get_definitions() sorts tools on every LLM iteration for prompt cache
stability. Cache the sorted result and invalidate on register/unregister
so the sort only runs when the tool set actually changes.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Three fixes in the API upload handling:
1. Multipart uploads now prefix filenames with a UUID to prevent
overwrites when two requests upload files with the same name.
2. JSON image_url content blocks with remote HTTPS URLs now return
a 400 error instead of silently dropping the image.
3. Model validation runs for both JSON and multipart requests,
fixing an inconsistency where multipart bypassed the check.
