fix: handle direct model answers in ReACT loop

The ReACT framework now properly handles cases where the model provides
a direct answer without calling tools. Previously, these answers were
ignored and the loop would continue until exhausting the budget.

Added test coverage for both scenarios (no tools, unused tools).

Fixes: #762

Signed-off-by: Mark Sturdevant <mark.sturdevant@ibm.com>

Author: markstur

mellea/stdlib/frameworks/react.py

@@ -106,9 +106,19 @@ async def react(
                 if tool_res.name == MELLEA_FINALIZER_TOOL:
                     is_final = True
 
-        if is_final:
-            assert len(tool_responses) == 1, "multiple tools were called with 'final'"
+        # Check if we should return: either finalizer was called or model gave direct answer
+        should_return = is_final or (step.tool_calls is None and step.value is not None)
 
+        if should_return:
+            if is_final:
+                assert len(tool_responses) == 1, (
+                    "multiple tools were called with 'final'"
+                )
+                if format is None:
+                    # The tool has already been called above.
+                    step._underlying_value = str(tool_responses[0].content)
+
+            # Apply format if requested (works for both finalizer and direct answer cases)
             if format is not None:
                 step, next_context = await mfuncs.aact(
                     action=ReactThought(),
@@ -122,9 +132,7 @@ async def react(
                 )
                 assert isinstance(next_context, ChatContext)
                 context = next_context
-            else:
-                # The tool has already been called above.
-                step._underlying_value = str(tool_responses[0].content)
+
             return step, context
 
     raise RuntimeError(f"could not complete react loop in {loop_budget} iterations")

test/stdlib/test_react_direct_answer.py

@@ -0,0 +1,75 @@
+"""Test ReACT framework handling of direct answers without tool calls."""
+
+import pytest
+
+from mellea.backends.tools import tool
+from mellea.stdlib.context import ChatContext
+from mellea.stdlib.frameworks.react import react
+from mellea.stdlib.session import start_session
+
+
+@pytest.mark.ollama
+@pytest.mark.llm
+async def test_react_direct_answer_without_tools():
+    """Test that ReACT handles direct answers when model doesn't call tools.
+
+    This tests the case where the model provides a direct answer in step.value
+    without making any tool calls. The fix ensures the loop terminates properly
+    instead of continuing until loop_budget is exhausted.
+    """
+    m = start_session()
+
+    # Ask a simple question that doesn't require tools
+    # The model should provide a direct answer without calling any tools
+    out, _ = await react(
+        goal="What is 2 + 2?",
+        context=ChatContext(),
+        backend=m.backend,
+        tools=[],  # No tools provided
+        loop_budget=3,  # Should complete in 1 iteration, not exhaust budget
+    )
+
+    # Verify we got an answer
+    assert out.value is not None
+    assert len(out.value) > 0
+
+    # The answer should contain "4" or "four"
+    answer_lower = out.value.lower()
+    assert "4" in answer_lower or "four" in answer_lower
+
+
+@pytest.mark.ollama
+@pytest.mark.llm
+async def test_react_direct_answer_with_unused_tools():
+    """Test that ReACT handles direct answers even when tools are available.
+
+    This tests the case where tools are provided but the model chooses to
+    answer directly without using them.
+    """
+    m = start_session()
+
+    # Create a dummy tool that won't be needed
+    @tool
+    def search_web(query: str) -> str:
+        """Search the web for information."""
+        return "Search results"
+
+    # Ask a question that doesn't need the tool
+    out, _ = await react(
+        goal="What is the capital of France?",
+        context=ChatContext(),
+        backend=m.backend,
+        tools=[search_web],
+        loop_budget=3,
+    )
+
+    # Verify we got an answer
+    assert out.value is not None
+    assert len(out.value) > 0
+
+    # The answer should mention Paris
+    answer_lower = out.value.lower()
+    assert "paris" in answer_lower
+
+
+# Made with Bob