diff --git a/src/langbot/pkg/agent/runner/interaction_manager.py b/src/langbot/pkg/agent/runner/interaction_manager.py
index 78d16855a..2fa371770 100644
--- a/src/langbot/pkg/agent/runner/interaction_manager.py
+++ b/src/langbot/pkg/agent/runner/interaction_manager.py
@@ -186,6 +186,8 @@ class InteractionManager:
         if not isinstance(capabilities, InteractionDeliveryCapabilities):
             capabilities = InteractionDeliveryCapabilities.model_validate(capabilities)
         supported_apis = adapter.get_supported_apis() if callable(getattr(adapter, 'get_supported_apis', None)) else []
+        if supported_apis and 'send_interaction' not in supported_apis:
+            capabilities = InteractionDeliveryCapabilities(text_fallback=capabilities.text_fallback)
         if supported_apis and 'interaction.acknowledge' not in supported_apis:
             capabilities.supports_updates = False
         normalized, degraded, use_text, issues = self._normalize_request(request, capabilities, on_unsupported)
@@ -265,7 +267,7 @@ class InteractionManager:
                 except Exception as exc:
                     self._warning(f'Failed to update interaction card: {exc}')
             if original_deadline is not None:
-                runtime['deadline_at'] = float(original_deadline) + time.time() - started_at
+                runtime['deadline_at'] = float(original_deadline) + (time.time() - started_at)
             return {
                 'status': 'timeout' if terminal == 'expired' else 'submitted',
                 'submission': submission,
@@ -287,7 +289,7 @@ class InteractionManager:
             raise
         finally:
             if original_deadline is not None:
-                runtime['deadline_at'] = float(original_deadline) + time.time() - started_at
+                runtime['deadline_at'] = float(original_deadline) + (time.time() - started_at)
             self._waiters.pop(key, None)
             self._responders.pop(key, None)
             self._callback_contexts.pop(key, None)
diff --git a/tests/unit_tests/agent/test_interaction_manager.py b/tests/unit_tests/agent/test_interaction_manager.py
index 37aa1345e..a85cf7cf8 100644
--- a/tests/unit_tests/agent/test_interaction_manager.py
+++ b/tests/unit_tests/agent/test_interaction_manager.py
@@ -1059,3 +1059,29 @@ async def test_unsupported_error_does_not_persist_request():
     )
     assert result['unsupported'][0]['path'] == 'platform'
     assert store.record is None
+
+
+@pytest.mark.asyncio
+async def test_advertised_card_shape_without_send_api_is_unsupported():
+    class UnavailableCardAdapter(BlockingAdapter):
+        def get_supported_apis(self):
+            return ['send_message']
+
+    store = BlockingStore()
+    manager = InteractionManager(SimpleNamespace(), store=store)
+    result = await manager.request_interaction(
+        session=_blocking_session(),
+        adapter=UnavailableCardAdapter(),
+        request_payload={
+            'interaction_id': 'unavailable',
+            'title': 'Approve?',
+            'actions': [
+                {'id': 'yes', 'label': 'Yes'},
+            ],
+        },
+        timeout=1,
+        on_unsupported='error',
+        responders='actor',
+    )
+    assert result['unsupported'][0]['reason'] == 'native_interactions_unavailable'
+    assert store.record is None