[BUG] Cann't Select text [ Code block ] while streaming!

## Describe the bug

When LLM start generating content we can't select text while streaming, especially in the code block!

## To Reproduce

ask any question that will generate code, try to select text while printing.

Reproduce the problem in the chat UI by asking a question that generates a code block, then try selecting text while the response streams. Trace the streaming response rendering and code-block display; done means text can be selected normally during generation, especially inside code blocks.

Written by the indexing model from the issue text.