refactor(core): dedupe shared config and runtime helpers

src/plugin-sdk/json-store.ts

@@ -0,0 +1,35 @@
+import crypto from "node:crypto";
+import fs from "node:fs";
+import path from "node:path";
+import { safeParseJson } from "../utils.js";
+
+export async function readJsonFileWithFallback<T>(
+  filePath: string,
+  fallback: T,
+): Promise<{ value: T; exists: boolean }> {
+  try {
+    const raw = await fs.promises.readFile(filePath, "utf-8");
+    const parsed = safeParseJson<T>(raw);
+    if (parsed == null) {
+      return { value: fallback, exists: true };
+    }
+    return { value: parsed, exists: true };
+  } catch (err) {
+    const code = (err as { code?: string }).code;
+    if (code === "ENOENT") {
+      return { value: fallback, exists: false };
+    }
+    return { value: fallback, exists: false };
+  }
+}
+
+export async function writeJsonFileAtomically(filePath: string, value: unknown): Promise<void> {
+  const dir = path.dirname(filePath);
+  await fs.promises.mkdir(dir, { recursive: true, mode: 0o700 });
+  const tmp = path.join(dir, `${path.basename(filePath)}.${crypto.randomUUID()}.tmp`);
+  await fs.promises.writeFile(tmp, `${JSON.stringify(value, null, 2)}\n`, {
+    encoding: "utf-8",
+  });
+  await fs.promises.chmod(tmp, 0o600);
+  await fs.promises.rename(tmp, filePath);
+}