Relocate CircuitBreaker from ingester/pollers to haiku/rag/circuit_breaker
so non-ingester callers (docling-serve provider) can reuse it without
depending on the ingester package.
Co-Authored-By: bryan davis <bryan@monkeytronics.org>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The jitter-before-first-sleep block was duplicated verbatim in
PeriodicPoller.run() and FSPoller._sweep_loop(). Move it to
BasePoller._stagger_start() with a named _STAGGER_FRACTION constant.
This also gives a testable seam outside the pragma-no-cover
event-loop glue methods.
All pollers sharing the same poll_interval_s previously woke up and
swept at exactly the same moment after startup. With 10+ sources
this causes a coordinated spike in listing traffic (S3 LIST, WebDAV
PROPFIND, HTTP HEAD) every interval.
Add a random initial delay of 0-25% of the poll interval after the
first sweep, applied to both PeriodicPoller and FSPoller's sweep
loop. Subsequent sweeps run on the normal fixed interval, now
staggered across sources.
