fix(linuxfs): treat the bridge session's stand-in render node as KGSL in the DRM preload

SessionService already exports BL_DRM_STANDIN for Mali bridge sessions; the
preload now honours it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/linuxfs/preload/drm.c

@@ -42,7 +42,9 @@ static int is_kgsl(int fd) {
   struct stat st;
   pthread_mutex_lock(&lock);
   if (kgsl_state == 0) {
-    kgsl_state = stat("/dev/kgsl-3d0", &st) == 0 ? 1 : -1;
+    /* KGSL, or the device the Mali bridge's session names as its render node (BL_DRM_STANDIN). */
+    const char *standin = getenv("BL_DRM_STANDIN");
+    kgsl_state = stat("/dev/kgsl-3d0", &st) == 0 || (standin && *standin && stat(standin, &st) == 0) ? 1 : -1;
     kgsl_dev = st.st_rdev;
   }
   pthread_mutex_unlock(&lock);