Clean-code TypeScript (depth)

On top of the base rules (strict tsconfig, ESLint+Prettier, Vitest).

Types

• No any. Use unknown at boundaries and narrow. Prefer type aliases + discriminated unions for state over booleans/optionals.
• Model impossible states out of existence (a union, not many independent flags). Exhaustiveness-check unions with a never default in switch.
• Derive types from runtime schemas (zod/TypeBox) at IO boundaries — one source of truth, not parallel interface + validator.

Correctness

• strictNullChecks on; handle null/undefined explicitly, no ! non-null assertions outside tests.
• await every promise or handle it; no floating promises. Promise.all for independent async, not sequential awaits.
• Readonly by default (readonly, as const); immutable data flow.

Style

• Named exports over default (grep + refactor friendliness). Small modules; pure functions; early returns.
• Narrow function signatures — take exactly what's used, not the whole object.

Smells

• any or as SomeType casts → narrow or fix the type at the source.
• Booleans multiplying into impossible combinations → discriminated union.
• A validator and an interface that can drift → derive the type from the schema.