Live cxpak MCP transport (RmcpCxpakClient) has zero tests

[lyubomir-bozhinov]

Severity: Medium (test coverage of the highest-risk code)

Problem

The live cxpak transport RmcpCxpakClient (src/cxpak.rs, ~lines 245-484) has no tests. Existing tests cover only RecordedClient, is_indexing, SpawnBackoff, and DTO defaults — shape checks. Untested: child-process spawn, the 15s handshake timeout, the 10s call timeout, index-warm polling, Arc-identity connection eviction, kill_child, and Drop teardown. Comments reference a #[tokio::test] teardown that does not exist.

Why it matters

This is the most failure-prone code in a crate other components depend on — process spawning and timeout/eviction logic — and it is entirely unverified. Regressions here surface as hangs or leaked child processes in every consumer.

Proposed fix

Add a fake-child / stub-server harness to exercise timeout, eviction, backoff, and teardown paths; add #[ignore] live smoke tests against a real cxpak binary for the happy path.

Acceptance criteria

• Timeout, connection-eviction, and Drop/kill_child paths have deterministic tests.
• A leaked-child assertion exists (no orphaned process after Drop).

[lyubomir-bozhinov]

Citation trim (verification sweep). Core finding stands: RmcpCxpakClient (cxpak.rs:285-474) has zero test coverage of its spawn/timeout/eviction/Drop paths; the #[cfg(test)] block only exercises RecordedCxpakClient/DTO/SpawnBackoff. But the sub-claim "comments reference a #[tokio::test] teardown that does not exist" overstates cxpak.rs:274-276, which is a design-rationale comment about #[tokio::test] scheduling semantics, not a dangling reference to a missing test. Drop that sub-claim; the coverage gap is the real issue.

[lyubomir-bozhinov]

Travels with the code: RmcpCxpakClient moves to cxpak as part of the fold (#4). An official Rust client belongs with its server, and it is the single largest thing in this repo.

Write the tests in cxpak, after the move — not here. Tests authored against a module about to change repos are work done twice. Keep this open to track the obligation; close it when cxpak carries both the client and its coverage.