fix(agent): preserve auto vision fallback for custom backends

tests/agent/test_vision_non_vision_fallthrough.py

@@ -6,11 +6,12 @@ the auto-detection should skip directly to aggregator fallbacks instead of
 sending an image payload to a text-only model.
 """
 
+from types import SimpleNamespace
 from unittest.mock import patch, MagicMock
 
 import pytest
 
-from agent.auxiliary_client import _is_likely_vision_model
+from agent.auxiliary_client import _is_likely_vision_model, call_llm
 
 
 # -- _is_likely_vision_model heuristic --
@@ -149,6 +150,67 @@ class TestVisionNonVisionFallthrough:
         assert client is mock_client
         assert model == "mimo-v2.5"
 
+    def test_named_custom_provider_unknown_model_is_trusted(self):
+        """Named custom providers should not be skipped by the name heuristic."""
+        mock_client = MagicMock()
+
+        with patch(
+            "agent.auxiliary_client._read_main_provider",
+            return_value="beans",
+        ), patch(
+            "agent.auxiliary_client._read_main_model",
+            return_value="my-company-vlm",
+        ), patch(
+            "agent.auxiliary_client._resolve_task_provider_model",
+            return_value=("auto", None, None, None, None),
+        ), patch(
+            "agent.auxiliary_client._get_named_custom_provider_entry",
+            return_value={"name": "beans", "base_url": "http://vlm.test/v1"},
+        ), patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "my-company-vlm"),
+        ):
+            from agent.auxiliary_client import resolve_vision_provider_client
+
+            provider, client, model = resolve_vision_provider_client()
+
+        assert provider == "beans"
+        assert client is mock_client
+        assert model == "my-company-vlm"
+
+    def test_named_custom_provider_can_declare_vision_model_override(self):
+        """Named custom providers can route vision to a dedicated model."""
+        mock_client = MagicMock()
+
+        with patch(
+            "agent.auxiliary_client._read_main_provider",
+            return_value="beans",
+        ), patch(
+            "agent.auxiliary_client._read_main_model",
+            return_value="chat-model",
+        ), patch(
+            "agent.auxiliary_client._resolve_task_provider_model",
+            return_value=("auto", None, None, None, None),
+        ), patch(
+            "agent.auxiliary_client._get_named_custom_provider_entry",
+            return_value={
+                "name": "beans",
+                "base_url": "http://vlm.test/v1",
+                "models": {"chat-model": {"vision_model": "vision-model"}},
+            },
+        ), patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "vision-model"),
+        ) as mock_resolve:
+            from agent.auxiliary_client import resolve_vision_provider_client
+
+            provider, client, model = resolve_vision_provider_client()
+
+        assert provider == "beans"
+        assert client is mock_client
+        assert model == "vision-model"
+        assert mock_resolve.call_args.args[:2] == ("beans", "vision-model")
+
     def test_non_vision_model_all_aggregators_fail(self):
         """Non-vision main + no aggregators available must return None."""
         with patch(
@@ -170,3 +232,49 @@ class TestVisionNonVisionFallthrough:
 
         assert client is None
         assert model is None
+
+
+class VisionUnsupportedError(Exception):
+    def __init__(self, message, status_code=400):
+        super().__init__(message)
+        self.status_code = status_code
+
+
+class TestVisionCapabilityFallback:
+    def test_call_llm_retries_auto_vision_on_capability_error(self):
+        """A text-only main provider should fall through to strict vision backends."""
+        primary_client = MagicMock()
+        fallback_client = MagicMock()
+        response = SimpleNamespace(
+            choices=[SimpleNamespace(message=SimpleNamespace(content="ok"))]
+        )
+
+        primary_client.chat.completions.create.side_effect = VisionUnsupportedError(
+            "This model does not support image input"
+        )
+        fallback_client.chat.completions.create.return_value = response
+
+        with patch(
+            "agent.auxiliary_client._resolve_task_provider_model",
+            return_value=("auto", None, None, None, None),
+        ), patch(
+            "agent.auxiliary_client.resolve_vision_provider_client",
+            return_value=("ollama-cloud", primary_client, "llama3"),
+        ), patch(
+            "agent.auxiliary_client._build_call_kwargs",
+            return_value={
+                "model": "llama3",
+                "messages": [{"role": "user", "content": "analyze"}],
+            },
+        ), patch(
+            "agent.auxiliary_client._try_vision_fallback",
+            return_value=(fallback_client, "google/gemini-3-flash-preview", "openrouter"),
+        ):
+            result = call_llm(
+                task="vision",
+                messages=[{"role": "user", "content": "analyze"}],
+            )
+
+        assert result is response
+        assert primary_client.chat.completions.create.call_count == 1
+        assert fallback_client.chat.completions.create.call_count == 1