No get_admin-style settleing of empty admin set post-recovery regression test #582

ProblemTests cover recovery happy paths but not a recovery that yields an empty/duplicate admin set (validate_admins_and_threshold should reject, but isn't asserted).

1. Empty-set recovery untested.
2. Duplicate admins untested.
3. Guard not pinned.

Solution

• Add tests for empty/duplicate recovery targets.
• Assert validate_admins_and_threshold catches them.

Acceptance Criteria

• Empty/duplicate recovery targets rejected.
• cargo test --workspace passes.

Note for Contributors: Write a clear PR description. Show the duplicate-target test.