Implement the 004-edit-combatant feature that adds the possibility to change a combatants name

specs/004-edit-combatant/plan.md

@@ -0,0 +1,70 @@
+# Implementation Plan: Edit Combatant
+
+**Branch**: `004-edit-combatant` | **Date**: 2026-03-03 | **Spec**: [spec.md](./spec.md)
+**Input**: Feature specification from `/specs/004-edit-combatant/spec.md`
+
+## Summary
+
+Add the ability to rename a combatant by id within an encounter. A pure domain function `editCombatant` validates the id and new name, returns the updated encounter with a `CombatantUpdated` event, or a `DomainError`. Wired through an application use case and exposed via the existing `useEncounter` hook to a minimal UI control.
+
+## 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**: Browser (localhost:5173)
+**Project Type**: Web application (monorepo: domain → application → web)
+**Performance Goals**: N/A — single-user local state, instant updates
+**Constraints**: Pure domain logic, no I/O in domain layer
+**Scale/Scope**: Single-user encounter tracker
+
+## Constitution Check
+
+*GATE: Must pass before Phase 0 research. Re-check after Phase 1 design.*
+
+| Principle | Status | Notes |
+|-----------|--------|-------|
+| I. Deterministic Domain Core | PASS | `editCombatant` is a pure function: same encounter + id + name → same result |
+| II. Layered Architecture | PASS | Domain function → use case → hook/UI. No layer violations. |
+| III. Agent Boundary | N/A | No agent layer involvement |
+| IV. Clarification-First | PASS | Spec is complete, no ambiguities remain |
+| V. Escalation Gates | PASS | All work is within spec scope |
+| VI. MVP Baseline Language | PASS | Spec uses "MVP baseline does not include" for out-of-scope items |
+| VII. No Gameplay Rules | PASS | Constitution contains no gameplay logic |
+
+## Project Structure
+
+### Documentation (this feature)
+
+```text
+specs/004-edit-combatant/
+├── plan.md
+├── research.md
+├── data-model.md
+├── quickstart.md
+├── contracts/
+└── tasks.md
+```
+
+### Source Code (repository root)
+
+```text
+packages/domain/src/
+├── edit-combatant.ts          # New: pure editCombatant function
+├── events.ts                  # Modified: add CombatantUpdated event
+├── types.ts                   # Unchanged (Combatant, Encounter, DomainError)
+├── index.ts                   # Modified: re-export editCombatant
+└── __tests__/
+    └── edit-combatant.test.ts # New: acceptance + invariant tests
+
+packages/application/src/
+├── edit-combatant-use-case.ts # New: use case wiring
+└── index.ts                   # Modified: re-export use case
+
+apps/web/src/
+├── hooks/use-encounter.ts     # Modified: add editCombatant action
+└── App.tsx                    # Modified: add rename UI control
+```
+
+**Structure Decision**: Follows the existing monorepo layout (`packages/domain` → `packages/application` → `apps/web`). Each new file mirrors the pattern established by `add-combatant` and `remove-combatant`.