add session summary for config validation refactoring

docs/session_summaries/2026-01-25-config-validation-refactoring.md

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+# Config Validation Refactoring
+
+## Session Summary
+
+Fixed TOML syntax errors in test configurations and implemented comprehensive config validation refactoring.
+
+## Changes Made
+
+### Phase 1: TOML Syntax Fixes
+- Fixed missing commas in orbit TOML blocks across 12 test config files
+- Commas added after semi_major_axis and eccentricity values
+
+### Phase 2: Config Validator Module Creation
+- Created `src/config_validator.h` - New module interface
+- Created `src/config_validator.cpp` - 6 validation functions:
+  - `validate_parent_index_ordering()` - Parent index ordering checks
+  - `validate_orbital_elements()` - Orbital elements validity
+  - `validate_initial_positions()` - Moved from simulation
+  - `validate_mass_ratios()` - Parent/child mass ratio validation (MIN_MASS_RATIO=1000)
+  - `validate_soi_overlap()` - Detect overlapping SOIs (error if true)
+  - `validate_nested_orbits()` - Moon orbit boundary checks
+  - `run_all_config_validations()` - Master validation wrapper
+
+### Phase 3: Module Integration
+- Updated `config_loader.cpp` to use `run_all_config_validations()`
+- Removed inline validation logic from config_loader
+- Removed `validate_initial_positions()` from simulation module
+- Updated Makefile to include config_validator.o
+
+### Phase 4: Test Updates
+- Deleted obsolete Test 1: "Earth should not become child of spacecraft"
+- Deleted obsolete Test 3: "detect placeholder config values"
+- Updated Test 4: "Mutual SOI" to expect load failure (config now invalid)
+
+### Phase 5: Documentation Updates
+- Updated `technical_reference.md` with all structural changes
+- Corrected OrbitalElements, CelestialBody, and Spacecraft structs
+- Added Config Validator module documentation
+- Updated Initialization Sequence to include validation step
+- Updated config examples to show orbit table format
+
+## Commits
+
+1. `4c8050b` - fix missing commas in orbit TOML blocks
+2. `528a843` - add config validation refactoring plan
+3. `3bd35bb` - create config_validator module and refactor validation logic
+4. `1d8e9c6` - remove obsolete tests from test_invalid_parent_assignment
+5. `84c1a4d` - update plan document to mark as complete
+6. `a51cf1a` - update technical reference after config validation refactoring
+
+## Results
+
+- **Net line count**: +220 lines (606 insertions, 386 deletions)
+- **Tests**: 30 test cases, 239,543 assertions - All passing
+- **Modules created**: 1 (config_validator)
+- **New files**: 2 (config_validator.h, config_validator.cpp)
+- **Modified files**: 7 (Makefile, config_loader.cpp/h, simulation.cpp/h, test_invalid_parent_assignment.cpp, technical_reference.md)
+- **Modified configs**: 13 test configs (TOML syntax fixes)
+
+## Validation Rules Implemented
+
+1. **Mass ratio validation**: For root children with radius > 50% of parent, require mass ratio ≥ 1000
+2. **SOI overlap validation**: Bodies sharing same parent must not have overlapping SOIs (error)
+3. **Nested orbit validation**: Moons (small radius, circular orbits) must orbit within 5x parent SOI
+4. **Existing validations**: Parent index ordering, orbital elements, initial positions
+
+## Remaining Issues
+
+None. All tasks completed successfully.
+
+## Next Steps
+
+No specific next steps identified. Config validation refactoring is complete and all tests passing.