Why

The in-process app-server-client tests were still building their configs from the ambient codex_home and letting the embedded app server create its own state DB when state_db was absent. That matters because in-process startup falls back to init_state_db_from_config(...) in that case, so tests can otherwise share persisted state instead of getting isolated fixtures: app-server/src/in_process.rs.

What changed

• Give each in-process test client its own temporary codex_home.
• Initialize the matching state DB from that per-client config and pass it into the client explicitly.
• Keep the temp directory alive for the lifetime of the test client through a small TestClient wrapper.
• Add tempfile as a dev dependency for the new harness.

The updated setup lives in app-server-client/src/lib.rs.

Testing

• Existing codex-app-server-client tests continue to exercise the updated in-process client path through the isolated helper.