Fix duplicated system instructions in Python telemetry

python/packages/core/agent_framework/observability.py

@@ -2155,13 +2155,15 @@ def _capture_messages(
     """Log messages with extra information."""
     from ._types import normalize_messages, prepend_instructions_to_messages
 
-    prepped = prepend_instructions_to_messages(normalize_messages(messages), system_instructions)
-    otel_messages: list[dict[str, Any]] = []
+    normalized_messages = normalize_messages(messages)
+    prepped = prepend_instructions_to_messages(normalized_messages, system_instructions)
+    span_messages: list[dict[str, Any]] = []
     for index, message in enumerate(prepped):
+        otel_message = _to_otel_message(message)
+        if index >= len(prepped) - len(normalized_messages):
+            span_messages.append(otel_message)
         # Reuse the otel message representation for logging instead of calling to_dict()
         # to avoid expensive Pydantic serialization overhead
-        otel_message = _to_otel_message(message)
-        otel_messages.append(otel_message)
         logger.info(
             otel_message,
             extra={
@@ -2171,9 +2173,9 @@ def _capture_messages(
             },
         )
     if finish_reason:
-        otel_messages[-1]["finish_reason"] = FINISH_REASON_MAP[finish_reason]
+        span_messages[-1]["finish_reason"] = FINISH_REASON_MAP[finish_reason]
     span.set_attribute(
-        OtelAttr.OUTPUT_MESSAGES if output else OtelAttr.INPUT_MESSAGES, json.dumps(otel_messages, ensure_ascii=False)
+        OtelAttr.OUTPUT_MESSAGES if output else OtelAttr.INPUT_MESSAGES, json.dumps(span_messages, ensure_ascii=False)
     )
     if system_instructions:
         if not isinstance(system_instructions, list):

python/packages/core/tests/core/test_observability.py

@@ -290,9 +290,9 @@ async def test_chat_client_observability_with_instructions(
     assert len(system_instructions) == 1
     assert system_instructions[0]["content"] == "You are a helpful assistant."
 
-    # Verify input_messages contains system message
+    # Verify input_messages excludes system instructions
     input_messages = json.loads(span.attributes[OtelAttr.INPUT_MESSAGES])
-    assert any(msg.get("role") == "system" for msg in input_messages)
+    assert [msg.get("role") for msg in input_messages] == ["user"]
 
 
 @pytest.mark.parametrize("enable_sensitive_data", [True], indirect=True)
@@ -2981,6 +2981,9 @@ async def test_system_instructions_preserves_non_ascii_characters(span_exporter:
     system_instructions = json.loads(system_instructions_json)
     assert system_instructions[0]["content"] == chinese_text
 
+    input_messages = json.loads(span.attributes[OtelAttr.INPUT_MESSAGES])
+    assert [msg.get("role") for msg in input_messages] == ["user"]
+
 
 @pytest.mark.parametrize("enable_sensitive_data", [True], indirect=True)
 async def test_tool_arguments_preserves_non_ascii_characters(span_exporter: InMemorySpanExporter):
@@ -3104,6 +3107,9 @@ async def test_agent_instructions_from_default_options(
     assert len(system_instructions) == 1
     assert system_instructions[0]["content"] == "Default system instructions."
 
+    input_messages = json.loads(span.attributes[OtelAttr.INPUT_MESSAGES])
+    assert [msg.get("role") for msg in input_messages] == ["user"]
+
 
 @pytest.mark.parametrize("enable_sensitive_data", [True], indirect=True)
 async def test_agent_instructions_from_options_override(