Files
ModelRouter/internal/provider
JianFeeeee 5b628b4d6f fix(scheduler): rebalance the pref score so metered sources aren't written off silently
Report: an allowance-metered source (sensenova) had its deepseek model sitting at
pref -10 while the WebUI showed zero failures. All three numbers were accurate,
and they exposed three compounding problems.

1. Quota exhaustion cost the SAME score as a real failure. RecordQuotaExhausted
   intentionally avoids failCount (an exhausted allowance is not a fault), so the
   UI showed fails=0 / cooling=false — yet it deducted the full prefFailStep (5).
   For a metered source, running out of budget is an everyday event, so the score
   drifted deep negative with no visible cause. Now quota and 429 events cost
   prefQuotaStep (1): the cooldown already keeps the slot out of rotation until
   the window resets, the score only needs a mild preference for slots with budget.

2. Recovery was 5:1 asymmetric. A failure cost -5 but a success only +1, so a
   slot at -10 needed ten consecutive successes just to reach neutral — which it
   could never get, because a low score makes the scheduler not pick it in the
   first place (starvation). Success now rewards prefSuccessStep (2): recovery
   from -10 needs five successes, while a real failure still outweighs one.

3. No idle decay. A penalised slot kept its negative score forever once it stopped
   being selected. Pref() now applies lazy decay: after prefDecayAfter (2 min) of
   no outcome, the score drifts one step back toward 0 per interval (never past
   0, never touches positive scores). Applied in Pref() and TryProbe(), so a
   naturally-recovered idle slot is schedulable again without needing a probe.

The failure penalty itself is unchanged (prefFailStep=5), so genuinely broken
upstreams are still marked as clearly worse than healthy ones.

Tests: quota penalty lighter than failure; 5 quota resets stay well above the
floor with failCount untouched; 429 is quota-class; recovery from -10 needs <=5;
idle decay rehabilitates a written-off slot, stops at 0, and never drags a
positive score; decay repeatedly lifts a slot off the prefMin floor. Updated the
two pre-existing tests that asserted the old -5/129 +1 values.
2026-08-31 11:50:47 +08:00
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