feat: Add graceful interrupt with silent restart

- ESC now sends SIGINT to interrupt generation gracefully
- Automatic silent restart with --continue after interrupt
- Added isRestarting flag to prevent session_ended during restart
- No UI messages during interrupt/restart cycle
- Removed SIGKILL fallback - SIGINT is sufficient

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/server.js

@@ -597,6 +597,7 @@ wss.on('connection', async (ws, req) => {
   let currentProject = null;
   let currentHostId = null;  // Track current host for restart
   let isInitialized = false;
+  let isRestarting = false;  // Flag to prevent session_ended during interrupt restart
   let currentPermissionMode = 'default';
   let savedPermissionMode = 'default';  // Store mode before plan mode switch
   let inPlanMode = false;  // Track if we're in plan mode (to require approval for ExitPlanMode)
@@ -646,7 +647,7 @@ wss.on('connection', async (ws, req) => {
     }
   };
 
-  const startClaudeSession = (projectPath, resume = true, hostId = null) => {
+  const startClaudeSession = (projectPath, resume = true, hostId = null, silent = false) => {
     if (claudeProcess) {
       console.log(`[${sessionId}] Killing existing Claude process`);
       claudeProcess.kill();
@@ -710,10 +711,13 @@ wss.on('connection', async (ws, req) => {
 
     sessions.set(sessionId, { process: claudeProcess, project: projectPath, host: host, hostId: hostId, user: wsUser });
 
+    // Only send session_started if not a silent restart (e.g., after interrupt)
+    if (!silent) {
       sendToClient('session_started', {
         sessionId,
         project: projectPath
       });
+    }
 
     // Send control protocol initialization after process starts
     const initializeControlProtocol = () => {
@@ -937,8 +941,11 @@ wss.on('connection', async (ws, req) => {
 
     claudeProcess.on('close', (code) => {
       console.log(`[${sessionId}] Claude process exited with code ${code}`);
+      // Don't send session_ended if we're restarting after interrupt
+      if (!isRestarting) {
         sendToClient('session_ended', { code });
         sessions.delete(sessionId);
+      }
       claudeProcess = null;
     });
 
@@ -984,34 +991,40 @@ wss.on('connection', async (ws, req) => {
           break;
 
         case 'stop_generation':
-          // Kill the process and restart with --continue to resume session
+          // Interrupt Claude and restart with --continue
+          // In JSON mode, SIGINT causes Claude to exit (unlike TUI mode where it just stops output)
+          // So we need to restart the session automatically
           if (claudeProcess) {
-            console.log(`[${sessionId}] Stop generation: killing process and restarting`);
+            console.log(`[${sessionId}] Stop generation: sending SIGINT and will restart`);
+
+            // Set flag to prevent session_ended from being sent
+            isRestarting = true;
 
             // Save current state for restart
             const restartProject = currentProject;
             const restartHost = currentHostId;
             const restartPermissionMode = currentPermissionMode;
 
-            // Kill the process
-            claudeProcess.kill('SIGKILL');
-            claudeProcess = null;
-            isInitialized = false;
-
-            // Notify frontend
+            // Notify frontend (no message - silent interrupt)
             sendToClient('generation_stopped', {
-              message: 'Generation stopped, reconnecting...',
               timestamp: Date.now()
             });
 
-            // Restart after a short delay
-            setTimeout(() => {
-              console.log(`[${sessionId}] Restarting session with --continue`);
-              startClaudeSession(restartProject, true, restartHost);
+            // Listen for exit and restart
+            claudeProcess.once('exit', (code) => {
+              console.log(`[${sessionId}] Claude exited with code ${code}, restarting with --continue`);
+              isInitialized = false;
 
-              // Restore permission mode after initialization
+              // Restart with --continue to resume conversation (silent = no session_started message)
+              setTimeout(() => {
+                startClaudeSession(restartProject, true, restartHost, true); // silent=true
                 savedPermissionMode = restartPermissionMode;
-            }, 500);
+                isRestarting = false;  // Clear flag after restart
+              }, 200);
+            });
+
+            // Send SIGINT (graceful interrupt)
+            claudeProcess.kill('SIGINT');
           } else {
             sendToClient('generation_stopped', {
               message: 'No active process',