Priority-based command queue for async task scheduling — Rust, Python, and Node.js

A3S Lane

A3S Lane is a priority-based command queue for async task scheduling. Six built-in lanes with configurable concurrency ensure control commands always preempt LLM generation. Available as a Rust crate, Python package, and Node.js module.

Key Features

Priority Scheduling — 6 built-in lanes. The highest-priority lane with pending work is always scheduled next.
Concurrency Control — Per-lane semaphore limits with configurable min/max.
Retry Policies — Exponential backoff and fixed-delay strategies.
Dead Letter Queue — Failed commands captured with full context for inspection.
Persistent Storage — Pluggable storage backend (local filesystem included).
Event Stream — EventStream implements futures_core::Stream; subscribe directly from the manager without threading EventEmitter manually.
Lane Pressure Events — queue.lane.pressure / queue.lane.idle when queue depth crosses a configured threshold.
Rate Limiting — Token bucket per lane (distributed feature).
Priority Boosting — Deadline-based automatic priority escalation (distributed feature).
Queue Partitioning — Round-robin and hash-based partitioning for multi-core parallelism.
Metrics & Alerts — Latency histograms, queue depth tracking, and configurable alert thresholds.
Graceful Shutdown — Drain pending commands before stopping.

Architecture

QueueManager
├── EventEmitter          ← broadcast pub/sub; subscribe() returns EventStream (Stream)
├── CommandQueue           ← scheduler (10ms poll loop)
│   ├── Lanes              ← HashMap<LaneId, Lane>
│   │   └── Lane           ← priority queue + concurrency semaphore
│   │       ├── Pending    ← VecDeque (FIFO within priority)
│   │       └── Config     ← timeout, retry, rate limit, boost, pressure threshold
│   ├── DeadLetterQueue    ← failed commands
│   └── Storage            ← optional persistence
├── Metrics                ← optional observability
└── Alerts                 ← optional monitoring