When generating multiple cover images in one conversation, the
accumulated tool results (each ~400KB base64) caused the OpenAI
conversation payload to exceed JSON parsing limits in the browser.
Fix:
- Strip coverImageUrl from invalidate action results (not needed by AI)
- Cap invalidate results to 4KB
- Cap all tool results to 8KB
- Prevents "JSON.parse: unexpected character" errors during batch ops
Co-Authored-By: claude-flow <ruv@ruv.net>