Treat explicit clusters as atomic aggregates

[SoundBlaster]

Summary

• What changed? Treat explicit semantic cluster specs as valid atomic aggregates when their blocking dependencies are declared member_contracts.
• Link related issue/task (if any): follow-up from make next-move on SG-SPEC-0063 / propose_retrospective_refactor.

Motivation

• Why is this change needed? SG-SPEC-0063 is an intentional realization/observation cluster with four member specs, but the generic atomicity validator treated four blocking children as split pressure.
• What problem, gap, or user need does it address? Prevents graph-health from pushing a valid semantic cluster into an impossible retrospective split proposal.

Goals

• What should this PR achieve? Remove the false-positive retrospective_refactor_candidate for explicit cluster aggregates while preserving atomicity pressure for ordinary broad hubs.
• What is intentionally out of scope? Raising the global atomicity_max_blocking_children threshold or changing canonical spec topology.

Changes

• Add explicit cluster-member dependency detection to tools/supervisor.py.
• Exempt only dependencies that are declared as specification.member_contracts under a cluster_contract.
• Add regression tests covering atomicity validation and graph-health behavior for explicit cluster aggregates.

Validation

• Tests added/updated for changed behavior
• Local checks passed

Commands run:

python3 -m pytest -q tests/test_supervisor.py -k 'cluster_member_dependencies or explicit_cluster_aggregate or healthy_multi_child_aggregate'
python3 - <<'PY'
import tools.supervisor as s
specs=s.load_specs()
idx=s.index_specs(specs)
node=idx['SG-SPEC-0063']
print('atomicity', s.validate_atomicity(node))
print('fanout', s.fan_out_legibility_profile(node,specs))
health=s.inspect_canonical_graph_health(node=node,specs=specs)['graph_health']
print('signals', health['signals'])
print('actions', health['recommended_actions'])
print('observations', [o['kind'] for o in health['observations']])
PY
git diff --check
make backlog
make next-move
ruff check tools/supervisor.py tests/test_supervisor.py
python3 -m compileall tools/supervisor.py
python3 -m pytest -q tests/test_supervisor.py

Results:

• Focused tests: 3 passed, 604 deselected
• Real SG-SPEC-0063 check: atomicity [], signals [], actions [], observation healthy_multi_child_aggregate
• make backlog: entry_count dropped from 97 to 31; SG-SPEC-0063 health item disappeared
• make next-move: now recommends proposal 0021 reobservation instead of SG-SPEC-0063
• ruff and compileall passed
• Full supervisor tests: 607 passed in 291.52s

Risks / Notes

• Backward compatibility impact: Ordinary specs with too many undeclared blocking dependencies still fail atomicity.
• Migration/config changes required: None.
• Known limitations: Explicit cluster detection depends on specification.cluster_contract plus specification.member_contracts; informal prose-only clusters are not exempt.

Checklist

• PR title clearly describes the change
• Scope is focused and minimal
• Documentation updated (or N/A)
• No secrets or sensitive data added