fix(ui): prevent errors when restoring invalid window (#1539)

- Add a check in Overlay:restore to ensure the window is valid before
  attempting to set the buffer, preventing errors if the window was
  closed.
- Scope the close keymap in chat buffer to the buffer only, avoiding
  global keymap pollution.

Closes #1535

Author: deathbeam

lua/CopilotChat/ui/chat.lua

@@ -161,7 +161,7 @@ local Chat = class(function(self, config, on_buf_create)
     function(bufnr)
       vim.keymap.set('n', config.mappings.close.normal, function()
         self.chat_overlay:restore(self.winnr, self.bufnr)
-      end)
+      end, { buffer = bufnr })
 
       vim.api.nvim_create_autocmd({ 'BufHidden', 'BufDelete' }, {
         buffer = bufnr,

lua/CopilotChat/ui/overlay.lua

@@ -116,6 +116,10 @@ function Overlay:restore(winnr, bufnr)
     self.on_hide(self.bufnr)
   end
 
+  if not vim.api.nvim_win_is_valid(winnr) then
+    return
+  end
+
   vim.api.nvim_win_set_buf(winnr, bufnr)
 
   if self.cursor then