fix(gemini): normalize tool call/response parts in captured input (#823)

Gemini's native `function_call`/`function_response` parts were passed
through to `$ai_input` verbatim, in a shape no PostHog consumer
recognizes. The trace renderer matches tool results against Anthropic
`tool_result`, Vercel `tool-result`, OpenAI Responses
`function_call_output`, and `{type: "function", tool_name, content}` —
none of which match — so tool responses never rendered, and the eval
formatter fell through to a raw `repr()` dump instead of a labeled tool
result.

The same SDK already normalized tool calls on the response path to
`{type: "function", function: {...}}`, which is why a call rendered in
the output but vanished once it appeared in the next request's history.

Normalize both part kinds in `_format_part`. Tool results use
`tool_name`/`content` rather than an id-carrying shape because Gemini
matches responses to calls by name and has no call ids to thread.

`$ai_output_choices` is unaffected: `format_gemini_response` hits its
explicit `function_call` branch before the `_format_part` fallback and
already emitted the normalized shape.

Fixes #725

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: marco-g-pm

.sampo/changesets/gentle-toolsmith-vellamo.md

@@ -0,0 +1,5 @@
+---
+pypi/posthog: patch
+---
+
+Normalize Gemini tool calls and tool responses in captured input so they render in traces and reach evaluations

posthog/ai/gemini/gemini_converter.py

@@ -55,15 +55,24 @@ def _format_part(part: Any) -> Optional[FormattedContentItem]:
     if "file_data" in plain:
         media = _format_media_payload(plain["file_data"])
         return {"type": _kind_from_mime(media.get("mime_type")), "file_data": media}
+    # Gemini-native function_call/function_response parts are normalized to the
+    # provider-agnostic tool-call/tool-result blocks. Emitting the raw Gemini
+    # shape leaves them unrenderable and invisible to evals.
     if "function_call" in plain:
+        call = to_plain(plain["function_call"]) or {}
         return {
-            "type": "function_call",
-            "function_call": to_plain(plain["function_call"]),
+            "type": "function",
+            "function": {
+                "name": call.get("name"),
+                "arguments": call.get("args"),
+            },
         }
     if "function_response" in plain:
+        response = to_plain(plain["function_response"]) or {}
         return {
-            "type": "function_response",
-            "function_response": to_plain(plain["function_response"]),
+            "type": "function",
+            "tool_name": response.get("name") or "",
+            "content": response.get("response"),
         }
     if not plain:
         return None

posthog/test/ai/gemini/test_gemini_converter.py

@@ -83,9 +83,14 @@ def test_function_call_and_response_turns_preserved(self):
             ),
         ]
         out = format_gemini_input(contents)
-        assert out[0]["content"][0]["type"] == "function_call"
-        assert out[0]["content"][0]["function_call"]["name"] == "get_weather"
-        assert out[1]["content"][0]["type"] == "function_response"
+        call = out[0]["content"][0]
+        assert call["type"] == "function"
+        assert call["function"] == {"name": "get_weather", "arguments": {"city": "SF"}}
+        result = out[1]["content"][0]
+        assert result["type"] == "function"
+        assert result["tool_name"] == "get_weather"
+        assert result["content"] == {"temp": "18C"}
+        assert "function" not in result
 
     def test_camel_case_dict_part_preserved(self):
         out = format_gemini_input(