fix: implement update_message() for guardrail redaction support

src/bedrock_agentcore/memory/integrations/strands/session_manager.py

@@ -628,36 +628,107 @@ def read_message(self, session_id: str, agent_id: str, message_id: int, **kwargs
             Optional[SessionMessage]: The message if found, None otherwise.
 
         Note:
-            This should not be called as (as of now) only the `update_message` method calls this method and
-            updating messages is not supported in AgentCore Memory.
+            This is primarily used internally by the `update_message` method to read
+            the original event before replacing it.
         """
         result = self.memory_client.gmdp_client.get_event(
             memoryId=self.config.memory_id, actorId=self.config.actor_id, sessionId=session_id, eventId=message_id
         )
         return SessionMessage.from_dict(result) if result else None
 
     def update_message(self, session_id: str, agent_id: str, session_message: SessionMessage, **kwargs: Any) -> None:
-        """Update message data.
+        """Update message data in AgentCore Memory.
 
-        Note: AgentCore Memory doesn't support updating events,
-        so this is primarily for validation and logging.
+        Since AgentCore Memory events are immutable, this method performs an update by
+        creating a new event with the updated content and deleting the old event.
+        This enables features like guardrail redaction via Strands' redact_latest_message().
+
+        If the message has not yet been persisted (e.g., still in the message buffer when
+        batch_size > 1), the buffered message is replaced in-place instead.
 
         Args:
             session_id (str): The session ID containing the message.
             agent_id (str): The agent ID associated with the message.
-            session_message (SessionMessage): The message to update.
+            session_message (SessionMessage): The message to update (with updated content
+                and the original message_id/eventId).
             **kwargs (Any): Additional keyword arguments.
 
         Raises:
-            SessionException: If session ID doesn't match configuration.
+            SessionException: If session ID doesn't match configuration or update fails.
         """
         if session_id != self.config.session_id:
             raise SessionException(f"Session ID mismatch: expected {self.config.session_id}, got {session_id}")
 
-        logger.debug(
-            "Message update requested for message: %s (AgentCore Memory doesn't support updates)",
-            {session_message.message_id},
-        )
+        old_message_id = session_message.message_id
+
+        # If message hasn't been persisted yet (still in buffer), update it there
+        if old_message_id is None:
+            if self._update_buffered_message(session_message):
+                logger.debug("Updated buffered message (not yet persisted to AgentCore Memory)")
+                return
+            logger.debug("Message has no event ID and was not found in buffer - skipping update")
+            return
+
+        # Create a new event with the updated message content
+        try:
+            updated_message = SessionMessage(
+                message=session_message.message,
+                message_id=0,
+                created_at=session_message.created_at,
+            )
+            new_event = self.create_message(session_id, agent_id, updated_message)
+        except Exception as e:
+            logger.error("Failed to update message in AgentCore Memory: %s", e)
+            raise SessionException(f"Failed to update message: {e}") from e
+
+        # Delete the old event; if this fails, roll back the newly created event
+        try:
+            self.memory_client.gmdp_client.delete_event(
+                memoryId=self.config.memory_id,
+                actorId=self.config.actor_id,
+                sessionId=session_id,
+                eventId=old_message_id,
+            )
+        except Exception as delete_error:
+            logger.warning(
+                "Failed to delete old event %s after creating replacement: %s. Attempting rollback.",
+                old_message_id,
+                delete_error,
+            )
+            new_event_id = new_event.get("eventId") if new_event else None
+            if new_event_id:
+                try:
+                    self.memory_client.gmdp_client.delete_event(
+                        memoryId=self.config.memory_id,
+                        actorId=self.config.actor_id,
+                        sessionId=session_id,
+                        eventId=new_event_id,
+                    )
+                    logger.info("Rolled back new event %s after failed delete of old event", new_event_id)
+                except Exception as rollback_error:
+                    logger.error(
+                        "Rollback failed: could not delete new event %s: %s. Both old (%s) and new events may exist.",
+                        new_event_id,
+                        rollback_error,
+                        old_message_id,
+                    )
+            raise SessionException(
+                f"Failed to update message: could not delete old event: {delete_error}"
+            ) from delete_error
+
+        # Update _latest_agent_message so it doesn't hold a stale eventId
+        new_event_id = new_event.get("eventId") if new_event else None
+        latest_messages = getattr(self, "_latest_agent_message", None)
+        if new_event_id and latest_messages and agent_id in latest_messages:
+            old_latest = latest_messages[agent_id]
+            if old_latest.message_id == old_message_id:
+                self._latest_agent_message[agent_id] = SessionMessage(
+                    message=session_message.message,
+                    message_id=new_event_id,
+                    created_at=session_message.created_at,
+                )
+
+        logger.info("Updated message in AgentCore Memory: replaced event %s", old_message_id)
 
     def list_messages(
         self,
@@ -857,6 +928,44 @@ def initialize(self, agent: "Agent", **kwargs: Any) -> None:
 
     # region Batching support
 
+    def _update_buffered_message(self, session_message: SessionMessage) -> bool:
+        """Attempt to update a message that is still in the send buffer.
+
+        When batch_size > 1, messages may not yet be persisted to AgentCore Memory.
+        This method finds the most recent buffered message matching the session_message's
+        content role and replaces it with the updated content.
+
+        Args:
+            session_message (SessionMessage): The message with updated content.
+
+        Returns:
+            bool: True if a buffered message was found and updated, False otherwise.
+        """
+        updated_messages = self.converter.message_to_payload(session_message)
+        if not updated_messages:
+            return False
+
+        is_blob = self.converter.exceeds_conversational_limit(updated_messages[0])
+
+        with self._message_lock:
+            # Search from the end (most recent) to find the message to update
+            for i in range(len(self._message_buffer) - 1, -1, -1):
+                buf = self._message_buffer[i]
+                if buf.session_id == self.config.session_id and buf.messages:
+                    # Match by role - the most recent message with the same role
+                    existing_role = buf.messages[0][1] if not buf.is_blob else None
+                    new_role = updated_messages[0][1] if not is_blob else None
+                    if existing_role == new_role:
+                        self._message_buffer[i] = BufferedMessage(
+                            session_id=buf.session_id,
+                            messages=updated_messages,
+                            is_blob=is_blob,
+                            timestamp=buf.timestamp,
+                            metadata=buf.metadata,
+                        )
+                        return True
+        return False
+
     def _flush_messages_only(self) -> list[dict[str, Any]]:
         """Flush only buffered messages to AgentCore Memory.
 

tests/bedrock_agentcore/memory/integrations/strands/test_agentcore_memory_session_manager.py

@@ -496,20 +496,74 @@ def test_read_message_not_found(self, session_manager, mock_memory_client):
 
         assert result is None
 
-    def test_update_message(self, session_manager):
-        """Test updating a message."""
-        message = SessionMessage(message={"role": "user", "content": [{"text": "Hello"}]}, message_id=1)
+    def test_update_message(self, session_manager, mock_memory_client):
+        """Test updating a persisted message creates new event and deletes old one."""
+        mock_memory_client.create_event.return_value = {"eventId": "new_event_456"}
+
+        message = SessionMessage(
+            message={"role": "user", "content": [{"text": "redacted"}]},
+            message_id="old_event_123",
+            created_at="2024-01-01T12:00:00Z",
+        )
 
-        # Should not raise any exceptions
         session_manager.update_message("test-session-456", "test-agent-123", message)
 
+        # Verify new event was created
+        mock_memory_client.create_event.assert_called_once()
+
+        # Verify old event was deleted
+        mock_memory_client.gmdp_client.delete_event.assert_called_once()
+        delete_kwargs = mock_memory_client.gmdp_client.delete_event.call_args.kwargs
+        assert delete_kwargs["eventId"] == "old_event_123"
+        assert delete_kwargs["memoryId"] == "test-memory-123"
+        assert delete_kwargs["actorId"] == "test-actor-789"
+        assert delete_kwargs["sessionId"] == "test-session-456"
+
     def test_update_message_wrong_session(self, session_manager):
         """Test updating a message with wrong session ID."""
         message = SessionMessage(message={"role": "user", "content": [{"text": "Hello"}]}, message_id=1)
 
         with pytest.raises(SessionException, match="Session ID mismatch"):
             session_manager.update_message("wrong-session-id", "test-agent-123", message)
 
+    def test_update_message_no_message_id(self, session_manager):
+        """Test updating a message with no message_id (not yet persisted) skips gracefully."""
+        message = SessionMessage(
+            message={"role": "user", "content": [{"text": "redacted"}]},
+            message_id=None,
+            created_at="2024-01-01T12:00:00Z",
+        )
+
+        # Should not raise - just skips since message isn't persisted and buffer is empty
+        session_manager.update_message("test-session-456", "test-agent-123", message)
+
+    def test_update_message_create_fails(self, session_manager, mock_memory_client):
+        """Test update_message raises SessionException when create fails."""
+        mock_memory_client.create_event.side_effect = Exception("API Error")
+
+        message = SessionMessage(
+            message={"role": "user", "content": [{"text": "redacted"}]},
+            message_id="old_event_123",
+            created_at="2024-01-01T12:00:00Z",
+        )
+
+        with pytest.raises(SessionException, match="Failed to update message"):
+            session_manager.update_message("test-session-456", "test-agent-123", message)
+
+    def test_update_message_delete_fails(self, session_manager, mock_memory_client):
+        """Test update_message raises SessionException when delete fails."""
+        mock_memory_client.create_event.return_value = {"eventId": "new_event_456"}
+        mock_memory_client.gmdp_client.delete_event.side_effect = Exception("Delete failed")
+
+        message = SessionMessage(
+            message={"role": "user", "content": [{"text": "redacted"}]},
+            message_id="old_event_123",
+            created_at="2024-01-01T12:00:00Z",
+        )
+
+        with pytest.raises(SessionException, match="Failed to update message"):
+            session_manager.update_message("test-session-456", "test-agent-123", message)
+
     def test_list_messages_with_limit(self, session_manager, mock_memory_client):
         """Test listing messages with limit."""
         mock_memory_client.list_events.return_value = [
@@ -1366,6 +1420,31 @@ def test_pending_message_count_with_buffered_messages(self, batching_session_man
         # Verify no events were sent (still buffered)
         mock_memory_client.create_event.assert_not_called()
 
+    def test_update_buffered_message(self, batching_session_manager, mock_memory_client):
+        """Test update_message replaces a buffered message in-place when message_id is None."""
+        # Add a user message to buffer
+        message = SessionMessage(
+            message={"role": "user", "content": [{"text": "offensive content"}]},
+            message_id=0,
+            created_at="2024-01-01T12:00:00Z",
+        )
+        batching_session_manager.create_message("test-session-456", "test-agent", message)
+        assert batching_session_manager.pending_message_count() == 1
+
+        # Update with redacted content (message_id=None simulates unbatched message)
+        redacted = SessionMessage(
+            message={"role": "user", "content": [{"text": "Message redacted by guardrail"}]},
+            message_id=None,
+            created_at="2024-01-01T12:00:00Z",
+        )
+        batching_session_manager.update_message("test-session-456", "test-agent", redacted)
+
+        # Buffer should still have 1 message but with updated content
+        assert batching_session_manager.pending_message_count() == 1
+        # No API calls should have been made (still buffered)
+        mock_memory_client.create_event.assert_not_called()
+        mock_memory_client.gmdp_client.delete_event.assert_not_called()
+
     def test_buffer_auto_flushes_at_batch_size(self, batching_session_manager, mock_memory_client):
         """Test buffer automatically flushes when reaching batch_size."""
         mock_memory_client.gmdp_client.create_event.return_value = {"eventId": "event_123"}