feat(execd): add WebSocket PTY support

[ctlaltlaltc]

Summary

For context regarding API separation and integration, Ref #455

• Add /pty/* REST endpoints to create, inspect, and delete PTY sessions (independent of existing /session/* flow)
• Add GET /pty/:id/ws WebSocket endpoint for bidirectional interactive terminal acce
• 1 MiB circular replay buffer — clients reconnect with ?since=<offset> for exact-once output delivery
• PTY mode (default) and pipe mode (?pty=0) both supported
• Windows build compatibility via stubs

Changes

File	Description
pkg/runtime/replay_buffer.go	Circular replay buffer
pkg/runtime/pty_session.go	PTY session struct + lifecycle (!windows)
pkg/runtime/pty_session_windows.go	Windows stubs
pkg/web/model/pty.go / pty_ws.go	REST + WS frame models
pkg/web/controller/pty_controller.go	REST handlers
pkg/web/controller/pty_ws.go	WebSocket handler
pkg/runtime/ctrl.go	+ptySessionMap sync.Map (only change)
pkg/web/router.go	Register /pty/* routes (only change)

Zero modifications to existing bashSession, RunInSession, or /session/* endpoints.

Test coverage

• replay_buffer_test.go — write/read, circular eviction, caught-up offset, large gap, concurrent (-race)
• pty_session_test.go — basic execution, PTY resize, ANSI sequences, pipe mode, reconnect replay
• pty_ws_test.go — 404 before upgrade, 409 already connected, ping/pong, stdin forwarding, replay on reconnect, exit
  frame, resize frame

Verified manually

• POST /pty → session created
• GET /pty/:id → {"running":true,"output_offset":18}
• wscat PTY mode and pipe mode (?pty=0)
• Reconnect with ?since=0 delivers prior output

Testing

• Not run (explain why)
• Unit tests
• Integration tests
• e2e / manual verification

Breaking Changes

• None
• Yes (describe impact and migration path)

Checklist

• Linked Issue or clearly described motivation
• Added/updated docs (if needed)
• Added/updated tests (if needed)
• Security impact considered
• Backward compatibility considered

[chatgpt-codex-connector]

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[Pangjiping]

Could you provide some manual test cases or screenshots for reference?

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 8dc470f9dd

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Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

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• Mark a draft as ready
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[ctlaltlaltc]

Could you provide some manual test cases or screenshots for reference?

Done.

https://gist.github.com/ctlaltlaltc/930aedb331caadd7fc1bffea74003a0a

execd.log in sandbox.

my xtermjs client connect to execd endpoint directly integrate.

[Pangjiping]

Could you provide some manual test cases or screenshots for reference?

Done.

https://gist.github.com/ctlaltlaltc/930aedb331caadd7fc1bffea74003a0a

execd.log in sandbox.

my xtermjs client connect to execd endpoint directly integrate.

Great Job. You can rebase main and fix the interface definition issue. #577

[ctlaltlaltc]

@Pangjiping Done, thanks review.

[Pangjiping]

LGTM.