[FEATURE] Cancel sub-agent actions

[dobesv]

📋 Prerequisites

• I have searched the existing issues to avoid creating a duplicate
• By submitting this issue, you agree to follow our Code of Conduct

📝 Feature Summary

Ability to cancel sub-agent session

❓ Problem Statement / Motivation

I was watching a session with sub-agents and the sub-agent went haywire polling something over and over. I wanted to kill it but no facility is provided for that.

💡 Proposed Solution

You can view the sub-agent activity but you cannot interrupt it. The fix would be some kind of interrupt or cancel button when viewing sub-agent activity.

🔄 Alternatives Considered

No response

🎯 Affected Service(s)

None

📚 Additional Context

No response

🙋 Are you willing to contribute?

• I am willing to submit a PR for this feature

[supreme-gg-gg]

I think there's no way to cancel an A2A task with the ADK executor right now as described in this issue, and Kagent doesn't not implement this yet, so it's not possible to cancel either main or subagent runs.

Once we have that (either wait until the open PR in ADK is merged or we implement our version), this would be possible by adding a cancellation propagation from main agent to subagent like how HITL events are propagated.