Extract wire debug redaction policy

[JerrettDavis]

Description

Extracts the pure secret-redaction logic used by opt-in Codex wire-debug capture from helpers.py into headroom.proxy.wire_debug_redaction_policy. This keeps the debug capture path behavior intact while making the sensitive-key policy directly testable.

Closes #

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Performance improvement
• Code refactoring (no functional changes)

Changes Made

• Added wire_debug_redaction_policy.py for secret-key matching and recursive wire-debug redaction.
• Kept existing helper entry points and private compatibility names delegating to the extracted policy.
• Added direct tests for direct secret headers, nested suffix-matched secrets, and key normalization.
• Carried forward the LiteLLM callback compatibility shim needed for current mypy on main.

Testing

• Unit tests pass (pytest)
• Linting passes (ruff check .)
• Type checking passes (mypy headroom)
• New tests added for new functionality
• Manual testing performed

Test Output

python -m pytest tests\test_wire_debug_redaction_policy.py
3 passed in 0.16s

python -m ruff check .
All checks passed!

python -m ruff format --check .
1095 files already formatted

python -m mypy headroom --ignore-missing-imports
Success: no issues found in 409 source files

gitleaks protect --staged --no-banner --redact
no leaks found

Real Behavior Proof

• Environment: Windows, Python 3.13.13, branch jd/architecture-slice-25.
• Exact command / steps: ran focused wire-debug redaction tests, ruff, ruff format check, mypy, and staged gitleaks scan.
• Observed result: redaction policy is directly covered and local lint/type/security checks pass.
• Not tested: full proxy wire-debug capture runtime; this slice preserves the existing helper entry points.

Review Readiness

• I have performed a self-review
• This PR is ready for human review

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have updated the CHANGELOG.md if applicable

Screenshots (if applicable)

N/A

Additional Notes

Documentation and changelog updates are N/A for this internal architecture-only refactor. The push reported existing default-branch Dependabot alerts; no staged secret leaks were found for this PR.

[github-actions]

PR governance

This PR follows the template and is marked ready for human review.