fix: harden cli credential sync

src/infra/json-file.ts

@@ -0,0 +1,21 @@
+import fs from "node:fs";
+import path from "node:path";
+
+export function loadJsonFile(pathname: string): unknown {
+  try {
+    if (!fs.existsSync(pathname)) return undefined;
+    const raw = fs.readFileSync(pathname, "utf8");
+    return JSON.parse(raw) as unknown;
+  } catch {
+    return undefined;
+  }
+}
+
+export function saveJsonFile(pathname: string, data: unknown) {
+  const dir = path.dirname(pathname);
+  if (!fs.existsSync(dir)) {
+    fs.mkdirSync(dir, { recursive: true, mode: 0o700 });
+  }
+  fs.writeFileSync(pathname, `${JSON.stringify(data, null, 2)}\n`, "utf8");
+  fs.chmodSync(pathname, 0o600);
+}