feat: add atomic JSON file state persistence for production runtime

src/lib/state-store.js

@@ -0,0 +1,37 @@
+"use strict";
+
+const fs = require("node:fs/promises");
+const path = require("node:path");
+
+class JsonFileStateStore {
+  constructor(filePath) {
+    this.filePath = filePath;
+  }
+
+  async load() {
+    try {
+      const raw = await fs.readFile(this.filePath, "utf8");
+      return JSON.parse(raw);
+    } catch (error) {
+      if (error && error.code === "ENOENT") {
+        return null;
+      }
+      throw error;
+    }
+  }
+
+  async save(state) {
+    const dir = path.dirname(this.filePath);
+    await fs.mkdir(dir, { recursive: true });
+
+    const tempPath = `${this.filePath}.tmp`;
+    const payload = JSON.stringify(state, null, 2);
+
+    await fs.writeFile(tempPath, payload, "utf8");
+    await fs.rename(tempPath, this.filePath);
+  }
+}
+
+module.exports = {
+  JsonFileStateStore,
+};