agent: composed abort for cursor bridge tools (request+run) - design follow-up

After fix of the exec-frame refusal regression, bridge tools execute under the run signal only. A future composed abort (AbortSignal.any of run + request signals threaded through a dual-signal factory contract) was evaluated and deliberately deferred: its request leg is empty on every reachable teardown path today (requestAbortController.abort only fires on caller abort and idle timeout, and the idle path re-arms during local work). Revisit if a real request-scoped teardown path appears. (2026-08-20 hyperdebate consensus.)

Start by reviewing the bridge-tool signal flow described here, including the run signal, requestAbortController, and dual-signal factory contract. Verify whether a real request-scoped teardown path exists beyond caller abort and idle timeout; done means reopening the composed-abort design only when such a path appears.

Written by the indexing model from the issue text.