fix: avoid double-prefixing instructor model strings

With LiteLLM models now carrying a real `provider` while `model` keeps
its `provider/name` form, `InternalInstructor` was building
`groq/groq/...` for `instructor.from_provider`. Skip the prefix when
the model string is already qualified.

lib/crewai/src/crewai/utilities/internal_instructor.py

@@ -105,7 +105,12 @@ class InternalInstructor(Generic[T]):
                 if value is not None:
                     extra_kwargs[attr] = value
 
-        return instructor.from_provider(f"{provider}/{model_string}", **extra_kwargs)
+        qualified_model = (
+            model_string
+            if not provider or model_string.startswith(f"{provider}/")
+            else f"{provider}/{model_string}"
+        )
+        return instructor.from_provider(qualified_model, **extra_kwargs)
 
     def _extract_provider(self) -> str:
         """Extract provider from LLM model name.

lib/crewai/tests/utilities/test_converter.py

@@ -1004,3 +1004,21 @@ def test_internal_instructor_omits_unset_base_url_and_api_key() -> None:
         InternalInstructor(content="x", model=SimpleModel, llm=mock_llm)
 
         mock_from_provider.assert_called_once_with("openai/gpt-4o")
+
+
+def test_internal_instructor_does_not_double_prefix_qualified_models() -> None:
+    from crewai.utilities.internal_instructor import InternalInstructor
+
+    mock_llm = Mock()
+    mock_llm.is_litellm = False
+    mock_llm.model = "groq/llama-3.3-70b"
+    mock_llm.provider = "groq"
+    mock_llm.base_url = None
+    mock_llm.api_key = None
+
+    with patch("instructor.from_provider") as mock_from_provider:
+        mock_from_provider.return_value = Mock()
+
+        InternalInstructor(content="x", model=SimpleModel, llm=mock_llm)
+
+        mock_from_provider.assert_called_once_with("groq/llama-3.3-70b")