## Why
Exec-server JSON-RPC payloads can contain decimals, exponent notation, and
integers outside the native 64-bit range. Decoding these values should preserve
their original JSON representation without weakening the existing message
complexity limit.
## What changed
- Enable `serde_json` arbitrary-precision number and raw-value support for the
exec-server protocol.
- Decode serde's number and raw-value wrappers in the bounded JSON visitor,
charging nested raw values against the 256K-value limit.
- Select the JSON-RPC envelope variant from its fields after bounded decoding so
arbitrary-precision values survive message deserialization.
## Testing
Add coverage for exact arbitrary-precision number round trips and for enforcing
the value limit inside raw-value wrappers.
GitOrigin-RevId: a6e0a3fba6f88e4e8a6ff414832f078beb2d2a70
## Why
The app-server and exec-server expose separate JSON-RPC APIs, but
exec-server currently sources its serialized protocol and envelope types
through app-server-oriented code. Giving each API an explicit owner
makes the crate boundary legible without introducing shared generic
envelopes.
## What changed
- Added `codex-exec-server-protocol` to own exec DTOs, process IDs, and
JSON-RPC envelopes.
- Updated exec-server clients, transports, handlers, and tests to use
the new crate.
- Exposed app-server's existing JSON-RPC types through a public `rpc`
module while retaining root re-exports.
- Preserved existing wire shapes, including exec `PathUri` behavior.
## Stack
This is PR 1 of 6. Next: [PR
#29721](https://github.com/openai/codex/pull/29721), which moves auth
mode below the app wire boundary.
## Validation
- Exec-server protocol and server coverage passed in the focused
protocol test runs.
- App-server protocol schema fixtures passed.
