kozan-scheduler — Task scheduler and async executor for Kozan.

Like Chrome's base/task/ + blink/platform/scheduler/. Standalone crate — zero dependency on kozan-core.

Architecture

Scheduler (MainThreadScheduler — the event loop)
├── TaskQueueManager (SequenceManager — priority picker)
│   └── TaskQueue × 6 (one per priority level)
├── MicrotaskQueue (drain after each macrotask)
├── LocalExecutor (!Send async runtime)
├── FrameScheduler (vsync-driven frame timing)
└── WakeReceiver (cross-thread task delivery)

Event loop algorithm (HTML spec)

loop {
    1. Receive cross-thread tasks
    2. Promote delayed tasks
    3. Poll async executor
    4. Pick ONE macrotask → run
    5. Drain ALL microtasks
    6. If frame due → callbacks → style → layout → paint
    7. Park until next event
}