diff --git a/app/src/features/human/voice/sttClient.test.ts b/app/src/features/human/voice/sttClient.test.ts
index d53606505..7398d0a24 100644
--- a/app/src/features/human/voice/sttClient.test.ts
+++ b/app/src/features/human/voice/sttClient.test.ts
@@ -92,4 +92,21 @@ describe('transcribeCloud', () => {
     const blob = new Blob([new Uint8Array([1])], { type: 'audio/webm' });
     expect(await transcribeCloud(blob)).toBe('');
   });
+
+  // Issue #1289: stale sidecar binaries surface a generic
+  // "unknown method" error. Frontend rewrites it to an actionable
+  // message so users know to restart the desktop app.
+  it('rewrites "unknown method" errors to an actionable restart hint', async () => {
+    const mock = callCoreRpc as ReturnType<typeof vi.fn>;
+    mock.mockRejectedValueOnce(new Error('unknown method: openhuman.voice_cloud_transcribe'));
+    const blob = new Blob([new Uint8Array([1])], { type: 'audio/webm' });
+    await expect(transcribeCloud(blob)).rejects.toThrow(/Restart the OpenHuman desktop app/i);
+  });
+
+  it('passes through non-unknown-method errors verbatim', async () => {
+    const mock = callCoreRpc as ReturnType<typeof vi.fn>;
+    mock.mockRejectedValueOnce(new Error('upstream STT failed: 502'));
+    const blob = new Blob([new Uint8Array([1])], { type: 'audio/webm' });
+    await expect(transcribeCloud(blob)).rejects.toThrow(/upstream STT failed/);
+  });
 });
diff --git a/app/src/features/human/voice/sttClient.ts b/app/src/features/human/voice/sttClient.ts
index 1bf6d1a14..06062792b 100644
--- a/app/src/features/human/voice/sttClient.ts
+++ b/app/src/features/human/voice/sttClient.ts
@@ -57,10 +57,28 @@ export async function transcribeCloud(
   );
 
   const rpcStart = Date.now();
-  const result = await callCoreRpc<CloudTranscribeResult>({
-    method: 'openhuman.voice_cloud_transcribe',
-    params,
-  });
+  let result: CloudTranscribeResult;
+  try {
+    result = await callCoreRpc<CloudTranscribeResult>({
+      method: 'openhuman.voice_cloud_transcribe',
+      params,
+    });
+  } catch (err) {
+    // Issue #1289: an "unknown method" error means the bundled core
+    // sidecar is older than the frontend (e.g. a stale dev build, or a
+    // cached binary the desktop auto-update hasn't refreshed yet).
+    // The raw "unknown method: openhuman.voice_cloud_transcribe" string
+    // is opaque to end users — surface an actionable message instead.
+    const msg = err instanceof Error ? err.message : String(err);
+    if (msg.includes('unknown method')) {
+      sttLog('transcribe rpc stale-sidecar path hit; rewriting unknown-method error: %s', msg);
+      throw new Error(
+        'Voice transcription is unavailable in this build. Restart the OpenHuman desktop app to pick up the latest core sidecar.'
+      );
+    }
+    sttLog('transcribe rpc failed (passthrough): %O', err);
+    throw err;
+  }
   const text = result?.text?.trim() ?? '';
   sttLog('transcribed chars=%d rpc_ms=%d', text.length, Math.round(Date.now() - rpcStart));
   return text;
diff --git a/tests/json_rpc_e2e.rs b/tests/json_rpc_e2e.rs
index bcb9f0bb2..6e734af35 100644
--- a/tests/json_rpc_e2e.rs
+++ b/tests/json_rpc_e2e.rs
@@ -3768,3 +3768,87 @@ async fn whatsapp_memory_doc_ingest_e2e() {
     mock_join.abort();
     rpc_join.abort();
 }
+
+/// Regression guard for issue #1289: `openhuman.voice_cloud_transcribe`
+/// must stay registered in the controller registry and reachable via
+/// JSON-RPC dispatch.
+///
+/// The user-visible symptom was "Voice transcription failed: unknown
+/// method: openhuman.voice_cloud_transcribe" — the frontend (mascot
+/// mic-only composer) was calling a method that wasn't reachable.
+/// This test pins both ends:
+///
+/// 1. `/schema` exposes `openhuman.voice_cloud_transcribe` so the
+///    discovery surface stays in sync with the live registry.
+/// 2. Calling the method over RPC does NOT hit the dispatcher's
+///    unknown-method branch (`Err("unknown method: …")`). The call may
+///    still fail downstream (missing audio, unauthenticated, missing
+///    upstream STT key) — but it must reach the registered handler,
+///    which proves the method is wired all the way through.
+#[tokio::test]
+async fn voice_cloud_transcribe_registered_e2e() {
+    let _env_lock = json_rpc_e2e_env_lock();
+    let tmp = tempdir().expect("tempdir");
+    let home = tmp.path();
+    let openhuman_home = home.join(".openhuman");
+
+    let _home_guard = EnvVarGuard::set_to_path("HOME", home);
+    let _workspace_guard = EnvVarGuard::unset("OPENHUMAN_WORKSPACE");
+    let _backend_url_guard = EnvVarGuard::unset("BACKEND_URL");
+    let _vite_backend_guard = EnvVarGuard::unset("VITE_BACKEND_URL");
+
+    let (mock_addr, mock_join) = serve_on_ephemeral(mock_upstream_router()).await;
+    let mock_origin = format!("http://{}", mock_addr);
+    write_min_config(&openhuman_home, &mock_origin);
+
+    let (rpc_addr, rpc_join) = serve_on_ephemeral(build_core_http_router(false)).await;
+    let rpc_base = format!("http://{}", rpc_addr);
+    tokio::time::sleep(Duration::from_millis(100)).await;
+
+    // ── 1. /schema must list openhuman.voice_cloud_transcribe ───────────────
+    let schema = reqwest::get(format!("{rpc_base}/schema"))
+        .await
+        .expect("GET /schema")
+        .json::<Value>()
+        .await
+        .expect("schema json");
+    let methods = schema["methods"]
+        .as_array()
+        .unwrap_or_else(|| panic!("/schema must expose methods array: {schema}"));
+    let names: Vec<&str> = methods
+        .iter()
+        .filter_map(|m| m.get("method").and_then(Value::as_str))
+        .collect();
+    assert!(
+        names.contains(&"openhuman.voice_cloud_transcribe"),
+        "voice_cloud_transcribe must appear in /schema dump (got {} methods)",
+        names.len()
+    );
+
+    // ── 2. RPC dispatch must NOT return "unknown method" ───────────────────
+    // Send a minimal payload — it'll fail downstream (no upstream STT
+    // configured in the mock), but the dispatcher should reach the
+    // handler, not the unknown-method branch.
+    let resp = post_json_rpc(
+        &rpc_base,
+        9101,
+        "openhuman.voice_cloud_transcribe",
+        json!({ "audio_base64": "" }),
+    )
+    .await;
+    // Inspect the full error blob, not just `error.message`. A future
+    // server-shape change that moves the dispatcher's unknown-method
+    // string into `error.data` would otherwise let this regression
+    // guard silently pass.
+    let err_blob = resp
+        .get("error")
+        .map(|e| e.to_string().to_ascii_lowercase())
+        .unwrap_or_default();
+    assert!(
+        !err_blob.contains("unknown method"),
+        "voice_cloud_transcribe must be a known method; full response: {resp}"
+    );
+
+    mock_join.abort();
+    rpc_join.abort();
+}