Function is_flow_ast_injection_request 

pub fn is_flow_ast_injection_request(type_expr: Option<&TypeExpr>) -> bool

Whether a Flow predicate’s raw leading type opts into the AST capability injected by the evaluator.

This contract is intentionally syntactic: aliases and nested capability shapes are not runtime injection requests. Keeping the check here gives the typechecker and evaluator one semantic owner for argument alignment.