typescript-game-state

Model phases as a discriminated union on a `kind` field instead of parallel boolean flags like `busy` and `submitted`. Read it with a switch whose default calls an `assertNever(x: never)` helper, so adding a phase produces compile errors at every unhandled site.

Define the keys as a const tuple, derive the union type from it, and store definitions in a `Record<Key, Def>` rather than a Partial. Resolve effects through a switch with an assertNever default so any missing case fails to compile.

Branded types intersect a primitive with a unique tag, such as `number & { __brand: 'CellIndex' }`, giving zero-runtime-cost nominal typing. Use them where two same-typed values are easily swapped, like cell indices and column numbers, but keep them out of view components.

No. The rules engine should be pure TypeScript with no `document`, `window`, or React imports, which makes it testable, replayable, and portable across web and native. This can be enforced mechanically by grepping the engine directory for renderer imports in CI.

It forces an undefined check whenever an array is indexed by a computed position, which is exactly how board cells are accessed. Without it, off-grid arithmetic silently yields undefined instead of failing at the access site.

Keep branded ids and exhaustive unions in the engine layer and let React components take plain props. Typing CSS class strings or building a type-level design system adds ceremony without safety, since utility CSS correctness comes from editor tooling rather than the type system.