TypeScript Code Style Guide

Types and Type Safety

Avoid explicit type annotations when TypeScript can infer
Avoid implicitly any; explicitly type when necessary
Use accurate types: prefer Record<PropertyKey, unknown> over object or any
Prefer interface for object shapes (e.g., React props); use type for unions/intersections
Prefer as const satisfies XyzInterface over plain as const
Prefer @ts-expect-error over @ts-ignore over as any
Avoid meaningless null/undefined parameters; design strict function contracts
Prefer ES module augmentation (declare module '...') over namespace; do not introduce namespace-based extension patterns
When a type needs extensibility, expose a small mergeable interface at the source type and let each feature/plugin augment it locally instead of centralizing all extension fields in one registry file
For package-local extensibility patterns like PipelineContext.metadata, define the metadata fields next to the processor/provider/plugin that reads or writes them

Async-first for IO: new IO code (fs, child_process, etc.) must use async APIs at its boundaries — use promise-based variants like import { readFile } from 'fs/promises', never *Sync by default. Function coloring is asymmetric: async→sync migration is never needed, while sync→async (when IO gets slower, gains concurrency, or grows a subprocess/network call) forces rewriting every caller up the chain — sync-first debt that compounds. Micro-costs of async (thread-pool dispatch, cache races) are not valid reasons: races are solved by caching the promise instead of the result
*Sync is acceptable in exactly one place: call sites locked inside a synchronous contract you don't control — an existing sync signature chain (don't virally refactor a legacy sync chain in a bugfix, but new standalone modules must not extend such chains), or sync-only callbacks like process.on('exit'). Module-load-time and CLI startup init are NOT exceptions — use top-level await (ESM) there