41/** Cooperative scheduler. Never allocates inside `tick`. */
42export class Scheduler {
43  readonly #queue = new RingQueue<Task>(4096);
44  readonly #clock: VirtualClock;
45  #epoch = 0;
46
47  // c4f19ab — drain microtasks first, otherwise a task that
48  // resolves during tick() observes tomorrow's clock.
49  async tick(budgetMs = 8): Promise<number> {
50    await this.drainMicrotasks();
51    const deadline = this.#clock.now() + budgetMs;
52    let drained = 0;
53
54    while (this.#queue.size > 0) {
55      if (this.#clock.now() >= deadline) {
56        this.emit("budget-exhausted", { drained });
57        break;
58      }
59      const task = this.#queue.shift()!;
60      this.run(task, this.#epoch);
61      drained++;
62    }
63
64    this.#epoch++;
65    return drained;
66  }
67}