## What changed
Serialize `ClientResponse` JSON-RPC results through the untagged
`ClientResponsePayload` enum, and serialize payloads directly instead of matching
on each variant. Preserve existing result shapes and request IDs.
## Testing
Add regression tests covering v1 and v2 payloads with integer and string request
IDs, legacy interrupt responses, and serialization errors from non-UTF-8 paths
on Unix across typed, borrowed, and owned response conversions.
GitOrigin-RevId: d46403b02f910a0d3e41a48a5bc6faa2581873e1
## What changed
- Keep `ClientResponsePayload` typed through the app-server outgoing queue and serialize it at the transport boundary, avoiding an intermediate `serde_json::Value` while preserving the JSON-RPC wire shape.
- Return a JSON-RPC internal error when a response cannot be serialized, including over remote control, and skip unserializable analytics responses.
- Scan reverse JSONL input a chunk at a time with a larger buffer instead of processing each byte individually.
## Testing
- Cover typed response serialization and serialization failures for direct and remote-control transports.
- Cover filtering unserializable responses from analytics.
GitOrigin-RevId: cc4fd7a43461a273315bb95261bd1ae3ff65fbf7
## Why
`pr17088` adds typed server-originated request/response plumbing, but
successful client responses are still erased into bare JSON-RPC `result`
values before app-server can make any typed decision about them.
This precursor PR keeps successful client responses typed until the
outgoing response seam. It is intentionally limited to
protocol/app-server plumbing so the analytics behavior change can review
separately on top.
## What changed
- Add `ClientResponsePayload` as the pre-serialization client response
body type.
- Route app-server successful response paths through the typed payload
seam while preserving existing handler-local analytics behavior.
- Keep `InterruptConversation` JSON-RPC-only because it has no
`ClientResponse` variant.
- Move the new payload conversion tests into a dedicated protocol test
module.
## Verification
- `cargo check -p codex-app-server`
- `cargo test -p codex-app-server-protocol`
Ahmed Ibrahim