fix: wait for PTY startup readiness

packages/pty/pty-local/README.md

@@ -6,7 +6,7 @@ Local `node-pty` backend for `ctx.pty`. It starts an interactive shell under the
 
 The plugin injects `pty`, `sandbox`, and `sandboxPolicy`, then registers the configured backend type (`shell`). `danger-full-access` starts the shell directly; confined modes wrap the exact shell argv through `ctx.sandbox`. The current session-level sandbox override is resolved at spawn and remains fixed for the PTY lifetime.
 
-Linux readiness combines a private bash prompt marker, foreground-process-group syscall inspection, silence fallback, and absolute timeout. macOS uses the prompt marker plus silence/timeout because it has no `/proc` syscall surface. Unrecognized or unreadable process state is never a positive exact-idle signal.
+Linux readiness combines a private bash prompt marker, foreground-process-group syscall inspection, silence fallback, and absolute timeout. macOS uses the prompt marker plus silence/timeout because it has no `/proc` syscall surface. Unrecognized or unreadable process state is never a positive exact-idle signal. During unpublished startup, a fallback requires observed output; zero-output silence cannot publish an empty session, and timeout rejects the spawn.
 
 ## Model Experience
 

packages/pty/pty-local/src/session.ts

@@ -148,6 +148,7 @@ export class LocalPtySession implements PtyBackendSession {
   private activeTimer: NodeJS.Timeout | undefined
   private activeAbort: (() => void) | undefined
   private promptSeen = false
+  private initializing = false
   private lastOutputAt = Date.now()
   private closePromise: Promise<void> | undefined
 
@@ -171,13 +172,19 @@ export class LocalPtySession implements PtyBackendSession {
   /**
    * Capture startup output through the same readiness contract as later sends.
    * @param signal - optional cancellation while the shell reaches its first prompt.
-   * @returns Resolves after startup readiness; rejects if the shell exits.
+   * @returns Resolves after startup readiness; rejects on exit or readiness timeout.
    */
   async initialize(signal?: AbortSignal): Promise<void> {
-    const operation = this.startSend({ text: '', submit: false, ...signal !== undefined ? { signal } : {} })
-    const result = await operation.done
-    if (result.waitReason === 'session_exit') throw new Error('PTY shell exited during startup')
-    this.motd = result.viewport
+    this.initializing = true
+    try {
+      const operation = this.startSend({ text: '', submit: false, ...signal !== undefined ? { signal } : {} })
+      const result = await operation.done
+      if (result.waitReason === 'session_exit') throw new Error('PTY shell exited during startup')
+      if (result.waitReason === 'timeout') throw new Error('PTY shell did not reach readiness before startup timeout')
+      this.motd = result.viewport
+    } finally {
+      this.initializing = false
+    }
   }
 
   startSend(request: PtySendRequest): PtySendOperation {
@@ -289,14 +296,15 @@ export class LocalPtySession implements PtyBackendSession {
       return
     }
     const elapsed = Date.now() - operation.startedAt
-    if (elapsed >= this.config.exactProbeAfterMs) {
+    const startupHasOutput = !this.initializing || this.scrollback.snapshot().text.length > 0
+    if (startupHasOutput && elapsed >= this.config.exactProbeAfterMs) {
       const pgid = this.inspector.foregroundPgid(this.pid)
       if (pgid !== undefined && this.inspector.isStdinWaiting(pgid)) {
         this.settleActive('stdin_read')
         return
       }
     }
-    if (Date.now() - this.lastOutputAt >= this.config.idleSilenceMs) {
+    if (startupHasOutput && Date.now() - this.lastOutputAt >= this.config.idleSilenceMs) {
       this.settleActive('inferred_idle')
       return
     }

packages/pty/pty-local/tests/session.spec.ts

@@ -219,6 +219,25 @@ describe('LocalPtySession readiness and output', () => {
     expect(cancellable.cancel()).toBe(true)
     await expect(cancellable.done).rejects.toThrow('write failed')
   })
+
+  it('does not treat zero-output startup silence as readiness and fails on startup timeout', async () => {
+    vi.useFakeTimers()
+    const terminal = new FakeTerminal()
+    const session = new LocalPtySession(terminal.asPty(), new FakeInspector(), config())
+    let settled = false
+    const initializing = session.initialize().then(() => { settled = true })
+    await vi.advanceTimersByTimeAsync(60)
+    expect(settled).toBe(false)
+    terminal.emitData('\x1b]133;D;0\x07dsh> ')
+    await vi.advanceTimersByTimeAsync(10)
+    await initializing
+
+    const timeoutTerminal = new FakeTerminal()
+    const timeout = new LocalPtySession(timeoutTerminal.asPty(), new FakeInspector(), config())
+    const timedOut = expect(timeout.initialize()).rejects.toThrow('startup timeout')
+    await vi.advanceTimersByTimeAsync(100)
+    await timedOut
+  })
 })
 
 describe('LocalPtySession bounds, signals, and teardown', () => {