The single- and multi-level suspend/restore tests gated their slow
leaf tool on a manual release channel closed 50ms after cancel().
That sleep was a guess at how long the suspend signal takes to reach
the running sub-agent, so the post-tool turn boundary could observe
the release before cancellation and complete the run instead of
checkpointing, making the assertions timing-dependent.
Expose the per-run suspend signal through SuspendSignalFrom in an
export_test shim and have the leaf tools block on it directly. The
tool now returns only once the graceful-suspend signal has actually
propagated to its agent, so suspension is observed deterministically
without sleeps or release channels.
Signed-off-by: Bryan Frimin <bryan@probo.com>
