GlassMorphTrigger class

Wraps the widget a GlassModalSheet morphs out of, so the trigger can empty itself while the morph runs and take the hit when the droplet comes home.

The builder receives a GlassMorphAnchor to pass to GlassModalSheet.show as morphFrom:

GlassMorphTrigger(
  builder: (context, anchor) => GlassButton(
    onTap: () => GlassModalSheet.show(
      context: context,
      morphFrom: anchor,
      builder: (context) => const MySheetBody(),
    ),
    child: const Icon(CupertinoIcons.add),
  ),
)

While the sheet is presented the child paints nothing — the morph's anchor blob stands in for it, so the two never appear at once. When the droplet lands, the child is restored and this widget runs the rest of the closing bounce on its own ticker, so it keeps easing home after the presented route is gone. The button is tappable throughout that tail, exactly as GlassMenu's trigger is: grabbing it cancels the bounce and opens again.

Without this wrapper GlassModalSheet.show still morphs (pass morphFromRect), but it blooms from a point instead of stretching a teardrop, because the anchor blob would otherwise duplicate a trigger it cannot hide.