Feature request: PTY allocation support in execd for interactive terminal sessions

[AlexandrePh]

Summary

The OpenSandbox execd API currently supports non-interactive command execution via POST /command with SSE output streaming. For interactive terminal use cases (e.g., attaching to a running agent's terminal, debugging sessions), we need PTY (pseudo-terminal) allocation support.

Current Behavior

ExecRequest only supports:

{
  "command": "string",
  "background": bool,
  "timeout": int
}

Output is streamed via SSE (stdout, stderr, exit events) — unidirectional, no stdin support.

Proposed Changes

1. Add tty: bool field to exec request — allocates a PTY for the command
2. WebSocket exec endpoint — bidirectional communication for interactive sessions:
   • Client sends stdin data as binary frames
   • Server sends stdout/stderr as binary frames
   • Support terminal resize events (SIGWINCH)
3. PTY lifecycle management — graceful shutdown, signal forwarding

Use Case

Building a worker interaction system where users can attach to get a raw terminal session inside a sandbox. This requires:

• Bidirectional I/O (stdin + stdout/stderr)
• PTY allocation for proper terminal behavior (line editing, colors, etc.)
• Terminal resize propagation

Suggested API

WS /v1/sandboxes/{id}/proxy/{port}/terminal
  Query params: ?cols=80&rows=24&command=bash

  Client → Server: binary frames (stdin bytes) + JSON control frames (resize)
  Server → Client: binary frames (stdout bytes)

Or extend the existing exec endpoint:

POST /command
{
  "command": "bash",
  "tty": true,
  "cols": 80,
  "rows": 24
}

With a WebSocket upgrade path for the response.