Models looked for generate_3d with mcp_search, which only searched MCP servers, and concluded it did not exist (the chat had been in plan mode, then switched to build). The search now lists matching built-in tools first: "available – call it directly" or "not in the read-only mode plan – ask the user to switch to build mode". Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>