perf(gateway): cache stable plugin index fingerprints

src/plugins/installed-plugin-index-record-reader.ts

@@ -1,3 +1,4 @@
+import crypto from "node:crypto";
 import fs from "node:fs";
 import path from "node:path";
 import type { PluginInstallRecord } from "../config/types.plugins.js";
@@ -239,8 +240,9 @@ const installRecordsCache = new Map<string, InstallRecordsCacheEntry>();
 
 function readFileSignature(filePath: string): string {
   try {
-    const stat = fs.statSync(filePath);
-    return `${stat.mtimeMs}:${stat.size}`;
+    const stat = fs.statSync(filePath, { bigint: true });
+    const hash = crypto.createHash("sha256").update(fs.readFileSync(filePath)).digest("base64url");
+    return `${stat.mtimeNs}:${stat.ctimeNs}:${stat.size}:${hash}`;
   } catch {
     return "missing";
   }