fixing dap-ui dependencies/timing, added <leader>cdu for dap-ui toggle

lua/config/keymaps.lua

@@ -55,4 +55,7 @@ if status_ok then
   vim.keymap.set("n", "<leader>cdh", function()
     require("dap.ui.widgets").hover()
   end, { desc = "DAP: Hover Variable Value" })
+  vim.keymap.set("n", "<leader>cdu", function()
+    require("dapui").toggle()
+  end, { desc = "Debug: Toggle UI" })
 end

lua/plugins/debugger.lua

@@ -131,9 +131,18 @@ return {
         })
 
         -- Automatically open/close DAP UI panels
-        dap.listeners.after.event_initialized["dapui_config"] = function() dapui.open() end
+        -- Defer the open so nvim-dap-ui's async (nio) element buffers are ready.
-        dap.listeners.before.event_terminated["dapui_config"] = function() dapui.close() end
+        -- Opening synchronously from inside the DAP event listener races buffer
-        dap.listeners.before.event_exited["dapui_config"] = function() dapui.close() end
+        -- creation and throws "layout.lua: Invalid buffer id: -1".
+        dap.listeners.after.event_initialized["dapui_config"] = function()
+            vim.schedule(function() dapui.open() end)
+        end
+        dap.listeners.before.event_terminated["dapui_config"] = function()
+            vim.schedule(function() dapui.close() end)
+        end
+        dap.listeners.before.event_exited["dapui_config"] = function()
+            vim.schedule(function() dapui.close() end)
+        end
 
         -- Step 2 & 3 configurations will go here...
         -- 1. Detect operating system