fix(cache): update LastAccess on file cache hit to prevent stale entries

internal/cache/file_cache.go

@@ -148,6 +148,17 @@ func (c *FileCache) Get(path string) (*FileEntry, bool) {
 		return entry, true
 	}
 
+	// 更新近似 LRU 访问时间（每 5 秒或超过 10% inactive 间隔才写，减少锁竞争）
+	const accessUpdateInterval = 5 * time.Second
+	if time.Since(entry.LastAccess) > accessUpdateInterval {
+		c.mu.Lock()
+		if e, ok := c.entries[path]; ok && e == entry {
+			e.LastAccess = time.Now()
+			c.lruList.MoveToFront(e.element)
+		}
+		c.mu.Unlock()
+	}
+
 	// 近似 LRU: 不更新 LastAccess/LRU 位置，直接返回
 	// 精确 LRU 由 Set/Delete/evict 操作保证
 	return entry, true

internal/cache/file_cache_test.go

@@ -0,0 +1,24 @@
+// Package cache 提供文件缓存功能测试。
+package cache
+
+import (
+	"testing"
+	"time"
+)
+
+func TestFileCacheLastAccessUpdatedOnHit(t *testing.T) {
+	c := NewFileCache(1, 1<<20, 10*time.Second)
+	c.Set("/x", []byte("data"), 4, time.Now(), "text/plain")
+
+	entry := c.entries["/x"]
+	before := entry.LastAccess
+	// 将访问时间设为过去，确保超过 accessUpdateInterval 阈值但不超过 inactive
+	entry.LastAccess = before.Add(-7 * time.Second)
+
+	c.Get("/x")
+	after := c.entries["/x"].LastAccess
+
+	if !after.After(before) {
+		t.Fatal("LastAccess was not updated on cache hit")
+	}
+}