fix(desktop): answer the bundled ConPTY's startup query so Windows shells start at once

The bundled ConPTY sends a device-attributes query as it starts and holds
the shell's output for three seconds when nothing answers, which an
agent's shell (no panel) never does. The session answers that first query
as xterm.js would and keeps it from the panel, so it is answered once.

Author: waleedlatif1

apps/desktop/src/main/terminal/session.test.ts

@@ -293,19 +293,57 @@ describe('TerminalSession command lifecycle', () => {
 describe('TerminalSession on Windows', () => {
   const marker = (body: string) => `\u001b]633;${body};test-nonce\u0007`
 
-  function windowsSession(): TerminalSession {
+  function sessionOn(
+    platform: NodeJS.Platform,
+    onData: (terminalId: string, data: string) => void = () => {}
+  ): TerminalSession {
     return TerminalSession.create({
       terminalId: 'terminal-windows',
       cwd: 'C:\\Users\\me',
       cols: 80,
       rows: 24,
-      platform: 'win32',
-      callbacks: { onData: () => {}, onState: () => {}, onCommand: () => {}, onExit: () => {} },
+      platform,
+      callbacks: { onData, onState: () => {}, onCommand: () => {}, onExit: () => {} },
     })
   }
 
+  const DEVICE_ATTRIBUTES_REPLY = '\u001b[?1;2c'
+
+  it("answers ConPTY's startup query once, which otherwise holds the shell back for 3 s", async () => {
+    vi.useFakeTimers()
+    let painted = ''
+    const session = sessionOn('win32', (_id, data) => {
+      painted += data
+    })
+    try {
+      ptyStub.dataHandler?.('\u001b[1t')
+      ptyStub.dataHandler?.('\u001b[c\u001b[?1004h')
+      // A program's own query later on is the panel's to answer.
+      ptyStub.dataHandler?.('\u001b[c')
+      await vi.advanceTimersByTimeAsync(50)
+
+      expect(ptyStub.writes.filter((write) => write === DEVICE_ATTRIBUTES_REPLY)).toHaveLength(1)
+      expect(painted).toBe('\u001b[1t\u001b[?1004h\u001b[c')
+    } finally {
+      session.dispose()
+    }
+  })
+
+  it('leaves the startup query of a macOS shell to the panel', async () => {
+    vi.useFakeTimers()
+    const session = sessionOn('darwin')
+    try {
+      ptyStub.dataHandler?.('\u001b[c')
+      await vi.advanceTimersByTimeAsync(50)
+
+      expect(ptyStub.writes).not.toContain(DEVICE_ATTRIBUTES_REPLY)
+    } finally {
+      session.dispose()
+    }
+  })
+
   it('starts the shell without the POSIX login flag, which Windows shells reject', () => {
-    const session = windowsSession()
+    const session = sessionOn('win32')
     try {
       expect(ptyStub.args).not.toContain('-l')
     } finally {
@@ -315,7 +353,7 @@ describe('TerminalSession on Windows', () => {
 
   it('ends the shell for a terminating signal, which node-pty refuses to send there', () => {
     ptyStub.signalsSupported = false
-    const session = windowsSession()
+    const session = sessionOn('win32')
     try {
       session.kill('SIGTERM')
       expect(ptyStub.ended).toBe(true)
@@ -325,7 +363,7 @@ describe('TerminalSession on Windows', () => {
   })
 
   it('names the tab after the last folder of a Windows path', () => {
-    const session = windowsSession()
+    const session = sessionOn('win32')
     try {
       ptyStub.dataHandler?.(marker('P;Cwd=D:\\\\work\\\\project'))
       expect(session.tabState(true).title).toBe('project')

apps/desktop/src/main/terminal/session.ts

@@ -220,6 +220,15 @@ const ALT_SCREEN_ENTER = '\u001b[?1049h'
 /** Restoring the normal screen: the full-screen program has quit. */
 const ALT_SCREEN_EXIT = '\u001b[?1049l'
 
+/**
+ * The bundled ConPTY asks the terminal for its device attributes as it starts and holds the
+ * shell's first output until it hears back, for three seconds when nothing answers. The session
+ * answers that one query itself, as xterm.js would, and keeps it from the panel so the reply is
+ * never sent twice; an agent's shell has no panel to answer it at all.
+ */
+const DEVICE_ATTRIBUTES_QUERY = '\u001b[c'
+const DEVICE_ATTRIBUTES_REPLY = '\u001b[?1;2c'
+
 /**
  * Scrollback the on-demand emulator keeps while rendering a read.
  *
@@ -356,6 +365,8 @@ export class TerminalSession {
   private startupBegunAt: number | null = null
   private readonly spawnedAt = Date.now()
   private altScreen = false
+  /** Whether ConPTY's startup query is still to be answered. */
+  private conptyQueryPending: boolean
   private foregroundCommand: string | null = null
   private foregroundToolCallId: string | null = null
   /**
@@ -390,6 +401,7 @@ export class TerminalSession {
     this.integrationDir = integrationDir
     this.shellName = shellName
     this.parser = new ShellIntegrationParser(nonce)
+    this.conptyQueryPending = platform === 'win32'
 
     this.pty.onData((chunk) => this.handleData(chunk))
     this.pty.onExit(() => this.handleExit())
@@ -865,7 +877,7 @@ export class TerminalSession {
   }
 
   private handleData(chunk: string): void {
-    const { text, markers } = this.parser.parse(chunk)
+    const { text, markers } = this.parser.parse(this.answerConptyQuery(chunk))
 
     for (const marker of markers) {
       this.applyMarker(marker)
@@ -890,6 +902,16 @@ export class TerminalSession {
     }
   }
 
+  /** Answers and removes ConPTY's startup device-attributes query, the first time it appears. */
+  private answerConptyQuery(chunk: string): string {
+    if (!this.conptyQueryPending) return chunk
+    const index = chunk.indexOf(DEVICE_ATTRIBUTES_QUERY)
+    if (index === -1) return chunk
+    this.conptyQueryPending = false
+    this.pty.write(DEVICE_ATTRIBUTES_REPLY)
+    return chunk.slice(0, index) + chunk.slice(index + DEVICE_ATTRIBUTES_QUERY.length)
+  }
+
   private applyMarker(
     marker: ReturnType<ShellIntegrationParser['parse']>['markers'][number]
   ): void {