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Learn how TypeScript discriminated unions model state so invalid combinations simply won't compile. Master the discriminant pattern, exhaustiveness checking with never, and dramatically cleaner reducers.

Most decorator migration failures stem from treating TC39 standard decorators as a drop-in replacement. The API changed fundamentally—here's how to convert experimentalDecorators without breaking production.

Five advanced patterns that unlock the full power of TypeScript's satisfies operator—from type-safe configs to branded types that bridge runtime validation with compile-time safety.