fix(deepagents): forward subagent results as text

[Alexander Olsen (aolsenjazz)]

Summary

A deep agent that delegates to a subagent 400s when that subagent uses an Anthropic server-side tool (web search, web fetch, code execution, MCP). The subagent's final-message content blocks e.g. server_tool_use/..._tool_result were forwarded verbatim as the task ToolMessage content. On the parent agent's next request they serialize into a tool_result, which Anthropic rejects:

400 invalid_request_error messages.N.content.0.tool_result.content.0: Input tag 'server_tool_use' found using 'type' does not match any of the expected tags: 'document','image','search_result','text','tool_reference'

Solution

Now matches the Python impl: forward only the subagent's text answer. returnCommandWithStateUpdate now walks back to the last AIMessage with non-empty text and uses that text (a string) as the ToolMessage content.

• Confirmed the Python deepagents impl is not affected (it forwards .text); this aligns JS with Python.
• Reproduced the 400 across {web_search, code_execution, web_fetch} × {claude-haiku-4-5, claude-sonnet-4-6} on the latest published packages; all green after the fix.

Tests

• New: subagent server-tool blocks are filtered from forwarded content.
• New: walk-back uses the last non-empty AIMessage, skipping a trailing empty message.
• Updated the Bug: returnCommandWithStateUpdate fails when lastMessage.content is an array with tool_use blocks #239/Bug: thinking blocks leak into ToolMessage from returnCommandWithStateUpdate #245 tests to assert the (now string) ToolMessage content.
• No regressions in subagent-related tests in the evals suite

[changeset-bot]

🦋 Changeset detected

Latest commit: b2daf40

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
deepagents	Patch
deepagents-acp	Patch
@deepagents/evals	Patch

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Project	Deployment	Actions	Updated (UTC)
deepagentsjs-ui	Ready	Preview, Comment	Jun 20, 2026 11:10pm

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commit: b2daf40

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