[BUG] AttributeError in AgentCoreMemorySessionManager when created_message is None

[Sami-Tanquary]

Describe the bug
When using Strands agents with tool calls on the AgentCore runtime, applying the upstream OpenTelemetry fix for Bedrock ConverseStream responses (PR #3990) consistently exposes a failure in the AgentCore Memory Strands session manager during message persistence.

Specifically, AgentCoreMemorySessionManager.append_message assumes the memory “create message/event” call always returns a dict, and crashes when it returns None:

created_message.get("eventId")
# AttributeError: 'NoneType' object has no attribute 'get'

This occurs when the session manager hook attempts to persist Strands message events generated during tool-use flows.

To Reproduce
Steps to reproduce the behavior:

1. Deploy a Strands agent configured to use AgentCore Memory on the AgentCore runtime.

2. Enable tool calling on the agent.

3. Apply the upstream OpenTelemetry Bedrock ConverseStream guard (PR #3990) to avoid the KeyError: 'output' crash (the runtime currently injects an AWS OpenTelemetry distro that predates this fix).

4. Invoke a tool during a normal agent turn (toolUse → toolResult).

5. Observe the agent invocation fail with:

AttributeError: 'NoneType' object has no attribute 'get'
  at bedrock_agentcore/memory/integrations/strands/session_manager.py:488

Expected behavior

• Applying the upstream OpenTelemetry fix should allow execution to proceed normally.

• If a memory persistence call fails or returns an empty response, the AgentCore Memory session manager should handle it gracefully (or surface a clear error), rather than crashing the agent event loop.

• Tool-use flows should not cause unhandled exceptions during memory message persistence.

Screenshots
N/A (stack trace and logs available).

Desktop (please complete the following information):
OS: Linux (AgentCore managed runtime)
Runtime: AWS Bedrock AgentCore
Python: 3.13
Strands Agents: 1.21.0
bedrock-agentcore: 1.2.0

Additional context

• The AgentCore runtime injects an AWS OpenTelemetry distro (telemetry.auto.version: 0.12.2-aws) that does not yet include the upstream OpenTelemetry fix for Bedrock ConverseStream (PR #3990).

• Applying that fix via monkey patch unblocks execution but consistently exposes this separate failure in the AgentCore Memory Strands integration.

• The failure occurs when the session manager hook attempts to persist Strands message events produced during tool-use flows; the persistence call returns None, which is not currently guarded against.