fix(signal): gate ACK reaction on non-empty early body check

Before sending the ACK reaction, verify the message has at least one
of: non-empty trimmed text, an attachment, or a quote. Without this
guard a whitespace-only message (bodyText === '' after trim) would
receive an ACK even though it is dropped by the later bodyText guard,
giving users a false 'message accepted' signal.

Adds two test cases:
- whitespace-only message → no ACK
- empty text but has attachment → ACK sent

Addresses: https://github.com/openclaw/openclaw/pull/31078#discussion_r2871918100

extensions/signal/src/monitor/event-handler.ack-reaction.test.ts

@@ -186,6 +186,34 @@ describe("Signal ACK reactions", () => {
     expect(sendReactionSignal).not.toHaveBeenCalled();
   });
 
+  it("does NOT send ack when message body is empty (whitespace-only text, no attachment, no quote)", async () => {
+    const deps = makeDeps();
+    const handler = createSignalEventHandler(deps);
+    await handler(
+      makeEvent({
+        dataMessage: { message: "   ", timestamp: 1700000000000 },
+      }),
+    );
+
+    expect(sendReactionSignal).not.toHaveBeenCalled();
+  });
+
+  it("sends ack when message has no text but has an attachment", async () => {
+    const deps = makeDeps();
+    const handler = createSignalEventHandler(deps);
+    await handler(
+      makeEvent({
+        dataMessage: {
+          message: "",
+          timestamp: 1700000000000,
+          attachments: [{ id: "att1", contentType: "image/png", size: 1024 }],
+        },
+      }),
+    );
+
+    expect(sendReactionSignal).toHaveBeenCalledTimes(1);
+  });
+
   it("sends ack BEFORE dispatch", async () => {
     const callOrder: string[] = [];
     vi.mocked(sendReactionSignal).mockImplementation(async () => {

extensions/signal/src/monitor/event-handler.ts

@@ -702,9 +702,15 @@ export function createSignalEventHandler(deps: SignalEventHandlerDeps) {
       return;
     }
 
+    // Early body guard: if the message has no text, no attachment, and no quote it will be
+    // dropped at the bodyText check below — don't send a false ACK in that case.
+    const hasEarlyBody = Boolean(
+      messageText || dataMessage.attachments?.length || dataMessage.quote?.text?.trim(),
+    );
+
     // Send ACK reaction immediately — before any awaited I/O (attachment fetch, read receipt)
     // so the user gets instant visual feedback that their message was received.
-    if (typeof envelope.timestamp === "number") {
+    if (hasEarlyBody && typeof envelope.timestamp === "number") {
       maybeSendSignalAckReaction({
         cfg: deps.cfg,
         agentId: route.agentId,