Harden InvoiceGuard stateful tools

tests/test_full_stack_contract.py

@@ -54,6 +54,9 @@ def test_full_stack_product_contract():
     assert card.runtime.platform_resources.databases
     assert card.runtime.platform_resources.databases[0].migrations.path == "db/migrations"
     assert card.workspace_access.enabled is True
+    assert [mode.value for mode in card.workspace_access.allowed_modes] == ["read_only"]
+    assert skills["record_decision"].policy.idempotent is False
+    assert skills["review_invoices"].input_schema["properties"]["case_id"]["maxLength"] == 120
 
 
 def test_review_success_fixture_is_deterministic():
@@ -130,3 +133,17 @@ def test_acceptance_calls_with_mocked_persistence_reload_and_decision():
         updated = asyncio.run(agent.record_decision(ctx, "studio-invoice-v1", DecisionInput(decision_id="d1", decision="hold", note="Investigate duplicate", invoice_number="INV-100")))
         assert updated["ok"] is True
         assert updated["decisions"][0]["decision"] == "hold"
+
+        invalid_reload = asyncio.run(agent.get_invoice_case(ctx, "bad case id"))
+        assert invalid_reload["ok"] is False
+        assert invalid_reload["code"] == "invalid_case_id"
+
+        invalid_decision = asyncio.run(
+            agent.record_decision(
+                ctx,
+                "bad case id",
+                DecisionInput(decision_id="d2", decision="hold"),
+            )
+        )
+        assert invalid_decision["ok"] is False
+        assert invalid_decision["code"] == "invalid_case_id"