Upgrade MyGo to v0.5.5

MyGo v0.5.5 returns ui.Element as a checked value handle instead of a
pointer. Migrated with `mygo migrate-ui`, then fixed what the codemod
leaves to review:

- Element nil checks become .Valid(); absent elements are ui.Element{}.
- Input handlers and paint callbacks run outside the build pass, where
  elements expire and Context methods are inert: read IsDisabled into a
  local during the build, keep a ui.Handle for Focus, use c.Services()
  for clipboard access, create ui.Local state during the build.
- Add core.AutoFocus: v0.5.5 records an overlay's opener after its
  content builds, so same-frame autofocus lost focus restore on close.
  It focuses one frame later; cascader rows defer their focus likewise.
- core.OverlayLayer identifies build passes by the root element, not
  c.Now(), which repeats across passes and under the Tester clock.
- Context menus survive the opening press counted as PressedOutside;
  split button tooltip no longer reorders its open menu; disabled
  menubar rows pass presses to the panel; Form defers blur-started
  async checks so the growing message no longer moves Submit away
  from the release; Combobox drops its disabled copy now that MyGo
  blocks typing under a disabled wrapper (canary flipped to a guard).
- The Tester clock is virtual: tests use Advance/Now instead of
  time.Sleep/time.Now and read element state inside the view. The web
  mirror advances the clock to wall time before each frame and input.
- AGENTS.md and docs describe the value Element API and the new pin.

Snapshot goldens are darwin-only and were not re-verified here.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

layout/app_shell.go

@@ -28,7 +28,7 @@ type AppShellOptions struct {
 
 // AppShellResult is an AppShell and its event in this frame.
 type AppShellResult struct {
-	Element *ui.Element
+	Element ui.Element
 	// Toggled reports the sidebar opened or collapsed.
 	Toggled bool
 }

layout/aspect_ratio.go

@@ -13,7 +13,7 @@ type AspectRatioOptions struct {
 }
 
 // AspectRatio centers the largest Ratio frame that fits; the child is centered, not stretched.
-func AspectRatio(c *ui.Context, opts AspectRatioOptions, child func()) *ui.Element {
+func AspectRatio(c *ui.Context, opts AspectRatioOptions, child func()) ui.Element {
 	if opts.Ratio < 0 {
 		panic("mujica: AspectRatio Ratio must be positive")
 	}

layout/container.go

@@ -62,7 +62,7 @@ type ContainerOptions struct {
 }
 
 // Container pads its children, caps their width and can center, fill and clip.
-func Container(c *ui.Context, opts ContainerOptions, children func()) *ui.Element {
+func Container(c *ui.Context, opts ContainerOptions, children func()) ui.Element {
 	if opts.MaxWidth < 0 {
 		panic("mujica: Container MaxWidth must not be negative")
 	}

layout/divider.go

@@ -22,7 +22,7 @@ type DividerOptions struct {
 }
 
 // Divider is a thin separating line. It never takes focus and its ornament is not read out.
-func Divider(c *ui.Context, opts DividerOptions) *ui.Element {
+func Divider(c *ui.Context, opts DividerOptions) ui.Element {
 	if opts.Vertical && opts.Label != "" {
 		panic("mujica: a vertical Divider cannot have a Label")
 	}

layout/grid.go

@@ -19,7 +19,7 @@ type GridOptions struct {
 }
 
 // Grid lays children out in columns and rows; GridCell places and spans them.
-func Grid(c *ui.Context, opts GridOptions, children func()) *ui.Element {
+func Grid(c *ui.Context, opts GridOptions, children func()) ui.Element {
 	if children == nil {
 		panic("mujica: Grid needs children")
 	}
@@ -48,7 +48,7 @@ type GridCellOptions struct {
 }
 
 // GridCell is one child of a Grid, placed and spanned by opts; build makes one element, stretched over the cell.
-func GridCell(c *ui.Context, opts GridCellOptions, build func()) *ui.Element {
+func GridCell(c *ui.Context, opts GridCellOptions, build func()) ui.Element {
 	if build == nil {
 		panic("mujica: GridCell needs build")
 	}
@@ -59,7 +59,7 @@ func GridCell(c *ui.Context, opts GridCellOptions, build func()) *ui.Element {
 		panic("mujica: GridCell spans must be positive, or -1 for the rest")
 	}
 	// A one-track grid stretches its child over the whole cell, as the grid does its own children.
-	e := ui.Grid(c).Columns(1).Rows(1)
+	e := ui.Grid(c).Columns(1).GridRows(1)
 	if opts.Column > 0 {
 		e.ColumnStart(opts.Column)
 	}

layout/scroll_area.go

@@ -24,11 +24,11 @@ type ScrollAreaOptions struct {
 }
 
 // ScrollArea scrolls children; state keeps and sets the offset, nil keeps it by place.
-func ScrollArea(c *ui.Context, state *ui.ScrollState, opts ScrollAreaOptions, children func()) *ui.Element {
+func ScrollArea(c *ui.Context, state *ui.ScrollState, opts ScrollAreaOptions, children func()) ui.Element {
 	if children == nil {
 		panic("mujica: ScrollArea needs children")
 	}
-	var e *ui.Element
+	var e ui.Element
 	switch opts.Direction {
 	case ScrollVertical:
 		e = ui.Scroll(c)

layout/split_pane.go

@@ -40,7 +40,7 @@ type SplitPaneOptions struct {
 
 // SplitPaneResult is a SplitPane and its events in this frame.
 type SplitPaneResult struct {
-	Element *ui.Element
+	Element ui.Element
 	Resized bool
 	Toggled bool
 }
@@ -80,7 +80,7 @@ func SplitPane(c *ui.Context, state *SplitPaneState, opts SplitPaneOptions, firs
 	var res SplitPaneResult
 	e.Children(func() {
 		// Sizes come from this inner box: the caller's border and padding stay outside it.
-		in := ui.Row(c).Key("in").Grow(1).MinWidth(0).AlignItems(ui.Stretch)
+		in := ui.Row(c.Key("in")).Grow(1).MinWidth(0).AlignItems(ui.Stretch)
 		if opts.Vertical {
 			in.Column().MinHeight(0)
 		}
@@ -94,7 +94,7 @@ func SplitPane(c *ui.Context, state *SplitPaneState, opts SplitPaneOptions, firs
 }
 
 // splitPaneBuild lays the panes, divider and drag handle out in the inner box in.
-func splitPaneBuild(c *ui.Context, in *ui.Element, state *SplitPaneState, opts SplitPaneOptions, lo, minSecond float32, res *SplitPaneResult, first, second func()) {
+func splitPaneBuild(c *ui.Context, in ui.Element, state *SplitPaneState, opts SplitPaneOptions, lo, minSecond float32, res *SplitPaneResult, first, second func()) {
 	k := core.Tokens(c)
 	u := core.Density(c).Unit()
 	was := in.Bounds()
@@ -123,7 +123,7 @@ func splitPaneBuild(c *ui.Context, in *ui.Element, state *SplitPaneState, opts S
 	}
 	firstShown := !(state.Collapsed && opts.Collapsible == SplitPaneFirst)
 	secondShown := !(state.Collapsed && opts.Collapsible == SplitPaneSecond)
-	along := func(el *ui.Element, v float32) {
+	along := func(el ui.Element, v float32) {
 		if opts.Vertical {
 			el.Height(v)
 		} else {
@@ -132,7 +132,7 @@ func splitPaneBuild(c *ui.Context, in *ui.Element, state *SplitPaneState, opts S
 	}
 	in.Children(func() {
 		if firstShown {
-			a := ui.Box(c).Key("first").Shrink(0).Clip()
+			a := ui.Box(c.Key("first")).Shrink(0).Clip()
 			switch {
 			case !secondShown:
 				a.Grow(1).Shrink(1)
@@ -145,7 +145,7 @@ func splitPaneBuild(c *ui.Context, in *ui.Element, state *SplitPaneState, opts S
 			}
 			a.Children(first)
 		}
-		div := ui.Box(c).Key("divider").Shrink(0).Focusable().FocusRing(false).Role(ui.RoleSplitter).Label(core.Msg(c, "split_pane.divider"))
+		div := ui.Box(c.Key("divider")).Shrink(0).Focusable().FocusRing(false).Role(ui.RoleSplitter).Label(core.Msg(c, "split_pane.divider"))
 		along(div, theme.BorderWidth)
 		if state.Collapsed {
 			div.Description(core.Msg(c, "split_pane.collapsed"))
@@ -154,7 +154,7 @@ func splitPaneBuild(c *ui.Context, in *ui.Element, state *SplitPaneState, opts S
 		}
 		splitPaneKeys(c, div, state, opts, lo, hi, u, resize, toggle)
 		if secondShown {
-			b := ui.Box(c).Key("second").Grow(1).Shrink(1).Clip()
+			b := ui.Box(c.Key("second")).Grow(1).Shrink(1).Clip()
 			if opts.Vertical {
 				b.MinHeight(0)
 			} else {
@@ -170,7 +170,7 @@ func splitPaneBuild(c *ui.Context, in *ui.Element, state *SplitPaneState, opts S
 			at = total - theme.BorderWidth
 		}
 		grip := 1.5 * u
-		handle := ui.Box(c).Key("handle").Absolute()
+		handle := ui.Box(c.Key("handle")).Absolute()
 		if opts.Vertical {
 			handle.Left(0).Right(0).Top(at - (grip-1)/2).Height(grip).Cursor(ui.CursorResizeNS)
 		} else {
@@ -238,7 +238,7 @@ func splitPaneFollow(state *SplitPaneState, opts SplitPaneOptions, want, lo, min
 }
 
 // splitPaneKeys moves the divider with the arrows, Home and End, and toggles the collapsible pane with Enter.
-func splitPaneKeys(c *ui.Context, div *ui.Element, state *SplitPaneState, opts SplitPaneOptions, lo, hi, u float32, resize func(float32), toggle func()) {
+func splitPaneKeys(c *ui.Context, div ui.Element, state *SplitPaneState, opts SplitPaneOptions, lo, hi, u float32, resize func(float32), toggle func()) {
 	back, forth := ui.KeyLeft, ui.KeyRight
 	if opts.Vertical {
 		back, forth = ui.KeyUp, ui.KeyDown

layout/stack.go

@@ -31,7 +31,7 @@ type StackOptions struct {
 }
 
 // Stack arranges children in a row or column. A child not built takes no room and no gap.
-func Stack(c *ui.Context, opts StackOptions, children func()) *ui.Element {
+func Stack(c *ui.Context, opts StackOptions, children func()) ui.Element {
 	if children == nil {
 		panic("mujica: Stack needs children")
 	}

layout/status_bar.go

@@ -47,7 +47,7 @@ type StatusBarOptions struct {
 
 // StatusBarResult is a StatusBar and its event in this frame.
 type StatusBarResult struct {
-	Element *ui.Element
+	Element ui.Element
 	// Clicked is the ID of the action item clicked, or empty.
 	Clicked string
 }
@@ -86,7 +86,7 @@ func StatusBar(c *ui.Context, opts StatusBarOptions) StatusBarResult {
 		return hasFocus
 	}
 	group := func(key string, items []StatusItem) {
-		ui.Row(c).Key(key).Gap(gap).Shrink(0).Dividers(theme.BorderWidth, k.Border).Children(func() {
+		ui.Row(c.Key(key)).Gap(gap).Shrink(0).Dividers(theme.BorderWidth, k.Border).Children(func() {
 			for _, it := range items {
 				if !hidden[it.ID] && item(it) {
 					*focused = it.ID
@@ -96,7 +96,7 @@ func StatusBar(c *ui.Context, opts StatusBarOptions) StatusBarResult {
 	}
 	e.Children(func() {
 		group("status_bar.left", opts.Left)
-		ui.Spacer(c).Key("status_bar.spacer")
+		ui.Spacer(c.Key("status_bar.spacer"))
 		if len(hidden) > 0 {
 			more := statusBarMore(c, len(hidden))
 			if wasFocused != "" && hidden[wasFocused] {
@@ -108,7 +108,7 @@ func StatusBar(c *ui.Context, opts StatusBarOptions) StatusBarResult {
 				slog.Debug("mujica: status_bar hidden items", "open", *open)
 			}
 			if *open {
-				ui.PopoverBase(c, more, open, func(panel *ui.Element) {
+				ui.PopoverBase(c, more, open, func(panel ui.Element) {
 					core.OverlayStyle(c, panel, core.OverlayEnter(c, panel))
 					panel.Margin(d.Unit(), 0, 0, 0).Padding(d.Unit()).Gap(d.Unit()).AlignItems(ui.Stretch)
 					for _, it := range statusBarAll(opts) {
@@ -126,9 +126,9 @@ func StatusBar(c *ui.Context, opts StatusBarOptions) StatusBarResult {
 }
 
 // statusBarMore is the "+N" button that opens the hidden items.
-func statusBarMore(c *ui.Context, n int) *ui.Element {
+func statusBarMore(c *ui.Context, n int) ui.Element {
 	k := core.Tokens(c)
-	b := ui.ButtonBase(c).Key("status_bar.more").MinHeight(theme.MinHitSize).MinWidth(theme.MinHitSize).
+	b := ui.ButtonBase(c.Key("status_bar.more")).MinHeight(theme.MinHitSize).MinWidth(theme.MinHitSize).
 		PaddingX(core.Density(c).Unit()).Radius(theme.ControlRadius).TextColor(k.Text).
 		Label(fmt.Sprintf(core.Msg(c, "status_bar.hidden"), n))
 	internal.Ring(b, k.Focus, theme.ControlRadius)
@@ -248,9 +248,9 @@ func statusBarItem(c *ui.Context, it StatusItem) (clicked, focused bool) {
 	default:
 		panic("mujica: invalid StatusItemTone")
 	}
-	var e *ui.Element
+	var e ui.Element
 	if it.Action {
-		e = ui.ButtonBase(c).Key(it.ID).MinHeight(theme.MinHitSize).MinWidth(theme.MinHitSize).Radius(theme.ControlRadius)
+		e = ui.ButtonBase(c.Key(it.ID)).MinHeight(theme.MinHitSize).MinWidth(theme.MinHitSize).Radius(theme.ControlRadius)
 		internal.Ring(e, k.Focus, theme.ControlRadius)
 		if e.Pressed() {
 			e.Background(k.Selection)
@@ -258,7 +258,7 @@ func statusBarItem(c *ui.Context, it StatusItem) (clicked, focused bool) {
 			e.Background(k.SurfaceHover)
 		}
 	} else {
-		e = ui.Row(c).Key(it.ID).MinHeight(theme.MinHitSize)
+		e = ui.Row(c.Key(it.ID)).MinHeight(theme.MinHitSize)
 	}
 	e.PaddingX(d.Unit()).Gap(d.Unit()).TextColor(fg).Shrink(0)
 	if it.Label != "" {

layout/title_bar.go

@@ -16,7 +16,7 @@ type TitleBarOptions struct {
 }
 
 // TitleBar is a window title row that drags the window and clears the system buttons.
-func TitleBar(c *ui.Context, title string, opts TitleBarOptions) *ui.Element {
+func TitleBar(c *ui.Context, title string, opts TitleBarOptions) ui.Element {
 	k := core.Tokens(c)
 	d := core.Density(c)
 	bar := c.TitleBar()