canonicalize_workflow_config was silently rebuilding any workflow with
ui.blueprint or ui.preset == still_graph from the canonical template on
every save, preflight, and read — making blueprint-based workflows
effectively read-only.
Add preserve_user_graph=True flag that skips the rebuild blocks. Only
create_workflow still uses preserve_user_graph=False so blueprints are
correctly expanded at creation time.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>