isolate codex transport tests from the developer's config

[rikbrown]

Problem

The five config::tests::codex_transport_* tests call clear_env(), which removes CCP_CONFIG_DIR, and then call codex_transport() without pointing it at a temp dir. The accessor falls back to paths::config_dir(), so the tests read the developer's real ~/.config/claude-code-proxy/config.json.

On any machine whose config sets codex.transport to something other than the default, cargo test fails:

test config::tests::codex_transport_defaults_to_websocket ... FAILED
test config::tests::codex_transport_empty_env_falls_back_to_websocket ... FAILED
test config::tests::codex_transport_env_websocket ... FAILED
test config::tests::codex_transport_invalid_env_falls_back_to_websocket ... FAILED
test config::tests::codex_transport_reads_env ... FAILED

Only one of those is a real assertion failure — the shared ENV_LOCK is then poisoned and takes the other four down with it, so a single config value presents as five failures.

Worth noting: CCP_CONFIG_DIR=$(mktemp -d) cargo test does not work around this, because clear_env() strips exactly that variable. The suite has to be isolated via HOME, which is not obvious.

Reproduce

mkdir -p /tmp/ccp-repro/.config/claude-code-proxy
printf '{"codex":{"transport":"auto"}}' > /tmp/ccp-repro/.config/claude-code-proxy/config.json
HOME=/tmp/ccp-repro XDG_CONFIG_HOME=/tmp/ccp-repro/.config cargo test config::tests::codex_transport

Fix

Point each of the five tests at a tempfile::TempDir via EnvGuard::set("CCP_CONFIG_DIR", ...) — the same shape codex_server_compaction_defaults_and_overrides and the other config accessor tests in the module already use. Assertions are unchanged, and clear_env() is deliberately left alone since other tests rely on the unset state.

I checked every other clear_env() caller in the module; they all either set CCP_CONFIG_DIR already or use load_config_for_env with an explicit dir, so this is the only instance.

Verification

• Repro above: 5 failed before, 6 passed; 0 failed after
• cargo clippy --all-targets -- -D warnings clean, cargo fmt --check clean
• Full suite with an isolated HOME: green

🤖 Generated with Claude Code

[raine]

Thanks for catching this! Merged.