Port from code-yeongyu/oh-my-openagent#6677 (credit: @niStee).
LiteLLM proxies stamp a structured `terminal_quota_exhausted` code on
hard-cap 429s. Hermes' `_status_429` handler always returns a verdict, so
`_by_error_code` (which maps _BILLING_ERROR_CODES to billing) never saw
the code: the exhausted key classified as rate_limit, earned the 429
cooldown, and got retried against a wall that cannot clear until someone
pays. Upstream this respawned duplicate subagent sessions.
- `_status_429` now honors a structured billing code first (decisive
signal outranks message heuristics).
- `terminal_quota_exhausted` joins _BILLING_ERROR_CODES so every path
(429, 402, status-less) agrees.
- "hard billing limit" free text joins _BILLING_PATTERNS ("billing hard
limit" was already there; providers use both orders). "terminal billing
limit" text is deliberately NOT matched: substring rules cannot negate
the "non-terminal billing limit" wording — the structured code covers it.
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