# ADR 0001: Web Stack And Engine Boundary

## Status

Accepted, 2026-06-11.

## Context

Idlegame is a text-first idle/incremental RPG. The UI is mostly panels, progress
bars, action lists, resources, logs, and branching story choices. It must run
well on phones from day one and remain easy to wrap later for desktop or mobile
stores.

## Decision

Use TypeScript strict, Vite, React 19, Zustand, Tailwind v4, Vitest, Biome, and
vite-plugin-pwa.

Keep gameplay rules in a pure TypeScript engine under `src/engine/`. React,
Zustand, browser storage, requestAnimationFrame, and lifecycle hooks belong
outside the engine.

Use plain JavaScript numbers behind `src/engine/num.ts` for M0/M1. Human-readable
values are a design pillar; a Decimal-style dependency is deferred until a later
layer proves it is needed.

## Consequences

- Engine behavior is headless-testable with Vitest.
- UI and wrapper changes should not force gameplay rewrites.
- Offline progress uses the same fixed-timestep simulation path as online play.
- Save/load validation sits at explicit boundaries with versioned schemas.
- Dependencies must be permissive; no GPL packages are allowed.