Parallel tool calls cancel sibling calls when one fails

Summary

When multiple tool calls are dispatched in parallel and one fails, the remaining sibling calls are silently cancelled with 'Cancelled: parallel tool call errored' — even though they are completely independent.

Environment

• Claude Code CLI: 2.1.160
• OS: Windows 11

Steps to reproduce

1. Dispatch 3 independent Bash tool calls in parallel
2. Arrange for one to fail (e.g. command not found)
3. Observe: remaining 2 are cancelled rather than completing independently

Expected

Each parallel call completes independently regardless of sibling failures.

Impact

Forces sequential retries for work that should be parallel.