Files
fips/src
Arjen ee5384f013 test(iface-binding): assert the fast path and the churn guard
Three gaps, two of them in tests that existed and asserted nothing.

**The netlink path was never asserted to be in use.** The 1 s poll is a
complete fallback and covers every wait in the suite, so the whole thing
passed with `open_link_socket()` hardcoded to Err — the fast path could have
been dead for a release and no test would have said so. The binder reports
which backing it got at startup, so case (g) asks it directly rather than
inferring from timing the poll would also satisfy, and the unit test that used
to write `let _ = w.is_event_driven();` now asserts it on Linux, where the
source is an unprivileged `AF_NETLINK` socket and falling back is a real loss
rather than a sandbox's prerogative.

**Churn damping had no end-to-end coverage**, which now matters twice over: it
bounds the recovery announcements, and since the detach edge withdraws peers
it is also the only thing bounding how often that withdrawal fires. Every flap
elsewhere in the suite is a single down/up with long settles either side —
exactly the shape the damper ignores. Case (h) drives four bindings that each
die inside `MIN_STABLE_BINDING`, asserts the guard engages, asserts it then
*suppresses* rather than merely counting, and asserts it is not a latch.

**`a_poisoned_binding_does_not_strand_the_transport` discarded its result.**
`let _ = eth.binding.tasks_alive();` left the entire point unasserted: reading
a poisoned lock as "alive" would have the binder believe a dead binding
healthy and never rebind, and treating it as an error would strand the
transport. `false` is what routes it back through detach and rebind, so say so.

`a_stop_racing_a_bind_leaves_nothing_behind` now asserts the error *kind*.
`bind_and_spawn` refuses at its presence probe long before the post-store
shutdown check, so `is_err()` alone passed on absence and would still pass
with that check deleted. The test keeps the coverage it genuinely has — stop
raises the flag before teardown, teardown leaves no socket and no loops — and
says plainly that the race it is named for needs a bind that succeeds, which
needs privilege no unit test has.

Both new cases were verified against the defect: with the netlink source
forced to Err, (g) fails; with `CHURN_THRESHOLD` raised out of reach, (h)
fails. Nothing else in the suite notices either.

One case was attempted and removed rather than shipped: `"interface
replaced"` cannot be produced deterministically, because the delete that
changes an ifindex fires a netlink event the binder acts on within
microseconds, so `gone` wins the race. It passed about one run in three.
reference/notes.md records the measurement and the two approaches that could
work.

Also fixes a real bug in the harness: `grep -q` under `set -o pipefail` exits
on its first match, `docker logs` takes SIGPIPE, and the pipeline reports
failure even though the line was found. That cost two false failures before it
was spotted; `log_count` reads the stream to the end.
2026-09-02 10:13:42 +01:00
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