Relationship scope completion ignores the selected control specification #1511

Problem

Validation bounds a participant relationship's scope_refs twice. Each ref must be an operating scope that both endpoints hold, and when the relationship names a control_specification_ref, every ref must also be inside the scope of that mixed-control policy's active controller states for the relationship's direction (_participant_relation_control and _participant_relation_control_scope, raes/validator/_participant_relationships.py:40-58 and :82-91 on dev a4357f9a). A ref outside it fails with "control_specification_ref must cover the selected relationship scope".

#1446 (for #1339) makes completion apply the first bound: scope_refs completes only the operating scopes that both endpoints hold, and authority_basis_refs only the source's authority anchors (_ENDPOINT_BOUNDED_REFINEMENTS, raes/language_service.py:57-62 at the PR head 3da60398). Completion does not apply the second bound, as the #1446 body notes. For a relationship with a control_specification_ref, completion therefore offers scopes that validation then rejects.

Scope

• When a relationship names a control_specification_ref that resolves to a mixed-control policy, limit scope_refs completion to the scopes that validation accepts for it, using the same controller-state selection as the validator.
• Keep the endpoint bound when no control specification is selected or it does not resolve.

Done when

• Every scope_refs candidate that completion offers for a relationship with a resolvable control_specification_ref validates.
• A test shows a scope that both endpoints hold but the control specification does not cover is not offered.

Related

• Make target eligibility explicit and align editor suggestions #1339, feat!: make reference eligibility explicit per purpose and align the editor with validation #1446 (noted the gap)