- Add file size pre-check via stat() before read_bytes() to prevent OOM
on oversized images/audio/video
- Fix _extract_post_content to extract media tags (file_key) from Feishu
post messages so videos are no longer silently dropped
- Add supports_vision=False guard to downgrade images to text placeholders
- Add video_mime_compat() for video format validation
- Use full file path in content_text so model read_file works if needed
- Pass input_limits to AgentLoop in nanobot.py facade
- Deduplicate _MEDIA_PLACEHOLDER_TYPES from LLMProvider constant
- Remove unused _extract_post_text legacy wrapper
- Add 14 new tests covering vision fallback, count limits, video compat
