Module hierarchy 

Parent-child task lifecycle coupling.

HierarchyTracker maintains the parent → children mapping and enforces lifecycle rules:

• Cascading cancellation: canceling a parent cascades to all non-terminal descendants via HierarchyTracker::collect_cancellation_cascade.
• Orphan prevention: HierarchyTracker::register_child rejects children of tasks already marked terminal.
• Depth limit: configurable maximum nesting depth (default 8 levels).

Invariants

• Tree structure is acyclic by construction (only append, no reparenting).
• Terminal state is tracked via HierarchyTracker::mark_terminal, called by the dispatch loop after all runs for a task reach terminal state.
• At bootstrap, tree registration happens before terminal marking, so orphan prevention never fires during WAL replay.

Structs

HierarchyTracker

Tracks parent-child task relationships and enforces lifecycle coupling.

Enums

HierarchyError

Error returned when registering a parent-child relationship fails.

Constants

DEFAULT_MAX_DEPTH

Default maximum nesting depth for task hierarchies.