fix(agent): accept JSON null pre-decision evidence

apps/api/tests/test_awooop_ansible_candidate_backfill_job.py

@@ -198,6 +198,7 @@ async def test_predecision_verifier_casts_json_health_to_jsonb(
 
     assert verified is True
     assert "CAST(mcp_health AS jsonb)" in statements[0]
+    assert "CAST(post_execution_state AS jsonb) = 'null'::jsonb" in statements[0]
 
 
 @pytest.mark.asyncio

apps/api/tests/test_awooop_truth_chain_service.py

@@ -2037,6 +2037,8 @@ def test_ansible_context_receipts_reference_pre_decision_evidence_without_conten
     loader_source = inspect.getsource(_load_pre_decision_context_runtime_stage_receipts)
     assert "evidence.collected_at <= candidate.created_at" in loader_source
     assert "evidence.post_execution_state IS NULL" in loader_source
+    assert "CAST(evidence.post_execution_state AS jsonb)" in loader_source
+    assert "= 'null'::jsonb" in loader_source
 
 
 def test_ansible_context_receipt_rejects_zero_success_mcp_attempts() -> None: