Deactivate alt modes on blur

src/components/Viewport.vue

@@ -329,11 +329,31 @@ function cleanupMouseHandlers() {
 function setupKeyboardHandlers() {
   window.addEventListener('keydown', onKeyDown)
   window.addEventListener('keyup', onKeyUp)
+  window.addEventListener('blur', onWindowBlur)
 }
 
 function cleanupKeyboardHandlers() {
   window.removeEventListener('keydown', onKeyDown)
   window.removeEventListener('keyup', onKeyUp)
+  window.removeEventListener('blur', onWindowBlur)
+}
+
+function onWindowBlur() {
+  // Reset all modifier states when window loses focus
+  // This prevents "stuck" modifiers when user alt-tabs or switches tabs
+  const needsUpdate =
+    isCtrlPressed || isShiftPressed || isAltPressed || isSpacePressed || isMiddleMouseDown
+
+  isCtrlPressed = false
+  isShiftPressed = false
+  isAltPressed = false
+  isSpacePressed = false
+  isMiddleMouseDown = false
+  controls.enabled = false
+
+  if (needsUpdate) {
+    updateGizmoVisibility()
+  }
 }
 
 function onKeyDown(event: KeyboardEvent) {