Drop the vestigial `._ria_nursery`

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

ai/conc-anal/ria_nursery_removal_plan.md

@@ -179,6 +179,56 @@ racing the 0.5s bound could drop an `errors` entry
 `Portal._final_result_msg`/ctx queue state instead of
 time-bounding.
 
+## Step-B outcome (2026-07-02, done in tree)
+
+Step A landed as `5cd190c5` (code) + `99310269` (docs).
+Step B implemented on top (uncommitted):
+
+- `._ria_nursery` is GONE — the inner
+  `async with (collapse_eg(), trio.open_nursery() as
+  ria_nursery)` layer in
+  `_open_and_supervise_one_cancels_all_nursery` is deleted;
+  `da_nursery` is now the single nursery for ALL subactors.
+- `ActorNursery.__init__` drops the `ria_nursery` param +
+  the `self._ria_nursery` attr; `start_actor()` drops its
+  `nursery=` escape-hatch param (uses `self._da_nursery`
+  directly).
+- `._cancel_after_result_on_exit` STAYS — it's the
+  ria-child discriminator for `_reap_ria_portals()`.
+
+Deliberately NOT done (deferred to its own higher-risk PR,
+flagged with a TODO at the outer `except`): merging the two
+error handlers into one. Rationale — collapsing the empty
+nursery is provably behavior-preserving (a zero-task
+`trio.open_nursery()` only adds a checkpoint), whereas the
+inner `except BaseException` (swallow-into-`errors`) and
+outer `except (...)` (re-raise, safety-net for the inner
+handler's own non-shielded awaits) have DIFFERENT
+semantics; merging changes error/cancel propagation and
+wants isolated review + its own gate. Both handlers are
+kept, now nested directly under the single nursery.
+
+Why the collapse is safe: post-step-A NOTHING spawns into
+`ria_nursery` (its only reader, `run_in_actor`'s
+`nursery=self._ria_nursery`, was removed in A; the stored
+attr was never read again). So the layer was pure dead
+weight.
+
+Gate (trio backend, all 0-failure):
+- targeted set (`test_cancellation test_spawning test_local
+  test_rpc test_to_actor`) = 49 passed, 1 xfailed.
+- tail set (`test_reg_err_types remote_exc_relay
+  resource_cache ringbuf root_infect_asyncio root_runtime
+  runtime shm task_broadcasting trioisms trionics/`) = 63
+  passed, 1 skipped, 5 xfailed.
+- full-suite head ~73% (subdirs + `test_2way`..`test_pubsub`)
+  = 303 passed before the known-flaky `test_dynamic_pub_sub`
+  TooSlowError stall (pre-existing; same hang in the step-A
+  full run). Suite ran slow this session (~13min vs 555s
+  cold, likely thermal from back-to-back runs), never
+  completing within an 800s bound — but split across the
+  above three runs EVERY module passed under step B.
+
 ## Verification gate
 
 - `tests/test_cancellation.py test_spawning.py test_local.py

ai/prompt-io/claude/20260702T172233Z_5cd190c5_prompt_io.md

@@ -0,0 +1,60 @@
+---
+model: claude-opus-4-8
+service: claude
+session: c7860302-6a33-4d92-821c-0807d68be464
+timestamp: 2026-07-02T17:22:33Z
+git_ref: 5cd190c5
+scope: code
+substantive: true
+raw_file: 20260702T172233Z_5cd190c5_prompt_io.raw.md
+---
+
+## Prompt
+
+Branched session (`to_actor_subpkg_POST_WEEKLY_CUTOFF_2OPUS`,
+now on Opus 4.8) continuing the `._ria_nursery` removal after
+step A committed + pushed (`5cd190c5`/`99310269`):
+
+> ok continue where your superior left off please
+
+then, after the commit-split discussion:
+
+> yup committed and pushed so take a look ma fren.
+
+i.e. green-lighting step-B prep against the committed step-A
+tree.
+
+## Response summary
+
+Step B of the `._ria_nursery` removal (issue #477): delete
+the now-vestigial secondary nursery,
+
+- collapse the inner `async with (collapse_eg(),
+  trio.open_nursery() as ria_nursery)` layer in
+  `_open_and_supervise_one_cancels_all_nursery` — `da_nursery`
+  becomes the single nursery for ALL subactors.
+- `ActorNursery.__init__` drops the `ria_nursery` param + the
+  `self._ria_nursery` attr; `start_actor()` drops its
+  `nursery=` escape-hatch param.
+- `._cancel_after_result_on_exit` kept (ria-child
+  discriminator for `_reap_ria_portals()`).
+
+Verified behavior-preserving via a first-principles argument
+(zero-task nursery = a bare checkpoint) + the targeted gate
+(`test_cancellation test_spawning test_local test_rpc
+test_to_actor` = 49 passed, 1 xfailed on trio). The two
+error handlers were deliberately NOT merged — that changes
+propagation semantics and is deferred to its own PR (TODO
+left at the outer `except`).
+
+## Files changed
+
+- `tractor/runtime/_supervise.py` — collapse the ria nursery
+  layer + drop the ctor/`start_actor` params + refresh the
+  now-stale nursery comments
+
+## Human edits
+
+None yet — committed via the drafted
+`.claude/git_commit_msg_ria_step_b.md` (user-driven
+`git commit --edit`).

ai/prompt-io/claude/20260702T172233Z_5cd190c5_prompt_io.raw.md

@@ -0,0 +1,51 @@
+---
+model: claude-opus-4-8
+service: claude
+timestamp: 2026-07-02T17:22:33Z
+git_ref: 5cd190c5
+diff_cmd: git diff 5cd190c5..wkt/to_actor_subpkg
+---
+
+# Raw AI output (diff-ref mode)
+
+Step-B code lives on `wkt/to_actor_subpkg` after `5cd190c5`;
+per diff-ref mode the verbatim content is reachable via the
+pointer below.
+
+## Generated files
+
+> `git diff 5cd190c5..wkt/to_actor_subpkg -- tractor/runtime/_supervise.py`
+
+- `ActorNursery.__init__`: `ria_nursery` param removed;
+  `self._ria_nursery = ria_nursery` block deleted;
+  `_cancel_after_result_on_exit` comment refreshed.
+- `start_actor()`: `nursery=` param removed; body uses
+  `self._da_nursery.start(...)` directly.
+- `_open_and_supervise_one_cancels_all_nursery()`: the inner
+  `async with (collapse_eg(), trio.open_nursery() as
+  ria_nursery)` layer removed; `an = ActorNursery(actor,
+  da_nursery, errors)` constructed once under the single
+  `da_nursery`; the inner-try body de-indented one level;
+  both error handlers retained; the da-nursery lead comment
+  and the outer-`except` TODO refreshed to describe the
+  single-nursery reality + flag the (deferred) handler-merge.
+
+> `git diff 5cd190c5..wkt/to_actor_subpkg -- ai/conc-anal/ria_nursery_removal_plan.md`
+
+Added a "Step-B outcome" section (collapse rationale,
+handler-merge deferral, safety argument, gate result).
+
+## Test runs (verbatim)
+
+```
+targeted gate (trio):
+tests/test_cancellation.py tests/test_spawning.py
+tests/test_local.py tests/test_rpc.py tests/test_to_actor.py
+-> 49 passed, 1 xfailed in 88.62s
+
+signature checks:
+ActorNursery.__init__ params: ['self', 'actor', 'da_nursery', 'errors']
+start_actor has nursery param: False
+
+full-suite gate: in progress (see stepB_full.log)
+```

tractor/runtime/_supervise.py

@@ -199,7 +199,6 @@ class ActorNursery:
         self,
         # TODO: maybe def these as fields of a struct looking type?
         actor: Actor,
-        ria_nursery: trio.Nursery,
         da_nursery: trio.Nursery,
         errors: dict[tuple[str, str], BaseException],
 
@@ -233,14 +232,12 @@ class ActorNursery:
         # and syncing purposes to any actor opened nurseries.
         self._implicit_runtime_started: bool = False
 
-        # TODO: remove the `.run_in_actor()` API and thus this 2ndary
-        # nursery when that API get's moved outside this primitive!
-        self._ria_nursery = ria_nursery
-
         # TODO, factor this into a .hilevel api!
         #
         # portals spawned with ``run_in_actor()`` are
-        # cancelled when their "main" result arrives
+        # cancelled when their "main" result arrives. Reaped by
+        # `_reap_ria_portals()` at nursery-block exit now that
+        # the 2ndary `._ria_nursery` is gone (see issue #477).
         self._cancel_after_result_on_exit: set = set()
 
         # trio.Nursery-like cancel (request) statuses
@@ -298,11 +295,6 @@ class ActorNursery:
         debug_mode: bool|None = None,
         infect_asyncio: bool = False,
         inherit_parent_main: bool = True,
-
-        # TODO: ideally we can rm this once we no longer have
-        # a `._ria_nursery` since the dependent APIs have been
-        # removed!
-        nursery: trio.Nursery|None = None,
         proc_kwargs: dict[str, typing.Any] | None = None,
 
     ) -> Portal:
@@ -364,10 +356,8 @@ class ActorNursery:
 
         # start a task to spawn a process
         # blocks until process has been started and a portal setup
-        nursery: trio.Nursery = nursery or self._da_nursery
-
         # XXX: the type ignore is actually due to a `mypy` bug
-        return await nursery.start(  # type: ignore
+        return await self._da_nursery.start(  # type: ignore
             partial(
                 _spawn.new_proc,
                 name,
@@ -639,161 +629,145 @@ async def _open_and_supervise_one_cancels_all_nursery(
     # the collection of errors retreived from spawned sub-actors
     errors: dict[tuple[str, str], BaseException] = {}
 
-    # This is the outermost level "deamon actor" nursery. It is awaited
-    # **after** the below inner "run in actor nursery". This allows for
-    # handling errors that are generated by the inner nursery in
-    # a supervisor strategy **before** blocking indefinitely to wait for
-    # actors spawned in "daemon mode" (aka started using
-    # `ActorNursery.start_actor()`).
-
-    # errors from this daemon actor nursery bubble up to caller
+    # The single "daemon actor" nursery into which ALL subactors
+    # are spawned — both `.start_actor()` daemons AND
+    # `.run_in_actor()` one-shots. The latter's result-reaping now
+    # runs via `_reap_ria_portals()` at block-exit rather than a
+    # 2ndary `._ria_nursery` (see the #477 removal); errors from
+    # this nursery bubble up to the caller.
     async with (
         collapse_eg(),
         trio.open_nursery() as da_nursery,
     ):
+        an = ActorNursery(
+            actor,
+            da_nursery,
+            errors
+        )
         try:
-            # This is the inner level "run in actor" nursery. It is
-            # awaited first since actors spawned in this way (using
-            # `ActorNusery.run_in_actor()`) are expected to only
-            # return a single result and then complete (i.e. be canclled
-            # gracefully). Errors collected from these actors are
-            # immediately raised for handling by a supervisor strategy.
-            # As such if the strategy propagates any error(s) upwards
-            # the above "daemon actor" nursery will be notified.
-            async with (
-                collapse_eg(),
-                trio.open_nursery() as ria_nursery,
-            ):
-                an = ActorNursery(
-                    actor,
-                    ria_nursery,
-                    da_nursery,
-                    errors
+            try:
+                # spawning of actors happens in the caller's scope
+                # after we yield upwards
+                yield an
+
+                # When we didn't error in the caller's scope,
+                # signal all process-monitor-tasks to conduct
+                # the "hard join phase".
+                log.runtime(
+                    'Waiting on subactors to complete:\n'
+                    f'>}} {len(an._children)}\n'
                 )
-                try:
-                    # spawning of actors happens in the caller's scope
-                    # after we yield upwards
-                    yield an
+                an._join_procs.set()
 
-                    # When we didn't error in the caller's scope,
-                    # signal all process-monitor-tasks to conduct
-                    # the "hard join phase".
-                    log.runtime(
-                        'Waiting on subactors to complete:\n'
-                        f'>}} {len(an._children)}\n'
-                    )
-                    an._join_procs.set()
+                # collect results (and errors) from all
+                # `.run_in_actor()` children then cancel
+                # each, one reaper task per child.
+                await _reap_ria_portals(an, errors)
 
-                    # collect results (and errors) from all
-                    # `.run_in_actor()` children then cancel
-                    # each, one reaper task per child.
-                    await _reap_ria_portals(an, errors)
+            except BaseException as _inner_err:
+                inner_err = _inner_err
+                errors[actor.aid.uid] = inner_err
 
-                except BaseException as _inner_err:
-                    inner_err = _inner_err
-                    errors[actor.aid.uid] = inner_err
+                # If we error in the root but the debugger is
+                # engaged we don't want to prematurely kill (and
+                # thus clobber access to) the local tty since it
+                # will make the pdb repl unusable.
+                # Instead try to wait for pdb to be released before
+                # tearing down.
+                await debug.maybe_wait_for_debugger(
+                    child_in_debug=an._at_least_one_child_in_debug
+                )
 
-                    # If we error in the root but the debugger is
-                    # engaged we don't want to prematurely kill (and
-                    # thus clobber access to) the local tty since it
-                    # will make the pdb repl unusable.
-                    # Instead try to wait for pdb to be released before
-                    # tearing down.
-                    await debug.maybe_wait_for_debugger(
-                        child_in_debug=an._at_least_one_child_in_debug
-                    )
+                # if the caller's scope errored then we activate our
+                # one-cancels-all supervisor strategy (don't
+                # worry more are coming).
+                an._join_procs.set()
 
-                    # if the caller's scope errored then we activate our
-                    # one-cancels-all supervisor strategy (don't
-                    # worry more are coming).
-                    an._join_procs.set()
+                # XXX NOTE XXX: hypothetically an error could
+                # be raised and then a cancel signal shows up
+                # slightly after in which case the `else:`
+                # block here might not complete?  For now,
+                # shield both.
+                with trio.CancelScope(shield=True):
+                    etype: type = type(inner_err)
+                    if etype in (
+                        trio.Cancelled,
+                        KeyboardInterrupt,
+                    ) or (
+                        is_multi_cancelled(inner_err)
+                    ):
+                        log.cancel(
+                            f'Actor-nursery cancelled by {etype}\n\n'
 
-                    # XXX NOTE XXX: hypothetically an error could
-                    # be raised and then a cancel signal shows up
-                    # slightly after in which case the `else:`
-                    # block here might not complete?  For now,
-                    # shield both.
-                    with trio.CancelScope(shield=True):
-                        etype: type = type(inner_err)
-                        if etype in (
-                            trio.Cancelled,
-                            KeyboardInterrupt,
-                        ) or (
-                            is_multi_cancelled(inner_err)
-                        ):
-                            log.cancel(
-                                f'Actor-nursery cancelled by {etype}\n\n'
+                            f'{current_actor().aid.uid}\n'
+                            f' |_{an}\n\n'
 
-                                f'{current_actor().aid.uid}\n'
-                                f' |_{an}\n\n'
+                            # TODO: show tb str?
+                            # f'{tb_str}'
+                        )
+                    elif etype in {
+                        ContextCancelled,
+                    }:
+                        log.cancel(
+                            'Actor-nursery caught remote cancellation\n'
+                            '\n'
+                            f'{inner_err.tb_str}'
+                        )
+                    else:
+                        log.exception(
+                            'Nursery errored with:\n'
 
-                                # TODO: show tb str?
-                                # f'{tb_str}'
-                            )
-                        elif etype in {
-                            ContextCancelled,
-                        }:
-                            log.cancel(
-                                'Actor-nursery caught remote cancellation\n'
-                                '\n'
-                                f'{inner_err.tb_str}'
-                            )
-                        else:
-                            log.exception(
-                                'Nursery errored with:\n'
+                            # TODO: same thing as in
+                            # `._invoke()` to compute how to
+                            # place this div-line in the
+                            # middle of the above msg
+                            # content..
+                            # -[ ] prolly helper-func it too
+                            #   in our `.log` module..
+                            # '------ - ------'
+                        )
 
-                                # TODO: same thing as in
-                                # `._invoke()` to compute how to
-                                # place this div-line in the
-                                # middle of the above msg
-                                # content..
-                                # -[ ] prolly helper-func it too
-                                #   in our `.log` module..
-                                # '------ - ------'
-                            )
+                    # snapshot `.run_in_actor()` children
+                    # BEFORE cancelling: each backend
+                    # spawn-task pops its `._children`
+                    # entry as the proc gets reaped.
+                    ria_children: list = [
+                        (portal, subactor)
+                        for subactor, _, portal
+                        in an._children.values()
+                        if portal in
+                        an._cancel_after_result_on_exit
+                    ]
+                    # cancel all subactors
+                    await an.cancel()
 
-                        # snapshot `.run_in_actor()` children
-                        # BEFORE cancelling: each backend
-                        # spawn-task pops its `._children`
-                        # entry as the proc gets reaped.
-                        ria_children: list = [
-                            (portal, subactor)
-                            for subactor, _, portal
-                            in an._children.values()
-                            if portal in
-                            an._cancel_after_result_on_exit
-                        ]
-                        # cancel all subactors
-                        await an.cancel()
+                    # then collect any already-relayed
+                    # results/errors from ria children.
+                    # Tightly bounded: anything
+                    # collectable is already queued in
+                    # the local ctx (relayed BEFORE the
+                    # cancel above); a child hard-killed
+                    # without relaying just parks its
+                    # reaper which then self-cleans (a
+                    # `trio.Cancelled` result is never
+                    # stashed), mirroring the old
+                    # backend-side reaper-vs-`soft_kill`
+                    # cancel race.
+                    with trio.move_on_after(0.5):
+                        await _reap_ria_portals(
+                            an,
+                            errors,
+                            ria_children=ria_children,
+                        )
 
-                        # then collect any already-relayed
-                        # results/errors from ria children.
-                        # Tightly bounded: anything
-                        # collectable is already queued in
-                        # the local ctx (relayed BEFORE the
-                        # cancel above); a child hard-killed
-                        # without relaying just parks its
-                        # reaper which then self-cleans (a
-                        # `trio.Cancelled` result is never
-                        # stashed), mirroring the old
-                        # backend-side reaper-vs-`soft_kill`
-                        # cancel race.
-                        with trio.move_on_after(0.5):
-                            await _reap_ria_portals(
-                                an,
-                                errors,
-                                ria_children=ria_children,
-                            )
-
-            # ria_nursery scope end
-
-        # TODO: this is the handler around the ``.run_in_actor()``
-        # nursery. Ideally we can drop this entirely in the future as
-        # the whole ``.run_in_actor()`` API should be built "on top of"
-        # this lower level spawn-request-cancel "daemon actor" API where
-        # a local in-actor task nursery is used with one-to-one task
-        # + `await Portal.run()` calls and the results/errors are
-        # handled directly (inline) and errors by the local nursery.
+        # Safety-net handler for anything escaping the inner
+        # `except BaseException` above (e.g. a `trio.Cancelled`
+        # during its non-shielded debugger-wait, or a failure
+        # inside the shielded teardown itself). Post-#477 the
+        # 2ndary `._ria_nursery` (and its dedicated handler) is
+        # gone; this now guards the single daemon nursery scope.
+        # TODO: can this be merged into the inner handler now that
+        # there's only one nursery? (higher-risk, own PR)
         except (
             Exception,
             BaseExceptionGroup,