fix(formatter): extend user message border when file parts precede text

Extend end_line passed to add_vertical_border when a message contains file parts
followed by non-synthetic text so extmarks are included and the vertical border
doesn't clip the content.

Author: sudo-tee

lua/opencode/ui/formatter.lua

@@ -355,7 +355,26 @@ function M._format_user_prompt(output, text, message)
     mention.highlight_mentions_in_output(output, text, mentions, start_line)
   end
 
-  M.add_vertical_border(output, start_line, end_line, 'OpencodeMessageRoleUser', -3)
+  local end_line_extmark_offset = 0
+  if message and message.parts then
+    local has_file_parts = false
+    local last_content_idx = 0
+    local text_idx = 0
+    for i, part in ipairs(message.parts) do
+      if part.type == 'file' then
+        has_file_parts = true
+        last_content_idx = i
+      elseif part.type == 'text' and not part.synthetic then
+        text_idx = i
+        last_content_idx = i
+      end
+    end
+    if has_file_parts and text_idx > 0 and text_idx == last_content_idx then
+      end_line_extmark_offset = 1
+    end
+  end
+
+  M.add_vertical_border(output, start_line, end_line + end_line_extmark_offset, 'OpencodeMessageRoleUser', -3)
 end
 
 ---@param output Output Output object to write to