Render and author optional-group as a third group-container kind beside
foreach/loop: register the node type (OptionalGroupNode) so it renders with a
header + defaultOn badge and parentId template children, treat it as a group
everywhere in workflow-flow-mapping (irToFlow children, flowToIr template
reassembly, cascade-delete, condition-editable), add a palette entry, and an
inspector defaultOn toggle. Includes a node-help entry and round-trip / toggle /
cascade-delete tests.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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