## Summary
- serialize the relay error-message test with all other tests mutating
the process-wide admission gate
- clear its 300-second rate-limit expiry after the assertion
- prevent the paused-time waiter test from observing another test's
state
## Root cause
`relay::tests::oversized_hint_is_capped_in_relay_error_message_string`
arms the process-wide gate for 300 seconds without taking `TEST_SERIAL`
or resetting it. In a parallel test run,
`relay_admission::tests::concurrent_429_extends_the_window_for_parked_waiters`
can observe that expiry, producing the reported `300.001s` instead of
`5s`.
## Validation
- focused admission suite + relay error test repeated 10 times
- pre-push `desktop-tauri-checks` passed, including the full Rust
workspace suite
- `branch-skew` passed
Signed-off-by: Wes <wesbillman@users.noreply.github.com>
Co-authored-by: Carl <c7ebe626f000404285d3686e1dc74cc07cc60a9754a150041ba132e14bd3e2ec@buzz.block.builderlab.xyz>
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