GTK action menu opens at button row, not below it (engine-drawn migration regression)

[JDonaghy]

Problem

After #395/PR #427 migrated the editor tab bar … action menu from native gtk4::PopoverMenu to the engine-drawn quadraui ContextMenu path, the menu opens at the row of the … button, overlapping the tab bar, instead of sitting below the button.

Root cause

src/gtk/click.rs:324-329:

ClickTarget::ActionMenuButton(group_id) => {
    let col = (x / char_width.max(1.0)) as u16;
    let row = (y / line_height.max(1.0)) as u16;
    engine.open_editor_action_menu(group_id, col, row);
    ...
}

The (col, row) derived here is the click point itself — i.e. the cell at which the user clicked the … button. This becomes screen_x / screen_y on ContextMenuState, then cm.screen_col * char_width / cm.screen_row * line_height as the anchor pixel coords in src/gtk/draw.rs:1955-1956.

src/render.rs::context_menu_panel_to_quadraui_context_menu doesn't set placement, so quadraui defaults to ContextMenuPlacement::AnchorPoint, which puts the menu's top-left at the anchor. Result: menu top-left == click position, so the menu starts at the button row and extends downward, overlapping the tab bar's first row.

Native popover behavior (pre-#395)

The native gtk4::PopoverMenu knew the trigger widget's bounds and auto-positioned itself just below the button. Migration lost that.

Fix options

1. (Preferred) Use ContextMenuPlacement::Below with the button's bounds. Engine-side change:

   • Extend open_editor_action_menu(group_id, x, y, height) (or similar) so the engine knows the trigger's height.
   • Adapter context_menu_panel_to_quadraui_context_menu sets placement = Below and calls layout_at(Rect::new(anchor_x, anchor_y, anchor_w, anchor_h), ...) in draw.rs.
   • Quadraui auto-flips to Above if there's no room below.
   • Platform-neutral; works for any future "menu-from-button" surface.

2. Quick hack: advance y by one cell in click.rs (let row = (y / line_height) as u16 + 1). 3-line GTK-only change but doesn't generalise.

Related

• Discovered during PR refactor: GTK action menu engine-drawn; drop dead right-click bodies (#395) #427 smoke testing.
• The bottom-bordered-row variant is tracked as a quadraui rasteriser bug at quadraui#205.
• Keyboard-focus-on-open variant is tracked separately (see related issue for context-menu keyboard nav).