[Bug] Parallel tool calls cancel all siblings on single error, which appears to cause model confusion

Question

**Bug Description**
When a single assistant message contains multiple tool calls and one of them exits non-zero, Claude Code cancels all the siblings and emits "Cancelled: parallel tool call ... errored". This confuses Opus 4.8 and makes it spiral into echoing things to test if its alive, like 'echo test123', 'echo alive', 'echo wakeup'.

**Environment Info**
- Platform: linux
- Terminal: ghostty
- Version: 2.1.158
- Feedback ID: b8d2cc19-b937-47ae-9e06-09d53061130a

**Errors**
```json
[]
```