fix: address session-store cache review feedback

src/config/cache-utils.ts

@@ -18,17 +18,18 @@ 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;
-  }
-}
+export type FileStatSnapshot = {
+  mtimeMs: number;
+  sizeBytes: number;
+};
 
-export function getFileSizeBytes(filePath: string): number | undefined {
+export function getFileStatSnapshot(filePath: string): FileStatSnapshot | undefined {
   try {
-    return fs.statSync(filePath).size;
+    const stats = fs.statSync(filePath);
+    return {
+      mtimeMs: stats.mtimeMs,
+      sizeBytes: stats.size,
+    };
   } catch {
     return undefined;
   }

src/config/sessions.cache.test.ts

@@ -220,12 +220,12 @@ describe("Session Store Cache", () => {
       "session:1": createSessionEntry({ sessionId: "id-1", displayName: "Original" }),
       "session:2": createSessionEntry({ sessionId: "id-2", displayName: "Added" }),
     };
+    const preWriteStat = fs.statSync(storePath);
     const json2 = JSON.stringify(store2, null, 2);
     fs.writeFileSync(storePath, json2);
 
     // Force mtime to match the cached value so only size differs
-    const stat = fs.statSync(storePath);
-    fs.utimesSync(storePath, stat.atime, stat.mtime);
+    fs.utimesSync(storePath, preWriteStat.atime, preWriteStat.mtime);
 
     // The cache should detect the size change and reload from disk
     const loaded2 = loadSessionStore(storePath);

src/config/sessions/store.ts

@@ -17,12 +17,7 @@ import {
   normalizeSessionDeliveryFields,
   type DeliveryContext,
 } from "../../utils/delivery-context.js";
-import {
-  getFileMtimeMs,
-  getFileSizeBytes,
-  isCacheEnabled,
-  resolveCacheTtlMs,
-} from "../cache-utils.js";
+import { getFileStatSnapshot, isCacheEnabled, resolveCacheTtlMs } from "../cache-utils.js";
 import { loadConfig } from "../config.js";
 import type { SessionMaintenanceConfig, SessionMaintenanceMode } from "../types.base.js";
 import { enforceSessionDiskBudget, type SessionDiskBudgetSweepResult } from "./disk-budget.js";
@@ -213,9 +208,11 @@ export function loadSessionStore(
   if (!opts.skipCache && isSessionStoreCacheEnabled()) {
     const cached = SESSION_STORE_CACHE.get(storePath);
     if (cached && isSessionStoreCacheValid(cached)) {
-      const currentMtimeMs = getFileMtimeMs(storePath);
-      const currentSizeBytes = getFileSizeBytes(storePath);
-      if (currentMtimeMs === cached.mtimeMs && currentSizeBytes === cached.sizeBytes) {
+      const currentFileStat = getFileStatSnapshot(storePath);
+      if (
+        currentFileStat?.mtimeMs === cached.mtimeMs &&
+        currentFileStat?.sizeBytes === cached.sizeBytes
+      ) {
         // Return a deep copy to prevent external mutations affecting cache
         return structuredClone(cached.store);
       }
@@ -230,7 +227,8 @@ export function loadSessionStore(
   // A short synchronous backoff (50 ms via `Atomics.wait`) is enough for the
   // writer to finish.
   let store: Record<string, SessionEntry> = {};
-  let mtimeMs = getFileMtimeMs(storePath);
+  let fileStat = getFileStatSnapshot(storePath);
+  let mtimeMs = fileStat?.mtimeMs;
   let serializedFromDisk: string | undefined;
   const maxReadAttempts = process.platform === "win32" ? 3 : 1;
   const retryBuf = maxReadAttempts > 1 ? new Int32Array(new SharedArrayBuffer(4)) : undefined;
@@ -247,7 +245,8 @@ export function loadSessionStore(
         store = parsed;
         serializedFromDisk = raw;
       }
-      mtimeMs = getFileMtimeMs(storePath) ?? mtimeMs;
+      fileStat = getFileStatSnapshot(storePath) ?? fileStat;
+      mtimeMs = fileStat?.mtimeMs;
       break;
     } catch {
       // File missing, locked, or transiently corrupt — retry on Windows.
@@ -295,7 +294,7 @@ export function loadSessionStore(
       loadedAt: Date.now(),
       storePath,
       mtimeMs,
-      sizeBytes: getFileSizeBytes(storePath),
+      sizeBytes: fileStat?.sizeBytes,
       serialized: serializedFromDisk,
     });
   }
@@ -664,7 +663,7 @@ function updateSessionStoreWriteCaches(params: {
   store: Record<string, SessionEntry>;
   serialized: string;
 }): void {
-  const mtimeMs = getFileMtimeMs(params.storePath);
+  const fileStat = getFileStatSnapshot(params.storePath);
   SESSION_STORE_SERIALIZED_CACHE.set(params.storePath, params.serialized);
   if (!isSessionStoreCacheEnabled()) {
     SESSION_STORE_CACHE.delete(params.storePath);
@@ -674,8 +673,8 @@ function updateSessionStoreWriteCaches(params: {
     store: structuredClone(params.store),
     loadedAt: Date.now(),
     storePath: params.storePath,
-    mtimeMs,
-    sizeBytes: getFileSizeBytes(params.storePath),
+    mtimeMs: fileStat?.mtimeMs,
+    sizeBytes: fileStat?.sizeBytes,
     serialized: params.serialized,
   });
 }