FragmentVariablePropagator

Propagates fragment variable usages into consuming operations.

GraphQL fragments can use variables (e.g. age(format: $format)) but cannot define them — the consuming operation must declare them. This class detects variables used by fragments that an operation spreads, and auto-propagates any missing ones into the operation's GraphQLOperationInfo.variables list and updates the operation document text to include the variable declarations.

A warning is emitted for each auto-propagated variable so users know they should declare it explicitly in their operation definition.

Auto-propagated variables default to String? (nullable String). Type inference from the schema is a planned follow-up.