Step B2 of the `._ria_nursery` removal (issue #477; see
`ai/conc-anal/ria_nursery_removal_plan.md`). With the 2ndary
nursery gone (step B), the two nested error handlers in
`_open_and_supervise_one_cancels_all_nursery` collapse to one,
- the outer `except (Exception, BaseExceptionGroup,
trio.Cancelled)` existed to catch errors bubbling from the
old `._ria_nursery.__aexit__` reaper-group; that nursery no
longer exists.
- trace shows the outer handler's `raise` was already DEAD: the
inner handler records `errors[uid]` as its first action, so
`errors` is always non-empty by the time anything could reach
the outer handler, and the `finally`'s raise-from-`errors`
always superseded the outer `raise`.
- so fold both into a single `except BaseException as
_scope_err` guarding the lone daemon nursery; the `finally`
(unchanged) still raises the collected `errors` as a single
exc or `BaseExceptionGroup`.
- drop the now-unused `outer_err`/`inner_err` locals.
Behaviour-preserving (net ~30 lines lighter); the big diff is
the one-level de-indent of the handler body. The two remaining
`maybe_wait_for_debugger()` guards collapse to the single
pre-teardown wait.
Prompt-IO: ai/prompt-io/claude/20260702T222544Z_9201a2ed_prompt_io.md
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Gud Boi
e617b498ec