Evaluate composition invariants over the composed union in Java

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Parent

#78

What to build

The Java side of #46. Composition unions Intent Fragments as chapter 40 specifies: order-independent, every collision an error, nothing merged. The identity and reference invariants are Complete OCL whose context is the composed union. Each negative fixture directory's diagnostics oracle is compared for every order of its fragments.

Acceptance criteria

• Every negative fixture directory yields its committed diagnostics set, for every fragment order.
• The composed union is identical under every fragment order.

Blocked by

• Refuse documents with OCL, addressed by JSON Pointer #85
• Model Platform Intent in Ecore, parse it, and check its cross-document references #86