Add run boundary effect diagnostics

[briancavalier]

Summary

• add an internal unhandled-effect diagnostic sentinel for run/runPromise/runTask parameter types
• preserve existing accepted runtime effects at each run boundary
• add focused type tests for accepted runtime effects, handled programs, and rejected residual effects

Validation

• corepack pnpm typecheck
• corepack pnpm test
• corepack pnpm build
• corepack pnpm lint

Manual check

• temporarily removed guessing-game handlePrint and confirmed runPromise now reports UnhandledEffectsError without explicit annotations

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Accept generics constrained to runtime effects

The new RunBoundary check rejects valid wrapper functions where E is already constrained to runtime effects (for example, <E extends Async | HandlerCapture<string> | Interrupt>(program: Fx<E, A>) => runTask(program)). With the current [Exclude<E, RuntimeEffects>] extends [never] condition, TypeScript does not reduce the generic case, so callers are forced to add unsafe casts (as now done in NodeRuntime.ts), which regresses API ergonomics and weakens compile-time guarantees for downstream users.

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