Implement the 005-set-initiative feature that adds initiative values to combatants with automatic descending sort and active turn preservation

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

specs/005-set-initiative/plan.md

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+# Implementation Plan: Set Initiative
+
+**Branch**: `005-set-initiative` | **Date**: 2026-03-04 | **Spec**: [spec.md](./spec.md)
+**Input**: Feature specification from `/specs/005-set-initiative/spec.md`
+
+## Summary
+
+Add an optional integer initiative property to combatants and a `setInitiative` domain function that sets/changes/clears the value and automatically reorders combatants descending by initiative (unset last, stable sort for ties). The active combatant's turn is preserved through reorders by tracking identity rather than position.
+
+## 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 browser (localhost:5173 dev)
+**Project Type**: Web application (monorepo: domain → application → web adapter)
+**Performance Goals**: N/A (local in-memory, trivial data sizes)
+**Constraints**: Pure domain functions, no I/O in domain layer
+**Scale/Scope**: Single-user, single encounter
+
+## Constitution Check
+
+*GATE: Must pass before Phase 0 research. Re-check after Phase 1 design.*
+
+| Principle | Status | Notes |
+|-----------|--------|-------|
+| I. Deterministic Domain Core | PASS | `setInitiative` is a pure function: same encounter + id + value → same result. No I/O, randomness, or clocks. |
+| II. Layered Architecture | PASS | Domain function in `packages/domain`, use case in `packages/application`, UI in `apps/web`. Dependency direction preserved. |
+| III. Agent Boundary | N/A | No agent layer involvement in this feature. |
+| IV. Clarification-First | PASS | Spec has no NEEDS CLARIFICATION markers. All design decisions are spec-driven. |
+| V. Escalation Gates | PASS | Feature scope matches spec exactly. No out-of-scope additions. |
+| VI. MVP Baseline Language | PASS | Spec uses "MVP baseline does not include" for secondary tiebreakers. |
+| VII. No Gameplay Rules | PASS | Constitution contains no gameplay mechanics; initiative logic is in the spec. |
+
+All gates pass. No violations to justify.
+
+**Post-Design Re-check**: All gates still pass. The `setInitiative` domain function is pure, layering is preserved, and no out-of-scope additions were introduced during design.
+
+## Project Structure
+
+### Documentation (this feature)
+
+```text
+specs/005-set-initiative/
+├── spec.md
+├── plan.md              # This file
+├── research.md          # Phase 0 output
+├── data-model.md        # Phase 1 output
+├── quickstart.md        # Phase 1 output
+├── contracts/           # Phase 1 output
+│   └── domain-api.md
+├── checklists/
+│   └── requirements.md
+└── tasks.md             # Phase 2 output (via /speckit.tasks)
+```
+
+### Source Code (repository root)
+
+```text
+packages/domain/src/
+├── types.ts                    # Modified: add initiative to Combatant
+├── events.ts                   # Modified: add InitiativeSet event
+├── set-initiative.ts           # New: setInitiative domain function
+├── index.ts                    # Modified: export setInitiative
+└── __tests__/
+    └── set-initiative.test.ts  # New: tests for setInitiative
+
+packages/application/src/
+├── set-initiative-use-case.ts  # New: setInitiativeUseCase
+└── index.ts                    # Modified: export use case
+
+apps/web/src/
+├── hooks/
+│   └── use-encounter.ts        # Modified: add setInitiative callback
+└── App.tsx                     # Modified: add initiative input field
+```
+
+**Structure Decision**: Follows existing monorepo layered structure. Each new domain operation gets its own file per established convention.
+
+## Complexity Tracking
+
+No constitution violations. Table not needed.