Deepgrain Foundry: move from a claude.ai artifact to a local repository

The game as of artifact version 24, ready for local development with
coding agents.

- Source split from three large files into 52 small ones under src/sim,
  src/render and src/ui, joined in the order in src/manifest.json by
  build.py. The joined code is unchanged apart from comments; every
  headless suite gives the same output, and screenshots in both looks
  are pixel-identical to before.
- Light tidying with no change in behaviour: one movement scan loop,
  shared hazard-stripe and belt shader helpers, unused code removed, a
  shared check helper for the test suites.
- World files can be exported as an ordinary download outside claude.ai.
- Tests: broken old scripts removed, experiments moved to tools/,
  test/run_all.py added. Tools: shot.py (repeatable screenshots),
  where.py, map.py.
- Docs: AGENTS.md, CLAUDE.md, NOTES.md (the owner's to-do inbox),
  docs/PROJECT_MAP.md, DESIGN.md, TESTING.md, systems notes, the
  owner's requests and an agent log.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K9kLmYADKSEjuwUN3rFxDA

src/ui/hud.js

@@ -0,0 +1,40 @@
+// The tool hotbar and what is selected.
+// ---------- HUD ----------
+function renderHotbar() {
+  const hb = $('hotbar'); hb.innerHTML = '';
+  TOOLS.forEach((t, k) => {
+    const b = el('button', { class: 'slot' + (k === GAME.tool ? ' on' : ''), title: `${t.name} (${t.key})`, 'aria-label': `${t.name} tool, key ${t.key}`, 'aria-pressed': k === GAME.tool });
+    b.innerHTML = `<span class="k">${t.key}</span>${ICONS[t.id]}`;
+    b.onclick = () => { selectTool(k); };
+    hb.appendChild(b);
+  });
+}
+function toolId() { return TOOLS[GAME.tool].id; }
+// Shift does two jobs. While you are steering the bot it boosts; while you are not,
+// it is the tool modifier (vacuum everything, blow a mix, fill a rectangle).
+function steering() { return ['w', 'a', 's', 'd', 'ArrowUp', 'ArrowDown', 'ArrowLeft', 'ArrowRight', ' '].some(k => keys.has(k)) || GAME.padRun > 0; }
+function modShift() { return keys.has('Shift') && !steering(); }
+// The loose material exactly under the cursor, or the nearest one touching it.
+function grainAt(ax, ay) {
+  if (ax < 0 || ay < 0 || ax >= W || ay >= H) return 0;
+  const i = ay * W + ax, m = mat[i];
+  if (occ[i]) { const e = ents.find(e => ax >= e.ix && ax < e.ix + BAR_W && ay >= e.iy && ay < e.iy + BAR_H); if (e) return e.m; }
+  if (PH[m] === PH_POWDER || (PH[m] === PH_LIQUID && player.flask)) return m;
+  return vacuumTargetAt(ax, ay, 1);
+}
+function selectTool(k) {
+  if (k === GAME.tool) return;
+  GAME.tool = k; GAME.drag = null; hudDirty = true; renderHotbar(); playSfx('ui');
+  if (toolId() === 'vacuum') ensureDropMat();
+}
+function bagMaterials() { return BAG_ORDER.filter(m => bag[m] > 0); }
+// Only auto-pick a material when the player has not chosen one. A chosen
+// material stays selected even after it runs out.
+function mixList() { return [...GAME.collect].filter(m => bag[m] > 0 && PH[m] !== PH_ITEM); }
+function ensureDropMat() {
+  if (GAME.blowMix && mixList().length < 1) GAME.blowMix = false;
+  if (bag[GAME.dropMat] > 0) return;
+  if (GAME.matChosen && GAME.dropMat) return;
+  const l = bagMaterials(); GAME.dropMat = l.length ? l[0] : 0;
+}
+function piece() { return PIECES[GAME.pieceIdx]; }