fix(respawn): use screen -X stuff for reliable input delivery

When writing to an attached PTY connected to screen, the input doesn't
reliably reach Claude CLI. This fix uses `screen -X stuff` command to
send input directly to the screen session, bypassing the PTY attachment.

Research findings:
- Claude CLI uses Ink (React for CLI) for terminal UI
- Ink's parseKeypress detects \r as key.return (Enter)
- screen -X stuff with $'...' syntax reliably sends literal characters

Changes:
- Add ScreenManager.sendInput() using screen -X stuff
- Modify Session.write() to prefer screen -X stuff when available
- Keep \r as Enter key (what Ink expects for key.return)

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

src/respawn-controller.ts

@@ -355,7 +355,7 @@ export class RespawnController extends EventEmitter {
     this.stepTimer = setTimeout(() => {
       const prompt = this.config.kickstartPrompt!;
       this.log(`Sending kickstart prompt: "${prompt}"`);
-      this.session.write(prompt + '\r');  // \r for PTY Enter key
+      this.session.write(prompt + '\r');  // \r triggers key.return in Ink/Claude CLI
       this.emit('stepSent', 'kickstart', prompt);
       this.setState('waiting_kickstart');
       this.promptDetected = false;
@@ -416,7 +416,7 @@ export class RespawnController extends EventEmitter {
     this.terminalBuffer = ''; // Clear buffer for fresh detection
 
     this.stepTimer = setTimeout(() => {
-      const input = this.config.updatePrompt + '\r';  // \r for PTY Enter key
+      const input = this.config.updatePrompt + '\r\n';  // CRLF for screen + Claude CLI
       this.log(`Sending update prompt: "${this.config.updatePrompt}"`);
       this.session.write(input);
       this.emit('stepSent', 'update', this.config.updatePrompt);
@@ -432,7 +432,7 @@ export class RespawnController extends EventEmitter {
 
     this.stepTimer = setTimeout(() => {
       this.log('Sending /clear');
-      this.session.write('/clear\r');  // \r for PTY Enter key
+      this.session.write('/clear\r\n');  // CRLF for screen + Claude CLI
       this.emit('stepSent', 'clear', '/clear');
       this.setState('waiting_clear');
       this.promptDetected = false;
@@ -445,7 +445,7 @@ export class RespawnController extends EventEmitter {
 
     this.stepTimer = setTimeout(() => {
       this.log('Sending /init');
-      this.session.write('/init\r');  // \r for PTY Enter key
+      this.session.write('/init\r\n');  // CRLF for screen + Claude CLI
       this.emit('stepSent', 'init', '/init');
       this.setState('waiting_init');
       this.promptDetected = false;

src/screen-manager.ts

@@ -457,4 +457,26 @@ export class ScreenManager extends EventEmitter {
       return false;
     }
   }
+
+  // Send input directly to screen session using screen -X stuff
+  // This bypasses the attached PTY and sends input directly to the screen
+  sendInput(sessionId: string, input: string): boolean {
+    const screen = this.screens.get(sessionId);
+    if (!screen) {
+      return false;
+    }
+
+    try {
+      // Use screen -X stuff with $'...' syntax to send literal characters
+      // \r (carriage return) is what Claude CLI expects for Enter
+      execSync(`screen -S ${screen.screenName} -X stuff $'${input.replace(/'/g, "'\\''")}'`, {
+        encoding: 'utf-8',
+        timeout: 5000
+      });
+      return true;
+    } catch (err) {
+      console.error('[ScreenManager] Failed to send input:', err);
+      return false;
+    }
+  }
 }

src/session.ts

@@ -898,7 +898,18 @@ export class Session extends EventEmitter {
   }
 
   // Send input to the PTY (for interactive sessions)
+  // When using screen, prefers screen -X stuff for reliable input delivery
   write(data: string): void {
+    // Try screen -X stuff first if we have a screen session
+    // This is more reliable for sending Enter key to Claude CLI
+    if (this._screenManager && this._screenSession) {
+      const success = this._screenManager.sendInput(this.id, data);
+      if (success) {
+        return;
+      }
+      // Fall through to PTY write if screen command failed
+    }
+
     if (this.ptyProcess) {
       this.ptyProcess.write(data);
     }