refactor: lint cleanups and helpers

src/infra/errors.ts

@@ -0,0 +1,26 @@
+export function extractErrorCode(err: unknown): string | undefined {
+  if (!err || typeof err !== "object") return undefined;
+  const code = (err as { code?: unknown }).code;
+  if (typeof code === "string") return code;
+  if (typeof code === "number") return String(code);
+  return undefined;
+}
+
+export function formatErrorMessage(err: unknown): string {
+  if (err instanceof Error) {
+    return err.message || err.name || "Error";
+  }
+  if (typeof err === "string") return err;
+  if (
+    typeof err === "number" ||
+    typeof err === "boolean" ||
+    typeof err === "bigint"
+  ) {
+    return String(err);
+  }
+  try {
+    return JSON.stringify(err);
+  } catch {
+    return Object.prototype.toString.call(err);
+  }
+}