type-safetylisted

# 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. ```ts 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()`. ```ts export const JOB_STATUS = { idle: "idle", running: "running", failed: "failed", } as const; export type JobStatus = (typeof JOB_STATUS)[keyof typeof JOB_S