Add speculative idle execution for warmInit (Phase 9).

Author: KubaO

builder/cpu-worker.mjs

@@ -19,6 +19,7 @@ import { deriveOfflinePage, deriveOfflinePageCached,
 import {
   createViews, scanAndClaim, onTaskDone,
   READY, F_ON_DEMAND, F_RUN_ON_MAIN,
+  F_RUN_WHEN_IDLE, F_UNIQUE_PER_WORKER,
   MAX_LANES,
 } from "./sab-scheduler.mjs";
 
@@ -191,6 +192,24 @@ parentPort.on("message", (msg) => {
   }
 });
 
+// ── Idle-task scan (speculative warmup) ─────────────────────────────────────
+
+function findIdleTask(views, lane) {
+  const count = Atomics.load(views.taskCount, 0);
+  for (let i = 0; i < count; i++) {
+    if (!(Atomics.load(views.flags, i) & F_RUN_WHEN_IDLE)) continue;
+    if (Atomics.load(views.flags, i) & F_UNIQUE_PER_WORKER) {
+      if (Atomics.load(views.perWorkerDone, i * MAX_LANES + lane) === 0)
+        return i;
+    } else {
+      if (Atomics.load(views.status, i) !== READY) continue;
+      if (Atomics.compareExchange(views.status, i, READY, CLAIMED) === READY)
+        return i;
+    }
+  }
+  return -1;
+}
+
 // ── Pull loop ───────────────────────────────────────────────────────────────
 
 async function pullLoop() {
@@ -200,6 +219,26 @@ async function pullLoop() {
     let taskIdx = scanAndClaim(views, myLane);
 
     if (taskIdx === -1) {
+      // Speculative: run idle-eligible tasks before sleeping
+      const idleTask = findIdleTask(views, myLane);
+      if (idleTask !== -1) {
+        const idleMeta  = taskMeta[idleTask];
+        const idleStart = Date.now();
+        try {
+          await handlers[idleMeta.handler]();
+        } catch (err) {
+          parentPort.postMessage({ taskFailed: idleTask, message: err.message, stack: err.stack });
+          return;
+        }
+        Atomics.store(views.perWorkerDone, idleTask * MAX_LANES + myLane, 1);
+        parentPort.postMessage({
+          warmInit: true,
+          timing:  { start: idleStart, end: Date.now() },
+          lane:    myLane,
+        });
+        continue;
+      }
+
       const gen = Atomics.load(views.notify, 0);
       // Double-check after reading gen (race: a task may have become
       // READY between the failed scan and this load).

builder/sab-scheduler.mjs

@@ -22,6 +22,7 @@ export const F_ON_DEMAND         = 1;
 export const F_UNIQUE_PER_WORKER = 2;
 export const F_RUN_ON_MAIN       = 4;
 export const F_PIN_TO_PRED       = 8;
+export const F_RUN_WHEN_IDLE    = 16;
 
 // ── SAB layout ───────────────────────────────────────────────────────────────
 //
@@ -142,6 +143,7 @@ export function allocSchedulerSAB(taskDefs, workerCount) {
     if (def?.unique_per_worker)   f |= F_UNIQUE_PER_WORKER;
     if (def?.runOnMain)           f |= F_RUN_ON_MAIN;
     if (def?.pin_to_predecessor)  f |= F_PIN_TO_PRED;
+    if (def?.run_when_idle)       f |= F_RUN_WHEN_IDLE;
     views.flags[i] = f;
 
     // successor edges
@@ -364,6 +366,7 @@ export function verifySchedulerSAB(taskDefs, views, idMapping) {
     if (def.unique_per_worker)   want |= F_UNIQUE_PER_WORKER;
     if (def.runOnMain)           want |= F_RUN_ON_MAIN;
     if (def.pin_to_predecessor)  want |= F_PIN_TO_PRED;
+    if (def.run_when_idle)       want |= F_RUN_WHEN_IDLE;
     if (views.flags[idx] !== want)
       errors.push(`flags "${name}": got ${views.flags[idx]}, want ${want}`);
   }

builder/tbdocs.mjs

@@ -240,6 +240,7 @@ const TASKS = {
     expected: [],
     on_demand: true,
     unique_per_worker: true,
+    run_when_idle: true,
     handler: "warmInit",
     submit() {},
   },