[danielkov]

Summary

Start all child cleanup tasks before awaiting their results during session shutdown, so slow child closes overlap instead of accumulating sequentially.

Technical details

Retain the existing five-second per-child timeout and cancellation-safe task ownership of children and capacity permits. Await every started cleanup task and propagate a failure without abandoning other children.

Add a gated ACP regression test that requires both children to receive close requests before either responds, covering normal completion and cancellation of the shutdown caller.

[kit-code-agent]

No issues found. The changes look good to merge.

_{Took 9 min 55 sec}