## Description
Extracts the sticky memory tool session tracker from
`headroom.proxy.helpers` into a focused state module.
`helpers.SessionToolTracker` remains as an env-aware compatibility
wrapper so existing injection and singleton call sites keep the same
API.
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.tool_injection_tracker.SessionToolTracker` as
the pure bounded LRU state holder.
- Replaced the large in-helper tracker implementation with a small
env-aware wrapper.
- Added direct tracker tests for unknown sessions, ordered golden bytes,
first-write wins, provider isolation, LRU eviction, and input
validation.
## 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_tool_injection_tracker.py tests/test_memory_tool_session_sticky.py tests/test_corrupt_golden_bytes_recovery.py
44 passed in 0.54s
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 direct tracker tests, sticky memory tool
tests, corrupt golden byte recovery tests, full ruff, format check,
mypy, and staged gitleaks scan.
- Observed result: Existing sticky injection behavior and recovery
behavior remain green while the tracker state domain is directly
covered.
- 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.
