Validado sobre o tip de `release/v3.8.51` depois de reconciliar com o #12620, que entrou primeiro nesta mesma sessão e ataca a mesma classe de problema por outra arquitetura.
**A colisão e como foi resolvida.** O #12620 consertou o GHSA-qv45-56jc-4wmj adicionando `RAW_CREDENTIAL_PATTERNS` a `error.ts` e importando-os em `upstreamErrorPassthrough.ts`. Este PR resolve o mesmo problema quebrando `error.ts` em `errorSanitization.ts` + `errorPathRedaction.ts`. Mantive a divisão em módulos deste PR, porque ao comparar os dois vocabulários o dele já era mais amplo: o `STRONG_CREDENTIAL_TOKEN` daqui cobre `sk-`/`sk_` **com lookbehind e uma variante para a forma embutida** (que pega `sk-proj-…`), mais Slack `xox-`, AWS `AKIA`/`ASIA`, `github_pat_`/`ghp_`/`glpat-` e JWT de três segmentos.
A única forma que o #12620 carregava e este conjunto não tinha era a chave do Google (`AIza…`) — adicionada aqui, com o mesmo quantificador limitado que os irmãos usam (AGENTS.md → PII §1, já que isso roda sobre corpos upstream não confiáveis).
**A verificação não foi por inspeção.** Rodei as suítes do próprio #12620 contra esta estrutura: **48/48** em `error-sanitizer-sk-key-qv45`, `bifrost-relay-response-leak-9m72`, `search-baseurl-client-override-3f8g` e `search-baseurl-ssrf-guard` — incluindo a asserção anti-drift daquela suíte, que é o oráculo certo aqui: *para todo corpo que a camada de passthrough recusa como vazante, o sanitizador de fallback não pode devolvê-lo intacto*. Ela passa, então a propriedade de segurança dos três GHSAs sobrevive à troca de arquitetura.
Os 21 arquivos de teste deste PR: **259/259**. `typecheck:core` limpo.
Validated on the resolved merge against the current tip (527da656 + the post-#11281 rebaseline): the single conflict was a comment-only collision in providers/[id]/models/route.ts (kept the tip's #10828-ordering note). Focused suites 125/125 across all 13 touched test files (build-sqlite-stub, cc-compatible, copilot-claude-messages, copilot-gemini-route, executor-github, ghe-copilot, github-copilot-discovery-token, github-copilot-model-discovery, noauth-sibling-7620, provider-header-profiles, provider-models-config, request-log-payloads, upstream-error-passthrough), typecheck:core clean, file-size/changelog-integrity OK. Merged --admin over the inherited 2026-08-23 base-red cluster (#9985) — the reds are proven tip failures (CLI catalog cluster + @testing-library allowlist, being drained by #11280), not from this diff. Note: the rebase means several items the body listed (relay x-relay-path SSRF, /v1/search blocked-providers, #10736 rotation fence, #10903, #10865, #10899, #10916) already landed upstream and are NOT in this delta — the delta is: better-sqlite3 build guard + build heap/worker caps + telemetry-off (#10060 re-derived), credential-echo passthrough refusal + OCR/moderation redaction + call-log key redaction, Copilot CLI 1.0.81-6 wire identity + Claude→/v1/messages name-matched routing + discovery token fix, CC model_not_found 400, compat overrides for no-auth aliases (#7620-pinned). The Copilot wire-identity change is the one to watch in production. Thank you @arminanton — and the ported-author credits in the commit history (@rqzbeh, yidecode, the #10899/#10916 authors) are preserved. Your config-posture finding (REQUIRE_API_KEY default vs 0.0.0.0) is noted for a maintainer decision, as you scoped it.
* feat(sse): selective upstream 4xx error passthrough util
* feat(sse): relay upstream 4xx error bodies verbatim on the Anthropic request path
createErrorResult() gains an opt-in 7th param opts.passthrough; when set and
the upstream body is eligible (per shouldPassthroughUpstreamError), the
returned response body is the upstream 4xx body verbatim instead of the
sanitized wrapper. Internal classification fields (error/rawMessage/
errorType/errorCode) are never affected.
Wired into chatCore.ts's 7 upstream-error createErrorResult call sites
(model_unavailable / context_overflow / generic upstream-error branches),
gated on sourceFormat === FORMATS.CLAUDE so only /v1/messages requests get
the verbatim body — OpenAI-format paths are unchanged.
* test(quality): register upstream-error-passthrough in stryker tap.testFiles
`tests/unit/upstream-error-passthrough.test.ts` covers `open-sse/utils/error.ts`,
an instrumented module, so `check:mutation-test-coverage --strict` requires it in
`tap.testFiles` — the gate flagged the drift on this PR.
