Factor the sub-actor relay loop out of
`dump_tree_on_sig()` into `_relay_sig_to_subactors()`
and chain both dump + relay in a single
`run_sync_soon` callback (`_dump_then_relay`) so the
parent's task-tree flushes BEFORE any sub receives
the signal — fixes a hierarchical-ordering race
where subs could dump ahead of the parent in the
muxed pty stream.
Also,
- gate file/tty sink writes behind `write_file` +
`write_tty` params on `dump_task_tree()`.
- use `actor.aid.uid` instead of deprecated `.uid`.
- update `test_shield_pause` expects to match the
new sequential parent -> relay-log -> sub ordering.
(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code