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A detailed account of migrating 200,000 lines from TypeScript 5.x to 6.0, covering the three breaking changes that generated thousands of errors, the migration strategy that failed first, and the tooling that ultimately saved the project.

Most async generator type errors stem from TypeScript's inability to infer yield types. This post reveals the three-parameter type system that eliminates inference failures in production code.

Stage 3 decorators bring runtime metadata, validation, and dependency injection patterns to production TypeScript. The performance trade-offs matter more than the syntax sugar.