The test_empty_list_returns_empty_content test expected empty-content
AIMessages to be filtered out, but the fix now always emits assistant
messages so tool calls can reference them via parentMessageId.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Verifies langchain_messages_to_copilotkit correctly concatenates all text
parts from list-style content blocks (Anthropic models). Includes
regression tests for the exact scenario from #1748 (text + image blocks)
and tests for string lists, mixed content, empty lists, and edge cases.