- Excel preview detects when a product already has a different STEP file linked
- Excel preview detects intra-Excel conflicts (same product, different CAD model names)
- Product STEP upload warns when replacing an existing file and shows render count
- All warnings are non-blocking (amber badges, toast warnings)
- LEARNINGS.md: all open items resolved
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>