The three tests of #373 run two branches with tokio::join! and rely on
the first branch being polled first: the check that starts first, or the
check that waits for a held turn before the time moves. tokio's join!
already starts with the first branch on its first poll, but rotates on
the next ones; `biased;` keeps the declared order on every poll and says
so in the code. The three mutations (no turn, time read before the turn,
guard dropped at once) were run again: same red tests.
Resolves#373
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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