perf(textures): warm the image worker pool on a timer after construction

src/core/lib/ImageWorker.test.ts

@@ -34,6 +34,10 @@ let createObjectURL: ReturnType<typeof vi.fn>;
 let revokeObjectURL: ReturnType<typeof vi.fn>;
 
 beforeEach(() => {
+  // The constructor schedules a warmup `setTimeout`. Fake timers keep that
+  // spawn under each test's control — otherwise it fires after the test ends,
+  // once `unstubAllGlobals` has removed `self`/`Worker`, and throws.
+  vi.useFakeTimers();
   FakeWorker.reset();
   createObjectURL = vi.fn(() => 'blob:fake-url');
   revokeObjectURL = vi.fn();
@@ -51,19 +55,39 @@ beforeEach(() => {
 });
 
 afterEach(() => {
+  // Discards any warmup timer the test left pending, before the globals it
+  // depends on are torn down.
+  vi.useRealTimers();
   vi.unstubAllGlobals();
 });
 
 const load = (mgr: ImageWorkerManager) =>
   void mgr.getImage('img.png', null, null, null, null, null);
 
 describe('ImageWorkerManager pool spawning', () => {
-  it('does not spawn any workers at construction', () => {
+  it('does not spawn any workers synchronously at construction', () => {
     new ImageWorkerManager(3, support);
-    // Spawning is lazy — nothing happens until the first image request.
+    // Spawning is deferred a macrotask so it stays off the synchronous
+    // renderer-construction path.
     expect(FakeWorker.instances.length).toBe(0);
   });
 
+  it('spawns the whole pool on the timer scheduled at construction', () => {
+    new ImageWorkerManager(3, support);
+    expect(FakeWorker.instances.length).toBe(0);
+    vi.runAllTimers();
+    expect(FakeWorker.instances.length).toBe(3);
+  });
+
+  it('does not respawn when the warmup timer fires after a lazy spawn', () => {
+    const mgr = new ImageWorkerManager(3, support);
+    load(mgr); // request beats the timer — spawns the pool lazily
+    expect(FakeWorker.instances.length).toBe(3);
+    vi.runAllTimers();
+    // Timer must be a no-op now, not a second pool.
+    expect(FakeWorker.instances.length).toBe(3);
+  });
+
   it('spawns the whole pool at once on the first image request', () => {
     const mgr = new ImageWorkerManager(3, support);
     load(mgr);

src/core/lib/ImageWorker.ts

@@ -198,11 +198,32 @@ export class ImageWorkerManager {
   ) {
     this.maxWorkers = numImageWorkers;
     this.createImageBitmapSupport = createImageBitmapSupport;
+    // Warm the pool on the next macrotask instead of waiting for the first
+    // image request. Spawning costs main-thread time (blob serialization +
+    // one Worker construction per slot); deferring it by a task keeps it off
+    // the synchronous renderer-construction path, while still having the pool
+    // ready before textures start arriving. `getImage` keeps its lazy spawn
+    // for a request that beats this timer.
+    setTimeout(() => {
+      // Not a hot path (fires once, at boot). The guard matters because this
+      // runs detached from any caller: `new Worker(blob:)` can throw outright
+      // where CSP forbids blob workers, and an uncaught throw here would take
+      // out whatever task the timer landed in. Swallowing it leaves the pool
+      // empty, so `getImage` retries the spawn inside its own try/catch and
+      // surfaces the failure as a rejected image promise — the pre-warmup
+      // behavior.
+      try {
+        this.spawnWorkers();
+      } catch (e) {
+        /* empty */
+      }
+    }, 0);
   }
 
   /**
    * Build the shared worker source once and spawn the full pool in a single
-   * burst. Called lazily on the first image request. No-op once spawned.
+   * burst. Scheduled from the constructor via `setTimeout`; also called
+   * lazily from `getImage` if a request arrives first. No-op once spawned.
    */
   private spawnWorkers(): void {
     if (this.workers.length > 0) {
@@ -333,8 +354,8 @@ export class ImageWorkerManager {
       try {
         let nextWorkerIndex = this.getNextWorkerIndex();
         if (nextWorkerIndex === -1) {
-          // Pool not spawned yet — spin up all workers at once on the first
-          // image request, off the boot/first-render critical path.
+          // Request beat the constructor's scheduled warmup — spin up the
+          // whole pool now rather than making this image wait a task.
           this.spawnWorkers();
           nextWorkerIndex = this.getNextWorkerIndex();
         }