# Implementation Plan: Display Initiative

**Branch**: `025-display-initiative` | **Date**: 2026-03-10 | **Spec**: [spec.md](./spec.md)
**Input**: Feature specification from `/specs/025-display-initiative/spec.md`

## Summary

Add initiative modifier and passive initiative display to the creature stat block panel. A pure domain function calculates initiative as DEX modifier + (proficiency multiplier × proficiency bonus) from bestiary data. The bestiary adapter parses the `initiative.proficiency` field from 5etools JSON. The stat block component displays the result as "Initiative +X (Y)" in the header area next to AC, matching the Monster Manual 2024 format.

## Technical Context

**Language/Version**: TypeScript 5.8 (strict mode, verbatimModuleSyntax)
**Primary Dependencies**: React 19, Vite 6, Tailwind CSS v4, Lucide React (icons)
**Storage**: N/A (no storage changes — purely derived from existing bestiary data)
**Testing**: Vitest
**Target Platform**: Browser (single-page web app)
**Project Type**: Web application (monorepo: domain → application → web adapter)
**Performance Goals**: N/A (simple arithmetic calculation, no performance concerns)
**Constraints**: Domain layer must remain pure — no I/O or framework imports
**Scale/Scope**: ~500 creatures in bestiary dataset

## Constitution Check

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

| Principle | Status | Notes |
|-----------|--------|-------|
| I. Deterministic Domain Core | PASS | Initiative calculation is a pure function: `(dex, cr, profMultiplier) → modifier`. No I/O, randomness, or clocks. |
| II. Layered Architecture | PASS | Domain: pure `calculateInitiative` function. Adapter: parse `initiative.proficiency` from raw JSON into `Creature` type. Web: display in `StatBlock` component. No layer violations. |
| III. Agent Boundary | N/A | No agent layer involvement. |
| IV. Clarification-First | PASS | Feature is fully specified — formula, display format, and positioning are all explicit. |
| V. Escalation Gates | PASS | Display-only scope is clearly bounded. FR-007 explicitly excludes initiative rolling. |
| VI. MVP Baseline Language | PASS | Spec uses "MVP baseline does not include automatic initiative rolling or encounter order integration." |
| VII. No Gameplay Rules | PASS | Initiative calculation formula is in the feature spec, not the constitution. |

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

## Project Structure

### Documentation (this feature)

```text
specs/025-display-initiative/
├── 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/
├── creature-types.ts        # MODIFY: add initiativeProficiency field to Creature
├── initiative.ts            # NEW: pure calculateInitiative function
├── index.ts                 # MODIFY: export new function and types
└── __tests__/
    └── initiative.test.ts   # NEW: tests for initiative calculation

apps/web/src/
├── adapters/
│   └── bestiary-adapter.ts  # MODIFY: parse initiative.proficiency from raw JSON
└── components/
    └── stat-block.tsx        # MODIFY: display initiative in header area
```

**Structure Decision**: Follows existing monorepo layout. New domain function in its own file (`initiative.ts`) matching the pattern of other domain functions (e.g., `hp-status.ts`). No new packages or layers needed.