Multi-core simulation: grain movement and heat across a worker pool (t88 phase 3)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/harness.js

@@ -81,3 +81,34 @@ function dump(run, x0, y0, x1, y1, withTemp) {
   }
 }
 module.exports.dump = dump;
+
+// Node uses exactly the browser worker entry point and scheduler.
+async function enableThreads(run, count) {
+  const { Worker } = require('worker_threads');
+  const entry = `const {parentPort}=require('worker_threads');
+    require(${JSON.stringify(__filename)}).load();
+    parentPort.on('message', data=>threadMessage(data));`;
+  const pool = { world: run('mat'), workers: [], slots: [], force: true };
+  try {
+    const ready = [];
+    for (let k = 0; k < count; k++) {
+      const worker = new Worker(entry, {eval:true}), slot = run('threadSlot()');
+      pool.workers.push(worker); pool.slots.push(slot);
+      ready.push(new Promise((resolve,reject) => {
+        const deadline = Date.now()+10000;
+        worker.once('error',reject);
+        const poll = () => {
+          if (Atomics.load(slot.control,0)) resolve();
+          else if (Date.now()>deadline) reject(Error('Worker startup timed out'));
+          else setTimeout(poll,1);
+        };
+        poll();
+      }));
+      worker.postMessage({world:run('threadWorld()'),slot});
+    }
+    await Promise.all(ready);
+    globalThis.__testPool = pool; run('simPool = globalThis.__testPool;'); delete globalThis.__testPool;
+    return async () => { run('simPool=null;'); await Promise.all(pool.workers.map(w=>w.terminate())); };
+  } catch (e) { await Promise.all(pool.workers.map(w=>w.terminate())); throw e; }
+}
+module.exports.enableThreads = enableThreads;