Add core-powered web sculpting studio with tablet controls

Add pressure-aware worker sculpting, bounded shared input, project files and history, and compact icon navigation with an XYZ orbit gizmo.

Amp-Thread-ID: https://ampcode.com/threads/T-01a0b4b4-202c-73f1-984d-9a55c88f9c83
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

server/web/assets/sculpt/mailbox.js

@@ -0,0 +1,48 @@
+// One latest target in a core shared row. Versions are snapshot tokens, not a
+// sample count. The producer never touches the consumer's acknowledgement.
+export class Mailbox {
+  constructor({ buffer, descriptor }) {
+    this.words = new Int32Array(buffer, descriptor.offset, 16);
+    this.scratch = new ArrayBuffer(4);
+    this.bits = new Int32Array(this.scratch);
+    this.float = new Float32Array(this.scratch);
+  }
+  encode(value) {
+    this.float[0] = value;
+    return this.bits[0];
+  }
+  decode(value) {
+    this.bits[0] = value;
+    return this.float[0];
+  }
+  write(stroke, sample, seed) {
+    const version = (Atomics.load(this.words, 0) + 2) | 0;
+    Atomics.store(this.words, 0, version - 1);
+    Atomics.store(this.words, 2, stroke);
+    Atomics.store(this.words, 3, this.encode(sample.x));
+    Atomics.store(this.words, 4, this.encode(sample.y));
+    Atomics.store(this.words, 5, this.encode(sample.pressure));
+    Atomics.store(this.words, 6, this.encode(seed ?? 0));
+    Atomics.store(this.words, 7, seed === undefined ? 0 : 1);
+    Atomics.store(this.words, 0, version);
+    return version;
+  }
+  read(stroke) {
+    const a = Atomics.load(this.words, 0);
+    if (a & 1 || a === Atomics.load(this.words, 1)) return null;
+    const id = Atomics.load(this.words, 2);
+    const x = this.decode(Atomics.load(this.words, 3));
+    const y = this.decode(Atomics.load(this.words, 4));
+    const pressure = this.decode(Atomics.load(this.words, 5));
+    const seed = this.decode(Atomics.load(this.words, 6));
+    const hasSeed = Atomics.load(this.words, 7);
+    if (a !== Atomics.load(this.words, 0) || id !== stroke) return null;
+    return { version: a, x, y, pressure, seed: hasSeed ? seed : undefined };
+  }
+  acknowledge(version) {
+    Atomics.store(this.words, 1, version);
+  }
+  get processed() {
+    return Atomics.load(this.words, 1);
+  }
+}