## MODIFIED 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
- **AND** response includes a human-readable message instructing refresh and retry
- **AND** response includes the current and provided version numbers

#### 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