fix(routing): fall back past HTTP 402 payment-required providers

[aliihsaad]

Problem

In the production Playground, Auto (chat route) returned a 502 on every message:

Provider error (GPT-OSS 120B (Cerebras)): Cerebras API error 402: Payment required to access this resource. Visit your billing tab.

Cerebras now blocks chat completions for all models until the account has a payment method, while GET /v1/models still lists them.

Root cause

classifyProviderError had no rule for HTTP 402, so the error fell to other (retryable: false):

• the proxy returned 502 immediately instead of trying the next model in the chain;
• recordTerminalProviderFailure records nothing for other, so the next request picked Cerebras again, forever.

Same bug class as the 410 fix in #8: an unclassified status code ends the fallback chain.

Fix

402 / "payment required" joins the existing account-denial branch in server/src/services/provider-errors.ts:

• retryable: true, so auto-route falls through to the next model;
• skipModel: false, so the model is not quarantined (the account is the problem);
• 24h key-scoped cooldown, so that credential is skipped for every model on the platform.

It is matched with /\b402\b/ (no false positives on numbers like 4020) and placed before the rate-limit branch, because some 402 bodies (Chutes) also say "quota".

Tests

• 4 classifier tests in account-denial-cooldown.test.ts
• End-to-end proxy test in proxy-model-hardening.test.ts: Cerebras 402 → Groq serves; the second request does not call Cerebras again; the model is not blocked. Returns 502 without the fix (verified by stashing the change).
• Server suite 345/345; tsc clean; server/dist rebuilt (provider-errors outputs only).

After merge

• Deploy to the VPS (git fetch origin && git reset --hard origin/main && systemctl restart llm-hub).
• The Cerebras account still needs a payment method, or its rows should be disabled. The key cooldown is in memory, so after a restart each Cerebras key fails once more before it is benched again.

🤖 Generated with Claude Code

[coderabbitai]

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