diff --git a/changelog.d/fixes/10727-meta-ai-ws-timeout-diagnostics.md b/changelog.d/fixes/10727-meta-ai-ws-timeout-diagnostics.md
new file mode 100644
index 0000000000..f204684baa
--- /dev/null
+++ b/changelog.d/fixes/10727-meta-ai-ws-timeout-diagnostics.md
@@ -0,0 +1 @@
+- **fix(executors):** the Meta AI (muse-spark-web) WebSocket send-message timeout now reports the socket's `readyState` at the moment it fires, so a "Meta AI WS timed out" failure can be told apart as either the connection never opening (`readyState=0`) or opening successfully and then going silent (`readyState=1`) — the exact ambiguity that made #10727 undiagnosable from logs alone (#10727).
diff --git a/open-sse/executors/muse-spark-web.ts b/open-sse/executors/muse-spark-web.ts
index f93191c312..a8052c4c65 100644
--- a/open-sse/executors/muse-spark-web.ts
+++ b/open-sse/executors/muse-spark-web.ts
@@ -1070,7 +1070,7 @@ async function wsChat(
 
     const fail = (error: string) => finish({ content: "", deltas: [], error });
 
-    timeout = setTimeout(() => fail("Meta AI WebSocket timed out"), 30000);
+    timeout = setTimeout(() => fail(`Meta AI WS timed out (readyState=${ws.readyState})`), 30000);
     abortHandler = () => fail("Request aborted");
     signal?.addEventListener("abort", abortHandler, { once: true });
 
diff --git a/tests/unit/muse-spark-ws-timeout-diagnostics-10727.test.ts b/tests/unit/muse-spark-ws-timeout-diagnostics-10727.test.ts
new file mode 100644
index 0000000000..98de83cce7
--- /dev/null
+++ b/tests/unit/muse-spark-ws-timeout-diagnostics-10727.test.ts
@@ -0,0 +1,164 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import {
+  MuseSparkWebExecutor,
+  __resetMuseSparkConversationCacheForTesting,
+  __setMuseSparkWebSocketForTesting,
+} from "../../open-sse/executors/muse-spark-web.ts";
+import { WebSocket } from "ws";
+
+// #10727: Meta AI (muse-spark-web) times out on the WS send-message step at
+// exactly the executor's hardcoded 30s timeout, with no onerror/onclose
+// firing first. The reporter's log shows the flow reaching wsChat and
+// hanging until the timeout fires, meaning Meta's gateway either never
+// truly opens the socket or silently drops frames after opening — but the
+// old flat "Meta AI WebSocket timed out" message could not distinguish
+// those two failure modes for whoever debugs the next occurrence.
+//
+// Root-causing (and fixing) the reverse-engineered private WS protocol
+// itself requires a live meta.ai session + a fresh DevTools capture (see
+// the plan-file's `needs-vps` verdict) — not achievable in this sandbox.
+// This regression test locks in the diagnosability improvement that *is*
+// verifiable here: the timeout error now reports the socket's readyState
+// at the moment it fires, so a future report can tell "never opened"
+// (readyState 0) apart from "opened but Meta went silent" (readyState 1).
+
+/**
+ * Intercepts only the wsChat 30000ms timeout registration and lets every
+ * other setTimeout (including the mock WebSocket's own onopen scheduling)
+ * run for real. Firing the captured callback directly — instead of
+ * advancing a fake clock — keeps the test fast and avoids interleaving
+ * bugs between fake timers and the executor's real async/await chain.
+ */
+function interceptWsTimeout(): { fire: () => void; restore: () => void } {
+  const original = globalThis.setTimeout;
+  let captured: (() => void) | null = null;
+  globalThis.setTimeout = ((cb: (...a: unknown[]) => void, ms?: number, ...args: unknown[]) => {
+    if (ms === 30000 && captured === null) {
+      captured = cb as () => void;
+      return 0 as unknown as ReturnType<typeof setTimeout>;
+    }
+    return original(cb as () => void, ms, ...args);
+  }) as typeof setTimeout;
+  return {
+    fire: () => {
+      assert.ok(captured, "the 30000ms wsChat timeout was never registered");
+      captured?.();
+    },
+    restore: () => {
+      globalThis.setTimeout = original;
+    },
+  };
+}
+
+class NeverOpensWebSocket {
+  onopen: (() => void) | null = null;
+  onmessage: ((evt: { data: string }) => void) | null = null;
+  onclose: (() => void) | null = null;
+  onerror: ((evt: Error) => void) | null = null;
+  readyState = WebSocket.CONNECTING;
+  url: string;
+  constructor(url: string) {
+    this.url = url;
+    // Never calls onopen, onmessage, onerror, or onclose — mirrors the
+    // reported symptom exactly: the socket just hangs until the timeout.
+  }
+  send(_data: Uint8Array | string) {}
+  close() {}
+}
+
+class OpensThenSilentWebSocket {
+  onopen: (() => void) | null = null;
+  onmessage: ((evt: { data: string }) => void) | null = null;
+  onclose: (() => void) | null = null;
+  onerror: ((evt: Error) => void) | null = null;
+  readyState = WebSocket.CONNECTING;
+  url: string;
+  constructor(url: string) {
+    this.url = url;
+    setTimeout(() => {
+      this.readyState = WebSocket.OPEN;
+      this.onopen?.();
+    }, 0);
+  }
+  send(_data: Uint8Array | string) {}
+  close() {}
+}
+
+function baseInput(connectionId: string): Parameters<MuseSparkWebExecutor["execute"]>[0] {
+  return {
+    model: "muse-spark",
+    body: { messages: [{ role: "user", content: "ping" }] },
+    stream: false,
+    credentials: {
+      apiKey: "ecto_1_sess=test123",
+      connectionId,
+      providerSpecificData: { authorization: "ecto1:test-auth-token" },
+    },
+    signal: null,
+    log: null,
+    upstreamExtraHeaders: undefined,
+  } as Parameters<MuseSparkWebExecutor["execute"]>[0];
+}
+
+test("#10727: WS timeout while still CONNECTING reports readyState=0 (never opened)", async () => {
+  __resetMuseSparkConversationCacheForTesting();
+  const executor = new MuseSparkWebExecutor();
+  const originalFetch = globalThis.fetch;
+  globalThis.fetch = async () => new Response("{}", { status: 200 });
+  const restore = __setMuseSparkWebSocketForTesting(
+    NeverOpensWebSocket as unknown as typeof WebSocket
+  );
+  const timeoutHook = interceptWsTimeout();
+  try {
+    const resultPromise = executor.execute(baseInput("conn-10727-never-opens"));
+    // Let the GraphQL warmup/mode-switch awaits and the WS constructor run
+    // before the 30s timeout is registered.
+    await new Promise((r) => setTimeout(r, 20));
+    timeoutHook.fire();
+
+    const result = await resultPromise;
+    assert.equal(result.response.status, 502);
+    const body = await result.response.json();
+    assert.match(
+      body.error.message,
+      /readyState=0/,
+      "timeout while the socket never left CONNECTING must report readyState=0"
+    );
+  } finally {
+    globalThis.fetch = originalFetch;
+    restore();
+    timeoutHook.restore();
+  }
+});
+
+test("#10727: WS timeout after a successful open reports readyState=1 (opened, then silent)", async () => {
+  __resetMuseSparkConversationCacheForTesting();
+  const executor = new MuseSparkWebExecutor();
+  const originalFetch = globalThis.fetch;
+  globalThis.fetch = async () => new Response("{}", { status: 200 });
+  const restore = __setMuseSparkWebSocketForTesting(
+    OpensThenSilentWebSocket as unknown as typeof WebSocket
+  );
+  const timeoutHook = interceptWsTimeout();
+  try {
+    const resultPromise = executor.execute(baseInput("conn-10727-opens-silent"));
+    // Let the GraphQL awaits run, the WS open (its own real setTimeout(...,0)),
+    // and the intro/prompt frames send before the 30s timeout is registered.
+    await new Promise((r) => setTimeout(r, 20));
+    timeoutHook.fire();
+
+    const result = await resultPromise;
+    assert.equal(result.response.status, 502);
+    const body = await result.response.json();
+    assert.match(
+      body.error.message,
+      /readyState=1/,
+      "timeout after the socket reached OPEN must report readyState=1, not the never-opened case"
+    );
+  } finally {
+    globalThis.fetch = originalFetch;
+    restore();
+    timeoutHook.restore();
+  }
+});