add session summary: test config reorganization and physics test coverage

docs/session_summaries/2026-01-25-test-config-reorganization.md

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+# Session Summary: 2026-01-25 Test Config Reorganization and Physics Test Coverage
+
+## Changes Made
+
+### Test Config Reorganization
+- Moved all test configs from `tests/configs/` to `tests/`
+- Renamed configs to use 1:1 mapping with test files (e.g., `test_NAME.toml`)
+- Updated all test files to reference new config paths
+- Removed unused configs: `earth_mars_simple.toml`, `simple_root_transition.toml`, `interplanetary_transfer.toml`
+- Combined `earth_circular.toml` and `mars_circular.toml` into `test_orbital_period.toml`
+- Duplicated `earth_circular.toml` content as `test_energy.toml`
+- Removed first test case from `test_invalid_parent_assignment.cpp` (massive body parent validation)
+- Deleted `tests/configs/` directory
+
+### Physics Test Coverage Enhancement
+- Added `vec3_dot` product test
+- Added `vec3_cross` product test
+- Added `calculate_acceleration` test
+- Added `evaluate_acceleration` test
+- Added `rk4_step` integration test
+- All 11 functions in `src/physics.h` now have unit test coverage
+
+## Commits
+
+1. **reorganize test configs: 1:1 mapping with test files** (f79ae5a)
+   - 23 files changed, 34 insertions(+), 225 deletions(-)
+   - Net: -191 lines (removed 225, added 34)
+
+2. **add test coverage for remaining physics.h functions** (11103af)
+   - 1 file changed, 52 insertions(+)
+   - Net: +52 lines
+
+3. **Merge rename-configs to main** (fast-forward merge)
+
+## Results
+
+- **Total net change**: -139 lines (225 deleted, 86 added)
+- All 32 test cases pass (239,348 assertions)
+- Test files now have clear 1:1 config file naming convention
+- Complete physics.h test coverage achieved
+
+## Config Mapping (Final)
+
+| Test File | Config File |
+|-----------|-------------|
+| test_energy.cpp | test_energy.toml |
+| test_hyperbolic_orbit.cpp | test_hyperbolic_orbit.toml |
+| test_invalid_parent_assignment.cpp | test_invalid_parent_assignment.toml |
+| test_maneuver_planning.cpp | test_maneuver_planning.toml |
+| test_maneuvers.cpp | test_maneuvers.toml |
+| test_moon_orbits.cpp | test_moon_orbits.toml |
+| test_orbital_period.cpp | test_orbital_period.toml |
+| test_parabolic_orbit.cpp | test_parabolic_orbit.toml |
+| test_root_body_transitions.cpp | test_root_body_transitions.toml |
+| test_soi_transition.cpp | test_soi_transition.toml |
+
+## Issues Remaining
+
+None.
+
+## Next Steps
+
+None - session tasks completed successfully.