# js/physics/ — agents.md
RC-375D84 S-2. Module map: `MODULES.md`; runtime model: `architecture.md`.

The physics **module** (aggregator). Deterministic, DOM-free.

- `index.js` is the ONLY public face: it builds the shared scope `P`, runs every
  submodule installer against it, and exports `ISLE_CORE` (20-key API, see the
  return literal — keep it key-for-key stable; adding a key is fine, renaming or
  dropping one is not).
- Submodules must load BEFORE this file in the browser (index.html order); under
  Node this file requires them in dependency order. Do not add a submodule
  without registering it in BOTH the index.html script list and this file's
  `require` list.
- The core is the simulation's single source of truth: `step(state, dt)` is the
  only thing that mutates gameplay state. Everything else is either setup
  (`createGame`), input translation (`launch`), or read-only queries
  (`activeBird`, `trajectory`, `aimVector`, `starsFor`, `birdsRemaining`).
- Invariants: fixed-timestep consumer (tests run 1/120 s); no `Math.random()`
  in gameplay paths (determinism is a test arm); no DOM access.
- New physics behavior lands in the owning submodule, NOT here. RC-375D84
  S-3..S-5 (landed 2026-09-29): topple/ owns board tip-over (Q1 full continuous
  rotation), collision/ owns velocity-aware crush + mass-weighted stacks (S-4),
  step/ owns the landed-bird state and its integration (S-5).