Module queue 

TaskQueue trait — abstraction over lease-based task scheduling.

The queue implements FOR UPDATE SKIP LOCKED-style claim semantics (Section 9.3): tasks are enqueued with priority and availability time, claimed with a lease TTL, and must be heartbeated to prevent reclamation.

Lease semantics (Section 10.2):

• Worker lease TTL: default 30s (configurable).
• Heartbeat every 5s while task executes.
• Scheduler reclaims stale leases after TTL + grace window.
• Reclaimed tasks move back to pending with incremented attempt.

Structs

ClaimRequest

Parameters for claiming tasks from the queue.

ConcurrencyConfig

Concurrency configuration for backpressure (Section 10.3).

QueueEntry

A single entry in the task queue.

QueueStats

Summary statistics for the queue.

Enums

QueueStatus

Status of a queue entry.

Traits

TaskQueue

Abstract task queue. Implementations must be thread-safe.