## Why
Automatic gRPC reconnection could spawn a replacement host while dispatching an RPC for an existing session. Host loss must remain visible so recovery can report lost state without replaying execution or completed external effects.
## What changed
- Bind each local host channel to one child process and allow only `OpenSession` to replace a dead host.
- Add caller-owned transport support to `GrpcCodeModeSessionProvider` and map local transport failures to `Unavailable` so initial connection failures use the existing bounded admission retries.
## Testing
Add regression coverage for child exit during initial connection and between channel selection and dispatch, concurrent session recovery, and child reaping after teardown. An integration test kills the host after a command completes and verifies that recovery reports the reset, clears stored state, and leaves the command's external effect unchanged.
Increase the remote MCP stalled-handshake test's initialization timeout and mock response delay to let requests reach the server on loaded CI workers.
GitOrigin-RevId: 4ffd810e4cfcfb7a56e606816aa867bc206a09b6
## What changed
- Include `environmentInfo` in the exec-server `initialize` response and seed the Rust client's metadata cache from it.
- Fall back to one lazy `environment/info` request when connecting to older servers that omit initialization metadata, then share the cached result across client clones and session recovery.
- Keep app-server `environment/info` requests uncached so they continue to probe the executor.
## Testing
- Cover initialization metadata, the legacy-server fallback, shared caching, accepted WebSocket environments, and repeated uncached app-server probes.
GitOrigin-RevId: 380132d9db183998d73e8c6b0954e4d70c7e8406
## What changed
Extend the executor-backed Streamable HTTP timeout test to cover both legacy
`initialize` and MCP 2026 `server/discover` requests. Verify that each stalled
handshake times out and releases the serial executor for subsequent requests.
GitOrigin-RevId: 3493904433c95265b9f645813723e890b7610abb
## Why
A streamable HTTP MCP handshake could time out while its executor-backed HTTP
request continued running, leaving the serial executor blocked for later
requests.
## What changed
- Track the remaining initialization deadline for streamable HTTP transports.
- Apply it to `initialize`, `notifications/initialized`, and discovery HTTP
requests, then clear it when the handshake finishes.
## Testing
- Added a regression test that stalls the remote MCP endpoint, waits for the
handshake timeout, and verifies that a subsequent executor request completes.
GitOrigin-RevId: d4980a332e898309c885cbaa4fdd598924b440e1
### Why
The RMCP layer needs a Streamable HTTP client that can talk either
directly over `reqwest` or through the executor HTTP runner without
duplicating MCP session logic higher in the stack. This PR adds that
client-side transport boundary so remote Streamable HTTP MCP can reuse
the same RMCP flow as the local path.
### What
- Add a shared `rmcp-client/src/streamable_http/` module with:
- `transport_client.rs` for the local-or-remote transport enum
- `local_client.rs` for the direct `reqwest` implementation
- `remote_client.rs` for the executor-backed implementation
- `common.rs` for the small shared Streamable HTTP helpers
- Teach `RmcpClient` to build Streamable HTTP transports in either local
or remote mode while keeping the existing OAuth ownership in RMCP.
- Translate remote POST, GET, and DELETE session operations into
executor `http/request` calls.
- Preserve RMCP session expiry handling and reconnect behavior for the
remote transport.
- Add remote transport coverage in
`rmcp-client/tests/streamable_http_remote.rs` and keep the shared test
support in `rmcp-client/tests/streamable_http_test_support.rs`.
### Verification
- `cargo check -p codex-rmcp-client`
- online CI
### Stack
1. #18581 protocol
2. #18582 runner
3. #18583 RMCP client
4. #18584 manager wiring and local/remote coverage
---------
Co-authored-by: Codex <noreply@openai.com>
aakash-oai