A health refresh interval of 0 turns background provider refreshes off,
but the inconclusive-probe retry only checked refreshOnInterval, so a
provider whose probe kept timing out was still probed four times in the
first five minutes. The retry now decides under the refresh semaphore
right before probing: it checks the effective interval (including a
setting changed while it slept), and uses the failure count as a probe
generation so a manual refresh that ran meanwhile makes the queued retry
a no-op instead of a redundant probe.

Also corrects the comment on the retry delay: 30s is shorter than the
staged Claude probe and the ACP probe deadlines; overlap is prevented by
the semaphore, not the delay.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>