fix: deep copy formatted_messages to prevent Groq message mutation (#562) (#598)

* fix: deep copy formatted_messages to prevent Groq structured output mutation corrupting fallback models (#562)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* test: trim Groq mutation tests to 3 focused regressions in test_llm_invoke.py (#562)

Replace 770 lines across 2 standalone test files with 3 focused regression
tests (~80 lines) in the existing test_llm_invoke.py, per PR #591 review.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Serhan <serhanasad2013@live.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

pdd/llm_invoke.py

@@ -1,6 +1,7 @@
 # Corrected code_under_test (llm_invoke.py)
 # Added optional debugging prints in _select_model_candidates
 
+import copy
 import os
 import pandas as pd
 import litellm
@@ -1971,7 +1972,7 @@ def calc_strength(candidate):
             # --- 5. Prepare LiteLLM Arguments ---
             litellm_kwargs: Dict[str, Any] = {
                 "model": model_name_litellm,
-                "messages": formatted_messages,
+                "messages": copy.deepcopy(formatted_messages),
                 # Use a local adjustable temperature to allow provider-specific fallbacks
                 "temperature": current_temperature,
                 # Retry on transient network errors (APIError, TimeoutError, ServiceUnavailableError)

tests/test_llm_invoke.py

@@ -1,5 +1,6 @@
 # Corrected unit_test (tests/test_llm_invoke.py)
 
+import copy
 import pytest
 import os
 import pandas as pd
@@ -4863,4 +4864,124 @@ def capture_completion(**kwargs):
 
         # time=None should be treated as 0, so no reasoning params
         assert "thinking" not in captured_kwargs
-        assert "reasoning_effort" not in captured_kwargs
+        assert "reasoning_effort" not in captured_kwargs
+
+
+# ---------------------------------------------------------------------------
+# Issue #562: Groq structured output mutation regression tests
+# ---------------------------------------------------------------------------
+
+class _GroqMutationFixture:
+    """Shared helpers for Groq message mutation tests."""
+
+    class SimpleResult(BaseModel):
+        answer: str
+        confidence: float
+
+    GROQ_SCHEMA_MARKER = "You must respond with valid JSON matching this schema"
+
+    @staticmethod
+    def _model(provider, model, elo, api_key):
+        return {
+            "provider": provider, "model": model, "input": 0.15,
+            "output": 0.60, "coding_arena_elo": elo,
+            "structured_output": True, "base_url": "", "api_key": api_key,
+            "max_tokens": "", "max_completion_tokens": "",
+            "reasoning_type": "none", "max_reasoning_tokens": 0,
+        }
+
+    @staticmethod
+    def _make_response(content):
+        resp = MagicMock()
+        choice = MagicMock()
+        choice.message.content = content
+        choice.finish_reason = "stop"
+        resp.choices = [choice]
+        usage = MagicMock()
+        usage.prompt_tokens = 100
+        usage.completion_tokens = 50
+        resp.usage = usage
+        return resp
+
+
+class TestGroqMessageMutation(_GroqMutationFixture):
+    """Regression tests for #562: Groq structured output must not corrupt
+    formatted_messages shared across fallback candidates."""
+
+    def _run(self, input_messages, candidates):
+        """Call llm_invoke with Groq failing, capture every litellm.completion call."""
+        import pdd.llm_invoke as _llm_mod
+
+        groq = self._model("Groq", "groq/llama-3.3-70b-versatile", 1200, "GROQ_API_KEY")
+        openai = self._model("OpenAI", "gpt-4o-mini", 1100, "OPENAI_API_KEY")
+        models = [self._model(*c) for c in candidates] if candidates else [groq, openai]
+
+        captured = []
+
+        def side_effect(**kwargs):
+            captured.append(copy.deepcopy(kwargs))
+            if "groq/" in kwargs.get("model", ""):
+                raise Exception("Groq API error")
+            resp = self._make_response(json.dumps({"answer": "4", "confidence": 0.99}))
+            _llm_mod._LAST_CALLBACK_DATA["cost"] = 0.001
+            _llm_mod._LAST_CALLBACK_DATA["input_tokens"] = 100
+            _llm_mod._LAST_CALLBACK_DATA["output_tokens"] = 50
+            return resp
+
+        with patch.dict(os.environ, {"PDD_FORCE_LOCAL": "1",
+                                      "GROQ_API_KEY": "k", "OPENAI_API_KEY": "k"}), \
+             patch("pdd.llm_invoke._ensure_api_key", return_value=True), \
+             patch("pdd.llm_invoke._select_model_candidates", return_value=models), \
+             patch("pdd.llm_invoke._load_model_data", return_value=pd.DataFrame(models)), \
+             patch("pdd.llm_invoke.litellm") as mock_litellm:
+            mock_litellm.completion = MagicMock(side_effect=side_effect)
+            mock_litellm.cache = None
+            mock_litellm.drop_params = True
+            llm_invoke(
+                messages=input_messages, strength=0.5, temperature=0.0,
+                time=0.0, output_pydantic=self.SimpleResult, use_cloud=False,
+            )
+        return captured
+
+    def test_groq_fallback_no_schema_in_messages(self):
+        """Core: after Groq fails, fallback gets clean messages (no JSON schema)."""
+        captured = self._run(
+            [{"role": "user", "content": "What is 2+2?"}],
+            [("Groq", "groq/llama-3.3-70b-versatile", 1200, "GROQ_API_KEY"),
+             ("OpenAI", "gpt-4o-mini", 1100, "OPENAI_API_KEY")],
+        )
+        assert len(captured) >= 2
+        for msg in captured[1]["messages"]:
+            assert self.GROQ_SCHEMA_MARKER not in msg.get("content", ""), \
+                "Fallback model received Groq schema instruction"
+
+    def test_groq_fallback_system_message_not_mutated(self):
+        """Dict overwrite: existing system message preserved for fallback."""
+        original = "You are a helpful math tutor."
+        captured = self._run(
+            [{"role": "system", "content": original},
+             {"role": "user", "content": "What is 2+2?"}],
+            [("Groq", "groq/llama-3.3-70b-versatile", 1200, "GROQ_API_KEY"),
+             ("OpenAI", "gpt-4o-mini", 1100, "OPENAI_API_KEY")],
+        )
+        assert len(captured) >= 2
+        fallback_sys = captured[1]["messages"][0]
+        assert fallback_sys["content"] == original, \
+            f"System message mutated: {fallback_sys['content'][:200]}"
+
+    def test_groq_multiple_failures_no_cumulative_corruption(self):
+        """Two Groq models fail; schema instructions must not accumulate."""
+        captured = self._run(
+            [{"role": "user", "content": "What is 2+2?"}],
+            [("Groq", "groq/llama-3.3-70b-versatile", 1200, "GROQ_API_KEY"),
+             ("Groq", "groq/mixtral-8x7b-32768", 1150, "GROQ_API_KEY"),
+             ("OpenAI", "gpt-4o-mini", 1100, "OPENAI_API_KEY")],
+        )
+        assert len(captured) >= 3
+        final = next(c for c in reversed(captured) if "groq/" not in c.get("model", ""))
+        schema_count = sum(
+            1 for m in final["messages"]
+            if self.GROQ_SCHEMA_MARKER in m.get("content", "")
+        )
+        assert schema_count == 0, \
+            f"Fallback got {schema_count} accumulated schema instructions"