Form-disjoint contract family generator for transfer measurement

[JeremyJC67]

Capability

A generator that emits two contract families sharing the same abstract constraints while sharing no surface
form. This is what makes it possible to distinguish a learned abstraction from a memorised surface pattern
when measuring transfer, and is the load-bearing axis of the placement study (#5).

Design

Separate abstract constraint (e.g. "an observation read before an intervening mutation must be re-read
before use") from surface instantiation (verbs, header names, schema, token encoding), then vary the
second while holding the first fixed.

Deliverable

• explicit constraint/surface separation in the generator
• families A and B: same constraint set, disjoint surface vocabularies
• a disjointness check that fails if any surface token appears in both families
• at least 3 constraints instantiated in both families

Gate

Current. Blocks M3 of #5.