fix: persist topic session files

src/config/cache-utils.ts

@@ -0,0 +1,27 @@
+import fs from "node:fs";
+
+export function resolveCacheTtlMs(params: {
+  envValue: string | undefined;
+  defaultTtlMs: number;
+}): number {
+  const { envValue, defaultTtlMs } = params;
+  if (envValue) {
+    const parsed = Number.parseInt(envValue, 10);
+    if (Number.isFinite(parsed) && parsed >= 0) {
+      return parsed;
+    }
+  }
+  return defaultTtlMs;
+}
+
+export function isCacheEnabled(ttlMs: number): boolean {
+  return ttlMs > 0;
+}
+
+export function getFileMtimeMs(filePath: string): number | undefined {
+  try {
+    return fs.statSync(filePath).mtimeMs;
+  } catch {
+    return undefined;
+  }
+}