fix: preserve provider request headers in logs

[rdself]

Purpose

Fix detailed call log Provider Request payloads so the headers shown there are the outbound provider request headers, not upstream response headers.

Changes

• Preserve executor-returned request headers when chatCore wraps streaming and non-streaming upstream responses.
• Keep response headers scoped to the Response object and dedup snapshot only.
• Add regression coverage for non-streaming logs, streaming logs, and CC-compatible request defaults.

Root Cause

chatCore replaced the executor result headers field with response.headers after wrapping provider responses. The detailed logger later treated that field as Provider Request headers, which made Cloudflare/Caddy response headers appear under Provider Request and hid request-only headers such as anthropic-beta.

Validation

• node --import tsx/esm --test tests/unit/provider-request-failure-pipeline.test.ts
• node --import tsx/esm --test tests/unit/executor-default-base.test.ts tests/unit/claude-code-compatible-request.test.ts tests/unit/request-logger-endpoints.test.ts
• npm run typecheck:core

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[gemini-code-assist]

Code Review

This pull request refactors header handling in handleChatCore to avoid variable shadowing and removes redundant header assignments. It also adds comprehensive unit tests to verify that upstream response headers (such as cf-ray and server) do not overwrite the original request headers in the providerRequest pipeline payload for both standard and streaming responses, and that Claude Code-compatible request logs preserve beta headers and summarized thinking configurations. Feedback is provided to normalize headers using normalizeHeaders before passing them to new Response to prevent potential runtime crashes on Node 24 due to undici private member access issues.

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[KooshaPari]

#5257 is ready for maintainer review/merge.

Current status:

• Fast Quality Gates: pass
• Unit Tests fast-path (1/2): pass
• Unit Tests fast-path (2/2): pass
• Vitest: pass
• dast-smoke: pass
• semgrep + semgrep-cloud: pass

The change is backend/logging-adjacent and all reported checks are green.