thread_sched_wait_events() returned thread_sched_wait_event when an
interrupt was already pending at entry, without looking at the fd, and
thread_io_wait() reported that as readiness: under RUBY_MN_THREADS=2,
IO#wait_readable on a pipe nobody wrote to returned truthy when a trap
arrived just before the wait.
A wakeup for a masked interrupt (a trap arriving inside a trap handler)
was reported as a timeout, so wait_readable(0.3) in a trap handler
returned nil at once.
Add thread_sched_wait_interrupted for both "stopped for an interrupt"
cases. thread_io_wait() now runs the whole wait under one tag, handles
the interrupt and waits again on the M:N scheduler until its deadline,
and treats a wakeup without an event before the deadline the same way.
At the deadline it probes the fd once. rb_thread_io_blocking_call()
retries func for every M:N outcome but unhandled.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
