Replace the fixed time.sleep(GRACE_PERIOD_S) in try_enter_observe_mode
with a threading.Condition.wait_for(predicate, timeout=grace_period_s)
that returns as soon as success_fraction of subscribed hrefs have
notified. Production data (fridge TP2X_REF_20K): all 13 hrefs notify
within ~0.34s of subscribe, so every successful first-refresh / observe
retry was waiting ~14.6s of dead time. AC retry cycles showed the same
16s-fetches-that-transition pattern.
No behavior change on the fallback path (fraction not reached → wait
the full ceiling → MODE_POLL, identical to today). GRACE_PERIOD_S and
SUCCESS_FRACTION unchanged. No smartthings_local library change.
blka
f19abc7936