fix(uart): el hook de TX de la Pi se reinstala cuando nace el bridge

Las rutas serie se construyen al cargar la pagina, pero el bridge de una
placa QEMU-Linux nace al pulsar Run: ensureSerialHook encontraba bridge
nulo, hacia no-op y nadie volvia a intentarlo — los bytes que el guest
transmitia por el header salian del backend (uart_tx) y morian en un
onUartTx sin instalar. reensureSerialHooks(boardId) repite el enganche
(idempotente por el flag) y el store lo llama al crear el bridge.

frontend/src/simulation/Interconnect.ts

@@ -747,6 +747,18 @@ export function notifyBoardReady(_boardId: string, wires: readonly Wire[]): void
   updateI2CBridges(wires);
 }
 
+/**
+ * Re-attempt the serial hook for a board whose sim/bridge did not exist
+ * when the routes were built. Routes are installed at page load; a Pi's
+ * bridge is created at Run — so the TX hook silently no-opped and the
+ * guest's UART bytes never reached the wire. The store calls this when
+ * the bridge connects; ensureSerialHook is idempotent via its flag.
+ */
+export function reensureSerialHooks(boardId: string): void {
+  const entry = boards.get(boardId);
+  if (entry && entry.serialFanout.size > 0) ensureSerialHook(entry);
+}
+
 /** For tests: reset all internal state. */
 export function resetInterconnect(): void {
   for (const r of routes.values()) r.teardown();

frontend/src/store/useSimulatorStore.ts

@@ -55,6 +55,7 @@ import { isBreadboard } from '../utils/breadboardNets';
 import { computeSeating } from '../utils/breadboardSnap';
 import { createSerialBatcher } from './serialBatcher';
 import {
+  reensureSerialHooks as icReensureSerialHooks,
   bindBoard as icBindBoard,
   unbindBoard as icUnbindBoard,
   updateWires as icUpdateWires,
@@ -1344,6 +1345,10 @@ export const useSimulatorStore = create<SimulatorState>((set, get) => {
           });
         };
         bridgeMap.set(id, bridge);
+        // The UART routes were built at page load, when this bridge did
+        // not exist — re-attempt the TX hook now that it does, or the
+        // guest's header-UART bytes never reach the canvas wire.
+        icReensureSerialHooks(id);
       } else if (isEsp32Kind(boardKind)) {
         wireEsp32Board(id, boardKind, pm);
       } else if (isStm32BoardKind(boardKind)) {