Why: A turn with no tool call can still say a document was generated and invent an artifact id, and the chat then shows only that text.
Evidence: go test ./internal/runtime/ ./internal/prompts/ -count=1. The guard fires on an unknown art id or a generation claim with no deliverable, cites an existing artifact without firing, and corrects at most once.
Impact: One extra model turn when the reply falsely claims a file. base.deliverables is now version 2 and forbids claiming a file or printing artifact ids.
Refs: feature/chat-timeline-preview
Co-authored-by: Cursor <cursoragent@cursor.com>