refactor(errors): migrate decisions to {code,msg}

lib/errors.ts

@@ -0,0 +1,20 @@
+export type ApiError = { code: number; msg: string }
+
+export type ApiDecision = { ok: true } | { ok: false; error: ApiError }
+
+export function isApiError(value: unknown): value is ApiError {
+  if (typeof value !== "object" || value === null) return false
+
+  const v = value as { code?: unknown; msg?: unknown }
+  return typeof v.code === "number" && typeof v.msg === "string"
+}
+
+export function toApiError(err: unknown): ApiError {
+  if (isApiError(err)) return err
+  if (err instanceof Error) return { code: 500, msg: err.message }
+  if (typeof err === "string") return { code: 500, msg: err }
+
+  return { code: 500, msg: "Unknown error" }
+}
+
+export type ApiResult<T> = { ok: true; data: T } | { ok: false; error: ApiError }