## Summary
This adds focused coverage for the simpler same-connection scalar
request path.
The exec-server connection already supports multiple in-flight JSON-RPC
scalar requests on one connection. This test locks in that behavior by
sending two normal requests before reading either response, without
adding a batch frame or any new API surface.
## What changed
- Added a processor-level test that initializes an exec-server
connection.
- Sends two scalar `environment/info` requests back-to-back on the same
connection.
- Verifies both responses come back on the same connection by request
id.
Checked locally with:
- `just test -p codex-exec-server
connection_accepts_pipelined_scalar_requests`
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