Expose input messages to BeforeInvocationEvent

src/strands/agent/agent.py

@@ -484,24 +484,23 @@ async def structured_output_async(self, output_model: Type[T], prompt: AgentInpu
         Raises:
             ValueError: If no conversation history or prompt is provided.
         """
-        self.hooks.invoke_callbacks(BeforeInvocationEvent(agent=self))
+        if not self.messages and not prompt:
+            raise ValueError("No conversation history or prompt provided")
+        temp_messages: Messages = self.messages + self._convert_prompt_to_messages(prompt)
+
+        self.hooks.invoke_callbacks(BeforeInvocationEvent(agent=self, messages=temp_messages))
+
         with self.tracer.tracer.start_as_current_span(
-            "execute_structured_output", kind=trace_api.SpanKind.CLIENT
+            "execute_structured_output",
+            attributes={
+                "gen_ai.system": "strands-agents",
+                "gen_ai.agent.name": self.name,
+                "gen_ai.agent.id": self.agent_id,
+                "gen_ai.operation.name": "execute_structured_output",
+            },
+            kind=trace_api.SpanKind.CLIENT,
         ) as structured_output_span:
             try:
-                if not self.messages and not prompt:
-                    raise ValueError("No conversation history or prompt provided")
-
-                temp_messages: Messages = self.messages + self._convert_prompt_to_messages(prompt)
-
-                structured_output_span.set_attributes(
-                    {
-                        "gen_ai.system": "strands-agents",
-                        "gen_ai.agent.name": self.name,
-                        "gen_ai.agent.id": self.agent_id,
-                        "gen_ai.operation.name": "execute_structured_output",
-                    }
-                )
                 if self.system_prompt:
                     structured_output_span.add_event(
                         "gen_ai.system.message",
@@ -606,7 +605,7 @@ async def _run_loop(self, messages: Messages, invocation_state: dict[str, Any])
         Yields:
             Events from the event loop cycle.
         """
-        self.hooks.invoke_callbacks(BeforeInvocationEvent(agent=self))
+        self.hooks.invoke_callbacks(BeforeInvocationEvent(agent=self, messages=messages))
 
         try:
             yield InitEventLoopEvent()

src/strands/hooks/events.py

@@ -6,7 +6,7 @@
 from dataclasses import dataclass
 from typing import Any, Optional
 
-from ..types.content import Message
+from ..types.content import Message, Messages
 from ..types.streaming import StopReason
 from ..types.tools import AgentTool, ToolResult, ToolUse
 from .registry import HookEvent
@@ -36,9 +36,13 @@ class BeforeInvocationEvent(HookEvent):
       - Agent.__call__
       - Agent.stream_async
       - Agent.structured_output
+
+    Attributes:
+        message: The input to the agent request (including current message and
+            any history if present)
     """
 
-    pass
+    messages: Messages
 
 
 @dataclass

tests/strands/agent/hooks/test_events.py

@@ -47,7 +47,7 @@ def initialized_event(agent):
 
 @pytest.fixture
 def start_request_event(agent):
-    return BeforeInvocationEvent(agent=agent)
+    return BeforeInvocationEvent(agent=agent, messages=Mock())
 
 
 @pytest.fixture

tests/strands/agent/test_agent.py

@@ -1007,13 +1007,15 @@ def test_agent_structured_output(agent, system_prompt, user, agenerator):
         type(user), [{"role": "user", "content": [{"text": prompt}]}], system_prompt=system_prompt
     )
 
-    mock_span.set_attributes.assert_called_once_with(
-        {
+    mock_otel_tracer.start_as_current_span.assert_called_once_with(
+        "execute_structured_output",
+        attributes={
             "gen_ai.system": "strands-agents",
             "gen_ai.agent.name": "Strands Agents",
             "gen_ai.agent.id": "default",
             "gen_ai.operation.name": "execute_structured_output",
-        }
+        },
+        kind=unittest.mock.ANY,
     )
 
     # ensure correct otel event messages are emitted

tests/strands/agent/test_agent_hooks.py

@@ -150,7 +150,10 @@ def test_agent__call__hooks(agent, hook_provider, agent_tool, mock_model, tool_u
 
     assert length == 12
 
-    assert next(events) == BeforeInvocationEvent(agent=agent)
+    assert next(events) == BeforeInvocationEvent(
+        agent=agent,
+        messages=agent.messages[0:1],
+    )
     assert next(events) == MessageAddedEvent(
         agent=agent,
         message=agent.messages[0],
@@ -199,9 +202,11 @@ def test_agent__call__hooks(agent, hook_provider, agent_tool, mock_model, tool_u
 @pytest.mark.asyncio
 async def test_agent_stream_async_hooks(agent, hook_provider, agent_tool, mock_model, tool_use, agenerator):
     """Verify that the correct hook events are emitted as part of stream_async."""
-    iterator = agent.stream_async("test message")
+    input_prompt = "test message"
+    input_messages: Messages = [{"role": "user", "content": [{"text": input_prompt}]}]
+    iterator = agent.stream_async(input_prompt)
     await anext(iterator)
-    assert hook_provider.events_received == [BeforeInvocationEvent(agent=agent)]
+    assert hook_provider.events_received == [BeforeInvocationEvent(agent=agent, messages=input_messages)]
 
     # iterate the rest
     async for _ in iterator:
@@ -211,7 +216,7 @@ async def test_agent_stream_async_hooks(agent, hook_provider, agent_tool, mock_m
 
     assert length == 12
 
-    assert next(events) == BeforeInvocationEvent(agent=agent)
+    assert next(events) == BeforeInvocationEvent(agent=agent, messages=input_messages)
     assert next(events) == MessageAddedEvent(
         agent=agent,
         message=agent.messages[0],
@@ -267,7 +272,15 @@ def test_agent_structured_output_hooks(agent, hook_provider, user, agenerator):
 
     assert length == 2
 
-    assert next(events) == BeforeInvocationEvent(agent=agent)
+    assert next(events) == BeforeInvocationEvent(
+        agent=agent,
+        messages=[
+            {
+                "content": [{"text": "example prompt"}],
+                "role": "user",
+            }
+        ],
+    )
     assert next(events) == AfterInvocationEvent(agent=agent)
 
     assert len(agent.messages) == 0  # no new messages added
@@ -284,7 +297,15 @@ async def test_agent_structured_async_output_hooks(agent, hook_provider, user, a
 
     assert length == 2
 
-    assert next(events) == BeforeInvocationEvent(agent=agent)
+    assert next(events) == BeforeInvocationEvent(
+        agent=agent,
+        messages=[
+            {
+                "content": [{"text": "example prompt"}],
+                "role": "user",
+            }
+        ],
+    )
     assert next(events) == AfterInvocationEvent(agent=agent)
 
     assert len(agent.messages) == 0  # no new messages added