- Add FixedCollectionValidator utility to handle all fixedCollection patterns
- Support validation for 12 different node types including Switch, If, Filter,
Summarize, Compare Datasets, Sort, Aggregate, Set, HTML, HTTP Request, and Airtable
- Refactor enhanced-config-validator to use the generic utility
- Add comprehensive tests with 19 test cases covering all node types
- Maintain backward compatibility with existing validation behavior
This prevents the 'propertyValues[itemName] is not iterable' error across all
susceptible n8n nodes, not just Switch/If/Filter.
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