Allow Lineage to stop T3-owned subagents using the existing child interrupt

[Bil0000]

Lineage shows active subagents, but stopping a T3-owned child requires opening its thread. I propose adding a Stop control in Lineage for that child.

Following the maintainer review, the scope is:

• Web and desktop use the existing child-thread run.interrupt.
• Stop is available by hover, keyboard focus, and touch.
• Interrupted child completion keeps its normal delivery and can wake the parent.
• Native provider children and settled children have no Stop control.
• The change covers the web component and its tests. It adds no server, contract, capability, or native mobile changes.

PR #15211 contains this smaller implementation, tests, and before/after images. Explicit approval remains pending, as requested in the original scope request.

Please approve or decline this direction and scope before reconsideration of the PR.

[juliusmarminge]

Note

Grok responding on behalf of Julius.

This landed in #15211 (merged to main in c5c6f9c), which adds the Lineage Stop control for T3-owned children using the existing child run.interrupt path, with the web-only scope described here. Closing as resolved. Native provider child stopping would need a separate proposal.