fix(pi): reiniciar en modo Linux vuelve a arrancar el guest

connect() se rendia si el socket no estaba CLOSED, y uno en CLOSING pasa
esa prueba: pulsar "Linux terminal" justo despues de una ejecucion
cerraba el socket y el arranque siguiente no hacia nada -- ni guest, ni
error, y la barra seguia mostrando Stop. Ahora solo se rinde con OPEN o
CONNECTING y descarta el que se esta cerrando.

startBoard marca ademas running en la rama Pi: el boton de Linux
reinicia la placa por su cuenta, sin pasar por la barra, asi que el flag
se quedaba con lo que hubiera dejado la ejecucion anterior.

frontend/src/simulation/RaspberryPi3Bridge.ts

@@ -105,7 +105,13 @@ export class RaspberryPi3Bridge {
   }
 
   connect(): void {
-    if (this.socket && this.socket.readyState !== WebSocket.CLOSED) return;
+    const state = this.socket?.readyState;
+    if (state === WebSocket.OPEN || state === WebSocket.CONNECTING) return;
+    // A socket in CLOSING is on its way out, not usable: the old guard
+    // treated it as live and returned, so "restart in Linux mode" right
+    // after a run silently did nothing — no boot, and the toolbar still
+    // showing Stop. Drop it and open a fresh one.
+    this.socket = null;
 
     const base = API_BASE();
     const wsProtocol = base.startsWith('https') ? 'wss:' : 'ws:';

frontend/src/store/useSimulatorStore.ts

@@ -1929,11 +1929,18 @@ export const useSimulatorStore = create<SimulatorState>((set, get) => {
         // booting a Linux guest (a backend process + ~90 s). The detector
         // lives in the overlay; `enginePinned` lets the user override it.
         const decision = decideEngine(boardId, board.enginePinned);
+        // `running` is set here (not only by the toolbar): the Linux-mode
+        // button restarts the board directly, and without this the flag
+        // kept whatever the previous run left, so the UI showed Stop for
+        // a board that was not running.
         set((s) => ({
           boards: s.boards.map((b) =>
-            b.id === boardId ? { ...b, engineMode: decision.engine } : b,
+            b.id === boardId
+              ? { ...b, engineMode: decision.engine, running: true }
+              : b,
           ),
           serialMonitorOpen: true,
+          ...(s.activeBoardId === boardId ? { running: true } : {}),
         }));
         if (decision.engine === 'instant') {
           const instant = getInstantEngine();