Type Safety

subroutine — type-safety discipline

Apply this to every TypeScript file. Read the nearest AGENTS.md first; the repo wins when it defines a stricter or different convention.

Prove types; do not silence the checker

• Never use any, as T, or non-null !. Narrow unknown, parse structured external data with the repo's schema library, and handle absence explicitly.
• Do not add lint disables to bypass these rules. A difficult type usually exposes a missing boundary or an imprecise model.
• as const is allowed for literals. Use satisfies when checking an object's shape without widening its inferred values.

const config = {
  mode: "strict",
  retries: 3,
} satisfies WorkerConfig;

const first = rows[0];
if (!first) return err({ code: "NOT_FOUND" });
return ok(first);

Let inference work

• Annotate exported API signatures and intentional boundaries; let local variables and callbacks infer.
• Derive types from their source (z.infer, Awaited<ReturnType<...>>, indexed access) instead of redeclaring the same shape.

Model finite states explicitly

• Prefer string-literal unions to TypeScript enum.
• Expose named value sets as object-as-const when callers need symbolic access.
• Match discriminated unions with more than two variants using ts-pattern .exhaustive().

export const JOB_STATUS = {
  idle: "idle",
  running: "running",
  failed: "failed",
} as const;
export type JobStatus = (typeof JOB_STATUS)[keyof typeof JOB_STATUS];

const label = match(status)
  .with("idle", () => "Idle")
  .with("running", () => "Running")
  .with("failed", () => "Failed")
  .exhaustive();

When using Drizzle/Postgres, prefer a typed text column plus boundary validation to pgEnum; database enum migrations make removal and renaming unnecessarily rigid. Skip this rule when the repository deliberately standardizes otherwise.