feat(map-editor): submenu support — View > Layers, Tools > Mode

One level of submenu nesting. View > Layers exposes all eight
terrain-stack layers as toggles, sharing state with the right-side
Layers panel. Tools > Mode mirrors the Mode-pill's auto/direct
toggle with a Tab hotkey shown on Direct. Submenu opens by clicking
the parent item; clicking elsewhere closes everything.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

init.lua

@@ -67,6 +67,7 @@ local state = (function()
         dirty           = false,
         picker_open     = false,            -- atlas+tile picker expanded? (legacy 0.1.0)
         menu_open         = nil,            -- 0.3.0: nil | <category_name> (e.g. "File")
+        submenu_open      = nil,            -- 0.3.0: label of the open submenu item within menu_open
         modal_open        = nil,            -- 0.3.0: nil | <modal_id>     (single-stack)
         show_layers_panel = true,           -- 0.3.0: Window > Layers Panel toggle
         show_palette      = true,           -- 0.3.0: Window > Palette toggle
@@ -149,7 +150,14 @@ local state = (function()
 
     function M.set_menu_open(name)      state.menu_open = name end
     function M.get_menu_open()          return state.menu_open end
-    function M.close_menu()             state.menu_open = nil end
+    function M.close_menu()
+        state.menu_open = nil
+        state.submenu_open = nil
+    end
+
+    function M.set_submenu_open(label)  state.submenu_open = label end
+    function M.get_submenu_open()       return state.submenu_open end
+    function M.close_submenu()          state.submenu_open = nil end
 
     function M.is_layers_panel_shown()  return state.show_layers_panel end
     function M.toggle_layers_panel()    state.show_layers_panel = not state.show_layers_panel end
@@ -200,6 +208,7 @@ local state = (function()
         state.snap_vertex = nil
         state.drag_paint = nil
         state.menu_open         = nil
+        state.submenu_open      = nil
         state.modal_open        = nil
         state.show_layers_panel = true
         state.show_palette      = true
@@ -511,6 +520,42 @@ local ui = (function()
         { type = "submenu", label = "Mode", items = nil },     -- populated in T10
     }
 
+    do
+        local layer_items = {}
+        for _, name in ipairs(LAYER_PANEL_ROWS) do
+            local layer_name = name
+            layer_items[#layer_items + 1] = {
+                type  = "toggle",
+                label = name,
+                is_on = function() return state.is_layer_visible(layer_name) end,
+                fire  = function() state.toggle_layer_visible(layer_name) end,
+            }
+        end
+        for _, it in ipairs(VIEW_ITEMS) do
+            if it.type == "submenu" and it.label == "Layers" then
+                it.items = layer_items
+                break
+            end
+        end
+    end
+
+    do
+        local mode_items = {
+            { type = "toggle", label = "Auto-Tile",
+              is_on = function() return mode_is("auto-tile") end,
+              fire  = function() actions.set_mode("auto-tile") end },
+            { type = "toggle", label = "Direct", hotkey = "Tab",
+              is_on = function() return mode_is("direct") end,
+              fire  = function() actions.set_mode("direct") end },
+        }
+        for _, it in ipairs(TOOLS_ITEMS) do
+            if it.type == "submenu" and it.label == "Mode" then
+                it.items = mode_items
+                break
+            end
+        end
+    end
+
     local WINDOW_ITEMS = {
         { type = "toggle", label = "Layers Panel",
           is_on = function() return state.is_layers_panel_shown() end,
@@ -768,6 +813,37 @@ local ui = (function()
             local hovered = in_rect(mx, my, row.x, row.y, row.w, row.h)
             draw_dropdown_item(row, hovered)
         end
+
+        -- Submenu render (one level deep)
+        local sub_label = state.get_submenu_open()
+        if sub_label then
+            for _, row in ipairs(dd.rows) do
+                local it = row.item
+                if it.type == "submenu" and it.label == sub_label and it.items then
+                    local sub_w = dropdown_width_for(it.items)
+                    local sub_x = dd.x + dd.w
+                    local sub_y = row.y
+                    local sub_h = 0
+                    for _, si in ipairs(it.items) do
+                        sub_h = sub_h + ((si.type == "separator") and 6 or DROPDOWN_ITEM_H)
+                    end
+                    sub_h = sub_h + DROPDOWN_PAD_Y * 2
+                    engine.render.draw_rect(sub_x, sub_y, sub_w, sub_h,
+                        rgba(COL_MODAL_BG, 0xFA))
+                    engine.render.draw_rect_lines(sub_x, sub_y, sub_w, sub_h,
+                        rgba(COL_MODAL_BORDER, 0xFF))
+                    local sy = sub_y + DROPDOWN_PAD_Y
+                    for _, si in ipairs(it.items) do
+                        local row_h = (si.type == "separator") and 6 or DROPDOWN_ITEM_H
+                        local sub_row = { item = si, x = sub_x, y = sy, w = sub_w, h = row_h }
+                        local hovered = in_rect(mx, my, sub_row.x, sub_row.y, sub_row.w, sub_row.h)
+                        draw_dropdown_item(sub_row, hovered)
+                        sy = sy + row_h
+                    end
+                    break
+                end
+            end
+        end
     end
 
     local function fire_item(it)
@@ -1215,7 +1291,9 @@ local ui = (function()
                         if button == "left" then
                             for _, row in ipairs(dd.rows) do
                                 if in_rect(mx, my, row.x, row.y, row.w, row.h) then
-                                    if row.item.type ~= "separator" then
+                                    if row.item.type == "submenu" then
+                                        state.set_submenu_open(row.item.label)
+                                    elseif row.item.type ~= "separator" then
                                         if fire_item(row.item) then
                                             state.close_menu()
                                         end
@@ -1229,6 +1307,39 @@ local ui = (function()
                     break
                 end
             end
+
+            -- Submenu items (one level deep)
+            local sub_label = state.get_submenu_open()
+            if sub_label then
+                for _, cat in ipairs(menu_bar_categories_layout()) do
+                    if cat.name == open_name then
+                        local dd2 = dropdown_layout(cat)
+                        for _, row in ipairs(dd2.rows) do
+                            local it = row.item
+                            if it.type == "submenu" and it.label == sub_label and it.items then
+                                local sub_x = dd2.x + dd2.w
+                                local sub_y = row.y
+                                local sy = sub_y + DROPDOWN_PAD_Y
+                                for _, si in ipairs(it.items) do
+                                    local row_h = (si.type == "separator") and 6 or DROPDOWN_ITEM_H
+                                    if in_rect(mx, my, sub_x, sy, dropdown_width_for(it.items), row_h) then
+                                        if si.type ~= "separator" then
+                                            if fire_item(si) then
+                                                state.close_menu()
+                                            end
+                                        end
+                                        return true
+                                    end
+                                    sy = sy + row_h
+                                end
+                                break
+                            end
+                        end
+                        break
+                    end
+                end
+            end
+
             -- Click outside the dropdown closes it (no return — fall through so
             -- the click can also hit other UI like canvas).
             state.close_menu()