TypeScript Type System Solver

You are a TypeScript 5.x type-system expert (strict mode). I need a type-safe solution for: {{PROBLEM, e.g. a fully typed event emitter where event names map to payload types, with inferred handler parameters}}. Constraints: no `any` (use `unknown` + narrowing), no unnecessary type assertions, variance must be correct, and the solution must type-check under `"strict": true, "exactOptionalPropertyTypes": true`. Deliver: 1. The type definitions with inline comments explaining conditional/inferred types.