Continuity rule: discrete params hold per cue; add DESIGN.md + AGENTS.md

Actors and objects change only at camera cuts. int/bool/discrete
params skip drift, lookahead and reactivity; discrete slowAxis steps
on the section-held journey. Venues fade instead of toggling on
interpolated popMul; roadside density is arrangement-only.

DESIGN.md collects the project's design decisions; AGENTS.md points
agents at it and the build-visualizer loop.

flow-state/AGENTS.md

@@ -0,0 +1,43 @@
+# AGENTS.md — flow-state
+
+## Design decisions
+
+All load-bearing decisions live in [`DESIGN.md`](./DESIGN.md). Read it before
+changing behaviour. Changing a decision means updating `DESIGN.md` **and**
+the gate that enforces it. `PLAN.md` is the full design; `EPIC-*.md` are the
+epic designs.
+
+## Adding / fixing a scene
+
+Follow the `build-visualizer` skill (`.claude/skills/build-visualizer/`).
+Short version:
+
+```bash
+npm run new:scene -- "Name" --family=<flow|organic|minimal|structural|geometric|glitch> --traits=...
+# ... write the scene() body ...
+npm run lint:scenes
+# open http://localhost:5180/checks.html?scene=Name
+```
+
+Verify in order: `lint:scenes` (~1s) → per-scene gate in `checks.html` →
+`checks.html?slow=1` once before committing. Each rung is ~10× the cost of
+the previous.
+
+## Rules that have bitten before (all in DESIGN.md §3–4)
+
+- Anything multiplying `u_time` must be `rate: true` — and rate params are
+  never modulated (drift/reactive/lookahead skip them).
+- Discrete params (`int`/`bool`/`discrete: true`) hold per cue and are
+  never reactive: **actors and objects change only at camera cuts.**
+- No contract-uniform reuse, no hardcoded colours (use `pal()`), base
+  image under every `prev()`, honour every declared trait, feed `sigCamera`
+  into the image.
+- No `Math.random` / wall-clock in render-path code; motion is analytic
+  `f(t, seed)` so seek === playback and preview === export.
+
+## Checks
+
+```bash
+npm test             # audio pipeline + venue/model headless tests
+npm run lint:scenes  # determinism grep + schema/shader agreement
+```