fix(aws): flatten tool blocks when toolConfig is omitted#5850
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AWS Bedrock's Converse API rejects requests with ValidationException when messages contain toolUse/toolResult blocks but toolConfig is missing. Previously, tool_choice="none" caused _get_tool_config() to return None entirely, breaking any draining agent handoff that returned (NewAgent, str) (issue #5589). Bedrock has no native "none" choice (only auto/any/tool), so emit toolConfig.tools and let toolChoice default to auto. Upstream filter in voice/generation.py:545 already discards any tool calls the model emits when tool_choice="none".
`if self._tool_call_id is None` was nested inside `if self._tool_call_id:`, so the inner branch could never run.
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theomonnom
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May 26, 2026
When tool_choice="none" (or tools is empty) but chat history contains toolUse/toolResult blocks, Bedrock Converse rejects the request because toolConfig is required whenever tool blocks appear in messages. Switch to the langchain-aws approach (PR #595): drop toolConfig entirely and rewrite tool blocks as plain text. The model genuinely cannot call a tool (no tools list is sent) but still sees what happened on prior turns.
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Summary
ValidationExceptionwhentool_choice=\"none\"is requested while the chat context containstoolUse/toolResultblocks.if self._tool_call_id is Nonebranch in_parse_chunk.Root cause
Bedrock Converse's
ToolChoiceunion only acceptsauto/any/tool— there is nonone. Two facts collide:To request "no tools this turn," we'd want to omit
toolConfigentirely.Bedrock rejects any request whose
messagescontaintoolUseortoolResultblocks unlesstoolConfigis also present:This bites every agent handoff that returns
(NewAgent(), \"string\"): the draining old agent is forced to generate the string reply withtool_choice=\"none\"while the just-completed tool call/result blocks are still in chat history.Fix
Follow the approach landed in langchain-ai/langchain-aws#595: when
toolConfigis going to be omitted (either becausetool_choice=\"none\"or because no tools are provided), rewrite anytoolUse/toolResultcontent blocks in the outgoing messages as plain text ([Called <name> with <args>],[Tool output: ...]). Bedrock no longer sees structured tool blocks, so the validation error disappears, and because notoolslist is sent the model genuinely cannot call a tool — no reliance on downstream filtering to suppress unwanted tool calls.Test plan
basic_agentexample with an(Agent, str)handoff tool againstus.anthropic.claude-sonnet-4-6; pre-fix request fails withValidationException, post-fix the handoff completes cleanly._flatten_tool_blocksconfirmstoolUseandtoolResultblocks are rewritten totextblocks while plain-text content passes through unchanged.