# 09 Ticket Hierarchy and Parent-Child Relationships

## Goal

Implement the parent-child ticket model, including nested parent trees and validation around which tickets are allowed to act as parents.

## Requirements

- A ticket may have zero or one parent ticket.
- Only tickets of type `Parent` may be selected as a parent target.
- A `Parent` ticket may itself have a parent ticket.
- `Task` and all other non-`Parent` types may have a parent but may not act as a parent.
- Parent tickets must show their children in a structured list.
- Nested child structures must be visually understandable, for example through indentation.

## Acceptance Criteria

- Assigning a non-`Parent` ticket as a parent is rejected.
- A `Parent` ticket can contain child tickets of multiple types.
- Nested parent chains are supported.
- The ticket detail view for a parent ticket shows its child tree.

## Out of Scope

- Automatic roll-up calculations
- Dependency graphs
- Parent-based board grouping