feat(merge-props): generic over the consumer's props — cast-free call sites

[ivanbanov]

Summary

mergeProps was typed Record<string, unknown> -> Record<string, unknown>, which forces every binding call site into a double cast:

const merged = mergeProps(props as Record<string, unknown>, bindings) as PressableProps

• cast in — framework prop types are interfaces without index signatures, not assignable to Record<string, unknown>
• cast out — the anonymous return can't spread onto a typed component

This makes it generic across the base (state-machine-utils) and all three adapters (react / native / opentui):

function mergeProps<Props extends object = Record<string, unknown>>(
  consumer: Props | undefined,
  library: Record<string, unknown>,
): Props & Record<string, unknown>

The return is the Object.assign-style intersection: assignable to the component's props (the JSX spread needs no cast) while the library's bindings stay reachable on the result — pure Props would have hidden them, which the existing tests caught immediately.

// call sites, after
const merged = mergeProps(props, normalize(api.parts.backdrop))
return <Pressable {...merged} />

Type-only; behavior unchanged. Downstream sweep: dunky/ui's react + native dialog bindings drop ~16 casts once this releases.

Test plan

• pnpm test:ci — 923 tests, 84 files (2 new type-preservation tests via expectTypeOf)
• pnpm typecheck / pnpm lint / pnpm format:check
• pnpm build — all packages

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
dunky-state-machine	Ready	Preview, Comment	Jul 19, 2026 11:22pm