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.
