P2-1/P2-3 from review:
- fetchCNQuota: credential-invalid now judged by StatusCode 401/403
(aligned with fetchCNBalance) instead of `!Success && !CredentialValid` —
CN quota service only sets CredentialValid=true on the success path, so
500/429/zhipu business errors were all misclassified as failed instead
of error.
- fetchCNBalance: snapshot carries new BalanceLow flag computed with the
scheduler's exact criterion (`!Available || allCNBalancesBelowThreshold`)
against Gateway.CNProviders.BalanceThreshold (ctor now takes cfg; wire
regenerated). quotaDegradedHint reports "balance low" instead of the old
`<=0` check, so an account already paused by the scheduler (balance 5 /
threshold 10) no longer shows green in the monitor.
- threshold helper falls back to viper default 0.5 for nil/<=0 config to
avoid a zero-threshold regression where balance=0 stops alerting.
Tests: CN quota status-code matrix (rewrites the test that cemented the
old behavior), balance-low matrix (below-threshold / unavailable /
multi-currency healthy), threshold-from-config; PayG stubs now set
Available explicitly (zero-value trap).
Randark
1128df2592