Implement the 023-clear-encounter feature that adds a clear encounter button with confirmation dialog to remove all combatants and reset round/turn counters, with the cleared state persisting across page refreshes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

specs/023-clear-encounter/plan.md

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+# Implementation Plan: Clear Encounter
+
+**Branch**: `023-clear-encounter` | **Date**: 2026-03-09 | **Spec**: [spec.md](./spec.md)
+**Input**: Feature specification from `/specs/023-clear-encounter/spec.md`
+
+## Summary
+
+Add a "Clear Encounter" action that removes all combatants and resets round/turn counters with a single confirmed click. Implementation follows the existing domain → application → adapter pattern with a new `clearEncounter` pure function, a use case orchestrator, and a clear button in the TurnNavigation component gated by `window.confirm()`.
+
+## Technical Context
+
+**Language/Version**: TypeScript 5.8 (strict mode, verbatimModuleSyntax)
+**Primary Dependencies**: React 19, Tailwind CSS v4, Lucide React (icons)
+**Storage**: Browser localStorage (existing adapter, updated to handle empty encounters)
+**Testing**: Vitest
+**Target Platform**: Web browser (single-page app)
+**Project Type**: Web application (monorepo: domain/application/web)
+**Performance Goals**: N/A (single synchronous state reset)
+**Constraints**: Local-first, single-user MVP
+**Scale/Scope**: Single encounter tracker screen
+
+## Constitution Check
+
+*GATE: Must pass before Phase 0 research. Re-check after Phase 1 design.*
+
+| Principle | Status | Notes |
+|-----------|--------|-------|
+| I. Deterministic Domain Core | PASS | `clearEncounter` is a pure function — same input always produces same output. No I/O, randomness, or clocks. |
+| II. Layered Architecture | PASS | Domain function → Application use case → React adapter. No layer violations. |
+| III. Agent Boundary | N/A | No agent layer involvement. |
+| IV. Clarification-First | PASS | No non-trivial assumptions — feature is straightforward. Confirmation UI (browser confirm) is a reasonable default documented in research. |
+| V. Escalation Gates | PASS | All work is within spec scope. |
+| VI. MVP Baseline Language | PASS | Spec uses "MVP baseline does not include" for undo and encounter history. |
+| VII. No Gameplay Rules | PASS | No gameplay mechanics in the plan. |
+
+**Post-Phase 1 re-check**: All gates still pass. The empty encounter bypass of `createEncounter()` is consistent with existing behavior (remove-combatant already produces empty combatant lists). No new layer violations introduced.
+
+## Project Structure
+
+### Documentation (this feature)
+
+```text
+specs/023-clear-encounter/
+├── plan.md              # This file
+├── research.md          # Phase 0 output
+├── data-model.md        # Phase 1 output
+├── quickstart.md        # Phase 1 output
+└── tasks.md             # Phase 2 output (/speckit.tasks command)
+```
+
+### Source Code (repository root)
+
+```text
+packages/domain/src/
+├── clear-encounter.ts           # New: pure clearEncounter function
+├── events.ts                    # Modified: add EncounterCleared event
+├── index.ts                     # Modified: export clearEncounter + event
+└── __tests__/
+    └── clear-encounter.test.ts  # New: domain function tests
+
+packages/application/src/
+├── clear-encounter-use-case.ts  # New: use case orchestrator
+└── index.ts                     # Modified: export use case
+
+apps/web/src/
+├── hooks/
+│   └── use-encounter.ts         # Modified: add clearEncounter callback
+├── persistence/
+│   └── encounter-storage.ts     # Modified: handle empty encounter in load
+├── components/
+│   └── turn-navigation.tsx      # Modified: add clear button
+└── App.tsx                      # Modified: wire clearEncounter prop
+```
+
+**Structure Decision**: Follows existing monorepo layout with strict domain → application → web layering. No new packages or directories needed. Three new files, six modified files.