Use local go cache/mod in build.sh and check gtk3 dev

cmd/gtkplayer/main.go

@@ -72,7 +72,7 @@ func newPane() *pane {
 		}
 		p.mpv = mpv
 
-		if w, ok := da.GetWindow(); ok && w != nil {
+		if w, err := da.GetWindow(); err == nil && w != nil {
 			if xid := getWindowID(w); xid != 0 {
 				_ = mpv.SetWID(xid)
 			}
@@ -215,4 +215,3 @@ func getWindowID(w *gdk.Window) uint64 {
 func gdkWindowGetXID(w *gdk.Window) uint {
 	return uint(w.GetXID())
 }
-

scripts/build-linux.sh

@@ -6,6 +6,10 @@ set -e
 
 PROJECT_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 BUILD_OUTPUT="$PROJECT_ROOT/vt_player"
+CACHE_ROOT="$PROJECT_ROOT/.cache"
+mkdir -p "$CACHE_ROOT/go-build" "$CACHE_ROOT/go-mod"
+export GOCACHE="$CACHE_ROOT/go-build"
+export GOMODCACHE="$CACHE_ROOT/go-mod"
 
 echo "════════════════════════════════════════════════════════════════"
 echo "  VT_Player Build Script"
@@ -42,6 +46,10 @@ fi
 if ! pkg-config --exists gl 2>/dev/null; then
     MISSING_DEPS+=("mesa-libGL-devel")
 fi
+# GTK for embedded player surface
+if ! pkg-config --exists gtk+-3.0 2>/dev/null; then
+    MISSING_DEPS+=("gtk3-devel/gtk-3-dev")
+fi
 # Runtime dependency: mpv
 if ! command -v mpv >/dev/null 2>&1; then
     MISSING_DEPS+=("mpv")