improve: address remaining code review findings

1. Lazy initialize FilerClient in mount for proxy-only setups
   - Only create FilerClient when VolumeServerAccess != "filerProxy"
   - Avoids wasted work when all reads proxy through filer
   - filerClient is nil for proxy mode, initialized for direct access

2. Fix inaccurate deprecation comment in filer.LookupFn
   - Updated comment to reflect current behavior (10k bounded cache)
   - Removed claim of "unbounded growth" after adding size limit
   - Still directs new code to wdclient.FilerClient for better features

3. Audit all MasterClient usages for KeepConnectedToMaster
   - Verified all production callers start KeepConnectedToMaster early
   - Filer, Shell, Master, Broker, Benchmark, Admin all correct
   - IAM creates MasterClient but never uses it (harmless)
   - Test code doesn't need KeepConnectedToMaster (mocks)

All callers properly follow the initialization pattern documented in
GetMaster(), preventing unexpected blocking or timeouts.

weed/filer/reader_at.go

@@ -28,11 +28,11 @@ var _ = io.Closer(&ChunkReadAt{})
 
 // LookupFn creates a basic volume location lookup function with simple caching.
 //
-// DEPRECATED: This function has several limitations:
-//   - Unbounded cache growth (no eviction or size limit)
-//   - No TTL for stale entries
-//   - No singleflight deduplication
-//   - No cache history for volume moves
+// DEPRECATED: This function has several limitations compared to wdclient.FilerClient:
+//   - Simple bounded cache (10k entries, no eviction policy or TTL for stale entries)
+//   - No singleflight deduplication (concurrent requests for same volume will duplicate work)
+//   - No cache history for volume moves (no fallback chain when volumes migrate)
+//   - No high availability (single filer address, no automatic failover)
 //
 // For NEW code, especially mount operations, use wdclient.FilerClient instead:
 //   filerClient := wdclient.NewFilerClient(filerAddresses, grpcDialOption, dataCenter, opts)

weed/mount/weedfs.go

@@ -101,6 +101,10 @@ type WFS struct {
 }
 
 func NewSeaweedFileSystem(option *Option) *WFS {
+	// Only create FilerClient for direct volume access modes
+	// When VolumeServerAccess == "filerProxy", all reads go through filer, so no volume lookup needed
+	var filerClient *wdclient.FilerClient
+	if option.VolumeServerAccess != "filerProxy" {
 		// Create FilerClient for efficient volume location caching
 		// Pass all filer addresses for high availability with automatic failover
 		// Configure URL preference based on VolumeServerAccess option
@@ -111,12 +115,13 @@ func NewSeaweedFileSystem(option *Option) *WFS {
 			}
 		}
 
-	filerClient := wdclient.NewFilerClient(
+		filerClient = wdclient.NewFilerClient(
 			option.FilerAddresses, // Pass all filer addresses for HA
 			option.GrpcDialOption,
 			option.DataCenter,
 			opts,
 		)
+	}
 
 	wfs := &WFS{
 		RawFileSystem: fuse.NewDefaultRawFileSystem(),
@@ -125,7 +130,7 @@ func NewSeaweedFileSystem(option *Option) *WFS {
 		inodeToPath:   NewInodeToPath(util.FullPath(option.FilerMountRootPath), option.CacheMetaTTlSec),
 		fhMap:         NewFileHandleToInode(),
 		dhMap:         NewDirectoryHandleToInode(),
-		filerClient:   filerClient,
+		filerClient:   filerClient, // nil for proxy mode, initialized for direct access
 		fhLockTable:   util.NewLockTable[FileHandleId](),
 	}