test(tui): two runtime_api configured_model tests hang under the broad 'config' filter, pass alone (test isolation)

Observed (two independent lane runs, 2026-09-17)

Running the broad name filter

cargo test -p codewhale-tui --lib --locked config

(which selects a large body of runtime_api::*config* tests — 779 completed ok), these two never finish:

test runtime_api::configured_model_api_tests::declared_model_posts_do_not_preserve_alias_at_wrong_endpoint has been running for over 60 seconds
test runtime_api::configured_model_api_tests::declared_model_posts_preserve_exact_identity_after_reload has been running for over 60 seconds

while running either alone is fast:

cargo test ... runtime_api::configured_model_api_tests::declared_model_posts_do_not_preserve_alias_at_wrong_endpoint -- --exact  => ok, 0.25s
cargo test ... runtime_api::configured_model_api_tests::declared_model_posts_preserve_exact_identity_after_reload -- --exact => ok, 0.79s

The same pair previously aborted the filter run with a thread stack overflow under the default 2 MiB test-thread stack; with RUST_MIN_STACK=16MiB (what scripts/dev-cargo.sh and CI set) there is no overflow, but the hang under concurrency remains.

Impact

The config filter cannot be used as a CI/lane gate: it never terminates, and it masks everything scheduled after it.

Suspicion (unconfirmed)

Shared process-wide state under concurrent test threads — env guards (lock_test_env), the rate-limit window, or a listener/server port — parks these two tests. Needs a --test-threads bisect and a task dump at the hang.

Reported by the Codewhale night program; no fix attempted.