# Implementation Plan: Remove Combatant

**Branch**: `003-remove-combatant` | **Date**: 2026-03-03 | **Spec**: [spec.md](./spec.md)
**Input**: Feature specification from `/specs/003-remove-combatant/spec.md`

## Summary

Add a `removeCombatant` pure domain function that removes a combatant by ID from an Encounter, correctly adjusts `activeIndex` to preserve turn integrity, keeps `roundNumber` unchanged, and emits a `CombatantRemoved` event. Wire through an application-layer use case and expose via a minimal UI remove action per combatant.

## Technical Context

**Language/Version**: TypeScript 5.x (strict mode, verbatimModuleSyntax)
**Primary Dependencies**: React 19, Vite
**Storage**: In-memory React state (local-first, single-user MVP)
**Testing**: Vitest
**Target Platform**: Web (localhost:5173 dev, production build via Vite)
**Project Type**: Web application (monorepo: packages/domain, packages/application, apps/web)
**Performance Goals**: N/A (local-first, small data sets)
**Constraints**: Domain must be pure (no I/O); layer boundaries enforced by automated script
**Scale/Scope**: Single-user, single encounter at a time

## Constitution Check

*GATE: Must pass before Phase 0 research. Re-check after Phase 1 design.*

| Principle | Status | Evidence |
|-----------|--------|----------|
| I. Deterministic Domain Core | PASS | `removeCombatant` is a pure function: same input → same output, no I/O |
| II. Layered Architecture | PASS | Domain function → use case → React hook/UI. No layer violations. |
| III. Agent Boundary | N/A | No agent layer involved in this feature |
| IV. Clarification-First | PASS | Spec fully specifies all activeIndex adjustment rules; no ambiguity |
| V. Escalation Gates | PASS | All functionality is within spec scope |
| VI. MVP Baseline Language | PASS | No permanent bans introduced |
| VII. No Gameplay Rules | PASS | Removal is encounter management, not gameplay mechanics |

**Gate result**: PASS — no violations.

## Project Structure

### Documentation (this feature)

```text
specs/003-remove-combatant/
├── plan.md
├── research.md
├── data-model.md
├── quickstart.md
└── tasks.md
```

### Source Code (repository root)

```text
packages/domain/src/
├── remove-combatant.ts          # Pure domain function
├── events.ts                    # Add CombatantRemoved to DomainEvent union
├── types.ts                     # Existing types (no changes expected)
├── index.ts                     # Re-export removeCombatant
└── __tests__/
    └── remove-combatant.test.ts # Acceptance scenarios from spec

packages/application/src/
├── remove-combatant-use-case.ts # Orchestrates store.get → domain → store.save
└── index.ts                     # Re-export use case

apps/web/src/
├── hooks/use-encounter.ts       # Add removeCombatant callback
└── App.tsx                      # Add remove button per combatant + event display
```

**Structure Decision**: Follows the existing monorepo layered architecture (packages/domain → packages/application → apps/web) exactly mirroring the addCombatant feature's file layout.