## Why
`codex-app-server` currently owns both request-processing code and
transport implementation details. Splitting the transport layer into its
own crate makes that boundary explicit, reduces the amount of
transport-specific dependency surface carried by `codex-app-server`, and
gives future transport work a narrower place to evolve.
## What changed
- Added `codex-app-server-transport` and moved the existing transport
tree into it, including stdio, unix socket, websocket, remote-control
transport, and websocket auth.
- Moved shared transport-facing message types into the new crate so both
the transport implementation and `codex-app-server` use the same
definitions.
- Kept processor-facing connection state and outbound routing in
`codex-app-server`, with the routing tests moved next to that local
wrapper.
- Updated workspace metadata, Bazel crate metadata, and
`codex-app-server` dependencies for the new crate boundary.
## Validation
- `cargo metadata --locked --no-deps`
- `git diff --check`
- Attempted `cargo test -p codex-app-server-transport`, `cargo test -p
codex-app-server`, `just fix -p codex-app-server-transport`, and `just
fix -p codex-app-server`; all were blocked before compilation by the
existing `packageproxy` resolution failure for locked `rustls-webpki =
0.103.13`.
- Attempted Bazel build / lockfile validation; those were blocked by
external fetch failures against BuildBuddy / GitHub while resolving
`v8`.
Ruslan Nigmatullin