## Summary
- add `ProcessOwnedCodeModeSessionProvider` and logical session
generation/rebinding state
- add the supervised child-process connection, reader/writer tasks, and
driver state machine
- make dropped execute/wait/open callers cancellation-safe with explicit
ownership handoff and durable cleanup
- validate cell/delegate lifecycle state and reject invalid protocol
transitions
- add end-to-end stdio coverage for delegates, cancellation, frame
limits, child loss, stale generations, replacement, and long-lived
sessions
## Why
This final stage exposes the process-owned client only after the wire
protocol, host-safe runtime, and standalone host are independently in
place. Transport failure is fail-stop: the client closes local state,
cancels callbacks, reaps the child, and lazily rebuilds a fresh host
generation rather than transactionally recovering the old connection.
## Stack
This is **4 of 4** in the process-owned code-mode session stack.
- Depends on #30111
- Full stack: #30108 → #30110 → #30111 → this PR
## Validation
- `just test -p codex-code-mode -p codex-code-mode-host` — 86 passed
- `just fix -p codex-code-mode`
- `just fix -p codex-code-mode-host`
- `just bazel-lock-update`
- `just bazel-lock-check`
- `bazel test //codex-rs/code-mode:code-mode-unit-tests
//codex-rs/code-mode-host:code-mode-host-unit-tests
//codex-rs/code-mode-host:code-mode-host-stdio-test
//codex-rs/code-mode-protocol:code-mode-protocol-unit-tests` — 4/4
passed
- `just fmt`
## Summary
- implement the standalone `codex-code-mode-host` stdio service
- route sessions, cells, delegate requests, responses, and cancellation
through a bounded host peer
- supervise request, writer, cell-forwarding, actor, and V8 failure
boundaries
- bound request/session tombstones and fail-stop the connection on
invalid protocol state
- add host-only duplex protocol tests and local Cargo/Bazel run recipes
## Why
This stage makes the host process independently runnable and reviewable
before exposing any remote client in Codex. Transport or runtime failure
closes the connection and relies on process replacement rather than
transactional recovery.
## Stack
This is **3 of 4** in the process-owned code-mode session stack.
- Depends on #30110
- The final client PR targets this branch
## Validation
- `just test -p codex-code-mode-host` — 7 host-only tests passed
- `just fix -p codex-code-mode-host`
- `just bazel-lock-update`
- `just bazel-lock-check`
- `just fmt`
This is phase 1 of a 4 phase stack:
1. **Add protocol and host crates for new IPC code mode implementation**
2. Create the new standalone binary
3. Create a new IPC `CodeModeSessionProvider` to use new binary
4. Remove v8 from core and only use IPC provider
## Add protocol and host crates for new IPC code mode implementation
Establish a clean process boundary without changing the existing
in-process behavior.
- Add the codex-code-mode-protocol crate for shared session, runtime,
response, and tool-definition types.
- Move protocol-facing code out of the V8-backed implementation.
- Add a buildable codex-code-mode-host crate as the foundation for the
standalone process.
- Keep the existing in-process runtime as the active implementation.
Channing Conger ·