# Data Model: Edit Combatant

**Feature**: 004-edit-combatant
**Date**: 2026-03-03

## Entities

### Combatant (unchanged)

| Field | Type | Notes |
|-------|------|-------|
| id | CombatantId (branded string) | Immutable identity |
| name | string | Mutable — this feature updates it |

### Encounter (unchanged structure)

| Field | Type | Notes |
|-------|------|-------|
| combatants | readonly Combatant[] | Edit replaces name in-place by mapping |
| activeIndex | number | Preserved during edit |
| roundNumber | number | Preserved during edit |

## Events

### CombatantUpdated (new)

| Field | Type | Notes |
|-------|------|-------|
| type | "CombatantUpdated" | Discriminant |
| combatantId | CombatantId | Which combatant was renamed |
| oldName | string | Name before edit |
| newName | string | Name after edit |

Added to the `DomainEvent` union type.

## State Transitions

### editCombatant(encounter, id, newName)

**Preconditions**:
- `newName` is non-empty and not whitespace-only
- `id` matches a combatant in `encounter.combatants`

**Postconditions**:
- The combatant with matching `id` has `name` set to `newName`
- `activeIndex` and `roundNumber` unchanged
- Combatant list order unchanged
- Exactly one `CombatantUpdated` event emitted

**Error cases**:
- `id` not found → `DomainError { code: "combatant-not-found" }`
- `newName` empty/whitespace → `DomainError { code: "invalid-name" }`

## Validation Rules

| Rule | Condition | Error Code |
|------|-----------|------------|
| Name must be non-empty | `newName.trim().length === 0` | `"invalid-name"` |
| Combatant must exist | No combatant with matching `id` | `"combatant-not-found"` |