Refactor api-proxy request pipeline into focused modules

[Copilot]

containers/api-proxy/proxy-request.js had grown into a multi-responsibility module (~764 LOC) combining deprecated-header learning, billing parsing, upstream response orchestration, and core proxy transport. This PR extracts those cohesive concerns into dedicated modules while preserving call sites and runtime behavior.

• Module split: deprecated header learning

  • Added containers/api-proxy/deprecated-header-tracker.js.
  • Moved the in-memory deprecated-header cache + learning/strip cycle:
    • getDeprecatedValuesForHeader
    • maybeStripLearnedHeaderValues
    • parseDeprecatedHeaderFromBody
    • learnAndStripDeprecatedHeaderValue
  • Exposed resetDeprecatedHeaderValuesForTests and wired existing test reset export to it.

• Module split: billing header parsing

  • Added containers/api-proxy/billing-headers.js.
  • Moved extractBillingHeaders into a dedicated utility module.
  • Kept export surface unchanged via proxy-request.js/server.js usage.

• Module split: upstream response handling

  • Added containers/api-proxy/upstream-response.js.
  • Extracted:
    • handleUpstreamResponse
    • logUpstreamAuthError
    • logRequestCompletion
  • Implemented via createUpstreamResponseHandlers(...) to inject existing dependencies without behavior drift.

• proxy-request.js trimmed to transport orchestration

  • Replaced inlined implementations with imports from the three new modules.
  • Kept proxyRequest, sendUpstreamRequest, buildRequestHeaders, and existing external exports/call paths intact.

// proxy-request.js
const {
  maybeStripLearnedHeaderValues,
  resetDeprecatedHeaderValuesForTests,
  parseDeprecatedHeaderFromBody,
  learnAndStripDeprecatedHeaderValue,
} = require('./deprecated-header-tracker');
const { extractBillingHeaders } = require('./billing-headers');
const { createUpstreamResponseHandlers } = require('./upstream-response');

const { handleUpstreamResponse } = createUpstreamResponseHandlers({ /* existing deps */ });

[github-actions]

✅ Coverage Check Passed

Overall Coverage

Metric	Base	PR	Delta
Lines	96.57%	96.62%	📈 +0.05%
Statements	96.44%	96.48%	📈 +0.04%
Functions	98.22%	98.22%	➡️ +0.00%
Branches	90.66%	90.70%	📈 +0.04%

📁 Per-file Coverage Changes (1 files)

File	Lines (Before → After)	Statements (Before → After)
src/config-writer.ts	89.3% → 90.9% (+1.65%)	89.3% → 90.9% (+1.65%)

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Coverage comparison generated by scripts/ci/compare-coverage.ts

[Copilot]

Pull request overview

This PR refactors the API proxy request pipeline by extracting billing parsing, deprecated header tracking, and upstream response handling into focused modules while preserving the existing proxy request surface.

Changes:

• Added focused modules for billing headers, deprecated-header learning/stripping, and upstream response orchestration.
• Rewired proxy-request.js to import those modules and keep existing exports intact.
• Preserved the existing test-facing reset and billing helper re-export paths.

Show a summary per file

File	Description
containers/api-proxy/proxy-request.js	Replaces inlined helper implementations with module imports and wires the response handler factory.
containers/api-proxy/upstream-response.js	Adds extracted upstream response logging, retry, streaming, token tracking, and completion handling.
containers/api-proxy/deprecated-header-tracker.js	Adds extracted module-level deprecated header cache and learn/strip helpers.
containers/api-proxy/billing-headers.js	Adds extracted billing/quota header parsing utility.

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• Files reviewed: 4/4 changed files
• Comments generated: 0