Greptile Summary

This PR centralizes the scattered header-merge and transport-assembly logic from three sites in model.ts into a new resolveProviderRequestConfig helper, adding internal placeholder slots for future auth/proxy/TLS policy work. The refactor faithfully preserves existing behavior — api, baseUrl, and headers outputs at each call site are semantically equivalent to the expressions they replace.

Confidence Score: 5/5

• Safe to merge; this is a pure behavioral-parity refactor with no functional changes to existing callers.
• All three call sites produce identical api/baseUrl/headers values after the refactor. The mergeProviderRequestHeaders function is correct — sanitizeModelHeaders upstream ensures inputs are either undefined or non-empty, so the Object.keys guard is sound. Placeholder proxy/tls types are intentionally locked to false for now. No P0 or P1 findings.
• No files require special attention.

_{Reviews (1): Last reviewed commit: "refactor(providers): add internal reques..." | Re-trigger Greptile}