typescript-conventions

strict: true + noUncheckedIndexedAccess in tsconfig, never any — use unknown with type guards.
ESM imports only, const over let, as const for literals, interface over type for objects.
import type for type-only imports to avoid runtime overhead. Discriminated unions for type-safe state.
Formatting/linting: a formatter + linter (e.g., Prettier + ESLint, or Biome). Type checking: tsc --noEmit in CI.
Testing: a fast test runner (e.g., Vitest or Jest), 80%+ coverage. Runtime validation at system boundaries with a schema validator (e.g., Zod).
Error handling: discriminated unions for expected errors, throw only for unexpected.
Package manager: a lockfile-based package manager (npm, pnpm, or yarn) with the lockfile committed, build: a bundler (e.g., tsup or esbuild).
Monorepo: workspace protocol (workspace:*), shared tsconfig base, a workspace manifest (e.g., pnpm-workspace.yaml).
Node.js: node: prefix for core modules, fetch over axios.
Security: npm audit/pnpm audit for dependency CVE scanning. Zero tolerance for critical/high vulnerabilities.
Anti-patterns: non-null assertions (!), type assertions (as), enum (use unions), @ts-ignore.

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