docs(plan): Kerr orbiting planets implementation plan (Phase 3.4)
9-task TDD plan implementing the Phase 3.4 spec. Path A: all orbital physics
on CPU, shader untouched.
Task ordering enforces a buildable chain:
- Task 0: add rand + rand_chacha (currently only transitive via bevy)
- Task 1: physics.rs Ω_φ + Ω_LT with 5 failing-first tests (χ=0 degeneracy,
strong-field > weak-field, monotonic-in-spin)
- Task 2: OrbitParams + orbit_position pure fn with 3 geometry invariants
(radius preserved, equatorial χ=0 stays in plane, motion over time)
- Task 3-4: orbit_system + BlackHoleParams fields (coupled, committed together)
- Task 5: spawn_planet_system (ChaCha8Rng, replaces spawn_default_planet) +
PlanetSystemDirty resource + plugin registration
- Task 6-7: UI header + dirty-flag wiring on seed/count/k change
- Task 8: integration test + visual tuning
Each task is bite-sized (2-5 min steps), exact file paths/line numbers,
complete code blocks, exact test commands. Self-reviewed against spec: all
sections covered, no placeholders, type names consistent across tasks.
xfy
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