Describe the bug
When AgentCoreMemorySessionManager is configured with filter_restored_tool_context=True, restoring a session can produce a message array that Bedrock Converse rejects.
_filter_restored_tool_context strips toolUse/toolResult blocks from restored history. A user turn that carried only a toolResult becomes empty and is dropped. Dropping it leaves the two surrounding assistant turns adjacent, which breaks Converse's strict role alternation. The history can also end up starting on an assistant turn.
On the next invocation Bedrock rejects the array. On models that reject assistant prefill it surfaces as:
ValidationException (ConverseStream): This model does not support assistant message prefill.
The conversation must end with a user message.
In a Strands agent on AgentCore Runtime this fails the event loop and the invocation returns a 500. The invalid array is built by the tool-use loop plus restore regardless of model — a prefill-tolerant model silently accepts it, so the issue can stay hidden until a model switch surfaces it (observed: the same restored history failed on Claude Opus 4.8 but was accepted by Claude Sonnet 4.6).
To Reproduce
A restored conversation of this shape is enough to trigger it:
user(query) → assistant(text + toolUse) → user(toolResult only) → assistant(answer)
- Configure
AgentCoreMemoryConfig(..., filter_restored_tool_context=True).
- Persist a turn where the assistant calls a tool and the following user turn contains only the
toolResult.
- Restore the session (e.g. construct a new
Agent with the same session manager) and invoke it.
- After stripping, the toolResult-only user turn is dropped and the history collapses to two adjacent
assistant turns; the next Converse call fails with the ValidationException above.
Expected behavior
After stripping tool blocks, the restored history should stay valid for Bedrock Converse: strict role alternation, starting on a user turn. Adjacent same-role turns left behind by the strip should be merged so the array remains valid once the runtime appends the next user turn before the model call.
Environment
bedrock-agentcore (Strands integration: bedrock_agentcore.memory.integrations.strands)- Strands agent running on Amazon Bedrock AgentCore Runtime
- Bedrock model that rejects assistant prefill,
ConverseStream
Describe the bug
When
AgentCoreMemorySessionManageris configured withfilter_restored_tool_context=True, restoring a session can produce a message array that Bedrock Converse rejects._filter_restored_tool_contextstripstoolUse/toolResultblocks from restored history. A user turn that carried only atoolResultbecomes empty and is dropped. Dropping it leaves the two surrounding assistant turns adjacent, which breaks Converse's strict role alternation. The history can also end up starting on an assistant turn.On the next invocation Bedrock rejects the array. On models that reject assistant prefill it surfaces as:
In a Strands agent on AgentCore Runtime this fails the event loop and the invocation returns a 500. The invalid array is built by the tool-use loop plus restore regardless of model — a prefill-tolerant model silently accepts it, so the issue can stay hidden until a model switch surfaces it (observed: the same restored history failed on Claude Opus 4.8 but was accepted by Claude Sonnet 4.6).
To Reproduce
A restored conversation of this shape is enough to trigger it:
AgentCoreMemoryConfig(..., filter_restored_tool_context=True).toolResult.Agentwith the same session manager) and invoke it.assistantturns; the next Converse call fails with the ValidationException above.Expected behavior
After stripping tool blocks, the restored history should stay valid for Bedrock Converse: strict role alternation, starting on a user turn. Adjacent same-role turns left behind by the strip should be merged so the array remains valid once the runtime appends the next user turn before the model call.
Environment
bedrock-agentcore(Strands integration:bedrock_agentcore.memory.integrations.strands)ConverseStream