+    ];
+    mockState.sandboxWorkspace = { workspaceDir: "/sandbox/workspace" };
+    mockState.stagedRelativePaths = ["media/inbound/report.pdf"];
+    const respond = vi.fn();
+    const context = createChatContext();
+    const pdf = Buffer.from("%PDF-1.4\n%µ¶\n1 0 obj\n<<>>\nendobj\n").toString("base64");
+
+    await runNonStreamingChatSend({
+      context,
+      respond,
+      idempotencyKey: "idem-non-image-absolutize",
+      message: "read this",
+      requestParams: {
+        attachments: [
+          {
+            type: "file",
+            mimeType: "application/pdf",
+            fileName: "report.pdf",
+            content: pdf,
+          },
+        ],
+      },
+      expectBroadcast: false,
+    });
+
+    // applyMediaUnderstanding resolves `path.isAbsolute(raw) ? raw : path.resolve(raw)`
+    // against the gateway CWD. Relative paths would miss the staged copy, so
+    // prestage rejoins the sandbox workspaceDir to keep the path absolute.
+    expect(mockState.lastDispatchCtx?.MediaPaths).toEqual([
+      "/sandbox/workspace/media/inbound/report.pdf",
+    ]);
+    expect(mockState.lastDispatchCtx?.MediaPath).toBe(
+      "/sandbox/workspace/media/inbound/report.pdf",
+    );
+    expect(mockState.lastDispatchCtx?.MediaStaged).toBe(true);
+  });
+
+  it("wraps stageSandboxMedia infrastructure errors as 5xx UNAVAILABLE and cleans up media-store files", async () => {
+    createTranscriptFixture("openclaw-chat-send-stage-unavailable-");
+    mockState.finalText = "ok";
+    mockState.sessionEntry = {
+      modelProvider: "test-provider",
+      model: "vision-model",
+    };
+    mockState.modelCatalog = [
+      {
+        provider: "test-provider",
+        id: "vision-model",
+        name: "Vision model",
+        input: ["text", "image"],
+      },
+    ];
+    mockState.savedMediaResults = [
+      { path: "/home/user/.openclaw/media/inbound/report.pdf", contentType: "application/pdf" },
+    ];
+    mockState.sandboxWorkspace = { workspaceDir: "/sandbox/workspace" };
+    mockState.stageSandboxMediaError = Object.assign(new Error("ENOSPC: no space left on device"), {
+      code: "ENOSPC",
+    });
+    const respond = vi.fn();
+    const context = createChatContext();
+    const pdf = Buffer.from("%PDF-1.4\n%µ¶\n1 0 obj\n<<>>\nendobj\n").toString("base64");
+
+    await runNonStreamingChatSend({
+      context,
+      respond,
+      idempotencyKey: "idem-stage-unavailable",
+      message: "read this",
+      requestParams: {
+        attachments: [
+          {
+            type: "file",
+            mimeType: "application/pdf",
+            fileName: "report.pdf",
+            content: pdf,
+          },
+        ],
+      },
+      expectBroadcast: false,
+      waitFor: "none",
+    });
+
+    // Plain Error from stageSandboxMedia would be misclassified as INVALID_REQUEST
+    // by the outer catch. Wrapping it in MediaOffloadError routes it to UNAVAILABLE
+    // so the client retries instead of treating it as a bad request.
+    expect(mockState.lastDispatchCtx).toBeUndefined();
+    expect(respond).toHaveBeenCalledTimes(1);
+    const [ok, payload, error] = respond.mock.calls[0] ?? [];
+    expect(ok).toBe(false);
+    expect(payload).toBeUndefined();
+    expect(error?.code).toBe(ErrorCodes.UNAVAILABLE);
+    expect(error?.message ?? String(error)).toMatch(/ENOSPC|non-image attachments/i);
+    // Orphaned media-store files are cleaned up before the 5xx surfaces.
+    expect(mockState.deleteMediaBufferCalls).toEqual([{ id: "saved-media", subdir: "inbound" }]);
+  });
+
   it("passes imageOrder for mixed inline and offloaded chat.send attachments", async () => {
     createTranscriptFixture("openclaw-chat-send-image-order-");
     mockState.finalText = "ok";
diff --git a/src/gateway/server-methods/chat.ts b/src/gateway/server-methods/chat.ts
index b52f7c45e53..9ef2aa4fcb2 100644
--- a/src/gateway/server-methods/chat.ts
+++ b/src/gateway/server-methods/chat.ts
@@ -15,6 +15,7 @@ import type { MsgContext, TemplateContext } from "../../auto-reply/templating.js
 import { extractCanvasFromText } from "../../chat/canvas-render.js";
 import { resolveSessionFilePath } from "../../config/sessions.js";
 import type { OpenClawConfig } from "../../config/types.openclaw.js";
+import { formatErrorMessage } from "../../infra/errors.js";
 import { jsonUtf8Bytes } from "../../infra/json-utf8-bytes.js";
 import { normalizeReplyPayloadsForDelivery } from "../../infra/outbound/payloads.js";
 import { getSessionBindingService } from "../../infra/outbound/session-binding-service.js";
@@ -51,18 +52,18 @@ import {
 } from "../chat-abort.js";
 import {
   type ChatImageContent,
+  MediaOffloadError,
   type OffloadedRef,
   parseMessageWithAttachments,
   resolveChatAttachmentMaxBytes,
 } from "../chat-attachments.js";
-import { MediaOffloadError } from "../chat-attachments.js";
 import {
   isToolHistoryBlockType,
   projectChatDisplayMessage,
   projectRecentChatDisplayMessages,
   resolveEffectiveChatHistoryMaxChars,
 } from "../chat-display-projection.js";
-import { stripEnvelopeFromMessage } from "../chat-sanitize.js";
+import { stripEnvelopeFromMessage, stripEnvelopeFromMessages } from "../chat-sanitize.js";
 import { augmentChatHistoryWithCliSessionImports } from "../cli-session-history.js";
 import { isSuppressedControlReplyText } from "../control-reply-text.js";
 import {
@@ -771,10 +772,19 @@ function buildChatSendTranscriptMessage(params: {
 }
 
 // Stages non-image offloads into the agent sandbox synchronously so chat.send
-// can surface 5xx before respond(). Throws MediaOffloadError on partial-stage
-// instead of silently losing files (channel path is best-effort; chat.send is
-// strong-delivery RPC). Callers MUST set ctx.MediaStaged=true when this runs
-// so the dispatch pipeline skips its own stageSandboxMedia pass.
+// can surface 5xx before respond(). Throws MediaOffloadError on any staging
+// failure (ENOSPC / EPERM / partial-stage) so the outer chat.send handler can
+// map it to UNAVAILABLE (5xx); plain Error would be misclassified as 4xx. All
+// offloaded refs are cleaned up from the media store before rethrow.
+// Callers MUST set ctx.MediaStaged=true when this runs so the dispatch
+// pipeline skips its own stageSandboxMedia pass.
+//
+// Returned paths are ABSOLUTE (pointing into the sandbox workspace when sandbox
+// is enabled, or the media-store origin when it is not). applyMediaUnderstanding
+// runs before any further staging in get-reply.ts and uses
+// `path.isAbsolute(raw) ? raw : path.resolve(raw)` against the gateway CWD, so
+// any relative path here would make media-understanding target the wrong host
+// path and silently skip file analysis.
 async function prestageNonImageOffloads(params: {
   offloadedRefs: OffloadedRef[];
   cfg: OpenClawConfig;
@@ -786,46 +796,58 @@ async function prestageNonImageOffloads(params: {
     return { paths: [], types: [] };
   }
 
-  const workspaceDir = resolveAgentWorkspaceDir(params.cfg, params.agentId);
-  const sandbox = await ensureSandboxWorkspaceForSession({
-    config: params.cfg,
-    sessionKey: params.sessionKey,
-    workspaceDir,
-  });
-  if (!sandbox) {
-    return {
-      paths: nonImage.map((ref) => ref.path),
-      types: nonImage.map((ref) => ref.mimeType),
+  try {
+    const workspaceDir = resolveAgentWorkspaceDir(params.cfg, params.agentId);
+    const sandbox = await ensureSandboxWorkspaceForSession({
+      config: params.cfg,
+      sessionKey: params.sessionKey,
+      workspaceDir,
+    });
+    if (!sandbox) {
+      return {
+        paths: nonImage.map((ref) => ref.path),
+        types: nonImage.map((ref) => ref.mimeType),
+      };
+    }
+
+    const stagingCtx: MsgContext = {
+      MediaPath: nonImage[0].path,
+      MediaPaths: nonImage.map((ref) => ref.path),
+      MediaType: nonImage[0].mimeType,
+      MediaTypes: nonImage.map((ref) => ref.mimeType),
     };
-  }
+    await stageSandboxMedia({
+      ctx: stagingCtx,
+      sessionCtx: stagingCtx as TemplateContext,
+      cfg: params.cfg,
+      sessionKey: params.sessionKey,
+      workspaceDir,
+    });
 
-  const stagingCtx: MsgContext = {
-    MediaPath: nonImage[0].path,
-    MediaPaths: nonImage.map((ref) => ref.path),
-    MediaType: nonImage[0].mimeType,
-    MediaTypes: nonImage.map((ref) => ref.mimeType),
-  };
-  await stageSandboxMedia({
-    ctx: stagingCtx,
-    sessionCtx: stagingCtx as TemplateContext,
-    cfg: params.cfg,
-    sessionKey: params.sessionKey,
-    workspaceDir,
-  });
+    const stagedPaths = stagingCtx.MediaPaths ?? [];
+    const stagedTypes = stagingCtx.MediaTypes ?? nonImage.map((ref) => ref.mimeType);
+    if (stagedPaths.length !== nonImage.length) {
+      throw new Error(
+        `non-image attachment staging incomplete: ${stagedPaths.length}/${nonImage.length} paths staged into sandbox workspace`,
+      );
+    }
 
-  const stagedPaths = stagingCtx.MediaPaths ?? [];
-  const stagedTypes = stagingCtx.MediaTypes ?? nonImage.map((ref) => ref.mimeType);
-  const allRewritten =
-    stagedPaths.length === nonImage.length && stagedPaths.every((p) => !path.isAbsolute(p));
-  if (!allRewritten) {
+    const absolutePaths = stagedPaths.map((p) =>
+      path.isAbsolute(p) ? p : path.join(sandbox.workspaceDir, p),
+    );
+    return { paths: absolutePaths, types: stagedTypes, workspaceDir: sandbox.workspaceDir };
+  } catch (err) {
     await Promise.allSettled(
       params.offloadedRefs.map((ref) => deleteMediaBuffer(ref.id, "inbound")),
     );
+    if (err instanceof MediaOffloadError) {
+      throw err;
+    }
     throw new MediaOffloadError(
-      `non-image attachment staging incomplete: ${stagedPaths.length}/${nonImage.length} paths rewritten into sandbox workspace`,
+      `[Gateway Error] Failed to stage non-image attachments into agent workspace: ${formatErrorMessage(err)}`,
+      { cause: err },
     );
   }
-  return { paths: stagedPaths, types: stagedTypes, workspaceDir: sandbox.workspaceDir };
 }
 
 function resolveChatSendTranscriptMediaFields(savedImages: SavedMedia[]) {
diff --git a/src/gateway/server-node-events.runtime.ts b/src/gateway/server-node-events.runtime.ts
index 01697810d6a..fa501faccb0 100644
--- a/src/gateway/server-node-events.runtime.ts
+++ b/src/gateway/server-node-events.runtime.ts
@@ -15,7 +15,7 @@ export { enqueueSystemEvent } from "../infra/system-events.js";
 export { deleteMediaBuffer } from "../media/store.js";
 export { normalizeMainKey, scopedHeartbeatWakeOptions } from "../routing/session-key.js";
 export { defaultRuntime } from "../runtime.js";
-export { parseMessageWithAttachments } from "./chat-attachments.js";
+export { parseMessageWithAttachments, resolveChatAttachmentMaxBytes } from "./chat-attachments.js";
 export { normalizeRpcAttachmentsToChatAttachments } from "./server-methods/attachment-normalize.js";
 export {
   loadSessionEntry,
diff --git a/src/gateway/server-node-events.test.ts b/src/gateway/server-node-events.test.ts
index c8324d75bfa..b084e7e05eb 100644
--- a/src/gateway/server-node-events.test.ts
+++ b/src/gateway/server-node-events.test.ts
@@ -90,6 +90,7 @@ const runtimeMocks = vi.hoisted(() => ({
   parseMessageWithAttachments: parseMessageWithAttachmentsMock,
   registerApnsRegistration: registerApnsRegistrationMock,
   requestHeartbeatNow: vi.fn(),
+  resolveChatAttachmentMaxBytes: vi.fn(() => 20 * 1024 * 1024),
   resolveGatewayModelSupportsImages: vi.fn(
     async ({
       loadGatewayModelCatalog,
diff --git a/src/gateway/server-node-events.ts b/src/gateway/server-node-events.ts
index 5fd94038cd0..31bcfc1595f 100644
--- a/src/gateway/server-node-events.ts
+++ b/src/gateway/server-node-events.ts
@@ -26,6 +26,7 @@ import {
   parseMessageWithAttachments,
   registerApnsRegistration,
   requestHeartbeatNow,
+  resolveChatAttachmentMaxBytes,
   resolveGatewayModelSupportsImages,
   resolveOutboundTarget,
   resolveSessionAgentId,
@@ -434,7 +435,7 @@ export const handleNodeEvent = async (ctx: NodeEventContext, nodeId: string, evt
         });
         try {
           const parsed = await parseMessageWithAttachments(message, normalizedAttachments, {
-            maxBytes: 5_000_000,
+            maxBytes: resolveChatAttachmentMaxBytes(cfg),
             log: ctx.logGateway,
             supportsInlineImages,
             // server-node-events dispatches via agentCommandFromIngress which