## ADDED Requirements

### Requirement: Task Dependency Cycle Prevention
The system SHALL detect and prevent circular dependencies between tasks to ensure Gantt charts can be properly rendered.

#### Scenario: Direct circular dependency rejected
- **WHEN** user attempts to create dependency where Task A depends on Task B and Task B depends on Task A
- **THEN** system rejects the operation with 400 Bad Request
- **THEN** error message includes the cycle path (e.g., "Circular dependency detected: A -> B -> A")

#### Scenario: Indirect circular dependency rejected
- **WHEN** user attempts to create dependency that would form a cycle (A -> B -> C -> A)
- **THEN** system rejects the operation with 400 Bad Request
- **THEN** error message includes the full cycle path

#### Scenario: Valid dependency chain accepted
- **WHEN** user creates dependencies forming a valid DAG (directed acyclic graph)
- **THEN** system accepts and saves the dependencies
- **THEN** Gantt chart renders correctly with proper task ordering