[ridho9]

Summary

• preserve Responses API input payloads when combo middleware runs
• map combo system_message overrides to Responses instructions instead of Chat messages
• add regression coverage for Responses payloads with and without an override

Tests

• node --import tsx/esm --test tests/unit/services-branch-hardening.test.ts ✅
• npm run lint ✅
• npm run check:changelog-integrity ✅
• npm run test:unit ⚠️ fails in files outside this PR's diff, including an undefined PROVIDER_BREAKER_FAILURE_STATUSES in src/sse/handlers/chat.ts, environment/docs contract drift, and stale catalog/UI expectations.
• npm run test:coverage ⚠️ exits on the same unrelated suite failures; its coverage gate passes: statements/lines 83.98%, branches 78.30%, functions 87.91% (all ≥60%).

Changed tests

• `tests/unit/services-branch-hardening.test.ts

[diegosouzapw]

Merged into release/v3.8.49 — thanks @ridho9! Validated via local merge-train (32-core .113) + a per-file discriminator confirming zero regressions vs the pure release tip; CI reds on this PR were pre-existing base-red drift (tracked separately). 🙏