# Data Model: Remove Combatant

**Feature**: 003-remove-combatant
**Date**: 2026-03-03

## Existing Entities (no changes)

### Encounter

| Field | Type | Description |
|-------|------|-------------|
| combatants | readonly Combatant[] | Ordered list of participants |
| activeIndex | number | Index of the combatant whose turn it is |
| roundNumber | number | Current round (≥ 1, never changes on removal) |

### Combatant

| Field | Type | Description |
|-------|------|-------------|
| id | CombatantId (branded string) | Unique identifier |
| name | string | Display name |

## New Event Type

### CombatantRemoved

| Field | Type | Description |
|-------|------|-------------|
| type | "CombatantRemoved" (literal) | Event discriminant |
| combatantId | CombatantId | ID of the removed combatant |
| name | string | Name of the removed combatant |

Added to the `DomainEvent` discriminated union alongside `TurnAdvanced`, `RoundAdvanced`, and `CombatantAdded`.

## New Domain Function

### removeCombatant

| Parameter | Type | Description |
|-----------|------|-------------|
| encounter | Encounter | Current encounter state |
| id | CombatantId | ID of combatant to remove |

**Returns**: `RemoveCombatantSuccess | DomainError`

### RemoveCombatantSuccess

| Field | Type | Description |
|-------|------|-------------|
| encounter | Encounter | Updated encounter after removal |
| events | DomainEvent[] | Exactly one CombatantRemoved event |

### DomainError (existing, reused)

Returned with code `"combatant-not-found"` when ID does not match any combatant.

## State Transition Rules

### activeIndex Adjustment

Given removal of combatant at index `removedIdx` with current `activeIndex`:

| Condition | New activeIndex |
|-----------|----------------|
| removedIdx > activeIndex | activeIndex (unchanged) |
| removedIdx < activeIndex | activeIndex - 1 |
| removedIdx === activeIndex, not last in list | activeIndex (next slides in) |
| removedIdx === activeIndex, last in list | 0 (wrap) |
| Only combatant removed (list becomes empty) | 0 |