Add session summary for 2026-01-05

docs/session_summaries/2026-01-05-soi-bug-and-dynamic-orbits.md

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+# SOI Bug Fix and Dynamic Orbital Rendering (2026-01-05)
+
+## Changes Made
+
+### Core Bug Fixes
+- Fixed SOI calculation bug: was using current distance instead of orbital semi_major_axis
+  - Caused incorrect SOI radii for eccentric orbits (e.g., comet at perihelion vs aphelion)
+  - Now properly uses stored orbital parameter from config file
+- Added parent change tracking to headless simulation mode for debugging SOI transitions
+
+### Test Refactoring
+- Refactored test to use same code path as simulation via `load_system_config()`
+  - Eliminated ~30 lines of manual body setup in test
+  - Ensures test and simulation behave identically
+- Added `config_loader.cpp` to test build dependencies
+- Refactored verbose test output into separate functions with compile-time flag
+  - Added `COMET_TEST_VERBOSE_OUTPUT` flag (default: 0)
+  - Moved output to `print_orbital_snapshots()` and `print_parent_changes()`
+
+### Graphics Enhancements
+- Implemented dynamic orbital rendering with real-time element calculation
+  - Orbits now update automatically when parent body changes
+  - Calculates orbital elements from current position/velocity relative to parent
+- Added support for parabolic trajectories (e ≈ 1)
+  - Limited to ±86° from periapsis to avoid infinite vertices
+- Added support for hyperbolic trajectories (e > 1)
+  - Limited to asymptotic angle to avoid infinite vertices
+- Properly orients orbits in 3D space using eccentricity vector and angular momentum
+
+### Code Structure
+Refactored renderer for separation of concerns:
+- `OrbitalBasis` struct - Holds orbital reference frame
+- `calculate_orbital_basis()` - Computes periapsis direction, normal, and perpendicular vectors
+- `orbital_to_cartesian()` - Transforms 2D orbital coordinates to 3D space
+- `draw_orbit_segment()` - Handles rendering of individual line segments
+- `render_elliptical_orbit()` - Draws closed elliptical paths (100 segments)
+- `render_hyperbolic_orbit()` - Draws open hyperbolic/parabolic paths (60 segments)
+
+### Test Configuration
+Enhanced `configs/test_simple.txt` with diverse orbit examples:
+- Parabolic object (e=1.0 at 0.5 AU, exactly at escape velocity)
+- Inclined asteroid (circular orbit with 30° inclination)
+- Hyperbolic visitor (e=1.5, interstellar trajectory)
+
+## Commits
+
+- `89931c3` Fix SOI calculation and orbit direction bugs
+- `8e21f71` Refactor test to use same code path as simulation
+- `232614d` Revert cross product direction in config_loader
+- `4a313f8` remove extra debugging not added by claude (user commit)
+- `c613d21` Refactor verbose test output to separate functions
+- `060ff40` Add dynamic orbital rendering with hyperbolic/parabolic support
+- `e1df0b4` Add diverse orbit examples to test_simple config
+
+## Results
+
+7 files changed, +209/-106 (net +103 lines)
+
+### Key Findings
+- Simulation and test now show identical behavior (parent change Sun→Mars at day 1532)
+- Comet enters Mars's SOI at 0.003787 AU (just within 0.003792 AU SOI radius)
+- Comet is ejected from solar system after Mars encounter (ends at 58.7 AU with e=1.0)
+- Renderer now correctly displays elliptical, parabolic, and hyperbolic trajectories
+- Orbits update dynamically when gravitational parent changes
+
+### Test Results
+All tests passing (21 assertions in 5 test cases) ✓
+
+## Outstanding Issues
+
+- Comet remains Mars's child after leaving Mars's SOI
+  - `find_dominant_body()` doesn't check if body is still within current parent's SOI
+  - Should switch back to grandparent (Sun) when exiting child SOI
+  - Results in comet staying as Mars-relative even after ejection