## Description
Extracts beta-header stickiness configuration parsing from
`headroom.proxy.helpers` into a focused policy module. This keeps the
environment-driven mode and LRU bound validation independently testable
while preserving the helper functions used by the session beta tracker.
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
- [x] Code refactoring (no functional changes)
## Changes Made
- Added `headroom.proxy.beta_header_policy` for beta sticky mode and
tracker session limit resolution.
- Kept `get_beta_header_sticky_mode()` and
`get_beta_tracker_max_sessions()` as compatibility wrappers in
`helpers.py`.
- Added direct unit tests for defaults, accepted values, and loud
rejection of invalid operator configuration.
## Testing
- [x] Unit tests pass (`pytest`)
- [x] Linting passes (`ruff check .`)
- [x] Type checking passes (`mypy headroom`)
- [x] New tests added for new functionality
- [ ] Manual testing performed
### Test Output
```text
python -m pytest tests/test_beta_header_policy.py tests/test_anthropic_beta_session_sticky.py tests/test_openai_beta_session_sticky.py
52 passed in 0.41s
python -m ruff check .
All checks passed!
python -m ruff format --check .
1069 files already formatted
python -m mypy headroom --ignore-missing-imports
Success: no issues found in 410 source files
gitleaks protect --staged --no-banner --redact
no leaks found
```
## Real Behavior Proof
- Environment: Windows, Python 3.13.13
- Exact command / steps: Ran focused beta policy tests, existing
Anthropic/OpenAI beta sticky suites, full ruff, format check, mypy, and
staged gitleaks scan.
- Observed result: Existing beta sticky behavior remains green while
extracted policy parsing is covered directly.
- Not tested: Full repository pytest suite locally; CI covers the
broader matrix.
## Review Readiness
- [x] I have performed a self-review
- [x] This PR is ready for human review
## Checklist
- [x] My code follows the project's style guidelines
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] 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 not applicable for this internal
refactor. The default-branch Dependabot alerts reported during push are
pre-existing and unrelated to this PR.
---------
Co-authored-by: Tejas Chopra <chopratejas@gmail.com>
