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,
@@ -639,37 +629,22 @@ 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
+    # The single "daemon actor" nursery into which ALL subactors
-    # **after** the below inner "run in actor nursery". This allows for
+    # are spawned — both `.start_actor()` daemons AND
-    # handling errors that are generated by the inner nursery in
+    # `.run_in_actor()` one-shots. The latter's result-reaping now
-    # a supervisor strategy **before** blocking indefinitely to wait for
+    # runs via `_reap_ria_portals()` at block-exit rather than a
-    # actors spawned in "daemon mode" (aka started using
+    # 2ndary `._ria_nursery` (see the #477 removal); errors from
-    # `ActorNursery.start_actor()`).
+    # this nursery bubble up to the caller.
-
-    # errors from this daemon actor nursery bubble up to caller
     async with (
         collapse_eg(),
         trio.open_nursery() as da_nursery,
-    ):
-        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:
             try:
                 # spawning of actors happens in the caller's scope
                 # after we yield upwards
@@ -785,15 +760,14 @@ async def _open_and_supervise_one_cancels_all_nursery(
                             ria_children=ria_children,
                         )
 
-            # ria_nursery scope end
+        # Safety-net handler for anything escaping the inner
-
+        # `except BaseException` above (e.g. a `trio.Cancelled`
-        # TODO: this is the handler around the ``.run_in_actor()``
+        # during its non-shielded debugger-wait, or a failure
-        # nursery. Ideally we can drop this entirely in the future as
+        # inside the shielded teardown itself). Post-#477 the
-        # the whole ``.run_in_actor()`` API should be built "on top of"
+        # 2ndary `._ria_nursery` (and its dedicated handler) is
-        # this lower level spawn-request-cancel "daemon actor" API where
+        # gone; this now guards the single daemon nursery scope.
-        # a local in-actor task nursery is used with one-to-one task
+        # TODO: can this be merged into the inner handler now that
-        # + `await Portal.run()` calls and the results/errors are
+        # there's only one nursery? (higher-risk, own PR)
-        # handled directly (inline) and errors by the local nursery.
         except (
             Exception,
             BaseExceptionGroup,