fix(harness-claude-code): exclude subagent messages from parent step usage and tool-call tracking

[felixarntz]

Same as #18631 - that PR lacked verified commits. Credit goes to @patrickswedish.

Background

Claude Code emits messages from Task-tool subagents with a non-null parent_tool_use_id.

The harness currently processes those messages as though they belong to the parent agent step. This causes subagent > activity to affect the parent step's usage accounting and exposes subagent tool calls/results as parent-step events.

The issue has been reproduced against the current harness behavior with a captured Claude Code stream.

Summary

This PR keeps the change narrowly scoped:

• ignore assistant messages associated with a subagent when tracking the parent step
• ignore corresponding subagent user/tool-result messages
• preserve normal parent-agent usage and tool-call handling
• add regression coverage using a representative subagent stream fixture
• add a patch changeset for @ai-sdk/harness-claude-code

No public API or normal main-agent behavior is changed.

Verification

The regression covers a stream where subagent messages contain a non-null parent_tool_use_id.

It verifies that:

• the parent step retains its own token usage
• subagent tool calls are not emitted as parent-step tool calls
• subagent tool results are not emitted as parent-step tool results

Validation on the final branch:

• TypeScript — passed
• Lint & Format — passed
• Build Packages — passed
• AI test matrix on Node 22, 24, and 26 — passed
• Codemod test matrix — passed
• Example builds — passed
• Changeset verification — passed

Related Issues

Fixes #18618.

Closes #18619.

[github-actions]

🚀 Published in:

Package	Version
ai	7.0.62 github npm
@ai-sdk/amazon-bedrock	5.0.54 github npm
@ai-sdk/angular	3.0.62 github npm
@ai-sdk/azure	4.0.41 github npm
@ai-sdk/code-mode	1.0.19 github npm
@ai-sdk/gmicloud	3.0.1 github npm
@ai-sdk/harness	1.0.68 github npm
@ai-sdk/harness-acp	1.0.5 github npm
@ai-sdk/harness-claude-code	1.0.70 github npm
@ai-sdk/harness-codex	1.0.70 github npm
@ai-sdk/harness-deepagents	1.0.67 github npm
@ai-sdk/harness-grok-build	1.0.4 github npm
@ai-sdk/harness-opencode	1.0.69 github npm
@ai-sdk/harness-pi	1.0.69 github npm
@ai-sdk/langchain	3.0.62 github npm
@ai-sdk/llamaindex	3.0.62 github npm
@ai-sdk/openai	4.0.40 github npm
@ai-sdk/otel	1.0.62 github npm
@ai-sdk/policy-opa	1.0.62 github npm
@ai-sdk/react	4.0.65 github npm
@ai-sdk/rsc	3.0.62 github npm
@ai-sdk/sandbox-just-bash	1.0.68 github npm
@ai-sdk/sandbox-vercel	1.0.68 github npm
@ai-sdk/svelte	5.0.62 github npm
@ai-sdk/tui	1.0.63 github npm
@ai-sdk/vue	4.0.62 github npm
@ai-sdk/workflow	1.0.62 github npm
@ai-sdk/workflow-harness	1.0.68 github npm
@ai-sdk/xai	4.0.36 github npm