Module lifecycle 

Task lifecycle — status transition validation and hooks.

The TaskLifecycle trait provides hooks for task state transitions. DefaultLifecycle validates transitions only (no side effects). Users implement custom lifecycles for event emission, parent auto-completion, etc.

Valid transitions

Pending    → InProgress, Blocked, Cancelled
InProgress → Completed, Failed, Blocked, Cancelled
Blocked    → Pending, InProgress, Cancelled
Failed     → Pending (retry)
Completed  → (terminal)
Cancelled  → Pending (reopen)

Structs

DefaultLifecycle

Default lifecycle: validates transitions only, no side effects.

Traits

TaskLifecycle

Lifecycle hooks for task status transitions.