diff --git a/frontend/src/__tests__/esp32-dht22-flow.test.ts b/frontend/src/__tests__/esp32-dht22-flow.test.ts
index c0e760ca..cf0abf77 100644
--- a/frontend/src/__tests__/esp32-dht22-flow.test.ts
+++ b/frontend/src/__tests__/esp32-dht22-flow.test.ts
@@ -337,6 +337,24 @@ describe('Esp32Bridge — sensor WebSocket protocol', () => {
     ]);
   });
 
+  it('connect() on a lingering (non-CLOSED) socket force-reconnects instead of no-op', () => {
+    // Regression: the agent leaves the board running (socket OPEN); the user's
+    // Run → startBoard → connect() must boot a FRESH session, not silently
+    // return because a socket already exists. Reproduces "run after the agent
+    // did nothing until I reloaded".
+    const firstWs = (bridge as any).socket as MockWebSocket;
+    expect(firstWs.readyState).toBe(MockWebSocket.OPEN);
+
+    bridge.connect(); // second connect while the first socket is still OPEN
+    const secondWs = (bridge as any).socket as MockWebSocket;
+
+    expect(firstWs.readyState).toBe(MockWebSocket.CLOSED); // old zombie torn down
+    expect(secondWs).not.toBe(firstWs); // a brand-new socket
+    secondWs.open();
+    const startMsg = secondWs.messages.find((m) => m.type === 'start_esp32');
+    expect(startMsg).toBeDefined(); // fresh boot actually happened
+  });
+
   it('sendSensorUpdate sends esp32_sensor_update message', () => {
     bridge.sendSensorUpdate(4, { temperature: 35, humidity: 70 });
     expect(ws.messages).toEqual([
diff --git a/frontend/src/simulation/Esp32Bridge.ts b/frontend/src/simulation/Esp32Bridge.ts
index d9dcea87..b396e97d 100644
--- a/frontend/src/simulation/Esp32Bridge.ts
+++ b/frontend/src/simulation/Esp32Bridge.ts
@@ -292,7 +292,31 @@ export class Esp32Bridge {
   }
 
   connect(): void {
-    if (this.socket && this.socket.readyState !== WebSocket.CLOSED) return;
+    // Force a clean reconnect. The old guard here was
+    //   if (this.socket && readyState !== CLOSED) return;
+    // which made connect() a SILENT NO-OP whenever a socket lingered in any
+    // non-CLOSED state (CONNECTING / OPEN / CLOSING). That's exactly the
+    // "el agente terminó, di Run y no funcionó; recargué y sí" bug: the
+    // agent's run_simulation left a live/half-dead socket, the backend QEMU
+    // session had ended, and the user's Run → startBoard → connect() returned
+    // without doing anything. A page reload worked only because it built a
+    // fresh bridge. Tearing the zombie socket down and opening a new one to
+    // the same session key is exactly what that reload does — the backend
+    // already handles a new WS replacing an existing session (that's why
+    // reload works), so it's safe to do it without the reload.
+    if (this.socket) {
+      try {
+        this.socket.onopen = null;
+        this.socket.onmessage = null;
+        this.socket.onclose = null;
+        this.socket.onerror = null;
+        this.socket.close();
+      } catch {
+        /* already closing/closed */
+      }
+      this.socket = null;
+      this._connected = false;
+    }
 
     const base = API_BASE();
     const wsProtocol = base.startsWith('https') ? 'wss:' : 'ws:';