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
Add environment manager that is a singleton and is created early in
app-server (before skill manager, before config loading).
Use an environment variable to point to a running exec server.
## Summary
- match the exec-process structure to filesystem PR #15232
- expose `ExecProcess` on `Environment`
- make `LocalProcess` the real implementation and `RemoteProcess` a thin
network proxy over `ExecServerClient`
- make `ProcessHandler` a thin RPC adapter delegating to `LocalProcess`
- add a shared local/remote process test
## Validation
- `just fmt`
- `CARGO_TARGET_DIR=~/.cache/cargo-target/codex cargo test -p
codex-exec-server`
- `just fix -p codex-exec-server`
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Co-authored-by: Codex <noreply@openai.com>
