debugui: fix hit testing for collapsed windows

Restrict collapsed window hit testing to the title bar so exposed
windows can receive input and move to the front. Share the visible
bounds calculation with input capture detection to track moved titles.

Closes #55

Co-Authored-By: Codex <noreply@openai.com>

Author: hajimehoshi

container.go

@@ -369,14 +369,21 @@ func (c *Context) bringToFront(cnt *container) {
 
 func (c *Context) hoveringRootContainer() *container {
 	p := c.pointingPosition()
-	for i := len(c.rootContainers) - 1; i >= 0; i-- {
-		cnt := c.rootContainers[i]
+	for _, cnt := range slices.Backward(c.rootContainers) {
 		if !cnt.open {
 			continue
 		}
-		if p.In(cnt.layout.Bounds) {
+		if p.In(cnt.visibleBounds(c.style().titleHeight)) {
 			return cnt
 		}
 	}
 	return nil
 }
+
+func (c *container) visibleBounds(titleHeight int) image.Rectangle {
+	bounds := c.layout.Bounds
+	if c.collapsed {
+		bounds.Max.Y = bounds.Min.Y + titleHeight
+	}
+	return bounds
+}

context.go

@@ -113,11 +113,7 @@ func (c *Context) update(f func(ctx *Context) error) (inputCapturingState InputC
 	// Check whether the cursor is on any of the root containers.
 	pt := c.pointingPosition()
 	for _, cnt := range c.rootContainers {
-		bounds := cnt.layout.Bounds
-		if cnt.collapsed {
-			bounds.Max.Y = cnt.layout.BodyBounds.Min.Y
-		}
-		if pt.In(bounds) {
+		if pt.In(cnt.visibleBounds(c.style().titleHeight)) {
 			inputCapturingState |= InputCapturingStateHover
 		}
 	}