[sjungwon03]

Closes #554. Refs #116; unresolved Jev #7 remains unchanged.

Registered nonstream upstream 429/503 previously became 502 even on the OpenRouter-compatible path. /api/v1 now retains an exact observed 429/503 only after required failed-attempt usage and outcome audit succeed; numeric error.code matches HTTP status. /v1 retains 502/symbolic errors. Fixed messages, safe unmapped metadata, request IDs, bounded Retry-After, IAM/limits, fallback and possible-billing accounting remain unchanged.

Known failure classes and terminal route results carry only an allowlisted scalar that agrees with both adapter classification and an observed-response flag. Missing, malformed, contradictory, mismatched or unclassified exception metadata cannot supply status authority. Other upstream statuses/timeouts stay generic 502. Local/persistence faults and successful/later generic fallback cannot inherit earlier status/hints; no raw body/header or new ledger/audit field is forwarded.

Plan: 554-upstream-statuses. Contract: observed statuses.

Validation:

• Initial red before implementation: 40 cases, 16 expected compatible missing-status failures, 24 passes.
• Initial green selection: 258 passed. A separate defensive red reproduced 2 contradictory no-response-state failures among 20 cases; constructors/coordinators now reject that metadata. Final focused provider/routing/errors/accounting/actual-SDK selection: 278 passed.
• Full npm run check: 7,785 total, 7,784 passed, zero failures/cancellations, one optional external PostgreSQL skip (~243sec). Typecheck, lint, planning/link/fixture-secret checks and all six offline integrity checks passed.
• Existing 42 lint warnings/65 infos are unchanged. Planning/links/fixture-secret scan, whitespace and CLAUDE.md symlink passed. Six source pins, dependencies and migrations are byte-unchanged.

Limits: client retry/backoff behavior may change with distinguishable 429/503; probes disable retries and do not certify automatic policies or prevent duplicate billing. The gateway adds no sleep/retry. Streaming, other statuses, precise provider error_type, HTTP-date/402 handling, live provider guarantees and full #116 remain separate work.

[sjungwon03-ai]

Review summary

Verdict: Approved

• Reviewed: Observed upstream 429/503 capture and validation, compatible-only status projection, legacy isolation, required usage/audit handoffs, fallback isolation, privacy boundaries, and regression coverage.
• Checks: All reported GitHub checks passed on 205c50019fceedcbc543dd18e827b47b2febc90b; local npm run typecheck and the five focused status, retry-hint, boundary, and actual-SDK test suites passed.