TypeScript type errors after package update -- declaration file conflicts

TypeScript compilation fails with type errors after updating packages. Errors reference node_modules type declarations. Types that worked before are now incompatible.

Common fixes: (1) Delete node_modules and reinstall: rm -rf node_modules package-lock.json && npm i. (2) Check for duplicate @types packages: npm ls @types/node. Multiple versions cause conflicts. (3) Use resolutions/overrides to force single version. (4) Check skipLibCheck in tsconfig.json -- set to true to skip type-checking node_modules (common workaround). (5) Ensure @types/* versions match their library versions.

TypeScript declaration files from different packages can conflict when they declare the same global types (like NodeJS namespace) with different definitions. Duplicate @types packages are the most common cause.