feat: Add pty support to Vercel sandbox

[scotttrinh]

Uses the recently published AsyncPTYSession class from vercel to implement pty support.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 6983993e94

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Close PTY session when readiness handshake fails

If AsyncPTYSession.open(...) succeeds but session.ready() times out or raises, cleanup calls _terminate_pty_entry(entry) while entry.session is still None, so the opened PTY connection is never closed. In flaky network conditions this leaves orphaned PTY processes/connections on the backend and can exhaust session limits over repeated retries. Assigning entry.session before awaiting readiness (or explicitly closing the local session in the exception path) avoids the leak.

Useful? React with 👍 / 👎.

[chatgpt-codex-connector]

Clean up unregistered PTY session on task cancellation

This startup path creates the reader task before registration, but the exception handling only catches Exception; asyncio.CancelledError (a BaseException) bypasses cleanup. If a caller cancels during pty_exec_start after the task/session are created, the PTY remains running but is never added to _pty_sessions, so it cannot be terminated via normal session bookkeeping.

Useful? React with 👍 / 👎.

[alfozan]

Two more sandbox PTY test scenarios:

Starting PTY with a one-shot command:

Example: pty_exec_start("echo PTY_ONE_SHOT")
Expected: command runs and returns output

PTY after stop/resume:

Flow:

• create sandbox
• stop()
• resume()
• start a new PTY shell
  Expected: PTY opens normally after resume