diff --git a/src/daemon/run-manager.ts b/src/daemon/run-manager.ts
index b67d4f1..5ed87e5 100644
--- a/src/daemon/run-manager.ts
+++ b/src/daemon/run-manager.ts
@@ -150,6 +150,7 @@ export const cancelRun = (runId: string): boolean => {
 };
 
 export const sendInput = (runId: string, text: string): boolean => {
+  if (!text || typeof text !== 'string') return false;
   const tracked = runs.get(runId);
   if (!tracked) return false;
   if (tracked.run.state !== 'input_required') return false;
diff --git a/src/daemon/websocket.ts b/src/daemon/websocket.ts
index cd71381..f54b3bd 100644
--- a/src/daemon/websocket.ts
+++ b/src/daemon/websocket.ts
@@ -52,6 +52,19 @@ const bufferMessage = (runId: string, msg: BufferedMessage): void => {
 const replayBuffer = (ws: WebSocket, runId: string): void => {
   const buf = runBuffers.get(runId);
   if (!buf) return;
+
+  // B3: Extend TTL when a client subscribes to prevent race between
+  // buffer expiry and replay delivery
+  const existingTimer = bufferTimers.get(runId);
+  if (existingTimer) {
+    clearTimeout(existingTimer);
+    const timer = setTimeout(() => {
+      runBuffers.delete(runId);
+      bufferTimers.delete(runId);
+    }, BUFFER_TTL_MS);
+    bufferTimers.set(runId, timer);
+  }
+
   logDebug(`Replaying ${buf.length} buffered messages for run ${runId}`);
   for (const msg of buf) {
     sendToClient(ws, msg);
diff --git a/src/hub/reconnection.ts b/src/hub/reconnection.ts
index 2521837..a1bd7dd 100644
--- a/src/hub/reconnection.ts
+++ b/src/hub/reconnection.ts
@@ -18,6 +18,7 @@ export const createReconnector = (opts: ReconnectorOptions): Reconnector => {
   let currentDelay = initialDelay;
   let timer: ReturnType<typeof setTimeout> | null = null;
   let stopped = false;
+  let running = false;
 
   const attempt = async (): Promise<void> => {
     if (stopped) return;
@@ -25,6 +26,7 @@ export const createReconnector = (opts: ReconnectorOptions): Reconnector => {
     try {
       await opts.onReconnect();
       currentDelay = initialDelay;
+      running = false;
     } catch (err) {
       opts.onError?.(err);
       timer = setTimeout(() => {
@@ -36,12 +38,15 @@ export const createReconnector = (opts: ReconnectorOptions): Reconnector => {
 
   return {
     start: () => {
+      if (running) return;
       stopped = false;
+      running = true;
       attempt();
     },
 
     stop: () => {
       stopped = true;
+      running = false;
       if (timer) {
         clearTimeout(timer);
         timer = null;