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## Description Cache-mode session tracking currently collapses unrelated conversations when they share a large static first system prompt. The fallback session-id hash ignores later system messages entirely, so dynamic per-conversation context can get cut out of the key and two different sessions reuse the same `PrefixCacheTracker`. This hashes the full ordered system-text payload instead, while leaving explicit `x-headroom-session-id` overrides untouched. Refs #1808. ## Type of Change - [x] 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 - Collected all system-text content when building the fallback cache session id. - Stopped truncating fallback session-id input to the first 500 characters of the first system message. - Added a regression that proves two conversations with different later system context no longer collide. - Added a preservation test that appending only non-system turns keeps the same fallback session id. - Applied the pinned Ruff formatter to three pre-existing files on the current base so the repo-wide lint job passes unchanged semantics. ## Testing - [x] Unit tests pass (`uv run pytest tests/test_cache/test_prefix_tracker.py -q`) - [x] Linting passes (`uv run ruff check headroom/cache/prefix_tracker.py tests/test_cache/test_prefix_tracker.py`) - [ ] Type checking passes (`uv run mypy headroom`) - [x] New tests added for new functionality when applicable - [ ] Manual testing performed ### Test Output ```text uv run pytest tests/test_cache/test_prefix_tracker.py -q 40 passed, 1 warning in 0.15s uv run ruff check headroom/cache/prefix_tracker.py tests/test_cache/test_prefix_tracker.py All checks passed! uv run ruff check . All checks passed! uv run ruff format --check . 1046 files already formatted ``` ## Real Behavior Proof - Environment: Windows, project `uv` environment, focused cache-tracker regression. - Exact command / steps: run `tests/test_cache/test_prefix_tracker.py` on `origin/main` with the new collision regression present, then rerun the same file on this branch. - Observed result: base returns the same session id for two conversations that differ only in a later system message and fails `assert id_a != id_b`; head passes the focused file and keeps the fallback session id stable when only non-system turns are appended. - Not tested: live proxy traffic through a real agentic client. ## 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 - [x] 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 - [x] I have updated the CHANGELOG.md if applicable ## Additional Notes This is only the session-collision half of #1808. The duplicate-response-header fix stays separate so this PR can reference the issue without claiming the whole bug report is resolved. The extra formatting-only diff comes from the current base failing the pinned full-repo Ruff format check. |
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| .. | ||
| __init__.py | ||
| test_anthropic.py | ||
| test_backends.py | ||
| test_base.py | ||
| test_client_integration.py | ||
| test_dynamic_detector.py | ||
| test_google.py | ||
| test_openai.py | ||
| test_prefix_tracker.py | ||
| test_registry.py | ||
| test_semantic.py | ||