## ADDED Requirements

### Requirement: Optimistic Locking for Task Updates
The system SHALL use optimistic locking to prevent concurrent update conflicts on tasks.

#### Scenario: Concurrent update detected
- **WHEN** user A and user B both load task at version 1
- **WHEN** user A saves changes, incrementing version to 2
- **WHEN** user B attempts to save with version 1
- **THEN** system returns 409 Conflict error
- **THEN** error message instructs user to refresh and retry

#### Scenario: Sequential updates succeed
- **WHEN** user loads task at version N
- **WHEN** user saves changes with correct version N
- **THEN** system accepts update and increments version to N+1

### Requirement: Soft Delete Cascade Restore
The system SHALL restore child tasks when parent task is restored from soft delete.

#### Scenario: Parent task restored with children
- **WHEN** soft-deleted parent task is restored
- **THEN** system identifies child tasks deleted at same timestamp
- **THEN** system recursively restores all matching child tasks
- **THEN** audit log records restoration of parent and children

#### Scenario: Selective restore without children
- **WHEN** user explicitly requests restore without cascade
- **THEN** only parent task is restored
- **THEN** child tasks remain in deleted state