Async background delegation can leave gateway sessions holding only a dispatched handle when the detached runner wedges before it can return and enqueue a completion. Enforce the configured child timeout in the async registry so the parent observes a terminal timeout event and the async slot is released.
Constraint: Issue #60203 reports long-lived gateway processes with background child delegates that never produce completion events despite child_timeout_seconds being configured.
Rejected: Relying only on _run_single_child timeout handling | it cannot finalize the async registry when the outer runner thread itself never reaches normal completion.
Confidence: high
Scope-risk: narrow
Directive: Keep background delegation completion owned by the async registry whenever detached workers can outlive the caller's immediate control.
Tested: .venv/bin/python -m pytest tests/tools/test_async_delegation.py tests/tools/test_delegate_subagent_timeout_diagnostic.py tests/tools/test_delegate.py -q
Tested: .venv/bin/python -m ruff check tools/async_delegation.py tools/delegate_tool.py tests/tools/test_async_delegation.py
Tested: git diff --check
Not-tested: Multi-day real gateway degradation; covered with deterministic stuck-runner registry tests.
izumi0uu
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