Step B of the `._ria_nursery` removal (issue #477; see
`ai/conc-anal/ria_nursery_removal_plan.md`). With step A having
rerouted `.run_in_actor()` children onto the daemon nursery,
the 2ndary "run-in-actor" nursery spawns nothing and its stored
ref is never read — pure dead weight,
- collapse the inner `async with trio.open_nursery() as
ria_nursery` layer in
`_open_and_supervise_one_cancels_all_nursery`; `da_nursery` is
now the single nursery for ALL subactors.
- `ActorNursery.__init__` loses the `ria_nursery` param + the
`self._ria_nursery` attr; `start_actor()` loses its `nursery=`
escape-hatch (spawns via `self._da_nursery` directly).
- `._cancel_after_result_on_exit` stays — still the ria-child
discriminator for `_reap_ria_portals()`.
Behavior-preserving: a zero-task `trio.open_nursery()` only adds
a checkpoint. The two error handlers are KEPT (now nested under
the single nursery); merging them changes error/cancel
propagation and is deferred to its own PR (TODO left at the
outer `except`).
Prompt-IO: ai/prompt-io/claude/20260702T172233Z_5cd190c5_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
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