c3b4fab764
When inferring a call expression with a union type context, we try narrowing to each element of the union. If nested calls have the same union as their parameter type, this would lead to exponential blowup. By tracking which unions we're already narrowing against, we skip redundant nested narrowing. On a synthetic benchmark with nested `list_schema()` calls: - 4-level nesting: >120s → 0.13s