diff --git a/extensions/acpx/src/runtime.ts b/extensions/acpx/src/runtime.ts
index e1f0024c699..28a6668c117 100644
--- a/extensions/acpx/src/runtime.ts
+++ b/extensions/acpx/src/runtime.ts
@@ -581,6 +581,8 @@ export class AcpxRuntime implements AcpRuntime {
         if (attachment.mediaType.startsWith("image/")) {
           blocks.push({ type: "image", mimeType: attachment.mediaType, data: attachment.data });
         }
+        // Non-image attachments (documents, PDFs, audio, video) are not supported
+        // as binary content blocks in the ACP protocol — skip silently.
       }
       child.stdin.end(blocks.length > 0 ? JSON.stringify(blocks) : input.text);
     } else {
diff --git a/src/auto-reply/reply/dispatch-acp.ts b/src/auto-reply/reply/dispatch-acp.ts
index 8fc7110fc4c..db290c1ea9d 100644
--- a/src/auto-reply/reply/dispatch-acp.ts
+++ b/src/auto-reply/reply/dispatch-acp.ts
@@ -64,7 +64,7 @@ function resolveAcpPromptText(ctx: FinalizedMsgContext): string {
   ]).trim();
 }
 
-const ACP_ATTACHMENT_MAX_BYTES = 10 * 1024 * 1024;
+const ACP_ATTACHMENT_MAX_BYTES = 10 * 1024 * 1024; // 10 MB — consistent with Telegram mediaMaxMb default
 
 async function resolveAcpAttachments(ctx: FinalizedMsgContext): Promise<AcpTurnAttachment[]> {
   const mediaAttachments = normalizeAttachments(ctx);