fix(chat): correct block selection logic by cursor (#1301)

Refactored Chat:get_block to properly select the closest block to the
cursor, considering the role filter and ensuring correct fallback to the
last matching block. This improves accuracy when interacting with chat
blocks in the UI.

Author: deathbeam

lua/CopilotChat/ui/chat.lua

@@ -124,27 +124,40 @@ end
 ---@param cursor boolean? If true, returns the block closest to the cursor position
 ---@return CopilotChat.ui.chat.Block?
 function Chat:get_block(role, cursor)
-  if not self:visible() then
-    return nil
-  end
+  if cursor then
+    if not self:visible() then
+      return nil
+    end
 
-  self:render()
-  local cursor_pos = vim.api.nvim_win_get_cursor(self.winnr)
-  local cursor_line = cursor_pos[1]
-  local closest_block = nil
-  local max_line_below_cursor = -1
-
-  for _, message in pairs(self.messages) do
-    local section = message.section
-    for _, block in ipairs(section.blocks) do
-      if block.start_line <= cursor_line and block.start_line > max_line_below_cursor then
-        max_line_below_cursor = block.start_line
-        closest_block = block
+    self:render()
+    local cursor_pos = vim.api.nvim_win_get_cursor(self.winnr)
+    local cursor_line = cursor_pos[1]
+    local closest_block = nil
+    local max_line_below_cursor = -1
+
+    for _, message in ipairs(self.messages) do
+      local section = message.section
+      local matches_role = not role or message.role == role
+      if matches_role and section and section.blocks then
+        for _, block in ipairs(section.blocks) do
+          if block.start_line <= cursor_line and block.start_line > max_line_below_cursor then
+            max_line_below_cursor = block.start_line
+            closest_block = block
+          end
+        end
       end
     end
+
+    return closest_block
   end
 
-  return closest_block
+  for i = #self.messages, 1, -1 do
+    local message = self.messages[i]
+    local matches_role = not role or message.role == role
+    if matches_role and message.section and message.section.blocks and #message.section.blocks > 0 then
+      return message.section.blocks[#message.section.blocks]
+    end
+  end
 end
 
 --- Get last message by role in the chat window.