diff --git a/src/infra/outbound/message-action-params.ts b/src/infra/outbound/message-action-params.ts
index e9672841e1c..b24146cb97c 100644
--- a/src/infra/outbound/message-action-params.ts
+++ b/src/infra/outbound/message-action-params.ts
@@ -169,6 +169,59 @@ function normalizeBase64Payload(params: { base64?: string; contentType?: string
   };
 }
 
+export type AttachmentMediaPolicy =
+  | {
+      mode: "sandbox";
+      sandboxRoot: string;
+    }
+  | {
+      mode: "host";
+      localRoots?: readonly string[];
+    };
+
+export function resolveAttachmentMediaPolicy(params: {
+  sandboxRoot?: string;
+  mediaLocalRoots?: readonly string[];
+}): AttachmentMediaPolicy {
+  const sandboxRoot = params.sandboxRoot?.trim();
+  if (sandboxRoot) {
+    return {
+      mode: "sandbox",
+      sandboxRoot,
+    };
+  }
+  return {
+    mode: "host",
+    localRoots: params.mediaLocalRoots,
+  };
+}
+
+function buildAttachmentMediaLoadOptions(params: {
+  policy: AttachmentMediaPolicy;
+  maxBytes?: number;
+}):
+  | {
+      maxBytes?: number;
+      sandboxValidated: true;
+      readFile: (filePath: string) => Promise<Buffer>;
+    }
+  | {
+      maxBytes?: number;
+      localRoots?: readonly string[];
+    } {
+  if (params.policy.mode === "sandbox") {
+    return {
+      maxBytes: params.maxBytes,
+      sandboxValidated: true,
+      readFile: (filePath: string) => fs.readFile(filePath),
+    };
+  }
+  return {
+    maxBytes: params.maxBytes,
+    localRoots: params.policy.localRoots,
+  };
+}
+
 async function hydrateAttachmentPayload(params: {
   cfg: OpenClawConfig;
   channel: ChannelId;
@@ -178,8 +231,7 @@ async function hydrateAttachmentPayload(params: {
   contentTypeParam?: string | null;
   mediaHint?: string | null;
   fileHint?: string | null;
-  sandboxRoot?: string;
-  mediaLocalRoots?: readonly string[];
+  mediaPolicy: AttachmentMediaPolicy;
 }) {
   const contentTypeParam = params.contentTypeParam ?? undefined;
   const rawBuffer = readStringParam(params.args, "buffer", { trim: false });
@@ -203,17 +255,10 @@ async function hydrateAttachmentPayload(params: {
       channel: params.channel,
       accountId: params.accountId,
     });
-    const sandboxRoot = params.sandboxRoot?.trim();
-    const media = sandboxRoot
-      ? await loadWebMedia(mediaSource, {
-          maxBytes,
-          sandboxValidated: true,
-          readFile: (filePath: string) => fs.readFile(filePath),
-        })
-      : await loadWebMedia(mediaSource, {
-          maxBytes,
-          localRoots: params.mediaLocalRoots,
-        });
+    const media = await loadWebMedia(
+      mediaSource,
+      buildAttachmentMediaLoadOptions({ policy: params.mediaPolicy, maxBytes }),
+    );
     params.args.buffer = media.buffer.toString("base64");
     if (!contentTypeParam && media.contentType) {
       params.args.contentType = media.contentType;
@@ -287,8 +332,7 @@ async function hydrateAttachmentActionPayload(params: {
   dryRun?: boolean;
   /** If caption is missing, copy message -> caption. */
   allowMessageCaptionFallback?: boolean;
-  sandboxRoot?: string;
-  mediaLocalRoots?: readonly string[];
+  mediaPolicy: AttachmentMediaPolicy;
 }): Promise<void> {
   const mediaHint = readStringParam(params.args, "media", { trim: false });
   const fileHint =
@@ -314,8 +358,7 @@ async function hydrateAttachmentActionPayload(params: {
     contentTypeParam,
     mediaHint,
     fileHint,
-    sandboxRoot: params.sandboxRoot,
-    mediaLocalRoots: params.mediaLocalRoots,
+    mediaPolicy: params.mediaPolicy,
   });
 }
 
@@ -326,8 +369,7 @@ export async function hydrateSetGroupIconParams(params: {
   args: Record<string, unknown>;
   action: ChannelMessageActionName;
   dryRun?: boolean;
-  sandboxRoot?: string;
-  mediaLocalRoots?: readonly string[];
+  mediaPolicy: AttachmentMediaPolicy;
 }): Promise<void> {
   if (params.action !== "setGroupIcon") {
     return;
@@ -342,8 +384,7 @@ export async function hydrateSendAttachmentParams(params: {
   args: Record<string, unknown>;
   action: ChannelMessageActionName;
   dryRun?: boolean;
-  sandboxRoot?: string;
-  mediaLocalRoots?: readonly string[];
+  mediaPolicy: AttachmentMediaPolicy;
 }): Promise<void> {
   if (params.action !== "sendAttachment") {
     return;
diff --git a/src/infra/outbound/message-action-runner.test.ts b/src/infra/outbound/message-action-runner.test.ts
index 054350a4043..127a3838031 100644
--- a/src/infra/outbound/message-action-runner.test.ts
+++ b/src/infra/outbound/message-action-runner.test.ts
@@ -512,6 +512,15 @@ describe("runMessageAction sendAttachment hydration", () => {
     expect((result.payload as { buffer?: string }).buffer).toBe(
       Buffer.from("hello").toString("base64"),
     );
+    const call = vi.mocked(loadWebMedia).mock.calls[0];
+    expect(call?.[1]).toEqual(
+      expect.objectContaining({
+        localRoots: expect.any(Array),
+      }),
+    );
+    expect((call?.[1] as { sandboxValidated?: boolean } | undefined)?.sandboxValidated).not.toBe(
+      true,
+    );
   });
 
   it("rewrites sandboxed media paths for sendAttachment", async () => {
@@ -530,6 +539,11 @@ describe("runMessageAction sendAttachment hydration", () => {
 
       const call = vi.mocked(loadWebMedia).mock.calls[0];
       expect(call?.[0]).toBe(path.join(sandboxDir, "data", "pic.png"));
+      expect(call?.[1]).toEqual(
+        expect.objectContaining({
+          sandboxValidated: true,
+        }),
+      );
     });
   });
 
diff --git a/src/infra/outbound/message-action-runner.ts b/src/infra/outbound/message-action-runner.ts
index 5031a2cdead..68a75f0c0a3 100644
--- a/src/infra/outbound/message-action-runner.ts
+++ b/src/infra/outbound/message-action-runner.ts
@@ -36,6 +36,7 @@ import {
   parseCardParam,
   parseComponentsParam,
   readBooleanParam,
+  resolveAttachmentMediaPolicy,
   resolveSlackAutoThreadId,
   resolveTelegramAutoThreadId,
 } from "./message-action-params.js";
@@ -759,10 +760,14 @@ export async function runMessageAction(
   }
   const dryRun = Boolean(input.dryRun ?? readBooleanParam(params, "dryRun"));
   const mediaLocalRoots = getAgentScopedMediaLocalRoots(cfg, resolvedAgentId);
+  const mediaPolicy = resolveAttachmentMediaPolicy({
+    sandboxRoot: input.sandboxRoot,
+    mediaLocalRoots,
+  });
 
   await normalizeSandboxMediaParams({
     args: params,
-    sandboxRoot: input.sandboxRoot,
+    sandboxRoot: mediaPolicy.mode === "sandbox" ? mediaPolicy.sandboxRoot : undefined,
   });
 
   await hydrateSendAttachmentParams({
@@ -772,8 +777,7 @@ export async function runMessageAction(
     args: params,
     action,
     dryRun,
-    sandboxRoot: input.sandboxRoot,
-    mediaLocalRoots,
+    mediaPolicy,
   });
 
   await hydrateSetGroupIconParams({
@@ -783,8 +787,7 @@ export async function runMessageAction(
     args: params,
     action,
     dryRun,
-    sandboxRoot: input.sandboxRoot,
-    mediaLocalRoots,
+    mediaPolicy,
   });
 
   const resolvedTarget = await resolveActionTarget({