feat: exec-server prep for unified exec

[jif-oai]

This PR partially rebase unified_exec on the exec-server and adapt the exec-server accordingly.

What changed in exec-server

1. Replaced the old "broadcast-driven; process-global" event model with process-scoped session events. The goal is to be able to have dedicated handler for each process.
2. Add to protocol contract to support explicit lifecycle status and stream ordering:

• WriteResponse now returns WriteStatus (Accepted, UnknownProcess, StdinClosed, Starting) instead of a bool.
• Added seq fields to output/exited notifications.
• Added terminal process/closed notification.

3. Demultiplexed remote notifications into per-process channels. Same as for the event sys
4. Local and remote backends now both implement ExecBackend.
5. Local backend wraps internal process ID/operations into per-process ExecProcess objects.
6. Remote backend registers a session channel before launch and unregisters on failed launch.

What changed in unified_exec

1. Added unified process-state model and backend-neutral process wrapper. This will probably disappear in the future, but it makes it easier to keep the work flowing on both side.

• UnifiedExecProcess now handles both local PTY sessions and remote exec-server processes through a shared ProcessHandle.
• Added ProcessState to track has_exited, exit_code, and terminal failure message consistently across backends.

2. Routed write and lifecycle handling through process-level methods.

Some rationals

1. The change centralizes execution transport in exec-server while preserving policy and orchestration ownership in core, avoiding duplicated launch approval logic. This comes from internal discussion.
2. Session-scoped events remove coupling/cross-talk between processes and make stream ordering and terminal state explicit (seq, closed, failed).
3. The failure-path surfacing (remote launch failures, write failures, transport disconnects) makes command tool output and cleanup behavior deterministic

Follow-ups:

• Unify the concept of thread ID behind an obfuscated struct
• FD handling
• Full zsh-fork compatibility
• Full network sandboxing compatibility
• Handle ws disconnection

[chatgpt-codex-connector]

💡 Codex Review

codex/codex-rs/exec-server/tests/exec_process.rs

Line 31 in 3ce6a55

process: environment.get_executor(),

Fix integration tests to use the renamed environment API

This test still calls environment.get_executor(), but the commit renamed the API to get_exec_backend(). As written, the integration test target will not compile, so CI coverage for exec-session behavior is broken until tests are updated to the new interface.

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[jif-oai]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 9e91c882fd

ℹ️ About Codex in GitHub

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