test-dup-setfl-race times out in the Release matrix lane #466

Background

test-dup-setfl-race (tests/test-dup-setfl-race.c) times out in the Runtime (Release) job on CI, on branches that do not touch its code path. In each run it passes under make check earlier in the same job, then hits the 30 s timeout in the elfuse lane of the test matrix, and passes on the qemu reference kernel in the same job. A normal run takes about two seconds, per the comment on ROUNDS.

The test only calls pipe, dup, fcntl(F_GETFL/F_SETFL), close and sched_yield from two threads. On #463 the next push, which changed no code, passed every lane.

Goal

The test either passes in its normal time or fails with a message, on every lane, so a red Release job means a regression.

Evidence

Not reproduced locally: 20 runs of build/elfuse build/test-dup-setfl-race on the #463 branch all exit 0. The runs above were found by listing the failed Runtime runs and searching their failed-job logs for the test name; a blank cell means that run's failed-step log did not show that result.

The timeout hides where it stalls. Both handshake loops in main spin on pause_ack < want && !stop, and stop is only set after the round loop ends, so if the flipper thread stops acknowledging, main spins until the 30 s timeout with nothing printed.