Doc the #477 migration outcome + one-shot-acm sketch

Fold the endeavour's resolution into the plan doc + log the
session per prompt-io policy,

- `ria_nursery_removal_plan.md`: RESOLVED section — migrate
  everything, remove the API; the migration-pattern table
  (blocking / fire-and-forget / fan-out / collect-don't-cancel
  / mutual-rendezvous), the semantic deltas (cancel-on-first +
  `collapse_eg()` chain collapse vs the old teardown-reap BEG),
  the excision inventory and the structural dissolution of the
  reap-hang class.
- adds the `to_actor.open_one_shot()` follow-up sketch: an
  `@acm` + private task-nursery over the existing blocking
  `run()` — done-`trio.Event` as a result memo (NOT a
  cancel-relay), no `Portal` in the iface, errors always
  propagate at scope exit; zero `_supervise` coupling.
- prompt-io entry `20260706T172818Z_ad42871e` (+ raw diff-ref
  companion) covering commits `d01a2123..ad42871e`.

(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

@@ -0,0 +1,460 @@
+# `_ria_nursery` removal plan (issue #477 follow-up)
+
+Goal: drop the secondary "run-in-actor" spawn nursery (and
+friends) from `ActorNursery`/spawn internals, now that
+`tractor.to_actor.run()` delivers one-shot semantics purely on
+the daemon-spawn + portal primitives.
+
+## Verified machinery map (2026-07-02, wkt @ a34aaf98)
+
+The entire mechanism is 4 files:
+
+- `runtime/_supervise.py`
+  - `ActorNursery.__init__(.., ria_nursery, ..)` stores
+    `._ria_nursery` (:202, :238); sole read is
+    `run_in_actor()` passing `nursery=self._ria_nursery`
+    (:442) into `start_actor()`'s `nursery:
+    trio.Nursery|None` escape-hatch param (:305, :367).
+  - `._cancel_after_result_on_exit: set` (:244) marks ria
+    portals (:457).
+  - `_open_and_supervise_one_cancels_all_nursery()` nests
+    `da_nursery` (:609) around `ria_nursery` (:622); the
+    `finally:` at the ria->da boundary (:747-766) raises
+    collected `errors` (single exc or BEG).
+- `runtime/_portal.py`
+  - `._expect_result_ctx` (:112) set by `_submit_for_result()`
+    (:142, sole caller `run_in_actor()`); consumed by
+    `wait_for_result()` (:167) + deprecated `result()` (:220).
+    The `None` branch (:184-196) returns the `NoResult`
+    sentinel (`_exceptions.py:1164`).
+- `spawn/_spawn.py`
+  - `exhaust_portal()` (:129): awaits
+    `portal.wait_for_result()`, CATCHES+RETURNS any exc
+    (never raises).
+  - `cancel_on_completion()` (:177): `exhaust_portal()` ->
+    on exc-result stash `errors[uid] = result` (:203) ->
+    ALWAYS `portal.cancel_actor()` (:218).
+- `spawn/_trio.py` (:195-222) + `spawn/_mp.py` (:187-213),
+  identical shape: after shielded
+  `await an._join_procs.wait()`, open a per-child local
+  nursery; IFF `portal in an._cancel_after_result_on_exit`
+  start `cancel_on_completion` alongside `soft_kill()`; when
+  `soft_kill` returns first, `nursery.cancel_scope.cancel()`
+  reaps the result-waiter.
+
+## The load-bearing semantic (already-deferred errors)
+
+Remote ria-child errors NEVER raise into `ria_nursery`:
+
+1. reaper tasks only START after `_join_procs.set()` (block
+   exit or the inner error handler),
+2. `exhaust_portal` swallows the exc into a return value,
+3. `cancel_on_completion` stashes it in `errors` + cancels
+   that child,
+4. the ria->da `finally:` re-raises collected `errors` (and
+   `an.cancel()`s any daemon stragglers).
+
+So mid-block there is NO error propagation from ria children
+(unless user code explicitly `await portal.wait_for_result()`s)
+— the two-nursery nesting only sequences "reap ria results
+BEFORE blocking on daemon join". A single-nursery impl only
+needs to preserve that sequencing, not any ASAP-cancel
+behavior.
+
+## Target design
+
+### step A: single-nursery `run_in_actor()` (mechanical)
+
+- `run_in_actor()` spawns via the DEFAULT (`_da_nursery`)
+  path — drop `nursery=self._ria_nursery`.
+- rename `._cancel_after_result_on_exit` ->
+  `._ria_portals: dict[portal, Actor]` (need the subactor ref
+  for `cancel_on_completion`).
+- move reaper start-up OUT of the backends into
+  `_open_and_supervise...`: immediately after EACH
+  `an._join_procs.set()` call-site (happy path :642, inner
+  error handler :661), start one
+  `cancel_on_completion(portal, subactor, errors)` task per
+  ria portal into `da_nursery`, then (happy path only)
+  `await` their completion BEFORE falling out of the
+  `try:`/`finally:` that raises `errors` — e.g. gather in a
+  dedicated inner `trio.open_nursery()` block replacing
+  today's `ria_nursery` join point.
+- delete the membership branch + local reaper nursery from
+  `_trio.py`/`_mp.py` (keep the `soft_kill()` call; the
+  per-child local nursery collapses to just `soft_kill`).
+- `_trio.py:310` `_children.pop()` etc. unchanged.
+
+### step B: delete the plumbing
+
+- `_open_and_supervise...`: drop the inner
+  `ria_nursery` + merge its `except BaseException` classify
+  logic into ONE handler on the (now single) nursery scope;
+  `ActorNursery.__init__` loses the `ria_nursery` param.
+- `start_actor()` loses the `nursery:` escape-hatch param
+  (the :302-304 TODO).
+- backends: no more `_cancel_after_result_on_exit` refs.
+
+### step C: (separate PRs) deprecate + migrate + excise
+
+- migrate in-repo `.run_in_actor()` usage to
+  `to_actor.run()`: tests 46 hits/9 files (test_cancellation
+  15, test_infected_asyncio 10, test_spawning 8, registrar 3,
+  adv_streaming 4, pubsub 2, rpc 1, runtime 1), examples 28
+  hits/13 files (debugging/* dominate), docs 20 hits/8 rst
+  files. NOTE: many sites also use deprecated
+  `Portal.result()`/`wait_for_result()` — these die with
+  `_expect_result_ctx`, so migration must land FIRST.
+- add `DeprecationWarning` to `run_in_actor()` (+
+  `_submit_for_result`/`wait_for_result`).
+- final excision: `run_in_actor()`, `_submit_for_result`,
+  `_expect_result_ctx`, `wait_for_result`/`result`,
+  `exhaust_portal`, `cancel_on_completion`, `NoResult`.
+
+## Risk register
+
+1. hard-killed ria child: today the backend-local
+   `nursery.cancel_scope.cancel()` discards a still-parked
+   reaper when the proc dies first; a da_nursery-hosted
+   reaper instead sees the transport break ->
+   `exhaust_portal` returns a `TransportClosed`-ish exc ->
+   NEW entry in `errors` that today gets discarded. Guard:
+   reap-gather block must cancel remaining reapers once all
+   ria procs are dead, or filter transport-death excs for
+   already-`cancel_called` children.
+2. error-path ordering: inner handler today sets
+   `_join_procs` THEN `an.cancel()`; reapers race the
+   cancel-RPC. Keep that ordering when moving reaper spawn.
+3. debugger interplay: `maybe_wait_for_debugger()` calls
+   (:654, :730) must stay BEFORE any reap/cancel issuance.
+4. `errors` double-entry: local body error (:646) + child's
+   relayed exc (via reaper) can both land for the same
+   scenario -> BEG shape changes vs today? (today has the
+   same dual-write sites; keep behavior identical.)
+5. mp backend parity: mirror every `_trio.py` edit in
+   `_mp.py` (identical block).
+
+## Step-A first-probe findings (2026-07-02, WIP in tree)
+
+Step A is IMPLEMENTED (uncommitted):
+`run_in_actor()` spawns via da_nursery; new
+`_supervise._reap_ria_portals()` helper; reap awaited after
+happy-path `_join_procs.set()`; error-path runs reap
+CONCURRENT with `an.cancel()` in the shielded block;
+backends stripped of the membership branch + per-child
+reaper nursery (+ dead imports).
+
+Probe history (trio backend):
+- `tests/test_to_actor.py` + `tests/test_spawning.py`:
+  20/20 PASS — incl. all `run_in_actor()` result
+  round-trips + `test_remote_error` (single erroring child,
+  body re-raise -> inner error path).
+- FIRST attempt ran the error-path reap CONCURRENT with
+  `an.cancel()` (mimicking the old backend-side race):
+  `test_cancellation.py::test_multierror` (2 erroring ria
+  children, body re-raises one) DEADLOCKED. Root cause per
+  the sequencing fix below: reap + cancel must NOT race at
+  this layer (suspected `._children` pop-during-iteration
+  and/or double-cancel RPC wedge; not fully root-caused
+  since the fix removes the race wholesale).
+- FIX (2nd attempt, current impl): error path SEQUENCES:
+  (1) snapshot ria `(portal, subactor)` pairs (backend
+  `finally`s pop `._children` as procs reap), (2)
+  `await an.cancel()`, (3) bounded reap over the snapshot.
+  Bound was first 3s -> blew the `fail_after` deadline in
+  `test_cancel_while_childs_child_in_sync_sleep` (hard-
+  killed grandchild never relays => reaper parks the full
+  bound). Tightened to 0.5s: anything collectable is
+  already queued in the local ctx (relayed BEFORE the
+  cancel); a parked reaper self-cleans (`trio.Cancelled`
+  results are never stashed).
+- RESULT: `tests/test_cancellation.py` FULLY GREEN
+  (20 passed, 1 xfailed, 77s); full-suite gate run kicked
+  off same session (see final report/next session).
+
+Remaining risk: on slow CI a relayed-but-undelivered error
+racing the 0.5s bound could drop an `errors` entry
+(BEG-shape flake); if observed, scale the bound via the
+`cpu_perf_headroom()`-style approach or peek
+`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.
+
+## Step-B2 outcome (2026-07-02, done in tree)
+
+Step B committed as `9201a2ed` (code) + `d2e812fb` (docs), then
+branched to `drop_ria_nursery`. Step B2 (the deferred
+handler-merge) implemented on top (uncommitted):
+
+- the two nested handlers in
+  `_open_and_supervise_one_cancels_all_nursery` collapse to
+  ONE `except BaseException as _scope_err` + the existing
+  `finally`. The `outer_err`/`inner_err` locals go away.
+
+Why it's safe (trace, not hope): the OLD inner handler records
+`errors[actor.aid.uid]` as its FIRST statement (before any
+await). So whenever an error path runs, `errors` is non-empty.
+The OLD outer handler was only reachable via leakage from the
+inner handler (it catches `BaseException`, so nothing from the
+`yield` scope bypasses it) — and by then `errors` is already
+populated, so the `finally`'s `raise` from `errors` ALWAYS
+superseded the outer handler's own `raise`. i.e. the outer
+`raise` was dead. The outer handler's other effects
+(`_scope_error`, a 2nd debugger-wait, child-cancel) are
+redundant with the merged handler + `finally`. So one handler
++ `finally` is observably equivalent.
+
+Residual nuance (accepted): in the rare "`trio.Cancelled`
+delivered during the non-shielded `maybe_wait_for_debugger`"
+path, the merged form may leave `_cancel_called` False (cancel
+happens after the wait), so `open_nursery`'s tb-hiding guard
+(`not cancel_called and _scope_error`) can show a tb it
+previously hid. More informative, not less; no test asserts on
+it.
+
+Gate (box ran ~2.7x slow this session, load-induced
+`TooSlowError` flakiness on timing tests — NOT code; see
+[[env_cpu_throttle_masquerades_as_regression]]):
+- baseline (pre-B2 tip `9201a2ed`) full suite
+  (`-k 'not dynamic_pub_sub'`) = 300 passed + 1
+  `test_ext_types_over_ipc` `TooSlowError` that passes 6/6 in
+  isolation (4.89s).
+- B2 error/cancel gate (`test_cancellation remote_exc_relay
+  inter_peer_cancellation advanced_faults oob_cancellation
+  to_actor spawning local rpc`) = 71 passed, 1 xfailed
+  (125s).
+- B2 full-suite run: see `b2_full.log` (result appended on
+  completion). RECOMMEND a clean full-suite run on a
+  normal-speed box before this merges.
+
+## Regression + fix: ria-reap hang (2026-07-02)
+
+Human hit a full-suite hang on
+`test_infected_asyncio.py::test_tractor_cancels_aio`. Bisected:
+passes at pre-ria `a34aaf98` (0.59s), hangs at B2 `e617b498`
+(90s+). Root-caused to the STEP-A reaper hoist (`5cd190c5`),
+NOT B2 (`_reap_ria_portals` is byte-identical A->B2).
+
+Bug: the test does `run_in_actor(asyncio_actor)` then a USER
+`portal.cancel_actor()` and exits the block cleanly -> the
+happy path's `await _reap_ria_portals()`, which waits UNBOUNDED
+on `cancel_on_completion -> wait_for_result()`. The child was
+cancelled out-of-band so no final result is relayed -> parked
+forever. The OLD spawn-backend reaper was raced against
+`soft_kill()` (per-child nursery `cancel_scope.cancel()` on
+subproc death); the hoist dropped that race.
+
+Fix: `_reap_ria_portals()` runs each `cancel_on_completion()`
+in a local nursery alongside a `proc.poll()` death-watch that
+cancels the parked reaper once the subproc exits — restoring
+the old race, backend-agnostic (guarded by
+`hasattr(proc, 'poll')` for a future `subint` handle).
+
+Why POLL (`proc.poll()`) not the event-driven `wait_func`:
+the mp waiter (`_spawn.proc_waiter`) does
+`wait_readable(proc.sentinel)`, and `soft_kill()` is ALREADY
+awaiting that same fd concurrently in the daemon nursery — a
+2nd `wait_readable` on one fd raises `trio.BusyResourceError`.
+(`trio.Process.wait()` IS multi-waiter-safe, but mp has no
+async equivalent.) `proc.poll()` — the same liveness check
+`soft_kill` itself falls back to — is the conflict-free common
+denominator. Verified: poll-fix passes on BOTH trio and
+mp_spawn.
+
+Also added a per-test anti-hang guard: wrapped
+`test_tractor_cancels_aio`'s `main()` in
+`with trio.fail_after(9 * cpu_perf_headroom())` — the blessed
+pattern (`pytest-timeout`'s global cap is intentionally off;
+breaks trio under fork backends, see `pyproject` NOTE). So a
+future recurrence FAILS FAST instead of hanging the suite.
+(Several other tests in the file are still guardless —
+`test_aio_simple_error`, `test_trio_error_cancels_intertask_chan`,
+`test_aio_errors_and_channel_propagates_and_closes` — candidate
+follow-up sweep.)
+
+Lesson: the B2 focused gate OMITTED `test_infected_asyncio`
+(and the full runs were clipped/slow), so the step-A hang
+slipped through. Any future ria-touching change MUST gate
+`test_infected_asyncio` explicitly.
+
+Gate: `test_tractor_cancels_aio` green (trio 1.53s, mp 3.98s);
+fix gate (`test_infected_asyncio test_cancellation test_to_actor
+test_spawning`) = 74 passed, 3 xfailed, 0 failures.
+
+## PAUSED (2026-07-02): re-assess the reaper's SCOPE
+
+User's insight (compelling — likely the real root cause of
+the hang, not just the missing proc-death race):
+
+> the "hoisting" of 5cd190c5 was just not really done right
+> — the hoist should have been into the `to_actor` scope,
+> not `_supervise`.
+
+The argument: `.run_in_actor()`'s result-waiting/reaping got
+hoisted into `_supervise._reap_ria_portals` (nursery-machinery
+scope), which has NO natural cancel-scope to bound a parked
+`wait_for_result()` — hence the awkward proc-death race +
+the poll-vs-`proc_waiter` dilemma. If the result-wait instead
+lived in the `to_actor` one-shot scope
+(`to_actor._invoke_in_subactor()`), it would sit right next to
+the caller's `an` + a local `trio` task-nursery + cancel-scope
+(the `trio.to_thread`-style model #477 actually wants) — so
+bounding/cancelling the wait is trivial and the hang
+dissolves from correct scoping rather than a bolt-on race.
+
+Follow-on to re-evaluate on resume:
+- should `_reap_ria_portals` exist AT ALL, or should
+  result-waiting move entirely into
+  `to_actor._invoke_in_subactor()`?
+- reimplement legacy `run_in_actor()` on top of
+  `to_actor.run()` so `_reap_ria_portals` +
+  `_cancel_after_result_on_exit` can be DROPPED from
+  `_supervise` entirely (the true #477 simplification)?
+- the poll-vs-event decision is MOOT under this re-scoping.
+
+State at pause: `test_infected_asyncio` anti-hang guard
+COMMITTED (`d1fb4a1a`, intentionally red w/o the fix — the
+user's failing-test-first convention). The poll-based reap
+fix in `_supervise.py` is UNCOMMITTED and likely SUPERSEDED
+by the re-scoping — do NOT land it as-is.
+
+## RESOLVED (2026-07-06): migrate everything, remove the API
+
+The PAUSED re-assessment concluded decisively: rather than
+re-scope `_reap_ria_portals` (or bolt any hack onto it), the
+`run_in_actor()` API itself was REMOVED — its non-blocking
+"result at teardown" semantic predates streaming and confused
+more than it served. Every in-repo caller was migrated
+per-file/-group (each its own commit, each gated):
+
+- tests: `test_infected_asyncio` `test_runtime` `test_rpc`
+  `test_spawning` `test_pubsub` `test_registrar`
+  `test_cancellation` (3 groups) `test_advanced_streaming`.
+- examples: 4 non-debugging + all 8 `debugging/` REPL scripts
+  (debugger suite byte-identical green, 28p/6s).
+- docs: 8 rst pages + the `experimental/_pubsub` docstring.
+
+Migration patterns (the `run_in_actor` shape -> successor):
+
+- blocking result        -> `to_actor.run(fn, an=an, ...)`
+- fire-&-forget/forever  -> bg `to_actor.run()` task in a local
+                            `trio` task-nursery (or `start_actor`
+                            + bg `Portal.run()` when a portal
+                            handle is needed)
+- concurrent fan-out     -> N bg `to_actor.run()` tasks / or
+                            `gather_contexts([p.open_context(..)])`
+- reap-all-error-collect -> the "collect don't cancel" pattern:
+                            each one-shot catches + stashes its
+                            `RemoteActorError`, group raised
+                            after the task-nursery joins (see
+                            `examples/debugging/multi_subactors.py`)
+- mutual-rendezvous      -> peers must OUTLIVE both dialogs:
+                            `start_actor()` daemons + concurrent
+                            `Portal.run()`s + explicit
+                            `an.cancel()` (eager one-shot reap
+                            races the slower peer's dial of the
+                            winner's dead sockaddr; found via
+                            `test_trynamic_trio` flake).
+
+Semantic deltas (tests loosened accordingly):
+
+- teardown-reap-all BEG-of-N is GONE: local task-nurseries are
+  cancel-on-first, raced siblings' `Cancelled`s are absorbed,
+  and the runtime's `collapse_eg()` unwraps every single-member
+  group at each actor boundary — a fully-raced nested tree
+  relays a bare (annotated) `RemoteActorError` chain.
+- `test_multierror_fast_nursery` deleted (pure reap-stress);
+  `test_nested_multierrors` re-purposed as deep-tree
+  cancel-cascade stress w/ a race-tolerant shape walk.
+
+Final excision (after zero callers remained): `run_in_actor()`,
+`._cancel_after_result_on_exit`, `_reap_ria_portals()`,
+`Portal._submit_for_result/._expect_result_ctx/
+.wait_for_result()/.result()`, `exhaust_portal()`,
+`cancel_on_completion()`, `NoResult` — net -402 lines. The
+reap-hang class (unbounded `wait_for_result` in machinery
+scope) dissolves structurally: the only result-wait left lives
+in the caller's task inside its own cancel-scope; the
+`d1fb4a1a` anti-hang guard test passes by construction. The
+poll-vs-`proc_waiter` debate is moot as predicted.
+
+## Follow-up sketch: `to_actor.open_one_shot()` (run-async parity)
+
+If deferred-result parity is ever wanted, the design that needs
+NO runtime coupling, NO returned `Portal` and NO cancel-relay
+`trio.Event` machinery:
+
+    async with to_actor.open_one_shot(
+        fn, an=an, **kws,
+    ) as one_shot:
+        ...                       # concurrent caller work
+        val = await one_shot.wait()   # optional; errors always
+                                      # propagate at scope exit
+
+an `@acm` that opens a private task-nursery, `start_soon`s ONE
+task running the existing blocking `run()` and stashes the
+value in a slot + sets a done-`trio.Event` (a memo, not a
+cancel relay). Cancellation = plain scope-cancel of the acm's
+nursery (the parked `Portal.run()` unwinds via `Cancelled`, the
+shielded `cancel_actor()` reap still runs); a child error
+raises into the acm scope so an un-`wait()`ed one-shot can
+never silently drop its error. i.e. the old reaper's job is
+done by scoping, not machinery. ~40 lines, all in
+`to_actor/_api.py`, zero `_supervise` involvement.
+
+## Verification gate
+
+- per-migration-commit module gates on `trio` (+ `mp_spawn`
+  spot-gates incl. `test_infected_asyncio` per the B2 lesson);
+  `tests/devx/test_debugger.py` for the REPL flows.
+- full suite on `trio` + `mp_spawn` at branch tip + CI matrix
+  via draft PR #484.

ai/prompt-io/claude/20260702T154255Z_65bf9df5_prompt_io.md

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+---
+model: claude-fable-5
+service: claude
+session: f6c84722-471a-4458-9a80-e453fea9029f
+timestamp: 2026-07-02T15:42:55Z
+git_ref: 65bf9df5
+scope: code
+substantive: true
+raw_file: 20260702T154255Z_65bf9df5_prompt_io.raw.md
+---
+
+## Prompt
+
+Driver prompt file `ai/prompt-io/prompts/issue_477.md`:
+
+> attempt to resolve
+> https://github.com/goodboy/tractor/issues/477
+> do it with /open-wkt.
+
+(plus a hard stop-for-human-review deadline of 12:50PM
+EST the same day)
+
+Issue #477 asks to factor `ActorNursery.run_in_actor()`
+(and possibly `Portal.run()`) out of the nursery
+internals into a new `tractor.to_actor` wrapper
+subpackage of "higher level one shot" single-remote-task
+APIs, adopting the `trio.to_thread`/`anyio.to_process`
+parlance, so that error collection/propagation moves up
+into the caller's local `trio` scope and the nursery's
+spawn machinery can eventually drop the
+`._ria_nursery` coupling.
+
+## Response summary
+
+First-cut `tractor.to_actor` subpkg delivering the
+one-shot API composed purely from the existing
+daemon-spawn + portal primitives (`start_actor()` +
+`Portal.run()` + `Portal.cancel_actor()`), leaving the
+legacy `.run_in_actor()` machinery untouched (formal
+deprecation deferred until in-repo usage migrates):
+
+- `to_actor.run(fn, **fn_kwargs) -> Any`: spawn a
+  subactor, schedule `fn` as its lone remote task, wait
+  on and return its result, ALWAYS reaping the subactor
+  (shield-safe `finally`). Remote errors raise in the
+  caller's task as boxed `RemoteActorError`s.
+- placement variants: `portal=` reuses a running actor
+  (no spawn/reap), `an=` spawns from a caller-managed
+  actor-nursery, neither opens a call-scoped private
+  `open_nursery()` (implicitly booting the runtime,
+  configurable via `runtime_kwargs`).
+- fail-fast validation before any spawn: non-streaming
+  async fn required; `portal=`/`an=` mutually
+  exclusive; `runtime_kwargs` rejected alongside any
+  placement opt.
+- `run_in_actor()` TODO/docstring now cross-reference
+  the successor API.
+
+## Files changed
+
+- `tractor/to_actor/__init__.py` — new subpkg,
+  re-exports `run`
+- `tractor/to_actor/_api.py` — `run()` +
+  `_invoke_in_subactor()` + `_validate_one_shot_fn()`
+- `tractor/__init__.py` — top-level `to_actor`
+  re-export
+- `tractor/runtime/_supervise.py` — comment/docstring
+  pointers from `run_in_actor()` to the successor
+- `tests/test_to_actor.py` — 11-test suite covering
+  all placement variants, error relay, the concurrent
+  worker-pool-ish pattern and arg validation
+- `examples/parallelism/to_actor_one_shots.py` —
+  runnable demo (auto-collected by
+  `test_docs_examples.py`)
+
+## Human edits
+
+None yet — pending human review (work paused before the
+12:50PM EST deadline per the driver prompt).

ai/prompt-io/claude/20260702T154255Z_65bf9df5_prompt_io.raw.md

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+---
+model: claude-fable-5
+service: claude
+timestamp: 2026-07-02T15:42:55Z
+git_ref: 65bf9df5
+diff_cmd: git diff main..wkt/to_actor_subpkg
+---
+
+# Raw AI output (diff-ref mode)
+
+All generated code is committed on the
+`wkt/to_actor_subpkg` branch; per diff-ref mode each
+file's verbatim content is reachable via the pointers
+below rather than duplicated here.
+
+## Generated files
+
+> `git diff main..wkt/to_actor_subpkg -- tractor/to_actor/__init__.py`
+
+New subpackage init: module docstring establishing the
+`trio.to_thread`/`anyio.to_process` "run it over there"
+parlance for actors, plus the single public re-export
+`run as run` from `._api`.
+
+> `git diff main..wkt/to_actor_subpkg -- tractor/to_actor/_api.py`
+
+The one-shot invocation impl, composed entirely from the
+lower level daemon-spawn + portal primitives as
+prescribed by issue #477:
+
+- `_validate_one_shot_fn()`: the `Portal.run()`
+  non-streaming-async-fn constraint checked up-front,
+  before any subactor is spawned.
+- `_invoke_in_subactor()`: `an.start_actor()` ->
+  `Portal.run()` -> always-reap via
+  `Portal.cancel_actor()` in a `finally` (the cancel
+  req's bounded wait is internally shielded so the reap
+  also runs under caller-scope cancellation).
+- `run()`: the public API. Placement options:
+  `portal=` (reuse a running actor, no spawn/reap),
+  `an=` (spawn from a caller-managed nursery), or
+  neither (private `open_nursery()` scoped to the call,
+  implicitly booting the runtime when needed, tunable
+  via pass-through `runtime_kwargs`). Spawn opts mirror
+  `ActorNursery.start_actor()`; `**fn_kwargs` are
+  relayed to the remote task. Errors raise in the
+  caller's task as boxed `RemoteActorError`s.
+  `runtime_kwargs` alongside any placement opt is a
+  hard `ValueError`, never silently ignored.
+
+> `git diff main..wkt/to_actor_subpkg -- tractor/__init__.py`
+
+Top-level `from . import to_actor as to_actor`
+re-export.
+
+> `git diff main..wkt/to_actor_subpkg -- tractor/runtime/_supervise.py`
+
+Comment/docstring-only: the `run_in_actor()` deprecation
+TODO now points at the implemented `.to_actor.run()`
+successor (checkbox ticked) and the method docstring
+gains a NOTE steering users to the new API; remaining
+TODO items are the `DeprecationWarning` emission +
+in-repo usage migration.
+
+> `git diff main..wkt/to_actor_subpkg -- tests/test_to_actor.py`
+
+11-test suite: private-nursery one-shot, implicit
+runtime boot via `runtime_kwargs`, remote-error relay to
+the caller's task (bare + caller-managed nursery),
+caller-nursery spawn, portal reuse w/o implicit reap,
+the concurrent worker-pool-ish pattern (local `trio`
+nursery x shared `an`), and the four validation
+rejections (sync fn, async-gen fn, `portal`+`an`
+combo, `runtime_kwargs`+placement combo).
+
+> `git diff main..wkt/to_actor_subpkg -- examples/parallelism/to_actor_one_shots.py`
+
+Runnable example (auto-collected by
+`test_docs_examples.py`): the fully-implicit one-shot
+plus the concurrent worker-pool-ish prime-check pattern
+against a shared caller-managed actor-nursery.
+
+## Test runs (verbatim)
+
+```
+tests/test_to_actor.py ..........                [100%]
+============= 10 passed in 4.29s =============
+```
+
+Regression subset for touched modules
+(`test_local.py test_rpc.py test_spawning.py
+test_cancellation.py`):
+
+```
+38 passed, 1 xfailed, 24 warnings in 80.71s (0:01:20)
+```
+
+(warnings are pre-existing stdlib `os.fork()`
+DeprecationWarnings from the mp spawn backends, not
+introduced by this change)

ai/prompt-io/claude/20260702T165806Z_a34aaf98_prompt_io.md

@@ -0,0 +1,78 @@
+---
+model: claude-fable-5
+service: claude
+session: f6c84722-471a-4458-9a80-e453fea9029f
+timestamp: 2026-07-02T16:58:06Z
+git_ref: a34aaf98
+scope: code
+substantive: true
+raw_file: 20260702T165806Z_a34aaf98_prompt_io.raw.md
+---
+
+## Prompt
+
+Follow-up round in the same session as the
+`tractor.to_actor` landing (see
+`20260702T154255Z_65bf9df5_prompt_io.md`). After
+committing that work the user green-lit the deferred
+items:
+
+> go go go on this with what time you have left, in
+> particular see if you can get the _ria_nursery
+> removal going!
+
+then extended the deadline twice to iterate on the
+discovered hang:
+
+> continue on this up until a 12:58:30 deadline
+
+and finally chose "Commit step A now" from the
+next-steps prompt.
+
+## Response summary
+
+Step A of the `._ria_nursery` removal (issue #477): hoist
+`.run_in_actor()` result-reaping out of the spawn
+backends into the `ActorNursery` machinery so ria
+children spawn via the default daemon nursery,
+
+- new `_supervise._reap_ria_portals()` runs one
+  `_spawn.cancel_on_completion()` task per ria child
+  AFTER `._join_procs` is set; happy path awaits it
+  right after `._join_procs.set()`.
+- error path SEQUENCES: snapshot ria
+  `(portal, subactor)` pairs -> `await an.cancel()` ->
+  0.5s-bounded reap. Two failed intermediates informed
+  this: a concurrent reap+cancel DEADLOCKED
+  `test_multierror`; a 3s bound blew
+  `test_cancel_while_childs_child_in_sync_sleep`'s
+  `fail_after` deadline.
+- backends (`spawn/_trio.py`, `spawn/_mp.py`) lose the
+  `._cancel_after_result_on_exit` membership branch,
+  per-child reaper nursery + dead imports.
+- design/probe-history doc:
+  `ai/conc-anal/ria_nursery_removal_plan.md` (from an
+  agent-verified machinery map).
+
+Verification: `test_cancellation.py` fully green
+(20 passed, 1 xfailed) incl. the previously-hung
+`test_multierror`; `test_to_actor`+`test_spawning`
+20/20; bounded full-suite gate SIGINT'd ~30s early at
+303 passed / 0 failures (user opted to commit on that
+signal, deferring the unbounded re-run to step-B
+verification).
+
+## Files changed
+
+- `tractor/runtime/_supervise.py` — `_reap_ria_portals()`
+  + two call-sites; `run_in_actor()` off the ria nursery
+- `tractor/spawn/_trio.py` — reaper branch + import drop
+- `tractor/spawn/_mp.py` — same as `_trio.py`
+- `ai/conc-anal/ria_nursery_removal_plan.md` — plan +
+  probe history
+
+## Human edits
+
+None yet — committed via the drafted
+`.claude/git_commit_msg_ria_step_a.md` (user-driven
+`git commit --edit`).

ai/prompt-io/claude/20260702T165806Z_a34aaf98_prompt_io.raw.md

@@ -0,0 +1,55 @@
+---
+model: claude-fable-5
+service: claude
+timestamp: 2026-07-02T16:58:06Z
+git_ref: a34aaf98
+diff_cmd: git diff a34aaf98..wkt/to_actor_subpkg
+---
+
+# Raw AI output (diff-ref mode)
+
+Step-A code is committed on `wkt/to_actor_subpkg`
+directly after `a34aaf98`; per diff-ref mode the verbatim
+content is reachable via the pointers below.
+
+## Generated files
+
+> `git diff a34aaf98..wkt/to_actor_subpkg -- tractor/runtime/_supervise.py`
+
+New `_reap_ria_portals(an, errors, ria_children=None)`
+helper (one `_spawn.cancel_on_completion()` task per ria
+child under `collapse_eg()` + a local nursery);
+`run_in_actor()` drops `nursery=self._ria_nursery`; happy
+path awaits the reap right after `._join_procs.set()`;
+inner error handler snapshots ria pairs, runs
+`await an.cancel()` then a `move_on_after(0.5)`-bounded
+reap over the snapshot.
+
+> `git diff a34aaf98..wkt/to_actor_subpkg -- tractor/spawn/_trio.py`
+> `git diff a34aaf98..wkt/to_actor_subpkg -- tractor/spawn/_mp.py`
+
+Both backends: the post-`_join_procs` block collapses to
+a bare `soft_kill()` (membership branch, per-child reaper
+nursery, reaper-cancel logging and the now-unused
+`cancel_on_completion` imports all removed).
+
+> `git diff a34aaf98..wkt/to_actor_subpkg -- ai/conc-anal/ria_nursery_removal_plan.md`
+
+Agent-verified machinery map, 3-step design (A/B/C),
+probe history (deadlock -> sequencing fix -> bound
+tightening) and risk register.
+
+## Test runs (verbatim)
+
+```
+tests/test_cancellation.py: 20 passed, 1 xfailed in 77.28s
+tests/test_to_actor.py + tests/test_spawning.py: 20 passed
+full-suite (SIGINT at 540s bound, ~30s short):
+303 passed, 9 skipped, 1 xfailed, 2 xpassed in 539.42s
+```
+
+Failed intermediates (not in final diff): concurrent
+reap+`an.cancel()` deadlocked `test_multierror`; a 3s
+reap bound blew
+`test_cancel_while_childs_child_in_sync_sleep`'s
+`fail_after` deadline.

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)
+```

ai/prompt-io/claude/20260702T222544Z_9201a2ed_prompt_io.md

@@ -0,0 +1,68 @@
+---
+model: claude-opus-4-8
+service: claude
+session: c7860302-6a33-4d92-821c-0807d68be464
+timestamp: 2026-07-02T22:25:44Z
+git_ref: 9201a2ed
+scope: code
+substantive: true
+raw_file: 20260702T222544Z_9201a2ed_prompt_io.raw.md
+---
+
+## Prompt
+
+Continuing on branch `drop_ria_nursery` after step B
+(`9201a2ed`). User green-lit the deferred error-handler merge:
+
+> yes, i checked us out on a new branch for the ria-tn removal;
+> work off the new wkt branch drop_ria_nursery.
+
+and (re the migration) "nope, later we'll do this", plus:
+
+> do ensure the test suite is green in the current state and
+> those going forward ya?
+
+and the standing reminder: no commits without a human ack.
+
+## Response summary
+
+Step B2 of the `._ria_nursery` removal (issue #477): merge the
+two nested error handlers in
+`_open_and_supervise_one_cancels_all_nursery` into one, now
+that the 2ndary nursery (whose `__aexit__` the outer handler
+originally guarded) is gone.
+
+Trace-driven justification (see
+`ai/conc-anal/ria_nursery_removal_plan.md` Step-B2 section):
+the old inner handler records `errors[uid]` as its FIRST
+action, so `errors` is always non-empty by the time control
+could reach the outer handler — making the outer handler's
+`raise` DEAD (always superseded by the `finally`'s
+raise-from-`errors`). Collapsing to a single
+`except BaseException as _scope_err` + the existing `finally`
+is therefore behavior-preserving.
+
+- removed the outer `try` + the
+  `except (Exception, BaseExceptionGroup, trio.Cancelled)`
+  handler; de-indented the inner handler one level.
+- dropped the now-unused `outer_err`/`inner_err` locals
+  (single `_scope_err`).
+- net ~30 lines lighter.
+
+Gated hard: baseline (pre-B2 tip) = 300 passed + 1
+load-induced `TooSlowError` flake (passes 6/6 in isolation);
+B2 error/cancel gate (`test_cancellation remote_exc_relay
+inter_peer_cancellation advanced_faults oob_cancellation
+to_actor spawning local rpc`) = 71 passed, 1 xfailed; B2
+full-suite run following.
+
+## Files changed
+
+- `tractor/runtime/_supervise.py` — collapse the two handlers
+  into one; drop `outer_err`/`inner_err`
+
+## Human edits
+
+None yet — committed via the drafted
+`.claude/git_commit_msg_ria_b2.md` (user-driven
+`git commit --edit`).

ai/prompt-io/claude/20260702T222544Z_9201a2ed_prompt_io.raw.md

@@ -0,0 +1,55 @@
+---
+model: claude-opus-4-8
+service: claude
+timestamp: 2026-07-02T22:25:44Z
+git_ref: 9201a2ed
+diff_cmd: git diff 9201a2ed..drop_ria_nursery
+---
+
+# Raw AI output (diff-ref mode)
+
+Step-B2 code lives on `drop_ria_nursery` after `9201a2ed`; per
+diff-ref mode the verbatim content is reachable via the pointer
+below.
+
+## Generated files
+
+> `git diff 9201a2ed..drop_ria_nursery -- tractor/runtime/_supervise.py`
+
+`_open_and_supervise_one_cancels_all_nursery`:
+- removed the outer `try:` wrapper and the
+  `except (Exception, BaseExceptionGroup, trio.Cancelled) as
+  _outer_err:` safety-net handler.
+- the former inner `except BaseException` is now THE handler,
+  renamed local `_inner_err` -> `_scope_err`, de-indented one
+  level; it sets `an._scope_error`, records `errors[uid]`,
+  waits on the debugger, `_join_procs.set()`, then a shielded
+  classify/log + snapshot-ria + `an.cancel()` + 0.5s-bounded
+  `_reap_ria_portals()`. No re-raise (the `finally` raises
+  from `errors`).
+- `finally` block unchanged.
+- dropped the `outer_err`/`inner_err` local decls at fn top.
+
+(The diff is large — ~119+/149- — because de-indenting the
+handler body one level rewrites every line in the block; the
+logic delta is just "two handlers -> one".)
+
+## Test runs (verbatim)
+
+```
+baseline (pre-B2, step-B tip 9201a2ed), full suite
+(dynamic_pub_sub deselected):
+1 failed, 300 passed, 9 skipped, 2 deselected, 1 xfailed,
+2 xpassed in 1499.49s
+  -> the 1 failure = test_ext_types_over_ipc[...] trio.TooSlowError
+     (load-induced; passes 6/6 in isolation in 4.89s)
+
+B2 error/cancel gate:
+tests/test_cancellation test_remote_exc_relay
+test_inter_peer_cancellation test_advanced_faults
+test_oob_cancellation test_to_actor test_spawning test_local
+test_rpc
+-> 71 passed, 1 xfailed in 125.26s
+
+B2 full-suite run: see b2_full.log
+```

ai/prompt-io/claude/20260706T172818Z_ad42871e_prompt_io.md

@@ -0,0 +1,81 @@
+---
+model: claude-fable-5
+service: claude
+session: 6db64ac6-6986-4505-9343-df4ee31e67db
+timestamp: 2026-07-06T17:28:18Z
+git_ref: ad42871e
+scope: code
+substantive: true
+raw_file: 20260706T172818Z_ad42871e_prompt_io.raw.md
+---
+
+## Prompt
+
+Resuming the `drop_ria_nursery` (wkt) branch after the human's
+review pause at `ba4af0ad`, with the directive:
+
+> we need to resolve the remaining outstandings ... to finish
+> this endeavour we ideally,
+> - finish the ria-tn hoist into the machinery in `to_actor` if
+>   possible.
+> - avoid supporting the `.run_in_actor()` non-blocking API
+>   going forward other then if we can re-wrap `to_actor.run()`
+>   per prior discussion with opus4.8.
+> - get the test harness completely green locally and in CI -
+>   AND ESPECIALLY without any hangs due to the "the old
+>   spawn-backend reaper raced `soft_kill()`'s scope-cancel"
+> - update all docs to reflect these changes once we're happy.
+
+plus mid-flight additions:
+
+> make sure both all the test and example code uses the naming
+> `an: ActorNursery` for variable names
+
+> where we at in terms of a potential hackaround design for
+> supporting a to_actor.run_async() ... without requiring the
+> same malarky ... with a `trio.Event` relay ... i'm totes fine
+> with rejigging the iface to NOT return a Portal as well.
+
+## Response summary
+
+Completed the entire #477 `run_in_actor` removal on
+`drop_ria_nursery` (16 commits this session), gated per-commit:
+
+- ported the remaining `test_cancellation` groups
+  (`some_cancels_all`, `nested_multierrors`+`spawn_and_error`,
+  SIGINT + sync-sleep) — one-shots become concurrent
+  `to_actor.run()` tasks in local task-nurseries; BEG-shape
+  assertions loosened for cancel-on-first + the runtime's
+  `collapse_eg()` single-member unwrap (a fully-raced nested
+  tree relays a bare annotated `RemoteActorError` chain).
+- fixed a pre-existing `UnboundLocalError` (`timeout` `match`
+  had no default arm for non-trio/MTF backends).
+- ported `test_dynamic_pub_sub`, 4 non-debugging examples, all
+  8 `debugging/` examples (debugger suite byte-identical,
+  28p/6s; `multi_subactors` introduces the "collect don't
+  cancel" reap-all replacement pattern), 8 docs pages + the
+  `experimental/_pubsub` docstring.
+- EXCISED the API + cluster: `run_in_actor`,
+  `_reap_ria_portals`, `_cancel_after_result_on_exit`,
+  `Portal._submit_for_result/_expect_result_ctx/
+  wait_for_result/result`, `exhaust_portal`,
+  `cancel_on_completion`, `NoResult` — net -402 lines. The
+  reap-hang class dissolves structurally (result-waits now only
+  in caller task-scope).
+- found + fixed a real migration race: mutual-rendezvous peers
+  (`test_trynamic_trio`, `a_trynamic_first_scene.py`) flaked
+  because an eagerly-reaped one-shot dies while its peer still
+  dials the registry-resolved (dead) sockaddr — such peers now
+  pin lifetimes via `start_actor()` + concurrent `Portal.run()`
+  + explicit `an.cancel()`.
+- `an: ActorNursery` naming sweep across tests/examples (±82
+  lines, scoped renames, prose untouched).
+- parked a `to_actor.open_one_shot()` design sketch (acm +
+  private task-nursery over blocking `run()`; done-Event as
+  memo not cancel-relay; no Portal) in the plan doc.
+
+## Files changed
+
+See commits `d01a2123..ad42871e` on `drop_ria_nursery`
+(tests, examples, docs, `tractor/{runtime,spawn,to_actor,msg}`
++ `_exceptions/_context/experimental`).

ai/prompt-io/claude/20260706T172818Z_ad42871e_prompt_io.raw.md

@@ -0,0 +1,39 @@
+---
+model: claude-fable-5
+service: claude
+timestamp: 2026-07-06T17:28:18Z
+git_ref: ad42871e
+diff_cmd: git diff ba4af0ad..ad42871e
+---
+
+# Raw AI output (diff-ref mode)
+
+This session's output spans the 16 migration/excision commits
+`d01a2123..ad42871e` on `drop_ria_nursery`; per diff-ref mode
+the verbatim content is reachable via the pointer below.
+
+## Generated files
+
+> `git diff ba4af0ad..ad42871e`
+
+Commit-wise (each `Gate:`-footed msg documents its own module
+gate):
+
+- `d01a2123` port `test_some_cancels_all`
+- `697c6152` fix unbound `timeout` (non-trio/MTF `match` arm)
+- `fa8799d5` port `test_nested_multierrors`
+- `f11754ce` port SIGINT + sync-sleep cancel tests
+- `cb6202e3` port `test_dynamic_pub_sub`
+- `d8af5f12` port non-debugging examples
+- `a3057cb2` port debugging examples (+ `test_debugger`
+  nested-nurseries final-shape expectations)
+- `d6bed7c4` port docs (8 rst pages)
+- `07e1669e` fix stale `@pub` docstring example
+- `2a59cefb` REMOVE `run_in_actor()` + the ria reap cluster
+  (net -402 lines)
+- `a297a32a` fix mutual-rendezvous premature-reap race
+- `ad42871e` `an: ActorNursery` naming sweep
+
+Plan/design record updated in
+`ai/conc-anal/ria_nursery_removal_plan.md` (RESOLVED section +
+the `to_actor.open_one_shot()` follow-up sketch).

ai/prompt-io/prompts/issue_477.md

@@ -0,0 +1,7 @@
+NOTE: you MUST pause this work at 12:50PM EST (BEFORE your weekly
+limit reset) for review by a human!
+
+---
+
+attempt to resolve https://github.com/goodboy/tractor/issues/477
+do it with /open-wkt.

docs/api/core.rst

@@ -37,7 +37,6 @@ Spawning actors
 
 .. autoclass:: ActorNursery
    :members: start_actor,
-             run_in_actor,
              cancel,
              cancel_called,
              cancelled_caught
@@ -47,10 +46,22 @@ Spawning actors
    :meth:`ActorNursery.start_actor` (daemon actor + portal) is the
    blessed spawning primitive; pair it with
    ``Portal.open_context()`` for SC-linked remote tasks.
-   :meth:`ActorNursery.run_in_actor` is a *convenience* one-shot —
-   spawn, run a single task, auto-cancel after the result — slated
-   to be rebuilt as a high-level wrapper, so don't design around
-   it as the core model.
+
+One-shot task actors
+--------------------
+
+.. autofunction:: tractor.to_actor.run
+
+.. note::
+
+   :func:`tractor.to_actor.run` (parlance of
+   ``trio.to_thread.run_sync()`` and friends) is the
+   *convenience* one-shot — spawn, run a single task, block on
+   its result, reap — built entirely on
+   :meth:`ActorNursery.start_actor` + :meth:`Portal.run` +
+   :meth:`Portal.cancel_actor`, so don't design around it as the
+   core model. It supersedes the removed (legacy, non-blocking)
+   ``ActorNursery.run_in_actor()``.
 
 .. deprecated:: 0.1.0a6
 
@@ -71,14 +82,12 @@ flowing back `exactly like trio`_.
    :members: run,
              run_from_ns,
              open_stream_from,
-             wait_for_result,
              cancel_actor,
              chan
 
 .. deprecated:: 0.1.0a6
 
-   ``Portal.result()`` warns; use :meth:`Portal.wait_for_result`.
-   The str-form ``Portal.run('mod.path', 'fn_name')`` also warns;
+   The str-form ``Portal.run('mod.path', 'fn_name')`` warns;
    pass a function *object* whose module is listed in the target's
    ``enable_modules``. ``Portal.channel`` is the legacy spelling
    of :attr:`Portal.chan`.

docs/guide/asyncio.rst

@@ -76,8 +76,8 @@ Just flip the flag on :meth:`tractor.ActorNursery.start_actor`:
             infect_asyncio=True,
         )
 
-The one-shot convenience ``ActorNursery.run_in_actor()`` accepts
-the same flag. The ``to_asyncio`` APIs may **only** be called from
+The one-shot convenience ``tractor.to_actor.run()`` accepts the
+same flag. The ``to_asyncio`` APIs may **only** be called from
 tasks inside an infected actor; calling them anywhere else raises
 a loud ``RuntimeError``. You can introspect at runtime with
 ``tractor.current_actor().is_infected_aio()``.
@@ -229,7 +229,7 @@ dialog, skip the channel ceremony and use
 
 It schedules the fn as an ``asyncio.Task``, waits for completion
 and hands the return value back to ``trio``; think of it as the
-cross-loop sibling of ``ActorNursery.run_in_actor()``. Errors and
+cross-loop sibling of ``tractor.to_actor.run()``. Errors and
 cancellation are translated exactly as for channels.
 
 Cross-loop errors and cancellation

docs/guide/cancellation.rst

@@ -64,11 +64,13 @@ What's going on here?
 - three healthy actors are spawned as daemons via
   :meth:`tractor.ActorNursery.start_actor`; left alone they'd
   happily idle forever,
-- a fourth actor runs ``assert_err()`` via ``.run_in_actor()`` and
-  promptly trips its ``assert 0``,
+- a fourth actor runs ``assert_err()`` via a blocking
+  ``tractor.to_actor.run()`` one-shot and promptly trips its
+  ``assert 0``,
 - the resulting ``AssertionError`` ships back over IPC as a
-  serialized error msg and re-raises *boxed* inside the nursery
-  block as a :class:`tractor.RemoteActorError`,
+  serialized error msg and re-raises *boxed* right at the call
+  inside the nursery block as a
+  :class:`tractor.RemoteActorError`,
 - the nursery reacts like any ``trio`` nursery would: it cancels
   the three healthy siblings (graceful runtime-cancel requests,
   acks awaited), reaps all four processes, then re-raises,

docs/guide/context.rst

@@ -15,8 +15,8 @@ a single `structured concurrency`_ (SC) scope over IPC.
    :alt: sequence diagram of the context handshake msg flow
 
 Pretty much everything else is (or is slated to be) built on this
-one primitive: ``ActorNursery.run_in_actor()`` is a convenience
-for "spawn, open a context, await the result, tear down"; plain
+one primitive: ``tractor.to_actor.run()`` is a convenience for
+"spawn, run the lone task, await the result, tear down"; plain
 ``Portal.run()`` RPC is planned to be re-implemented on top of it;
 the multi-process debugger's tree-wide REPL lock rides one. Grok
 this page and the rest of the library reads as convenience

docs/guide/parallelism.rst

@@ -119,15 +119,16 @@ Run a func in a process
 
 Even a pool can be overkill; "run this one async func in a
 subprocess and give me the result" is a one-liner via
-:meth:`tractor.ActorNursery.run_in_actor`,
+:func:`tractor.to_actor.run`,
 
 .. literalinclude:: ../../examples/parallelism/single_func.py
    :caption: examples/parallelism/single_func.py
    :language: python
 
-``run_in_actor()`` is a *convenience wrapper* — spawn an actor, run
-exactly one task in it, reap on result — not the core spawning
-model (that's :meth:`tractor.ActorNursery.start_actor` plus
+``to_actor.run()`` is a *convenience wrapper* — spawn an actor,
+run exactly one task in it, block on and return its result, reap
+— not the core spawning model (that's
+:meth:`tractor.ActorNursery.start_actor` plus
 :meth:`tractor.Portal.open_context`; see :doc:`/guide/context`).
 But for this fire-and-collect shape it's exactly the right amount
 of typing.

docs/guide/rpc.rst

@@ -80,28 +80,30 @@ One special namespace exists: ``'self'`` resolves to the remote
 how internal machinery (cancel requests, registry ops) travels;
 don't build your app on it.
 
-One-shot results: ``wait_for_result()``
----------------------------------------
-A portal returned from
-:meth:`~tractor.ActorNursery.run_in_actor` has exactly one
-"main" task running remotely; that task's ``return`` value is
-delivered as the portal's *final result*:
+One-shot subactors: ``to_actor.run()``
+--------------------------------------
+When a subactor's *entire job* is a single function call, skip
+the portal plumbing with :func:`tractor.to_actor.run`: spawn,
+run the lone task, return its result and reap the process — all
+in one blocking call:
 
 .. code:: python
 
-    portal = await an.run_in_actor(fib, n=10)
-    final = await portal.wait_for_result()
+    final = await tractor.to_actor.run(fib, an=an, n=10)
 
 Semantics worth knowing:
 
 - it blocks until the remote task returns, re-raising any
-  remote error in the usual boxed form.
-- once resolved it's idempotent: later calls return the same
-  cached value.
-- a *daemon* portal (from ``start_actor()``) has no main task,
-  so there's no final result to wait for: you'll get a warning
-  plus a ``NoResult`` sentinel. Results of individual daemon
-  calls come straight back from each ``await portal.run()``.
+  remote error in the usual boxed form right in the calling
+  task.
+- "placement" is composable: ``an=`` spawns from an existing
+  actor-nursery, ``portal=`` reuses an already-running actor
+  (no spawn/reap, just a ``Portal.run()``), and passing
+  neither opens a private call-scoped nursery (booting the
+  runtime if needed).
+- concurrency composes the plain ``trio`` way: schedule
+  multiple ``run()`` calls into a local task nursery (see
+  ``examples/parallelism/to_actor_one_shots.py``).
 
 Pure RPC daemons: ``run_daemon()``
 ----------------------------------

docs/guide/spawning.rst

@@ -103,19 +103,22 @@ What's going on here?
   on him **forever**. Daemon lifetimes are *yours* to end; that
   explicitness is the point.
 
-``run_in_actor()``: quick one-shot parallelism
+``to_actor.run()``: quick one-shot parallelism
 ----------------------------------------------
-:meth:`~tractor.ActorNursery.run_in_actor` is the convenience
-wrapper: spawn an actor, run exactly one async function in it,
-then reap the process as soon as the result arrives.
+:func:`tractor.to_actor.run` is the convenience wrapper: spawn
+an actor, run exactly one async function in it, block on the
+result, then reap the process — the distributed sibling of
+``trio.to_thread.run_sync()``.
 
 .. code:: python
 
-    async with tractor.open_nursery() as an:
-        portal = await an.run_in_actor(burn_cpu)
+    async with (
+        tractor.open_nursery() as an,
+        trio.open_nursery() as tn,
+    ):
         # burn rubber in the parent too...
-        await burn_cpu()
-        total = await portal.wait_for_result()
+        tn.start_soon(burn_cpu)
+        total = await tractor.to_actor.run(burn_cpu, an=an)
 
 A few details worth knowing:
 
@@ -124,18 +127,21 @@ A few details worth knowing:
 - the function's module is auto-added to the child's
   ``enable_modules`` allowlist.
 - extra ``**kwargs`` are forwarded to the function itself.
-- the child is *auto-cancelled* once its "main" result lands;
-  at nursery exit these run-once children are always reaped
-  first (causality_ is paramount!).
+- the call blocks until the result (or error) lands and the
+  child is *auto-cancelled* (reaped) right after — so remote
+  errors raise directly in your calling task (causality_ is
+  paramount!).
+- "placement" composes: ``an=`` spawns from a caller-managed
+  actor-nursery, ``portal=`` reuses an already-running actor
+  (no spawn/reap), and passing neither opens a private
+  call-scoped nursery (booting the runtime if needed).
 
 .. note::
 
-   ``run_in_actor()`` is a convenience, **not** the core model.
-   The source literally marks it for an eventual rebuild as
-   a thin "hilevel" wrapper on top of
-   :meth:`~tractor.Portal.open_context` (the modern inter-actor
-   task API). Teach your fingers to use it for quick
-   fire-and-collect parallelism — think a per-function
+   ``to_actor.run()`` is a convenience, **not** the core model —
+   it's built *entirely* on ``start_actor()`` + ``Portal.run()``
+   + ``Portal.cancel_actor()``. Teach your fingers to use it for
+   quick fire-and-collect parallelism — think a per-function
    trio-parallel_ style one-shot — and reach for
    ``start_actor()`` + ``open_context()`` for anything
    long-lived, stateful or streaming
@@ -145,9 +151,9 @@ Actor lifetimes and teardown order
 ----------------------------------
 So we have two lifetime flavors:
 
-- **run-once** (``run_in_actor()``): lives exactly as long as
+- **one-shot** (``to_actor.run()``): lives exactly as long as
   its single task; reaped the moment its result (or error)
-  arrives.
+  arrives back in the (blocking) call.
 - **daemon** (``start_actor()``): lives until *someone* cancels
   it — an explicit ``await portal.cancel_actor()``, a bulk
   ``await an.cancel()``, or the one-cancels-all strategy kicking
@@ -155,11 +161,12 @@ So we have two lifetime flavors:
 
 On a clean exit of the nursery block the teardown order is:
 
-1. the nursery waits on every run-once actor's final result;
-   any errors from these are raised immediately so your code
-   (acting as supervisor) gets first crack at handling them.
-2. then it waits on daemon actors — **indefinitely**. If you
-   spawned a daemon, you own its lifetime.
+1. one-shot actors never make it to nursery exit: each is
+   reaped inside its own ``to_actor.run()`` call, any error
+   raising immediately in the calling task so your code
+   (acting as supervisor) gets first crack at handling it.
+2. the nursery then waits on daemon actors — **indefinitely**.
+   If you spawned a daemon, you own its lifetime.
 
 When a child *is* cancelled, teardown is graceful-first per SC
 discipline: the runtime sends an IPC cancel request and gives

docs/start/quickstart.rst

@@ -43,24 +43,20 @@ Run it::
 What's going on here?
 
 - ``trio.run(main)`` starts the **root actor**; the ``tractor``
-  runtime boots *implicitly* inside ``tractor.open_nursery()``
+  runtime boots *implicitly* inside ``tractor.to_actor.run()``
   whenever it isn't already up. No special entrypoint, no
   framework takeover - it's just a ``trio`` app,
 - inside ``main()`` a *subactor* is spawned via
-  ``ActorNursery.run_in_actor()`` and told to run exactly one
+  ``tractor.to_actor.run()`` and told to run exactly one
   function: ``cellar_door()``,
-- you get back a ``Portal``: your handle for invoking tasks in
-  the new process's (separate!) memory domain. We lean on it
-  much harder in the next section,
 - the subactor, *some_linguist*, boots a fresh ``trio.run()`` in
   a **new process** and executes ``cellar_door()`` as its *main
   task* (note the child proving it is *not* the root with
   ``tractor.is_root_process()``), then ships the return value
   back over IPC,
-- the parent grabs that *final result* with
-  ``await portal.wait_for_result()``, much like you'd expect
-  from a "future" - except causality is preserved: the nursery
-  block only exits once the child is *done*, dead, and reaped.
+- the call *blocks* until that final result arrives, then
+  returns it - causality is preserved: your task only proceeds
+  once the child is *done*, dead, and reaped.
 
 .. margin:: Just need a worker pool?
 
@@ -71,19 +67,22 @@ What's going on here?
 
 .. note::
 
-   ``run_in_actor()`` is the *convenience* wrapper: one-shot
+   ``to_actor.run()`` (parlance of ``trio.to_thread`` and
+   friends) is the *convenience* wrapper: one-shot
    spawn-run-reap semantics for when a subactor's entire job is
    a single function call. The core primitives are
-   ``ActorNursery.start_actor()`` (next up) paired with
+   ``ActorNursery.start_actor()`` (next up) — which hands you
+   a ``Portal``, your handle for invoking tasks in the new
+   process's (separate!) memory domain — paired with
    ``Portal.open_context()`` for full, SC-linked cross-actor
    dialogs - see :doc:`/guide/context`.
 
 Daemon actors and RPC
 ---------------------
-A ``run_in_actor()``-spawned actor terminates when its main task
-returns. But often you want long-lived *daemon* actors instead:
-spawned once, then serving (allowlisted) RPC requests until told
-otherwise. That's ``start_actor()``:
+A ``to_actor.run()`` one-shot subactor terminates when its lone
+task returns. But often you want long-lived *daemon* actors
+instead: spawned once, then serving (allowlisted) RPC requests
+until told otherwise. That's ``start_actor()``:
 
 .. literalinclude:: ../../examples/actor_spawning_and_causality_with_daemon.py
    :caption: examples/actor_spawning_and_causality_with_daemon.py
@@ -91,9 +90,9 @@ otherwise. That's ``start_actor()``:
 
 Two lifetime rules to internalize:
 
-- a ``run_in_actor()`` actor lives exactly as long as its main
-  task; the nursery waits for that function (and thus the
-  process) to complete before unblocking,
+- a ``to_actor.run()`` one-shot actor lives exactly as long as
+  its lone task; the call blocks until that function (and thus
+  the process) completes,
 - a ``start_actor()`` actor *lives forever* - an RPC daemon the
   nursery will happily wait on **indefinitely** - until some
   task explicitly cancels it via ``Portal.cancel_actor()`` (as

examples/a_trynamic_first_scene.py

@@ -21,23 +21,35 @@ async def main():
     """Main tractor entry point, the "master" process (for now
     acts as the "director").
     """
-    async with tractor.open_nursery() as n:
+    async with tractor.open_nursery() as an:
         print("Alright... Action!")
 
-        donny = await n.run_in_actor(
-            say_hello,
-            name='donny',
-            # arguments are always named
-            other_actor='gretchen',
-        )
-        gretchen = await n.run_in_actor(
-            say_hello,
-            name='gretchen',
-            other_actor='donny',
-        )
-        print(await gretchen.wait_for_result())
-        print(await donny.wait_for_result())
-        print("CUTTTT CUUTT CUT!!! Donny!! You're supposed to say...")
+        # both actors wait on (then dial!) the *other*, so each
+        # must outlive both hellos: spawn as daemons, run the
+        # hellos concurrently, reap only once both complete.
+        portals: dict[str, tractor.Portal] = {
+            name: await an.start_actor(
+                name,
+                enable_modules=[__name__],
+            )
+            for name in ('donny', 'gretchen')
+        }
+
+        async def run_and_print(name: str, other_actor: str):
+            print(
+                await portals[name].run(
+                    say_hello,
+                    other_actor=other_actor,
+                )
+            )
+
+        async with trio.open_nursery() as tn:
+            tn.start_soon(run_and_print, 'donny', 'gretchen')
+            tn.start_soon(run_and_print, 'gretchen', 'donny')
+
+        await an.cancel()
+
+    print("CUTTTT CUUTT CUT!!! Donny!! You're supposed to say...")
 
 
 if __name__ == '__main__':

examples/actor_spawning_and_causality.py

@@ -10,17 +10,14 @@ async def cellar_door():
 async def main():
     """The main ``tractor`` routine.
     """
-    async with tractor.open_nursery() as n:
-
-        portal = await n.run_in_actor(
+    # spawn a subactor, run ``cellar_door()`` as its lone task,
+    # block until its result arrives and the subactor is reaped.
+    print(
+        await tractor.to_actor.run(
             cellar_door,
             name='some_linguist',
         )
-
-    # The ``async with`` will unblock here since the 'some_linguist'
-    # actor has completed its main task ``cellar_door``.
-
-    print(await portal.wait_for_result())
+    )
 
 
 if __name__ == '__main__':

examples/actor_spawning_and_causality_with_daemon.py

@@ -12,9 +12,9 @@ async def movie_theatre_question():
 async def main():
     """The main ``tractor`` routine.
     """
-    async with tractor.open_nursery() as n:
+    async with tractor.open_nursery() as an:
 
-        portal = await n.start_actor(
+        portal = await an.start_actor(
             'frank',
             # enable the actor to run funcs from this current module
             enable_modules=[__name__],

examples/asynchronous_generators.py

@@ -15,9 +15,9 @@ async def stream_forever() -> AsyncIterator[int]:
 
 async def main():
 
-    async with tractor.open_nursery() as n:
+    async with tractor.open_nursery() as an:
 
-        portal = await n.start_actor(
+        portal = await an.start_actor(
             'donny',
             enable_modules=[__name__],
         )

examples/debugging/multi_nested_subactors_error_up_through_nurseries.py

@@ -1,3 +1,5 @@
+from functools import partial
+
 import trio
 import tractor
 
@@ -21,25 +23,36 @@ async def breakpoint_forever():
 async def spawn_until(depth=0):
     """"A nested nursery that triggers another ``NameError``.
     """
-    async with tractor.open_nursery() as n:
+    async with (
+        tractor.open_nursery() as an,
+        trio.open_nursery() as tn,
+    ):
         if depth < 1:
 
-            await n.run_in_actor(breakpoint_forever)
-
-            p = await n.run_in_actor(
-                name_error,
-                name='name_error'
+            tn.start_soon(
+                partial(
+                    tractor.to_actor.run,
+                    breakpoint_forever,
+                    an=an,
+                )
             )
+
             await trio.sleep(0.5)
             # rx and propagate error from child
-            await p.result()
+            await tractor.to_actor.run(
+                name_error,
+                an=an,
+                name='name_error',
+            )
 
         else:
             # recusrive call to spawn another process branching layer of
-            # the tree
+            # the tree; blocks (up) each level until the leaf's
+            # `name_error` relays through.
             depth -= 1
-            await n.run_in_actor(
+            await tractor.to_actor.run(
                 spawn_until,
+                an=an,
                 depth=depth,
                 name=f'spawn_until_{depth}',
             )
@@ -65,35 +78,34 @@ async def main():
              └─ python -m tractor._child --uid ('spawn_until_0', 'de918e6d ...)
 
     """
-    async with tractor.open_nursery(
-        debug_mode=True,
-        loglevel='pdb',
-    ) as n:
-
-        # spawn both actors
-        portal = await n.run_in_actor(
-            spawn_until,
-            depth=3,
-            name='spawner0',
+    async with (
+        tractor.open_nursery(
+            debug_mode=True,
+            loglevel='pdb',
+        ) as an,
+        trio.open_nursery() as tn,
+    ):
+        # spawn both spawner trees as concurrent one-shots; the
+        # first tree's (relayed) error cancels the other.
+        tn.start_soon(
+            partial(
+                tractor.to_actor.run,
+                spawn_until,
+                an=an,
+                depth=3,
+                name='spawner0',
+            )
         )
-        portal1 = await n.run_in_actor(
-            spawn_until,
-            depth=4,
-            name='spawner1',
+        tn.start_soon(
+            partial(
+                tractor.to_actor.run,
+                spawn_until,
+                an=an,
+                depth=4,
+                name='spawner1',
+            )
         )
 
-        # TODO: test this case as well where the parent don't see
-        # the sub-actor errors by default and instead expect a user
-        # ctrl-c to kill the root.
-        with trio.move_on_after(3):
-            await trio.sleep_forever()
-
-        # gah still an issue here.
-        await portal.result()
-
-        # should never get here
-        await portal1.result()
-
 
 if __name__ == '__main__':
     trio.run(main)

examples/debugging/multi_subactor_root_errors.py

@@ -15,12 +15,12 @@ async def name_error():
 async def spawn_error():
     """"A nested nursery that triggers another ``NameError``.
     """
-    async with tractor.open_nursery() as n:
-        portal = await n.run_in_actor(
+    async with tractor.open_nursery() as an:
+        return await tractor.to_actor.run(
             name_error,
+            an=an,
             name='name_error_1',
-            )
-        return await portal.result()
+        )
 
 
 async def main():
@@ -38,29 +38,36 @@ async def main():
         - root actor should then fail on assert
         - program termination
     """
-    async with tractor.open_nursery(
-        debug_mode=True,
-        loglevel='devx',
-    ) as n:
+    async with (
+        tractor.open_nursery(
+            debug_mode=True,
+            loglevel='devx',
+        ) as an,
+        trio.open_nursery() as tn,
+    ):
+        # spawn both actors..
+        portal = await an.start_actor(
+            'name_error',
+            enable_modules=[__name__],
+        )
+        portal1 = await an.start_actor(
+            'spawn_error',
+            enable_modules=[__name__],
+        )
 
-        # spawn both actors
-        portal = await n.run_in_actor(
-            name_error,
-            name='name_error',
-        )
-        portal1 = await n.run_in_actor(
-            spawn_error,
-            name='spawn_error',
-        )
+        # ..and bg-schedule their erroring tasks.
+        tn.start_soon(portal.run, name_error)
+        tn.start_soon(portal1.run, spawn_error)
+
+        # yield to the bg tasks so both RPC requests are
+        # submitted (and start crashing) before the root's own
+        # error below (the legacy `run_in_actor()` submitted
+        # in-line with each spawn).
+        await trio.sleep(0.5)
 
         # trigger a root actor error
         assert 0
 
-        # attempt to collect results (which raises error in parent)
-        # still has some issues where the parent seems to get stuck
-        await portal.result()
-        await portal1.result()
-
 
 if __name__ == '__main__':
     trio.run(main)

examples/debugging/multi_subactors.py

@@ -17,12 +17,12 @@ async def name_error():
 async def spawn_error():
     """"A nested nursery that triggers another ``NameError``.
     """
-    async with tractor.open_nursery() as n:
-        portal = await n.run_in_actor(
+    async with tractor.open_nursery() as an:
+        return await tractor.to_actor.run(
             name_error,
+            an=an,
             name='name_error_1',
         )
-        return await portal.result()
 
 
 async def main():
@@ -36,17 +36,39 @@ async def main():
     `-python -m tractor._child --uid ('spawn_error', '52ee14a5 ...)
        `-python -m tractor._child --uid ('name_error', '3391222c ...)
     """
+    errors: list[BaseException] = []
+
     async with tractor.open_nursery(
         debug_mode=True,
         # loglevel='runtime',
-    ) as n:
+    ) as an:
 
-        # Spawn both actors, don't bother with collecting results
-        # (would result in a different debugger outcome due to parent's
-        # cancellation).
-        await n.run_in_actor(breakpoint_forever)
-        await n.run_in_actor(name_error)
-        await n.run_in_actor(spawn_error)
+        async def run_and_collect(fn):
+            '''
+            One-shot whose (boxed) error is stashed instead of
+            raised so a sibling's crash never cancels the others
+            before they've had their own debugger sessions (the
+            "collect all errors" the legacy `run_in_actor()` API
+            did implicitly at nursery teardown).
+
+            '''
+            try:
+                await tractor.to_actor.run(fn, an=an)
+            except tractor.RemoteActorError as rae:
+                errors.append(rae)
+
+        # Spawn all one-shot task actors, collecting (vs.
+        # raising) their errors.
+        async with trio.open_nursery() as tn:
+            tn.start_soon(run_and_collect, breakpoint_forever)
+            tn.start_soon(run_and_collect, name_error)
+            tn.start_soon(run_and_collect, spawn_error)
+
+        if errors:
+            raise BaseExceptionGroup(
+                'multi_subactors errored!',
+                errors,
+            )
 
 
 if __name__ == '__main__':

examples/debugging/open_ctx_modnofound.py

@@ -21,8 +21,8 @@ async def main() -> None:
 
     async with tractor.open_nursery(
         debug_mode=True,
-    ) as n:
-        portal = await n.start_actor(
+    ) as an:
+        portal = await an.start_actor(
             'ctx_child',
 
             # XXX: we don't enable the current module in order

examples/debugging/per_actor_debug.py

@@ -6,14 +6,14 @@ async def die():
 
 
 async def main():
-    async with tractor.open_nursery() as tn:
+    async with tractor.open_nursery() as an:
 
-        debug_actor = await tn.start_actor(
+        debug_actor = await an.start_actor(
             'debugged_boi',
             enable_modules=[__name__],
             debug_mode=True,
         )
-        crash_boi = await tn.start_actor(
+        crash_boi = await an.start_actor(
             'crash_boi',
             enable_modules=[__name__],
             # debug_mode=True,

examples/debugging/root_cancelled_but_child_is_in_tty_lock.py

@@ -1,3 +1,5 @@
+from functools import partial
+
 import trio
 import tractor
 
@@ -10,14 +12,14 @@ async def name_error():
 async def spawn_until(depth=0):
     """"A nested nursery that triggers another ``NameError``.
     """
-    async with tractor.open_nursery() as n:
+    async with tractor.open_nursery() as an:
         if depth < 1:
-            # await n.run_in_actor('breakpoint_forever', breakpoint_forever)
-            await n.run_in_actor(name_error)
+            await tractor.to_actor.run(name_error, an=an)
         else:
             depth -= 1
-            await n.run_in_actor(
+            await tractor.to_actor.run(
                 spawn_until,
+                an=an,
                 depth=depth,
                 name=f'spawn_until_{depth}',
             )
@@ -37,28 +39,33 @@ async def main():
        └─ python -m tractor._child --uid ('name_error', '6c2733b8 ...)
 
     '''
-    async with tractor.open_nursery(
-        debug_mode=True,
-        enable_transports=['uds'],  # TODO, apss this via osenv?
-        loglevel='devx',  # XXX, required for test!
-    ) as n:
+    async with (
+        tractor.open_nursery(
+            debug_mode=True,
+            enable_transports=['uds'],  # TODO, apss this via osenv?
+            loglevel='devx',  # XXX, required for test!
+        ) as an,
+        trio.open_nursery() as tn,
+    ):
+        # spawn the deeper tree in the bg..
+        tn.start_soon(
+            partial(
+                tractor.to_actor.run,
+                spawn_until,
+                an=an,
+                depth=1,
+                name='spawner1',
+            )
+        )
 
-        # spawn both actors
-        portal = await n.run_in_actor(
+        # ..while blocking on the shallow (faster to fail) tree
+        # whose propagated error triggers nursery cancellation.
+        await tractor.to_actor.run(
             spawn_until,
+            an=an,
             depth=0,
             name='spawner0',
         )
-        portal1 = await n.run_in_actor(
-            spawn_until,
-            depth=1,
-            name='spawner1',
-        )
-
-        # nursery cancellation should be triggered due to propagated
-        # error from child.
-        await portal.result()
-        await portal1.result()
 
 
 if __name__ == '__main__':

examples/debugging/root_timeout_while_child_crashed.py

@@ -13,17 +13,24 @@ async def main():
     simultaneously.
 
     '''
-    async with tractor.open_nursery(
-        debug_mode=True,
-        # loglevel='debug'  # ?XXX required?
-    ) as n:
-
-        # spawn both actors
-        portal = await n.run_in_actor(key_error)
+    async with (
+        tractor.open_nursery(
+            debug_mode=True,
+            # loglevel='debug'  # ?XXX required?
+        ) as an,
+        trio.open_nursery() as tn,
+    ):
+        # spawn the actor..
+        portal = await an.start_actor(
+            'key_error',
+            enable_modules=[__name__],
+        )
         print(
             f'Child is up @ {portal.chan.aid.reprol()}'
         )
-
+        # ..then schedule its erroring task in the bg while the
+        # root blocks below.
+        tn.start_soon(portal.run, key_error)
 
         # XXX: originally a bug caused by this is where root would enter
         # the debugger and clobber the tty used by the repl even though

examples/debugging/shielded_pause.py

@@ -74,11 +74,11 @@ async def cancelled_before_pause(
 async def main():
     async with tractor.open_nursery(
         debug_mode=True,
-    ) as n:
-        portal: tractor.Portal = await n.run_in_actor(
+    ) as an:
+        await tractor.to_actor.run(
             cancelled_before_pause,
+            an=an,
         )
-        await portal.wait_for_result()
 
         # ensure the same works in the root actor!
         await pm_on_cancelled()

examples/debugging/subactor_bp_in_ctx.py

@@ -58,8 +58,8 @@ async def main():
         debug_mode=True,
         enable_transports=[tpt],
         loglevel='devx',
-    ) as n:
-        p = await n.start_actor(
+    ) as an:
+        p = await an.start_actor(
             'bp_boi',
             enable_modules=[__name__],
         )

examples/debugging/subactor_breakpoint.py

@@ -17,12 +17,14 @@ async def main():
     async with tractor.open_nursery(
         debug_mode=True,
         loglevel='cancel',
-    ) as n:
+    ) as an:
 
-        portal = await n.run_in_actor(
+        # parks awaiting a result which only arrives once the
+        # user quits (`BdbQuit`s) the child's REPL loop.
+        await tractor.to_actor.run(
             breakpoint_forever,
+            an=an,
         )
-        await portal.wait_for_result()
 
 
 if __name__ == '__main__':

examples/debugging/subactor_error.py

@@ -12,16 +12,12 @@ async def main():
     ) as an:
 
         # TODO: ideally the REPL arrives at this frame in the parent,
-        # ABOVE the @api_frame of `Portal.run_in_actor()` (which
-        # should eventually not even be a portal method ... XD)
+        # ABOVE the @api_frame of `to_actor.run()` ..
         # await tractor.pause()
-        p: tractor.Portal = await an.run_in_actor(name_error)
 
-        # with this style, should raise on this line
-        await p.wait_for_result()
-
-        # with this alt style should raise at `open_nusery()`
-        # return await p.wait_for_result()
+        # the one-shot blocks on the subactor's result so the
+        # boxed `NameError` raises right here.
+        await tractor.to_actor.run(name_error, an=an)
 
 
 if __name__ == '__main__':

examples/debugging/sync_bp.py

@@ -90,7 +90,7 @@ async def main() -> None:
 
         # TODO: 3 sub-actor usage cases:
         # -[x] via a `.open_context()`
-        # -[ ] via a `.run_in_actor()` call
+        # -[ ] via a `to_actor.run()` call
         # -[ ] via a `.run()`
         # -[ ] via a `.to_thread.run_sync()` in subactor
         async with p.open_context(

examples/infected_asyncio_echo_server.py

@@ -50,8 +50,8 @@ async def trio_to_aio_echo_server(
 
 async def main():
 
-    async with tractor.open_nursery() as n:
-        p = await n.start_actor(
+    async with tractor.open_nursery() as an:
+        p = await an.start_actor(
             'aio_server',
             enable_modules=[__name__],
             infect_asyncio=True,

examples/integration/open_context_and_sleep.py

@@ -29,9 +29,9 @@ async def main() -> None:
     ))
     await proc.wait()
     # await trio.sleep_forever()
-    # async with tractor.open_nursery() as n:
+    # async with tractor.open_nursery() as an:
 
-    #     portal = await n.start_actor(
+    #     portal = await an.start_actor(
     #         'rpc_server',
     #         enable_modules=[__name__],
     #     )

examples/parallelism/concurrent_actors_primes.py

@@ -55,7 +55,7 @@ async def worker_pool(workers=4):
     Yes, the workers stay alive (and ready for work) until you close
     the context.
     """
-    async with tractor.open_nursery() as tn:
+    async with tractor.open_nursery() as an:
 
         portals = []
         snd_chan, recv_chan = trio.open_memory_channel(len(PRIMES))
@@ -65,7 +65,7 @@ async def worker_pool(workers=4):
             # this starts a new sub-actor (process + trio runtime) and
             # stores it's "portal" for later use to "submit jobs" (ugh).
             portals.append(
-                await tn.start_actor(
+                await an.start_actor(
                     f'worker_{i}',
                     enable_modules=[__name__],
                 )
@@ -80,10 +80,10 @@ async def worker_pool(workers=4):
             async def send_result(func, value, portal):
                 await snd_chan.send((value, await portal.run(func, n=value)))
 
-            async with trio.open_nursery() as n:
+            async with trio.open_nursery() as tn:
 
                 for value, portal in zip(sequence, itertools.cycle(portals)):
-                    n.start_soon(
+                    tn.start_soon(
                         send_result,
                         worker_func,
                         value,
@@ -98,7 +98,7 @@ async def worker_pool(workers=4):
         yield _map
 
         # tear down all "workers" on pool close
-        await tn.cancel()
+        await an.cancel()
 
 
 async def main():

examples/parallelism/single_func.py

@@ -25,17 +25,15 @@ async def burn_cpu():
 
 async def main():
 
-    async with tractor.open_nursery() as n:
+    async with trio.open_nursery() as tn:
 
-        portal = await n.run_in_actor(burn_cpu)
+        # burn rubber in the parent too
+        tn.start_soon(burn_cpu)
 
-        #  burn rubber in the parent too
-        await burn_cpu()
+        # run the same func as the lone task in a subactor,
+        # block on (and collect) its result
+        pid = await tractor.to_actor.run(burn_cpu)
 
-        # wait on result from target function
-        pid = await portal.wait_for_result()
-
-    # end of nursery block
     print(f"Collected subproc {pid}")
 
 

examples/parallelism/to_actor_one_shots.py

@@ -0,0 +1,83 @@
+'''
+`tractor.to_actor.run()`: one-shot single-task subactor
+invocation, the SC-parallelism sibling of
+`trio.to_thread.run_sync()` (and `anyio.to_process`).
+
+Each call spawns a subactor, schedules the async fn as
+its lone remote task, waits on the result and reaps the
+subactor. Concurrency composes the plain `trio` way:
+schedule multiple one-shot calls in a local task nursery
+against a shared actor-nursery; any remote error raises
+directly in the task which scheduled it.
+
+'''
+import math
+
+import tractor
+import trio
+
+
+async def is_prime(
+    n: int,
+) -> bool:
+    if n < 2:
+        return False
+    if n == 2:
+        return True
+    if n % 2 == 0:
+        return False
+
+    sqrt_n = int(math.floor(math.sqrt(n)))
+    for i in range(3, sqrt_n + 1, 2):
+        if n % i == 0:
+            return False
+    return True
+
+
+async def main() -> None:
+
+    # fully implicit one-shot: boots the actor-runtime,
+    # spawns a subactor, runs the task, reaps the
+    # subactor, tears the runtime back down.
+    assert await tractor.to_actor.run(
+        is_prime,
+        n=2,
+    )
+
+    # the "worker-pool-ish" pattern from the original
+    # `concurrent.futures` example: one subactor per
+    # input, all concurrent, results and errors
+    # collected by caller-side tasks.
+    results: dict[int, bool] = {}
+
+    async def check(
+        an: tractor.ActorNursery,
+        n: int,
+        i: int,
+    ) -> None:
+        results[n] = await tractor.to_actor.run(
+            is_prime,
+            an=an,
+            name=f'prime_checker_{i}',
+            n=n,
+        )
+
+    inputs: list[int] = [
+        7,
+        8,
+        3691,
+        3693,
+    ]
+    async with (
+        tractor.open_nursery() as an,
+        trio.open_nursery() as tn,
+    ):
+        for i, n in enumerate(inputs):
+            tn.start_soon(check, an, n, i)
+
+    for n, prime in sorted(results.items()):
+        print(f'{n} is prime: {prime}')
+
+
+if __name__ == '__main__':
+    trio.run(main)

examples/remote_error_propagation.py

@@ -7,19 +7,20 @@ async def assert_err():
 
 
 async def main():
-    async with tractor.open_nursery() as n:
+    async with tractor.open_nursery() as an:
         real_actors = []
         for i in range(3):
-            real_actors.append(await n.start_actor(
+            real_actors.append(await an.start_actor(
                 f'actor_{i}',
                 enable_modules=[__name__],
             ))
 
-        # start one actor that will fail immediately
-        await n.run_in_actor(assert_err)
+        # run one one-shot task actor that will fail immediately;
+        # its error raises right here in the caller's task..
+        await tractor.to_actor.run(assert_err, an=an)
 
-    # should error here with a ``RemoteActorError`` containing
-    # an ``AssertionError`` and all the other actors have been cancelled
+    # ..as a ``RemoteActorError`` containing an ``AssertionError``
+    # and all the other actors have been cancelled
 
 
 if __name__ == '__main__':

examples/rpc_bidir_streaming.py

@@ -31,9 +31,9 @@ async def simple_rpc(
 
 async def main() -> None:
 
-    async with tractor.open_nursery() as n:
+    async with tractor.open_nursery() as an:
 
-        portal = await n.start_actor(
+        portal = await an.start_actor(
             'rpc_server',
             enable_modules=[__name__],
         )

tests/devx/test_debugger.py

@@ -849,43 +849,36 @@ def test_multi_nested_subactors_error_through_nurseries(
             break
 
     # boxed source errors
+    #
+    # NB post-#477 (`to_actor.run()` one-shots in local
+    # task-nurseries) the final relay is the LAST-released
+    # (leaf) REPL's error chain: it wins each level's
+    # relay-vs-cancel race so every level's single-member
+    # group gets unwrapped by the runtime's `collapse_eg()`
+    # (annotated at each actor boundary) while the sibling
+    # tree ('spawner1') is cancelled + absorbed. The legacy
+    # `run_in_actor()` teardown-reap instead grouped BOTH the
+    # `name_error` and bp-quit chains into the final dump
+    # (the previously-unexplained "extra" patterns).
     expect_patts: list[str] = [
-        "NameError: name 'doggypants' is not defined",
         "tractor._exceptions.RemoteActorError:",
-        "('name_error'",
 
-        # first level subtrees
-        # "tractor._exceptions.RemoteActorError: ('spawner0'",
-        "src_uid=('spawner0'",
-
-        # "tractor._exceptions.RemoteActorError: ('spawner1'",
-
-        # propagation of errors up through nested subtrees
-        # "tractor._exceptions.RemoteActorError: ('spawn_until_0'",
-        # "tractor._exceptions.RemoteActorError: ('spawn_until_1'",
-        # "tractor._exceptions.RemoteActorError: ('spawn_until_2'",
-        # ^-NOTE-^ old RAE repr, new one is below with a field
-        # showing the src actor's uid.
-        "src_uid=('spawn_until_2'",
+        # each level's unwrapped-single-member-group
+        # annotation + the first-level subtree's boundary
+        # footer.
+        "( ^^^ this exc was collapsed from a group ^^^ )",
+        "------ ('spawner0'",
     ]
-    # XXX, I HAVE NO IDEA why these patts only show on the
-    # `trio`-spawner but it seems to have something to do with
-    # what gets dumped in prior-prompt latches somehow??
-    # TODO for claude, explain and or work through how this is
-    # happening but ONLY WHEN RUN FROM THE TEST, bc when i try to
-    # run the test script manually the correct output ALWAYS seems
-    # to be in the last `str(child.before.decode())` output !?!?
     if (
         not is_forking_spawner
         and
         last_send_char == 'q'
     ):
         expect_patts += [
-            # expect the pdb-quit exc.
+            # expect the pdb-quit exc relayed from the leaf's
+            # bp-loop child.
             "bdb.BdbQuit",
-            # BUT WHY these dude!?
-            "src_uid=('spawn_until_0'",
-            "relay_uid=('spawn_until_1'",
+            "src_uid=('breakpoint_forever'",
         ]
 
     assert_before(

tests/discovery/test_registrar.py

@@ -46,9 +46,9 @@ async def test_reg_then_unreg(
 
     async with tractor.open_nursery(
         registry_addrs=[reg_addr],
-    ) as n:
+    ) as an:
 
-        portal = await n.start_actor('actor', enable_modules=[__name__])
+        portal = await an.start_actor('actor', enable_modules=[__name__])
         uid = portal.channel.aid.uid
 
         async with tractor.get_registry(reg_addr) as aportal:
@@ -62,7 +62,7 @@ async def test_reg_then_unreg(
                 # XXX: can we figure out what the listen addr will be?
                 assert sockaddrs
 
-        await n.cancel()  # tear down nursery
+        await an.cancel()  # tear down nursery
 
         await trio.sleep(0.1)
         assert uid not in aportal.actor._registry
@@ -89,9 +89,9 @@ async def test_reg_then_unreg_maddr(
 
     async with tractor.open_nursery(
         registry_addrs=[maddr_str],
-    ) as n:
+    ) as an:
 
-        portal = await n.start_actor(
+        portal = await an.start_actor(
             'actor_maddr',
             enable_modules=[__name__],
         )
@@ -105,7 +105,7 @@ async def test_reg_then_unreg_maddr(
                 sockaddrs = actor._registry[uid]
                 assert sockaddrs
 
-        await n.cancel()
+        await an.cancel()
 
         await trio.sleep(0.1)
         assert uid not in aportal.actor._registry
@@ -152,23 +152,37 @@ async def test_trynamic_trio(
     for the directed subs.
 
     '''
-    async with tractor.open_nursery() as n:
+    async with tractor.open_nursery() as an:
         print("Alright... Action!")
 
-        donny = await n.run_in_actor(
-            ria_fn,
-            other_actor='gretchen',
-            reg_addr=reg_addr,
-            name='donny',
-        )
-        gretchen = await n.run_in_actor(
-            ria_fn,
-            other_actor='donny',
-            reg_addr=reg_addr,
-            name='gretchen',
-        )
-        print(await gretchen.result())
-        print(await donny.result())
+        # donny + gretchen each wait on (then dial!) the *other*, so
+        # both actors must OUTLIVE both hellos: spawn as daemons and
+        # only reap after both tasks complete. NB a pair of eagerly
+        # reaped `to_actor.run()` one-shots races: the first to
+        # finish dies while the other may still be dialing its
+        # registry-resolved (now dead) sockaddr -> conn-refused.
+        portals: dict[str, tractor.Portal] = {
+            name: await an.start_actor(
+                name,
+                enable_modules=[__name__],
+            )
+            for name in ('donny', 'gretchen')
+        }
+
+        async def _direct(this_name: str, other_actor: str):
+            res = await portals[this_name].run(
+                ria_fn,
+                other_actor=other_actor,
+                reg_addr=reg_addr,
+            )
+            print(res)
+
+        async with trio.open_nursery() as tn:
+            tn.start_soon(_direct, 'donny', 'gretchen')
+            tn.start_soon(_direct, 'gretchen', 'donny')
+
+        # both hellos have completed; reap the thespians.
+        await an.cancel()
         print("CUTTTT CUUTT CUT!!?! Donny!! You're supposed to say...")
 
 
@@ -270,13 +284,15 @@ async def spawn_and_check_registry(
                         portals = {}
                         for i in range(3):
                             name = f'a{i}'
-                            if with_streaming:
-                                portals[name] = await an.start_actor(
-                                    name=name, enable_modules=[__name__])
-
-                            else:  # no streaming
-                                portals[name] = await an.run_in_actor(
-                                    trio.sleep_forever, name=name)
+                            # a daemon subactor is alive + registered
+                            # without a "main" task; the streaming
+                            # branch below uses the module funcs, the
+                            # non-streaming case just needs it up (was
+                            # `run_in_actor(trio.sleep_forever)`).
+                            portals[name] = await an.start_actor(
+                                name=name,
+                                enable_modules=[__name__],
+                            )
 
                         # wait on last actor to come up
                         async with tractor.wait_for_actor(name):

tests/test_advanced_streaming.py

@@ -3,6 +3,7 @@ Advanced streaming patterns using bidirectional streams and contexts.
 
 '''
 from collections import Counter
+from functools import partial
 import itertools
 import platform
 from typing import Type
@@ -173,8 +174,8 @@ def test_dynamic_pub_sub(
     # test. Picked backend-aware: under `trio` backend spawn is
     # cheap (~1s for `cpus` actors) but fork-based backends pay
     # a per-spawn cost (forkserver round-trip + IPC peer-handshake)
-    # that can stack up over `cpus - 1` sequential `n.run_in_actor()`
-    # calls — especially on UDS under cross-pytest contention
+    # that can stack up over the `cpus - 1` one-shot
+    # (`to_actor.run()`) spawns — especially on UDS under cross-pytest contention
     # (#451 / #452). 4s was flaking right at the edge under fork
     # backends — bumped to 8s with diag-snapshot-on-timeout via
     # `fail_after_w_trace` so a borderline run still fails loud
@@ -214,33 +215,55 @@ def test_dynamic_pub_sub(
                     f'enter `fail_after_w_trace({fail_after_s})` scope'
                 )
                 try:
-                    async with tractor.open_nursery(
-                        registry_addrs=[reg_addr],
-                        debug_mode=debug_mode,
-                    ) as n:
+                    async with (
+                        tractor.open_nursery(
+                            registry_addrs=[reg_addr],
+                            debug_mode=debug_mode,
+                        ) as an,
+                        # bg-schedules the forever-streaming
+                        # one-shots below; the user-cancel raise
+                        # cancels them all, each reaping its
+                        # subactor via `to_actor.run()`'s
+                        # (shielded) `Portal.cancel_actor()`.
+                        trio.open_nursery() as tn,
+                    ):
                         test_log.cancel(
                             'test_dynamic_pub_sub: '
                             'actor nursery opened'
                         )
 
                         # name of this actor will be same as target func
-                        await n.run_in_actor(publisher)
+                        tn.start_soon(
+                            partial(
+                                tractor.to_actor.run,
+                                publisher,
+                                an=an,
+                            )
+                        )
 
                         for i, sub in zip(
                             range(cpus - 2),
                             itertools.cycle(_registry.keys())
                         ):
-                            await n.run_in_actor(
-                                consumer,
-                                name=f'consumer_{sub}',
-                                subs=[sub],
+                            tn.start_soon(
+                                partial(
+                                    tractor.to_actor.run,
+                                    consumer,
+                                    an=an,
+                                    name=f'consumer_{sub}',
+                                    subs=[sub],
+                                )
                             )
 
                         # make one dynamic subscriber
-                        await n.run_in_actor(
-                            consumer,
-                            name='consumer_dynamic',
-                            subs=list(_registry.keys()),
+                        tn.start_soon(
+                            partial(
+                                tractor.to_actor.run,
+                                consumer,
+                                an=an,
+                                name='consumer_dynamic',
+                                subs=list(_registry.keys()),
+                            )
                         )
 
                         # block until "cancelled by user"
@@ -347,10 +370,10 @@ def test_reqresp_ontopof_streaming():
             timeout = 4
 
         with trio.move_on_after(timeout):
-            async with tractor.open_nursery() as n:
+            async with tractor.open_nursery() as an:
 
                 # name of this actor will be same as target func
-                portal = await n.start_actor(
+                portal = await an.start_actor(
                     'dual_tasks',
                     enable_modules=[__name__]
                 )
@@ -413,9 +436,9 @@ def test_sigint_both_stream_types():
 
     async def main():
         with trio.fail_after(timeout):
-            async with tractor.open_nursery() as n:
+            async with tractor.open_nursery() as an:
                 # name of this actor will be same as target func
-                portal = await n.start_actor(
+                portal = await an.start_actor(
                     '2_way',
                     enable_modules=[__name__]
                 )
@@ -528,8 +551,8 @@ def test_local_task_fanout_from_stream(
 
         async with tractor.open_nursery(
             debug_mode=debug_mode,
-        ) as tn:
-            p: tractor.Portal = await tn.start_actor(
+        ) as an:
+            p: tractor.Portal = await an.start_actor(
                 'inf_streamer',
                 enable_modules=[__name__],
             )

tests/test_cancellation.py

@@ -2,6 +2,7 @@
 Cancellation and error propagation
 
 """
+from functools import partial
 import os
 import signal
 import platform
@@ -16,6 +17,10 @@ from tractor._testing import (
     tractor_test,
 )
 from tractor._testing.trace import FailAfterWTraceFactory
+from tractor.trionics import (
+    collapse_eg,
+    gather_contexts,
+)
 from .conftest import no_windows
 
 
@@ -68,6 +73,23 @@ async def assert_err(delay=0):
     assert 0
 
 
+@tractor.context
+async def assert_err_ctx(
+    ctx: tractor.Context,
+    delay: float = 0,
+) -> None:
+    '''
+    `@context` shim around `assert_err()` so the multi-actor error
+    tests can fan-out one-shot erroring subactors via
+    `Portal.open_context()` + `gather_contexts()` instead of the
+    removed `ActorNursery.run_in_actor()` (#477).
+
+    '''
+    await ctx.started()
+    await trio.sleep(delay)
+    assert 0
+
+
 async def sleep_forever():
     await trio.sleep_forever()
 
@@ -104,24 +126,19 @@ def test_remote_error(
     async def main():
         async with tractor.open_nursery(
             registry_addrs=[reg_addr],
-        ) as nursery:
+        ) as an:
 
-            # on a remote type error caused by bad input args
-            # this should raise directly which means we **don't** get
-            # an exception group outside the nursery since the error
-            # here and the far end task error are one in the same?
-            portal = await nursery.run_in_actor(
-                assert_err,
-                name='errorer',
-                **args
-            )
-
-            # get result(s) from main task
+            # `to_actor.run()` blocks on the one-shot's result and
+            # raises the remote error directly here in the caller's
+            # task (a bad-arg `TypeError` likewise relays as a
+            # `RemoteActorError`).
             try:
-                # this means the root actor will also raise a local
-                # parent task error and thus an eg will propagate out
-                # of this actor nursery.
-                await portal.result()
+                await tractor.to_actor.run(
+                    assert_err,
+                    an=an,
+                    name='errorer',
+                    **args
+                )
             except tractor.RemoteActorError as err:
                 assert err.boxed_type == errtype
                 print("Look Maa that actor failed hard, hehh")
@@ -162,114 +179,49 @@ def test_multierror(
     set_fork_aware_capture, #: Callable,
 ):
     '''
-    Verify we raise a ``BaseExceptionGroup`` out of a nursery where
-    more then one actor errors.
+    Verify concurrent one-shot subactors erroring propagate a remote
+    error out of the `gather_contexts()` fan-out — grouped as a
+    `BaseExceptionGroup`, or (under cancel-on-first, where the 2nd
+    errorer is cancelled before relaying its own exc) collapsed to a
+    single `RemoteActorError`.
+
+    NB the legacy `run_in_actor()` reaped *all* children at nursery
+    teardown so this always yielded a BEG-of-N; the `to_actor`
+    fan-out is cancel-on-first, so accept either shape.
 
     '''
     async def main():
         async with tractor.open_nursery(
             registry_addrs=[reg_addr],
-        ) as nursery:
+        ) as an:
 
-            await nursery.run_in_actor(assert_err, name='errorer1')
-            portal2 = await nursery.run_in_actor(assert_err, name='errorer2')
+            portals = [
+                await an.start_actor(
+                    f'errorer{i}',
+                    enable_modules=[__name__],
+                )
+                for i in range(2)
+            ]
 
-            # get result(s) from main task
-            try:
-                await portal2.result()
-            except tractor.RemoteActorError as err:
-                assert err.boxed_type is AssertionError
-                print("Look Maa that first actor failed hard, hehh")
-                raise
+            # both one-shot subactors error concurrently, so the
+            # `gather_contexts()` task-nursery collects them into a
+            # `BaseExceptionGroup` (was two non-blocking
+            # `run_in_actor()`s reaped at nursery teardown).
+            async with gather_contexts(
+                mngrs=[
+                    p.open_context(assert_err_ctx)
+                    for p in portals
+                ],
+            ):
+                pass
 
-        # here we should get a ``BaseExceptionGroup`` containing exceptions
-        # from both subactors
-
-    with pytest.raises(BaseExceptionGroup):
+    with pytest.raises((
+        BaseExceptionGroup,
+        tractor.RemoteActorError,
+    )):
         trio.run(main)
 
 
-@pytest.mark.parametrize(
-    'delay',
-    (0, 0.5),
-    ids='delays={}'.format,
-)
-@pytest.mark.parametrize(
-    'num_subactors',
-    range(25, 26),
-    ids= 'num_subs={}'.format,
-)
-def test_multierror_fast_nursery(
-    reg_addr: tuple,
-    start_method: str,
-    num_subactors: int,
-    delay: float,
-    set_fork_aware_capture,
-    fail_after_w_trace: FailAfterWTraceFactory,
-):
-    '''
-    Verify we raise a ``BaseExceptionGroup`` out of a nursery where
-    more then one actor errors and also with a delay before failure
-    to test failure during an ongoing spawning.
-
-    '''
-    async def main():
-        # budget = 2× natural trio-backend cascade time for
-        # 25 errorer subactors (~14s observed). on-timeout
-        # diag snapshot → if the cancel cascade hangs
-        # (observed under MTF backend with N>=14 errorer
-        # subactors) we get a fresh ptree/wchan/py-spy dump
-        # on disk INSTEAD of an opaque pytest timeout-kill.
-        # See `tractor/_testing/trace.py` for the helper.
-        async with fail_after_w_trace(30.0):
-            async with tractor.open_nursery(
-                registry_addrs=[reg_addr],
-            ) as nursery:
-
-                for i in range(num_subactors):
-                    await nursery.run_in_actor(
-                        assert_err,
-                        name=f'errorer{i}',
-                        delay=delay
-                    )
-
-    # with pytest.raises(trio.MultiError) as exc_info:
-    # NOTE, `trio.TooSlowError` from `fail_after_w_trace`
-    # bubbles UN-wrapped if `open_nursery.__aexit__` never
-    # gets re-entered; wrapped inside a `BaseExceptionGroup`
-    # if it did. Accept both shapes so the matcher itself
-    # doesn't lie about *what* failed.
-    with pytest.raises(
-        (BaseExceptionGroup, trio.TooSlowError),
-    ) as exc_info:
-        trio.run(main)
-
-    if isinstance(exc_info.value, trio.TooSlowError):
-        pytest.fail(
-            f'cancel cascade hung past 12s '
-            f'(num_subactors={num_subactors}, delay={delay}); '
-            f'see stderr for `fail_after_w_trace` snapshot path'
-        )
-
-    assert exc_info.type == ExceptionGroup
-    err = exc_info.value
-    exceptions = err.exceptions
-
-    if len(exceptions) == 2:
-        # sometimes oddly now there's an embedded BrokenResourceError ?
-        for exc in exceptions:
-            excs = getattr(exc, 'exceptions', None)
-            if excs:
-                exceptions = excs
-                break
-
-    assert len(exceptions) == num_subactors
-
-    for exc in exceptions:
-        assert isinstance(exc, tractor.RemoteActorError)
-        assert exc.boxed_type is AssertionError
-
-
 async def do_nothing():
     pass
 
@@ -296,16 +248,16 @@ def test_cancel_single_subactor(
         '''
         async with tractor.open_nursery(
             registry_addrs=[reg_addr],
-        ) as nursery:
+        ) as an:
 
-            portal = await nursery.start_actor(
+            portal = await an.start_actor(
                 'nothin', enable_modules=[__name__],
             )
             assert (await portal.run(do_nothing)) is None
 
             if mechanism == 'nursery_cancel':
                 # would hang otherwise
-                await nursery.cancel()
+                await an.cancel()
             else:
                 raise mechanism
 
@@ -337,8 +289,8 @@ async def test_cancel_infinite_streamer(
         trio.fail_after(4),
         trio.move_on_after(1) as cancel_scope
     ):
-        async with tractor.open_nursery() as n:
-            portal = await n.start_actor(
+        async with tractor.open_nursery() as an:
+            portal = await an.start_actor(
                 'donny',
                 enable_modules=[__name__],
             )
@@ -351,36 +303,36 @@ async def test_cancel_infinite_streamer(
 
     # we support trio's cancellation system
     assert cancel_scope.cancelled_caught
-    assert n.cancel_called
+    assert an.cancel_called
 
 
 @pytest.mark.parametrize(
     'num_actors_and_errs',
     [
-        # daemon actors sit idle while single task actors error out
+        # daemon actors sit idle while one-shot task actors error out
         (1, tractor.RemoteActorError, AssertionError, (assert_err, {}), None),
         (2, BaseExceptionGroup, AssertionError, (assert_err, {}), None),
         (3, BaseExceptionGroup, AssertionError, (assert_err, {}), None),
 
-        # 1 daemon actor errors out while single task actors sleep forever
+        # 1 daemon actor errors out while one-shot task actors sleep forever
         (3, tractor.RemoteActorError, AssertionError, (sleep_forever, {}),
          (assert_err, {}, True)),
-        # daemon actors error out after brief delay while single task
+        # daemon actors error out after brief delay while one-shot task
         # actors complete quickly
         (3, tractor.RemoteActorError, AssertionError,
          (do_nuthin, {}), (assert_err, {'delay': 1}, True)),
-        # daemon complete quickly delay while single task
+        # daemon complete quickly delay while one-shot task
         # actors error after brief delay
         (3, BaseExceptionGroup, AssertionError,
          (assert_err, {'delay': 1}), (do_nuthin, {}, False)),
     ],
     ids=[
-        '1_run_in_actor_fails',
-        '2_run_in_actors_fail',
-        '3_run_in_actors_fail',
+        '1_one_shot_fails',
+        '2_one_shots_fail',
+        '3_one_shots_fail',
         '1_daemon_actors_fail',
-        '1_daemon_actors_fail_all_run_in_actors_dun_quick',
-        'no_daemon_actors_fail_all_run_in_actors_sleep_then_fail',
+        '1_daemon_actors_fail_all_one_shots_dun_quick',
+        'no_daemon_actors_fail_all_one_shots_sleep_then_fail',
     ],
 )
 @tractor_test(
@@ -399,12 +351,22 @@ async def test_some_cancels_all(
 
     This is the first and only supervisory strategy at the moment.
 
+    One-shot subactors run as concurrent `to_actor.run()` tasks
+    in a local task-nursery so their errors raise WHILE the
+    actor-nursery block is still open (vs the legacy
+    `run_in_actor()` teardown-reap); the first error cancels the
+    sibling one-shots (whose `trio.Cancelled`s the task-nursery
+    absorbs) so the group shape is 1..num_actors
+    `RemoteActorError`s depending on relay-vs-cancel timing —
+    with `collapse_eg()` unwrapping the deterministic
+    single-error cases to a bare `RemoteActorError`.
+
     '''
     (
         num_actors,
         first_err,
         err_type,
-        ria_func,
+        one_shot_func,
         da_func,
     ) = num_actors_and_errs
     try:
@@ -418,51 +380,64 @@ async def test_some_cancels_all(
                     enable_modules=[__name__],
                 ))
 
-            func, kwargs = ria_func
-            riactor_portals = []
-            for i in range(num_actors):
-                # start actor(s) that will fail immediately
-                riactor_portals.append(
-                    await an.run_in_actor(
-                        func,
-                        name=f'actor_{i}',
-                        **kwargs
+            func, kwargs = one_shot_func
+            async with (
+                collapse_eg(),
+                trio.open_nursery() as tn,
+            ):
+                for i in range(num_actors):
+                    # schedule one-shot task actor(s); errors
+                    # raise into this task-nursery scope.
+                    tn.start_soon(
+                        partial(
+                            tractor.to_actor.run,
+                            func,
+                            an=an,
+                            name=f'actor_{i}',
+                            **kwargs,
+                        )
                     )
-                )
 
-            if da_func:
-                func, kwargs, expect_error = da_func
-                for portal in dactor_portals:
-                    # if this function fails then we should error here
-                    # and the nursery should teardown all other actors
-                    try:
-                        await portal.run(func, **kwargs)
+                if da_func:
+                    func, kwargs, expect_error = da_func
+                    for portal in dactor_portals:
+                        # if this function fails then we should error
+                        # here and the nursery should teardown all
+                        # other actors
+                        try:
+                            await portal.run(func, **kwargs)
 
-                    except tractor.RemoteActorError as err:
-                        assert err.boxed_type == err_type
-                        # we only expect this first error to propogate
-                        # (all other daemons are cancelled before they
-                        # can be scheduled)
-                        num_actors = 1
-                        # reraise so nursery teardown is triggered
-                        raise
-                    else:
-                        if expect_error:
-                            pytest.fail(
-                                "Deamon call should fail at checkpoint?")
+                        except tractor.RemoteActorError as err:
+                            assert err.boxed_type == err_type
+                            # we only expect this first error to propogate
+                            # (all other daemons are cancelled before they
+                            # can be scheduled)
+                            num_actors = 1
+                            # reraise so nursery teardown is triggered
+                            raise
+                        else:
+                            if expect_error:
+                                pytest.fail(
+                                    "Deamon call should fail at checkpoint?")
 
-        # should error here with a ``RemoteActorError`` or ``MultiError``
+        # should error here with a `RemoteActorError` or a beg of them
 
-    except first_err as _err:
+    except (
+        BaseExceptionGroup,
+        tractor.RemoteActorError,
+    ) as _err:
         err = _err
         if isinstance(err, BaseExceptionGroup):
-            assert len(err.exceptions) == num_actors
+            # only the concurrent multi-error cases can group; the
+            # relay-vs-cancel race means anywhere from 1 (all
+            # siblings cancelled before relaying) up to all
+            # `num_actors` errors may populate the group.
+            assert first_err is BaseExceptionGroup
+            assert 1 <= len(err.exceptions) <= num_actors
             for exc in err.exceptions:
-                if isinstance(exc, tractor.RemoteActorError):
-                    assert exc.boxed_type == err_type
-                else:
-                    assert isinstance(exc, trio.Cancelled)
-        elif isinstance(err, tractor.RemoteActorError):
+                assert isinstance(exc, tractor.RemoteActorError)
+                assert exc.boxed_type == err_type
+        else:
             assert err.boxed_type == err_type
 
         assert an.cancel_called is True
@@ -475,8 +450,20 @@ async def spawn_and_error(
     breadth: int,
     depth: int,
 ) -> None:
+    '''
+    Recursively spawn a breadth-wide level of erroring one-shot
+    subactors as concurrent `to_actor.run()` tasks; the leaf level
+    errors ~simultaneously and each level's task-nursery groups
+    whatever `RemoteActorError`s relay before the first one's
+    cancel wins, boxing the (`ExceptionGroup`-shaped) group into
+    this actor's own relayed error.
+
+    '''
     name = tractor.current_actor().name
-    async with tractor.open_nursery() as nursery:
+    async with (
+        tractor.open_nursery() as an,
+        trio.open_nursery() as tn,
+    ):
         for i in range(breadth):
 
             if depth > 0:
@@ -496,7 +483,14 @@ async def spawn_and_error(
                 kwargs = {
                     'name': f'{name}_errorer_{i}',
                 }
-            await nursery.run_in_actor(*args, **kwargs)
+            tn.start_soon(
+                partial(
+                    tractor.to_actor.run,
+                    *args,
+                    an=an,
+                    **kwargs,
+                )
+            )
 
 
 # NOTE: `main_thread_forkserver` capture-fd hang class is no
@@ -538,7 +532,11 @@ async def test_nested_multierrors(
     depth: int,
 ):
     '''
-    Test that failed actor sets are wrapped in `BaseExceptionGroup`s.
+    Test that a nested tree of concurrently failing one-shot
+    subactors tears down cleanly, relaying (whatever subset of)
+    the leaf `AssertionError`s (that win the per-level
+    relay-vs-cancel race) re-boxed/grouped at each actor
+    boundary.
 
     Parametrized over recursion `depth ∈ {1, 3}`:
 
@@ -588,6 +586,13 @@ async def test_nested_multierrors(
     # fork-spawn jitter + UDS-contention widens both `t1` and
     # `t2` further.
     #
+    # NB post-#477 (`to_actor.run()` fan-out in a local
+    # task-nursery) a race-tripped sibling's `Cancelled` is
+    # ABSORBED by the task-nursery instead of landing in the
+    # group — the raced case now shows as a *smaller* BEG, so
+    # this marker should consistently `xpass`; drop it once CI
+    # confirms.
+    #
     # With `strict=False` the clean-cascade cases (most
     # depth=1 runs, rare depth=3 runs) report as `xpassed`
     # while the race-tripped cases report as `xfailed` —
@@ -672,6 +677,14 @@ async def test_nested_multierrors(
             timeout = 16
         case ('main_thread_forkserver', 3):
             timeout = 30
+        # any other fork-based backend (`mp_spawn` et al) pays
+        # the same per-spawn round-trip costs as MTF so rides
+        # its budgets; without a default arm `timeout` is left
+        # unbound -> `UnboundLocalError` at the scaling below.
+        case (_, 1):
+            timeout = 16
+        case (_, 3):
+            timeout = 30
 
     # inflate the budget by the throttle headroom probed above so
     # a slow box doesn't masquerade as a deadline regression.
@@ -684,67 +697,82 @@ async def test_nested_multierrors(
 
     async with fail_after_w_trace(timeout):
         try:
-            async with tractor.open_nursery() as nursery:
+            async with (
+                tractor.open_nursery() as an,
+                trio.open_nursery() as tn,
+            ):
                 for i in range(subactor_breadth):
-                    await nursery.run_in_actor(
-                        spawn_and_error,
-                        name=f'spawner_{i}',
-                        breadth=subactor_breadth,
-                        depth=depth,
+                    tn.start_soon(
+                        partial(
+                            tractor.to_actor.run,
+                            spawn_and_error,
+                            an=an,
+                            name=f'spawner_{i}',
+                            breadth=subactor_breadth,
+                            depth=depth,
+                        )
                     )
-        except BaseExceptionGroup as err:
-            assert len(err.exceptions) == subactor_breadth
-            for subexc in err.exceptions:
-
-                # verify first level actor errors are wrapped as remote
-                if _friggin_windows:
-
+        except (
+            BaseExceptionGroup,
+            tractor.RemoteActorError,
+        ) as err:
+            # group membership is bounded by the relay-vs-cancel
+            # race: the first spawner-tree's error cancels its
+            # siblings, whose own errors only group when relayed
+            # first; a fully-raced tree even collapses (via the
+            # runtime's own `collapse_eg()` unwrapping each level's
+            # single-member group) to a bare `RemoteActorError`
+            # re-boxing the leaf `AssertionError` at every actor
+            # boundary. The deterministic exact-breadth nested-BEG
+            # was the legacy `run_in_actor()` reap-all-at-teardown.
+            subexcs: list[BaseException] = (
+                err.exceptions
+                if isinstance(err, BaseExceptionGroup)
+                else [err]
+            )
+            assert 1 <= len(subexcs) <= subactor_breadth
+            for subexc in subexcs:
+                if (
+                    _friggin_windows
+                    and
+                    isinstance(subexc, trio.Cancelled)
+                ):
                     # windows is often too slow and cancellation seems
                     # to happen before an actor is spawned
-                    if isinstance(subexc, trio.Cancelled):
-                        continue
+                    continue
 
-                    elif isinstance(subexc, tractor.RemoteActorError):
-                        # on windows it seems we can't exactly be sure wtf
-                        # will happen..
-                        assert subexc.boxed_type in (
-                            tractor.RemoteActorError,
-                            trio.Cancelled,
-                            BaseExceptionGroup,
-                        )
+                assert isinstance(subexc, tractor.RemoteActorError)
 
-                    elif isinstance(subexc, BaseExceptionGroup):
-                        for subsub in subexc.exceptions:
-
-                            if subsub in (tractor.RemoteActorError,):
-                                subsub = subsub.boxed_type
-
-                            assert type(subsub) in (
-                                trio.Cancelled,
-                                BaseExceptionGroup,
-                            )
-                else:
-                    assert isinstance(subexc, tractor.RemoteActorError)
-
-                if depth > 0 and subactor_breadth > 1:
-                    # XXX not sure what's up with this..
-                    # on windows sometimes spawning is just too slow and
-                    # we get back the (sent) cancel signal instead
-                    if _friggin_windows:
-                        if isinstance(subexc, tractor.RemoteActorError):
-                            assert subexc.boxed_type in (
-                                BaseExceptionGroup,
-                                tractor.RemoteActorError
-                            )
-                        else:
-                            assert isinstance(subexc, BaseExceptionGroup)
-                    else:
-                        assert subexc.boxed_type is ExceptionGroup
-                else:
-                    assert subexc.boxed_type in (
-                        tractor.RemoteActorError,
-                        trio.Cancelled
+                accepted: tuple[Type[BaseException], ...] = (
+                    # ≥2 sub-tree errors relayed before the
+                    # cancel-cascade won → grouped per-level.
+                    ExceptionGroup,
+                    # every level collapsed down to its lone
+                    # relayed (leaf) error.
+                    AssertionError,
+                    # a mid-level spawner relays an
+                    # already-boxed (collapsed) leaf chain,
+                    # re-boxing the `RemoteActorError` itself.
+                    tractor.RemoteActorError,
+                    # under heavy load a runtime-internal reap
+                    # deadline can inject a `trio.Cancelled`
+                    # into a child's group before relay (the
+                    # same class the depth=3 throttle-xfail
+                    # covers) upgrading it from an
+                    # `ExceptionGroup`.
+                    BaseExceptionGroup,
+                )
+                if _friggin_windows:
+                    # on windows it seems we can't exactly be
+                    # sure wtf will happen..
+                    accepted += (
+                        trio.Cancelled,
                     )
+                assert subexc.boxed_type in accepted
+        else:
+            pytest.fail(
+                'Should have raised a (grouped) `RemoteActorError`?'
+            )
 
 
 @no_windows
@@ -764,8 +792,8 @@ def test_cancel_via_SIGINT(
         with trio.fail_after(2):
             async with tractor.open_nursery(
                 registry_addrs=[reg_addr],
-            ) as tn:
-                await tn.start_actor('sucka')
+            ) as an:
+                await an.start_actor('sucka')
                 if 'mp' in start_method:
                     time.sleep(0.1)
                 os.kill(pid, signal.SIGINT)
@@ -809,11 +837,13 @@ def test_cancel_via_SIGINT_other_task(
     ):
         async with tractor.open_nursery(
             registry_addrs=[reg_addr],
-        ) as tn:
+        ) as an:
+            # just keep a set of (daemon) subactors alive for the
+            # SIGINT to cancel (was 3 `run_in_actor(sleep_forever)`
+            # one-shots — a daemon needs no "main" task to idle).
             for i in range(3):
-                await tn.run_in_actor(
-                    sleep_forever,
-                    name='namesucka',
+                await an.start_actor(
+                    f'namesucka_{i}',
                 )
             task_status.started()
             await trio.sleep_forever()
@@ -854,8 +884,11 @@ async def spin_for(period=3):
 async def spawn_sub_with_sync_blocking_task():
     async with tractor.open_nursery() as an:
         print('starting sync blocking subactor..\n')
-        await an.run_in_actor(
+        # one-shot: parks HERE awaiting the sync-sleeping
+        # grandchild's result until cancelled from above.
+        await tractor.to_actor.run(
             spin_for,
+            an=an,
             name='sleeper',
         )
         print('exiting first subactor layer..\n')
@@ -961,10 +994,18 @@ def test_cancel_while_childs_child_in_sync_sleep(
                     debug_mode=debug_mode,
                     registry_addrs=[reg_addr],
                 ) as an,
+                trio.open_nursery() as tn,
             ):
-                await an.run_in_actor(
-                    spawn_sub_with_sync_blocking_task,
-                    name='sync_blocking_sub',
+                # bg one-shot: parks on the middle actor's result
+                # (itself parked on the sync-sleeping grandchild)
+                # until the `assert 0` below cancels this scope.
+                tn.start_soon(
+                    partial(
+                        tractor.to_actor.run,
+                        spawn_sub_with_sync_blocking_task,
+                        an=an,
+                        name='sync_blocking_sub',
+                    )
                 )
                 await trio.sleep(1)
 
@@ -1013,8 +1054,8 @@ def test_fast_graceful_cancel_when_spawn_task_in_soft_proc_wait_for_daemon(
         start = time.time()
         try:
             async with trio.open_nursery() as nurse:
-                async with tractor.open_nursery() as tn:
-                    p = await tn.start_actor(
+                async with tractor.open_nursery() as an:
+                    p = await an.start_actor(
                         'fast_boi',
                         enable_modules=[__name__],
                     )

tests/test_child_manages_service_nursery.py

@@ -156,8 +156,8 @@ def test_actor_managed_trio_nursery_task_error_cancels_aio(
     async def main():
 
         # cancel the nursery shortly after boot
-        async with tractor.open_nursery() as n:
-            p = await n.start_actor(
+        async with tractor.open_nursery() as an:
+            p = await an.start_actor(
                 'nursery_mngr',
                 infect_asyncio=asyncio_mode,  # TODO, is this enabling debug mode?
                 enable_modules=[__name__],

tests/test_infected_asyncio.py

@@ -24,6 +24,7 @@ from tractor import (
     current_actor,
     Actor,
     to_asyncio,
+    to_actor,
     RemoteActorError,
     ContextCancelled,
 )
@@ -110,8 +111,9 @@ def test_trio_cancels_aio_on_actor_side(
                 registry_addrs=[reg_addr],
                 debug_mode=debug_mode,
             ) as an:
-                await an.run_in_actor(
+                await to_actor.run(
                     trio_cancels_single_aio_task,
+                    an=an,
                     infect_asyncio=True,
                 )
 
@@ -157,6 +159,28 @@ async def asyncio_actor(
         raise
 
 
+@tractor.context
+async def sleep_forever_aio_ctx(
+    ctx: tractor.Context,
+    expect_err: str = 'trio.Cancelled',
+) -> None:
+    '''
+    `@context` shim so a parent can spawn a forever-sleeping
+    infected-`asyncio` task via `Portal.open_context()` and cancel it
+    (via `Portal.cancel_actor()` or an enclosing `trio` cancel scope),
+    asserting the graceful `trio.Cancelled` teardown.
+
+    Replaces the legacy `ActorNursery.run_in_actor()` spawn the
+    aio-cancel tests below used to rely on (removed with #477).
+
+    '''
+    await ctx.started()
+    await asyncio_actor(
+        target='aio_sleep_forever',
+        expect_err=expect_err,
+    )
+
+
 def test_aio_simple_error(
     reg_addr: tuple[str, int],
     debug_mode: bool,
@@ -172,8 +196,9 @@ def test_aio_simple_error(
             registry_addrs=[reg_addr],
             debug_mode=debug_mode,
         ) as an:
-            await an.run_in_actor(
+            await to_actor.run(
                 asyncio_actor,
+                an=an,
                 target='sleep_and_err',
                 expect_err='AssertionError',
                 infect_asyncio=True,
@@ -207,18 +232,34 @@ def test_tractor_cancels_aio(
 
     '''
     async def main():
-        async with tractor.open_nursery(
-            debug_mode=debug_mode,
-            registry_addrs=[reg_addr],
-        ) as an:
-            portal = await an.run_in_actor(
-                asyncio_actor,
-                target='aio_sleep_forever',
-                expect_err='trio.Cancelled',
-                infect_asyncio=True,
-            )
-            # cancel the entire remote runtime
-            await portal.cancel_actor()
+        # anti-hang wall-clock cap: a per-test `trio.fail_after`
+        # is the blessed guard here since `pytest-timeout`'s
+        # global cap is intentionally off (see the `pyproject`
+        # NOTE — it breaks trio under fork backends). Generous +
+        # CPU-headroom-scaled bc this is an anti-hang guard, not
+        # a perf assertion; a wedged ria-reaper once hung this
+        # test forever (the `._ria_nursery`-removal regression).
+        from .conftest import cpu_perf_headroom
+        with trio.fail_after(9 * cpu_perf_headroom()):
+            async with tractor.open_nursery(
+                debug_mode=debug_mode,
+                registry_addrs=[reg_addr],
+            ) as an:
+                p: tractor.Portal = await an.start_actor(
+                    'aio_daemon',
+                    enable_modules=[__name__],
+                    infect_asyncio=True,
+                )
+                async with (
+                    # `.cancel_actor()` below tears the ctx down
+                    expect_ctxc(yay=True),
+                    p.open_context(
+                        sleep_forever_aio_ctx,
+                    ) as (ctx, first),
+                ):
+                    # cancel the entire remote runtime while its
+                    # infected-`asyncio` task sleeps forever
+                    await p.cancel_actor()
 
     trio.run(main)
 
@@ -236,13 +277,19 @@ def test_trio_cancels_aio(
         with trio.move_on_after(1):
             async with tractor.open_nursery(
                 registry_addrs=[reg_addr],
-            ) as tn:
-                await tn.run_in_actor(
-                    asyncio_actor,
-                    target='aio_sleep_forever',
-                    expect_err='trio.Cancelled',
+            ) as an:
+                p: tractor.Portal = await an.start_actor(
+                    'aio_daemon',
+                    enable_modules=[__name__],
                     infect_asyncio=True,
                 )
+                async with p.open_context(
+                    sleep_forever_aio_ctx,
+                ) as (ctx, first):
+                    # block until the enclosing `move_on_after`
+                    # cancels this `trio` scope, tearing down the
+                    # infected-aio task via ctx cancellation
+                    await trio.sleep_forever()
 
     trio.run(main)
 
@@ -392,17 +439,16 @@ def test_aio_cancelled_from_aio_causes_trio_cancelled(
         async with tractor.open_nursery(
             registry_addrs=[reg_addr],
         ) as an:
-            p: tractor.Portal = await an.run_in_actor(
-                asyncio_actor,
-                target='aio_cancel',
-                expect_err='tractor.to_asyncio.AsyncioCancelled',
-                infect_asyncio=True,
-            )
-            # NOTE: normally the `an.__aexit__()` waits on the
-            # portal's result but we do it explicitly here
-            # to avoid indent levels.
+            # `to_actor.run()` blocks on the one-shot's result and
+            # relays the remote error here in the caller's task.
             with trio.fail_after(1 + delay):
-                await p.wait_for_result()
+                await to_actor.run(
+                    asyncio_actor,
+                    an=an,
+                    target='aio_cancel',
+                    expect_err='tractor.to_asyncio.AsyncioCancelled',
+                    infect_asyncio=True,
+                )
 
     with pytest.raises(
         expected_exception=(RemoteActorError, ExceptionGroup),
@@ -603,13 +649,13 @@ def test_basic_interloop_channel_stream(
             async with tractor.open_nursery(
                 registry_addrs=[reg_addr],
             ) as an:
-                portal = await an.run_in_actor(
+                # should raise RAE diectly
+                await to_actor.run(
                     stream_from_aio,
+                    an=an,
                     infect_asyncio=True,
                     fan_out=fan_out,
                 )
-                # should raise RAE diectly
-                await portal.result()
 
     trio.run(main)
 
@@ -622,13 +668,13 @@ def test_trio_error_cancels_intertask_chan(
         async with tractor.open_nursery(
             registry_addrs=[reg_addr],
         ) as an:
-            portal = await an.run_in_actor(
+            # should trigger remote actor error
+            await to_actor.run(
                 stream_from_aio,
+                an=an,
                 trio_raise_err=True,
                 infect_asyncio=True,
             )
-            # should trigger remote actor error
-            await portal.result()
 
     with pytest.raises(RemoteActorError) as excinfo:
         trio.run(main)
@@ -658,14 +704,14 @@ def test_trio_closes_early_causes_aio_checkpoint_raise(
                 # enable_stack_on_sig=True,
                 registry_addrs=[reg_addr],
             ) as an:
-                portal = await an.run_in_actor(
+                # should raise RAE diectly
+                print('waiting on final infected subactor result..')
+                res: None = await to_actor.run(
                     stream_from_aio,
+                    an=an,
                     trio_exit_early=True,
                     infect_asyncio=True,
                 )
-                # should raise RAE diectly
-                print('waiting on final infected subactor result..')
-                res: None = await portal.wait_for_result()
                 assert res is None
                 print(f'infected subactor returned result: {res!r}\n')
 
@@ -709,15 +755,15 @@ def test_aio_exits_early_relays_AsyncioTaskExited(
                 debug_mode=debug_mode,
                 # enable_stack_on_sig=True,
             ) as an:
-                portal = await an.run_in_actor(
+                # should raise RAE diectly
+                print('waiting on final infected subactor result..')
+                res: None = await to_actor.run(
                     stream_from_aio,
+                    an=an,
                     infect_asyncio=True,
                     trio_exit_early=False,
                     aio_exit_early=True,
                 )
-                # should raise RAE diectly
-                print('waiting on final infected subactor result..')
-                res: None = await portal.wait_for_result()
                 assert res is None
                 print(f'infected subactor returned result: {res!r}\n')
 
@@ -749,17 +795,19 @@ def test_aio_errors_and_channel_propagates_and_closes(
             registry_addrs=[reg_addr],
             debug_mode=debug_mode,
         ) as an:
-            portal = await an.run_in_actor(
+            # should trigger RAE directly, not an eg.
+            await to_actor.run(
                 stream_from_aio,
+                an=an,
                 aio_raise_err=True,
                 infect_asyncio=True,
             )
-            # should trigger RAE directly, not an eg.
-            await portal.result()
 
     with pytest.raises(
-        # NOTE: bc we directly wait on `Portal.result()` instead
-        # of capturing it inside the `ActorNursery` machinery.
+        # NOTE: bc `to_actor.run()` blocks on + relays the result
+        # in the caller's task (not captured inside the
+        # `ActorNursery` teardown machinery) we get a direct RAE,
+        # not an eg.
         expected_exception=RemoteActorError,
     ) as excinfo:
         trio.run(main)

tests/test_inter_peer_cancellation.py

@@ -163,12 +163,12 @@ def test_do_not_swallow_error_before_started_by_remote_contextcancelled(
     async def main():
         async with tractor.open_nursery(
             debug_mode=debug_mode,
-        ) as n:
-            portal = await n.start_actor(
+        ) as an:
+            portal = await an.start_actor(
                 'errorer',
                 enable_modules=[__name__],
             )
-            await n.start_actor(
+            await an.start_actor(
                 'sleeper',
                 enable_modules=[__name__],
             )

tests/test_pubsub.py

@@ -139,9 +139,9 @@ async def test_required_args(callwith_expecterror):
         with pytest.raises(err):
             await func(**kwargs)
     else:
-        async with tractor.open_nursery() as n:
+        async with tractor.open_nursery() as an:
 
-            portal = await n.start_actor(
+            portal = await an.start_actor(
                 name='pubber',
                 enable_modules=[__name__],
             )
@@ -176,33 +176,55 @@ def test_multi_actor_subs_arbiter_pub(
 
     async def main():
 
-        async with tractor.open_nursery(
-            registry_addrs=[reg_addr],
-            enable_modules=[__name__],
-        ) as n:
+        async with (
+            tractor.open_nursery(
+                registry_addrs=[reg_addr],
+                enable_modules=[__name__],
+            ) as an,
+            trio.open_nursery() as tn,
+        ):
 
             name = 'root'
 
             if pub_actor == 'streamer':
                 # start the publisher as a daemon
-                master_portal = await n.start_actor(
+                master_portal = await an.start_actor(
                     'streamer',
                     enable_modules=[__name__],
                 )
                 name = 'streamer'
 
-            even_portal = await n.run_in_actor(
-                subs,
-                which=['even'],
-                name='evens',
-                pub_actor_name=name
+            # spawn the two subscriber actors as daemons and run
+            # `subs()` on each as a background task (was the legacy
+            # `run_in_actor()`); keep the portals for the explicit
+            # `cancel_actor()` teardown below. Each runner swallows
+            # the teardown error that `cancel_actor()` relays.
+            async def _run_subs(
+                portal: tractor.Portal,
+                which: list[str],
+            ) -> None:
+                try:
+                    await portal.run(
+                        subs,
+                        which=which,
+                        pub_actor_name=name,
+                    )
+                except (
+                    tractor.RemoteActorError,
+                    tractor.ContextCancelled,
+                ):
+                    pass  # expected once we `cancel_actor()` below
+
+            even_portal = await an.start_actor(
+                'evens',
+                enable_modules=[__name__],
             )
-            odd_portal = await n.run_in_actor(
-                subs,
-                which=['odd'],
-                name='odds',
-                pub_actor_name=name
+            odd_portal = await an.start_actor(
+                'odds',
+                enable_modules=[__name__],
             )
+            tn.start_soon(_run_subs, even_portal, ['even'])
+            tn.start_soon(_run_subs, odd_portal, ['odd'])
 
             async with tractor.wait_for_actor('evens'):
                 # block until 2nd actor is initialized
@@ -257,6 +279,9 @@ def test_multi_actor_subs_arbiter_pub(
             else:
                 await master_portal.cancel_actor()
 
+            # drop the bg `subs()` runners now the subs are cancelled
+            tn.cancel_scope.cancel()
+
     trio.run(main)
 
 
@@ -269,9 +294,9 @@ def test_single_subactor_pub_multitask_subs(
         async with tractor.open_nursery(
             registry_addrs=[reg_addr],
             enable_modules=[__name__],
-        ) as n:
+        ) as an:
 
-            portal = await n.start_actor(
+            portal = await an.start_actor(
                 'streamer',
                 enable_modules=[__name__],
             )

tests/test_ringbuf.py

@@ -131,9 +131,12 @@ def test_ringbuf(
                         child_read_shm,
                         **common_kwargs,
                         total_bytes=total_bytes,
-                    ) as (sctx, _sent),
+                    ) as (rctx, _sent),
                 ):
-                    await recv_p.result()
+                    # ctx-acm exits await each child task's
+                    # `Return` (the prior `recv_p.result()` here
+                    # was a daemon-portal no-op).
+                    pass
 
                 await send_p.cancel_actor()
                 await recv_p.cancel_actor()

tests/test_rpc.py

@@ -107,12 +107,13 @@ def test_rpc_errors(
             # do that if actually debugging subactor but keep it
             # disabled for the test.
             # debug_mode=True,
-        ) as n:
+        ) as an:
 
             actor = tractor.current_actor()
             assert actor.is_registrar
-            await n.run_in_actor(
+            await tractor.to_actor.run(
                 sleep_back_actor,
+                an=an,
                 actor_name=subactor_requests_to,
 
                 name='subactor',

tests/test_runtime.py

@@ -78,13 +78,12 @@ async def test_lifetime_stack_wipes_tmpfile(
             async with tractor.open_nursery(
                 loglevel=loglevel,
             ) as an:
-                await (  # inlined `tractor.Portal`
-                    await an.run_in_actor(
-                        crash_and_clean_tmpdir,
-                        tmp_file_path=path,
-                        error=error_in_child,
-                    )
-                ).result()
+                await tractor.to_actor.run(
+                    crash_and_clean_tmpdir,
+                    an=an,
+                    tmp_file_path=path,
+                    error=error_in_child,
+                )
     except (
         tractor.RemoteActorError,
         BaseExceptionGroup,

tests/test_spawning.py

@@ -48,9 +48,11 @@ async def spawn(
             actor: tractor.Actor = tractor.current_actor()
             assert actor.is_registrar == should_be_root
 
-            # spawns subproc here
-            portal: tractor.Portal = await an.run_in_actor(
-                fn=spawn,
+            # recursively spawn this same `spawn()` fn as the lone
+            # task of a one-shot child subactor and get its result.
+            result = await tractor.to_actor.run(
+                spawn,
+                an=an,
 
                 # spawning args
                 name='sub-actor',
@@ -62,16 +64,6 @@ async def spawn(
                 data=data_to_pass_down,
                 reg_addr=reg_addr,
             )
-
-            assert len(an._children) == 1
-            assert (
-                portal.channel.aid.uid
-                in
-                tractor.current_actor().ipc_server._peers
-            )
-
-            # get result from child subactor
-            result = await portal.result()
             assert result == 10
             return result
     else:
@@ -79,7 +71,7 @@ async def spawn(
         return 10
 
 
-def test_run_in_actor_same_func_in_child(
+def test_to_actor_run_same_func_in_child(
     reg_addr: tuple,
     debug_mode: bool,
 ):
@@ -159,21 +151,16 @@ async def test_most_beautiful_word(
         async with tractor.open_nursery(
             debug_mode=debug_mode,
         ) as an:
-            portal = await an.run_in_actor(
+            res: Any = await tractor.to_actor.run(
                 cellar_door,
+                an=an,
                 return_value=return_value,
                 name='some_linguist',
             )
-
-            res: Any = await portal.wait_for_result()
             assert res == return_value
-    # The ``async with`` will unblock here since the 'some_linguist'
-    # actor has completed its main task ``cellar_door``.
-
-    # this should pull the cached final result already captured during
-    # the nursery block exit.
-    res: Any = await portal.wait_for_result()
-    assert res == return_value
+    # The ``async with`` unblocks here — the 'some_linguist'
+    # one-shot actor completed its lone task ``cellar_door`` and
+    # was reaped by `to_actor.run()`.
     print(res)
 
 
@@ -215,9 +202,10 @@ def test_loglevel_propagated_to_subactor(
             start_method=start_method,
             registry_addrs=[reg_addr],
 
-        ) as tn:
-            await tn.run_in_actor(
+        ) as an:
+            await tractor.to_actor.run(
                 check_loglevel,
+                an=an,
                 loglevel=level,
                 level=level,
             )
@@ -267,11 +255,11 @@ async def check_parent_main_inheritance(
     return has_data
 
 
-def test_run_in_actor_can_skip_parent_main_inheritance(
+def test_to_actor_run_can_skip_parent_main_inheritance(
     start_method: str,  # <- only support on `trio` backend rn.
 ):
     '''
-    Verify ``inherit_parent_main=False`` on ``run_in_actor()``
+    Verify ``inherit_parent_main=False`` on ``to_actor.run()``
     prevents parent ``__main__`` data from reaching the child.
 
     '''
@@ -284,21 +272,21 @@ def test_run_in_actor_can_skip_parent_main_inheritance(
         async with tractor.open_nursery(start_method='trio') as an:
 
             # Default: child receives parent __main__ bootstrap data
-            replaying = await an.run_in_actor(
+            await tractor.to_actor.run(
                 check_parent_main_inheritance,
+                an=an,
                 name='replaying-parent-main',
                 expect_inherited=True,
             )
-            await replaying.result()
 
             # Opt-out: child gets no parent __main__ data
-            isolated = await an.run_in_actor(
+            await tractor.to_actor.run(
                 check_parent_main_inheritance,
+                an=an,
                 name='isolated-parent-main',
                 inherit_parent_main=False,
                 expect_inherited=False,
             )
-            await isolated.result()
 
     trio.run(main)
 

tests/test_to_actor.py

@@ -0,0 +1,271 @@
+'''
+`tractor.to_actor`: one-shot single-remote-task API suite.
+
+Verifies the "spiritual successor" to (and replacement of)
+the removed legacy `ActorNursery.run_in_actor()`; see
+https://github.com/goodboy/tractor/issues/477
+
+'''
+from functools import partial
+
+import pytest
+import trio
+import tractor
+from tractor import (
+    RemoteActorError,
+    to_actor,
+)
+from tractor._testing import tractor_test
+
+
+async def add_one(
+    n: int,
+) -> int:
+    return n + 1
+
+
+async def raise_value_error() -> None:
+    raise ValueError('kaboom')
+
+
+@tractor_test
+async def test_one_shot_in_private_nursery(
+    start_method: str,
+    debug_mode: bool,
+):
+    '''
+    No `an`/`portal` provided: a private actor-nursery
+    is opened (and torn down) scoped to just the call.
+
+    '''
+    assert await to_actor.run(
+        add_one,
+        n=1,
+    ) == 2
+
+
+def test_one_shot_boots_implicit_runtime(
+    reg_addr: tuple,
+    start_method: str,
+    loglevel: str,
+):
+    '''
+    Outside any actor-runtime `to_actor.run()` boots one
+    implicitly (just like bare `open_nursery()` usage)
+    configured via pass-through `runtime_kwargs`.
+
+    '''
+    async def main() -> None:
+        assert tractor.current_actor(
+            err_on_no_runtime=False,
+        ) is None
+        result = await to_actor.run(
+            add_one,
+            n=41,
+            runtime_kwargs=dict(
+                registry_addrs=[reg_addr],
+                start_method=start_method,
+                loglevel=loglevel,
+            ),
+        )
+        assert result == 42
+
+    trio.run(main)
+
+
+@tractor_test
+async def test_remote_error_relayed_to_caller_task(
+    start_method: str,
+    debug_mode: bool,
+):
+    '''
+    A remote task error is raised directly in the
+    caller's task as a boxed `RemoteActorError` instead
+    of surfacing at actor-nursery teardown as with the
+    removed legacy `.run_in_actor()` API.
+
+    '''
+    with pytest.raises(RemoteActorError) as excinfo:
+        await to_actor.run(raise_value_error)
+
+    assert excinfo.value.boxed_type is ValueError
+
+
+@tractor_test
+async def test_spawn_from_caller_nursery(
+    start_method: str,
+    debug_mode: bool,
+):
+    '''
+    Pass a caller-managed `an: ActorNursery` for the
+    spawn; the subactor is still one-shot reaped by the
+    time the call returns.
+
+    '''
+    async with tractor.open_nursery() as an:
+        assert await to_actor.run(
+            add_one,
+            an=an,
+            n=10,
+        ) == 11
+
+
+@tractor_test
+async def test_remote_error_from_caller_nursery(
+    start_method: str,
+    debug_mode: bool,
+):
+    '''
+    With a caller-managed `an` the remote error also
+    surfaces in the caller's task, INSIDE the nursery
+    block, allowing inline (supervision-style) handling.
+
+    '''
+    async with tractor.open_nursery() as an:
+        with pytest.raises(RemoteActorError) as excinfo:
+            await to_actor.run(
+                raise_value_error,
+                an=an,
+            )
+
+        assert excinfo.value.boxed_type is ValueError
+
+
+@tractor_test
+async def test_reuse_existing_actor_via_portal(
+    start_method: str,
+    debug_mode: bool,
+):
+    '''
+    Pass `portal=` to schedule the one-shot task in an
+    already-running actor; no spawn, no implicit reap.
+
+    '''
+    async with tractor.open_nursery() as an:
+        portal: tractor.Portal = await an.start_actor(
+            'one_shot_worker',
+            enable_modules=[__name__],
+        )
+        for i in range(3):
+            assert await to_actor.run(
+                add_one,
+                portal=portal,
+                n=i,
+            ) == i + 1
+
+        # still alive: caller owns the actor's lifetime.
+        await portal.cancel_actor()
+
+
+@tractor_test
+async def test_concurrent_one_shots_from_task_nursery(
+    start_method: str,
+    debug_mode: bool,
+):
+    '''
+    The worker-pool-ish pattern from #477: concurrency
+    is composed with a plain (caller-side) `trio` task
+    nursery scheduling multiple one-shot calls against
+    a shared caller-managed actor-nursery; error
+    collection thus lives entirely in caller-code.
+
+    '''
+    results: dict[int, int] = {}
+
+    async def one_shot(
+        an: tractor.ActorNursery,
+        i: int,
+    ) -> None:
+        results[i] = await to_actor.run(
+            add_one,
+            an=an,
+            name=f'one_shot_{i}',
+            n=i,
+        )
+
+    async with (
+        tractor.open_nursery() as an,
+        trio.open_nursery() as tn,
+    ):
+        for i in range(4):
+            tn.start_soon(one_shot, an, i)
+
+    assert results == {
+        i: i + 1 for i in range(4)
+    }
+
+
+def test_rejects_sync_fn():
+    '''
+    Non-async callables error BEFORE any spawn (or even
+    runtime-boot) happens.
+
+    '''
+    def not_async() -> None:
+        ...
+
+    with pytest.raises(TypeError):
+        trio.run(
+            partial(
+                to_actor.run,
+                not_async,
+            )
+        )
+
+
+def test_rejects_streaming_fn():
+    '''
+    Async-gen (streaming) fns are not one-shot-able,
+    same constraint as `Portal.run()`.
+
+    '''
+    async def agen():
+        yield 1
+
+    with pytest.raises(TypeError):
+        trio.run(
+            partial(
+                to_actor.run,
+                agen,
+            )
+        )
+
+
+def test_rejects_portal_and_an_combo():
+    '''
+    `portal=` and `an=` are mutually exclusive
+    placement options.
+
+    '''
+    with pytest.raises(ValueError):
+        trio.run(
+            partial(
+                to_actor.run,
+                add_one,
+                portal=object(),
+                an=object(),
+                n=1,
+            )
+        )
+
+
+def test_rejects_runtime_kwargs_with_placement():
+    '''
+    `runtime_kwargs` only applies when the call opens
+    its own private actor-nursery; passing it alongside
+    a placement opt is an error, never silently
+    ignored.
+
+    '''
+    with pytest.raises(ValueError):
+        trio.run(
+            partial(
+                to_actor.run,
+                add_one,
+                an=object(),
+                runtime_kwargs=dict(
+                    loglevel='cancel',
+                ),
+                n=1,
+            )
+        )

tractor/__init__.py

@@ -62,6 +62,7 @@ from .devx import (
     post_mortem as post_mortem,
 )
 from . import msg as msg
+from . import to_actor as to_actor
 from ._root import (
     run_daemon as run_daemon,
     open_root_actor as open_root_actor,

tractor/_context.py

@@ -780,7 +780,7 @@ class Context:
         # `Portal.open_context()` has been opened since it's
         # assumed that other portal APIs like,
         #  - `Portal.run()`,
-        #  - `ActorNursery.run_in_actor()`
+        #  - `to_actor.run()`
         # do their own error checking at their own call points and
         # result processing.
 

tractor/_exceptions.py

@@ -1161,10 +1161,6 @@ class TransportClosed(Exception):
         )
 
 
-class NoResult(RuntimeError):
-    "No final result is expected for this actor"
-
-
 class ModuleNotExposed(ModuleNotFoundError):
     "The requested module is not exposed for RPC"
 

tractor/experimental/_pubsub.py

@@ -221,16 +221,19 @@ def pub(
         import tractor
 
         async with tractor.open_nursery() as n:
-            portal = n.run_in_actor(
+            portal = await n.start_actor(
                 'publisher',  # actor name
-                partial(      # func to execute in it
+                enable_modules=[__name__],
+            )
+            async with portal.open_stream_from(
+                partial(  # func to execute in it
                     pub_service,
                     topics=('clicks', 'users'),
                     task_name='source1',
                 )
-            )
-            async for value in await portal.result():
-                print(f"Subscriber received {value}")
+            ) as stream:
+                async for value in stream:
+                    print(f"Subscriber received {value}")
 
 
     Here, you don't need to provide the ``ctx`` argument since the

tractor/msg/types.py

@@ -304,12 +304,11 @@ class Start(
 
     It is called by all the following public APIs:
 
-    - `ActorNursery.run_in_actor()`
+    - `to_actor.run()`
 
     - `Portal.run()`
           `|_.run_from_ns()`
           `|_.open_stream_from()`
-          `|_._submit_for_result()`
 
     - `Context.open_context()`
 

tractor/runtime/_portal.py

@@ -50,13 +50,11 @@ from ..ipc import Channel
 from ..log import get_logger
 from ..msg import (
     # Error,
-    PayloadMsg,
     NamespacePath,
     Return,
 )
 from .._exceptions import (
     ActorTooSlowError,
-    NoResult,
     TransportClosed,
 )
 from .._context import (
@@ -102,14 +100,6 @@ class Portal:
     ) -> None:
 
         self._chan: Channel = channel
-        # during the portal's lifetime
-        self._final_result_pld: Any|None = None
-        self._final_result_msg: PayloadMsg|None = None
-
-        # When set to a ``Context`` (when _submit_for_result is called)
-        # it is expected that ``result()`` will be awaited at some
-        # point.
-        self._expect_result_ctx: Context|None = None
         self._streams: set[MsgStream] = set()
 
         # TODO, this should be PRIVATE (and never used publicly)! since it's just
@@ -137,102 +127,6 @@ class Portal:
         )
         return self.chan
 
-    # TODO: factor this out into a `.highlevel` API-wrapper that uses
-    # a single `.open_context()` call underneath.
-    async def _submit_for_result(
-        self,
-        ns: str,
-        func: str,
-        **kwargs
-    ) -> None:
-
-        if self._expect_result_ctx is not None:
-            raise RuntimeError(
-                'A pending main result has already been submitted'
-            )
-
-        self._expect_result_ctx: Context = await self.actor.start_remote_task(
-            self.channel,
-            nsf=NamespacePath(f'{ns}:{func}'),
-            kwargs=kwargs,
-            portal=self,
-        )
-
-    # TODO: we should deprecate this API right? since if we remove
-    # `.run_in_actor()` (and instead move it to a `.highlevel`
-    # wrapper api (around a single `.open_context()` call) we don't
-    # really have any notion of a "main" remote task any more?
-    #
-    # @api_frame
-    async def wait_for_result(
-        self,
-        hide_tb: bool = True,
-    ) -> Any:
-        '''
-        Return the final result delivered by a `Return`-msg from the
-        remote peer actor's "main" task's `return` statement.
-
-        '''
-        __tracebackhide__: bool = hide_tb
-        # Check for non-rpc errors slapped on the
-        # channel for which we always raise
-        exc = self.channel._exc
-        if exc:
-            raise exc
-
-        # not expecting a "main" result
-        if self._expect_result_ctx is None:
-            peer_id: str = f'{self.channel.aid.reprol()!r}'
-            log.warning(
-                f'Portal to peer {peer_id} will not deliver a final result?\n'
-                f'\n'
-                f'Context.result() can only be called by the parent of '
-                f'a sub-actor when it was spawned with '
-                f'`ActorNursery.run_in_actor()`'
-                f'\n'
-                f'Further this `ActorNursery`-method-API will deprecated in the'
-                f'near fututre!\n'
-            )
-            return NoResult
-
-        # expecting a "main" result
-        assert self._expect_result_ctx
-
-        if self._final_result_msg is None:
-            try:
-                (
-                    self._final_result_msg,
-                    self._final_result_pld,
-                ) = await self._expect_result_ctx._pld_rx.recv_msg(
-                    ipc=self._expect_result_ctx,
-                    expect_msg=Return,
-                )
-            except BaseException as err:
-                # TODO: wrap this into `@api_frame` optionally with
-                # some kinda filtering mechanism like log levels?
-                __tracebackhide__: bool = False
-                raise err
-
-        return self._final_result_pld
-
-    # TODO: factor this out into a `.highlevel` API-wrapper that uses
-    # a single `.open_context()` call underneath.
-    async def result(
-        self,
-        *args,
-        **kwargs,
-    ) -> Any|Exception:
-        typname: str = type(self).__name__
-        log.warning(
-            f'`{typname}.result()` is DEPRECATED!\n'
-            f'\n'
-            f'Use `{typname}.wait_for_result()` instead!\n'
-        )
-        return await self.wait_for_result(
-            *args,
-            **kwargs,
-        )
-
     async def _cancel_streams(self):
         # terminate all locally running async generator
         # IPC calls

tractor/runtime/_supervise.py

@@ -20,7 +20,6 @@
 """
 from contextlib import asynccontextmanager as acm
 from functools import partial
-import inspect
 from typing import (
     TYPE_CHECKING,
 )
@@ -199,7 +198,6 @@ 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],
 
@@ -233,16 +231,6 @@ 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
-        self._cancel_after_result_on_exit: set = set()
-
         # trio.Nursery-like cancel (request) statuses
         self._cancelled_caught: bool = False
         self._cancel_called: bool = False
@@ -298,11 +286,6 @@ 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 +347,8 @@ 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,
@@ -382,80 +363,6 @@ class ActorNursery:
             )
         )
 
-    # TODO: DEPRECATE THIS:
-    # -[ ] impl instead as a hilevel wrapper on
-    #   top of a `@context` style invocation.
-    #  |_ dynamic @context decoration on child side
-    #  |_ implicit `Portal.open_context() as (ctx, first):`
-    #    and `return first` on parent side.
-    #  |_ mention how it's similar to `trio-parallel` API?
-    # -[ ] use @api_frame on the wrapper
-    async def run_in_actor(
-        self,
-
-        fn: typing.Callable,
-        *,
-
-        name: str | None = None,
-        bind_addrs: UnwrappedAddress|None = None,
-        rpc_module_paths: list[str] | None = None,
-        enable_modules: list[str] | None = None,
-        loglevel: str | None = None,  # set log level per subactor
-        infect_asyncio: bool = False,
-        inherit_parent_main: bool = True,
-        proc_kwargs: dict[str, typing.Any] | None = None,
-
-        **kwargs,  # explicit args to ``fn``
-
-    ) -> Portal:
-        '''
-        Spawn a new actor, run a lone task, then terminate the actor and
-        return its result.
-
-        Actors spawned using this method are kept alive at nursery teardown
-        until the task spawned by executing ``fn`` completes at which point
-        the actor is terminated.
-
-        '''
-        __runtimeframe__: int = 1  # noqa
-        mod_path: str = fn.__module__
-
-        if name is None:
-            # use the explicit function name if not provided
-            name = fn.__name__
-
-        proc_kwargs = dict(proc_kwargs or {})
-        portal: Portal = await self.start_actor(
-            name,
-            enable_modules=[mod_path] + (
-                enable_modules or rpc_module_paths or []
-            ),
-            bind_addrs=bind_addrs,
-            loglevel=loglevel,
-            # use the run_in_actor nursery
-            nursery=self._ria_nursery,
-            infect_asyncio=infect_asyncio,
-            inherit_parent_main=inherit_parent_main,
-            proc_kwargs=proc_kwargs
-        )
-
-        # XXX: don't allow stream funcs
-        if not (
-            inspect.iscoroutinefunction(fn) and
-            not getattr(fn, '_tractor_stream_function', False)
-        ):
-            raise TypeError(f'{fn} must be an async function!')
-
-        # this marks the actor to be cancelled after its portal result
-        # is retreived, see logic in `open_nursery()` below.
-        self._cancel_after_result_on_exit.add(portal)
-        await portal._submit_for_result(
-            mod_path,
-            fn.__name__,
-            **kwargs
-        )
-        return portal
-
     # @api_frame
     async def cancel(
         self,
@@ -584,167 +491,118 @@ async def _open_and_supervise_one_cancels_all_nursery(
     # normally don't need to show user by default
     __tracebackhide__: bool = hide_tb
 
-    outer_err: BaseException|None = None
-    inner_err: BaseException|None = None
-
     # 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; one-shot (`to_actor.run()`) subactors are
+    # result-waited and reaped in their caller's own task-scope
+    # (see the #477 `.run_in_actor()`/`._ria_nursery` 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
+            # 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'
-                    )
-                    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()
 
-                except BaseException as _inner_err:
-                    inner_err = _inner_err
-                    errors[actor.aid.uid] = inner_err
+        # Single one-cancels-all handler for the (now single)
+        # daemon nursery. Pre-#477 a 2ndary `._ria_nursery`
+        # required a separate *outer* handler to catch errors
+        # bubbling from its task-reaping `__aexit__`; with that
+        # nursery gone this lone handler covers every scope
+        # error. NB: we deliberately do NOT re-raise here — the
+        # `finally` below raises the collected `errors` (as a
+        # single exc or `BaseExceptionGroup`), which already
+        # superseded the old outer handler's `raise` anyway
+        # since `errors` is populated (below) before any await.
+        except BaseException as _scope_err:
+            an._scope_error = _scope_err
+            errors[actor.aid.uid] = _scope_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 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'
-
-                                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: 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..
-                                # '------ - ------'
-                            )
-
-                        # cancel all subactors
-                        await an.cancel()
-
-            # 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.
-        except (
-            Exception,
-            BaseExceptionGroup,
-            trio.Cancelled
-        ) as _outer_err:
-            outer_err = _outer_err
-
-            an._scope_error = outer_err or inner_err
-
-            # XXX: yet another guard before allowing the cancel
-            # sequence in case a (single) child is 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 actor-local error was raised while waiting on
-            # ".run_in_actor()" actors then we also want to cancel all
-            # remaining sub-actors (due to our lone strategy:
-            # one-cancels-all).
-            if an._children:
-                log.cancel(
-                    'Actor-nursery cancelling due error type:\n'
-                    f'{outer_err}\n'
-                )
-                with trio.CancelScope(shield=True):
-                    await an.cancel()
-            raise
+            # 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(_scope_err)
+                if etype in (
+                    trio.Cancelled,
+                    KeyboardInterrupt,
+                ) or (
+                    is_multi_cancelled(_scope_err)
+                ):
+                    log.cancel(
+                        f'Actor-nursery cancelled by {etype}\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'{_scope_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..
+                        # '------ - ------'
+                    )
+
+                # cancel all subactors
+                await an.cancel()
 
         finally:
-            # No errors were raised while awaiting ".run_in_actor()"
-            # actors but those actors may have returned remote errors as
-            # results (meaning they errored remotely and have relayed
-            # those errors back to this parent actor). The errors are
-            # collected in ``errors`` so cancel all actors, summarize
-            # all errors and re-raise.
+            # an error was stashed by the handler above (or by
+            # a spawn task via the shared `errors` dict) so
+            # cancel any remaining subactors, summarize and
+            # re-raise.
             if errors:
                 if an._children:
                     with trio.CancelScope(shield=True):

tractor/spawn/_mp.py

@@ -48,7 +48,6 @@ from ._entry import _mp_main
 # by `try_set_start_method()` after module load time.
 from . import _spawn
 from ._spawn import (
-    cancel_on_completion,
     proc_waiter,
     soft_kill,
 )
@@ -187,30 +186,14 @@ async def mp_proc(
         with trio.CancelScope(shield=True):
             await actor_nursery._join_procs.wait()
 
-        async with trio.open_nursery() as nursery:
-            if portal in actor_nursery._cancel_after_result_on_exit:
-                nursery.start_soon(
-                    cancel_on_completion,
-                    portal,
-                    subactor,
-                    errors
-                )
-
-            # This is a "soft" (cancellable) join/reap which
-            # will remote cancel the actor on a ``trio.Cancelled``
-            # condition.
-            await soft_kill(
-                proc,
-                proc_waiter,
-                portal
-            )
-
-            # cancel result waiter that may have been spawned in
-            # tandem if not done already
-            log.warning(
-                "Cancelling existing result waiter task for "
-                f"{subactor.aid.uid}")
-            nursery.cancel_scope.cancel()
+        # This is a "soft" (cancellable) join/reap which
+        # will remote cancel the actor on a ``trio.Cancelled``
+        # condition.
+        await soft_kill(
+            proc,
+            proc_waiter,
+            portal
+        )
 
     finally:
         # hard reap sequence

tractor/spawn/_spawn.py

@@ -126,98 +126,6 @@ def try_set_start_method(
     return _ctx
 
 
-async def exhaust_portal(
-
-    portal: Portal,
-    actor: Actor
-
-) -> Any:
-    '''
-    Pull final result from portal (assuming it has one).
-
-    If the main task is an async generator do our best to consume
-    what's left of it.
-    '''
-    __tracebackhide__ = True
-    try:
-        log.debug(
-            f'Waiting on final result from {actor.aid.uid}'
-        )
-
-        # XXX: streams should never be reaped here since they should
-        # always be established and shutdown using a context manager api
-        final: Any = await portal.wait_for_result()
-
-    except (
-        Exception,
-        BaseExceptionGroup,
-    ) as err:
-        # we reraise in the parent task via a ``BaseExceptionGroup``
-        return err
-
-    except trio.Cancelled as err:
-        # lol, of course we need this too ;P
-        # TODO: merge with above?
-        log.warning(
-            'Cancelled portal result waiter task:\n'
-            f'uid: {portal.channel.aid}\n'
-            f'error: {err}\n'
-        )
-        return err
-
-    else:
-        log.debug(
-            f'Returning final result from portal:\n'
-            f'uid: {portal.channel.aid}\n'
-            f'result: {final}\n'
-        )
-        return final
-
-
-async def cancel_on_completion(
-
-    portal: Portal,
-    actor: Actor,
-    errors: dict[tuple[str, str], Exception],
-
-) -> None:
-    '''
-    Cancel actor gracefully once its "main" portal's
-    result arrives.
-
-    Should only be called for actors spawned via the
-    `Portal.run_in_actor()` API.
-
-    => and really this API will be deprecated and should be
-    re-implemented as a `.hilevel.one_shot_task_nursery()`..)
-
-    '''
-    # if this call errors we store the exception for later
-    # in ``errors`` which will be reraised inside
-    # an exception group and we still send out a cancel request
-    result: Any|Exception = await exhaust_portal(
-        portal,
-        actor,
-    )
-    if isinstance(result, Exception):
-        errors[actor.aid.uid]: Exception = result
-        log.cancel(
-            'Cancelling subactor runtime due to error:\n\n'
-            f'Portal.cancel_actor() => {portal.channel.aid}\n\n'
-            f'error: {result}\n'
-        )
-
-    else:
-        log.runtime(
-            'Cancelling subactor gracefully:\n\n'
-            f'Portal.cancel_actor() => {portal.channel.aid}\n\n'
-            f'result: {result}\n'
-        )
-
-    # cancel the process now that we have a final result
-    await portal.cancel_actor()
-
-
 async def hard_kill(
     proc: trio.Process,
 
@@ -461,8 +369,8 @@ async def new_proc(
 
 
 # NOTE: bottom-of-module to avoid a circular import since the
-# backend submodules pull `cancel_on_completion`/`soft_kill`/
-# `hard_kill`/`proc_waiter` from this module.
+# backend submodules pull `soft_kill`/`hard_kill`/`proc_waiter`
+# from this module.
 from ._trio import trio_proc
 from ._mp import mp_proc
 

tractor/spawn/_trio.py

@@ -50,7 +50,6 @@ from tractor.msg import (
     pretty_struct,
 )
 from ._spawn import (
-    cancel_on_completion,
     hard_kill,
     soft_kill,
 )
@@ -195,31 +194,14 @@ async def trio_proc(
         with trio.CancelScope(shield=True):
             await actor_nursery._join_procs.wait()
 
-        async with trio.open_nursery() as nursery:
-            if portal in actor_nursery._cancel_after_result_on_exit:
-                nursery.start_soon(
-                    cancel_on_completion,
-                    portal,
-                    subactor,
-                    errors
-                )
-
-            # This is a "soft" (cancellable) join/reap which
-            # will remote cancel the actor on a ``trio.Cancelled``
-            # condition.
-            await soft_kill(
-                proc,
-                trio.Process.wait,  # XXX, uses `pidfd_open()` below.
-                portal
-            )
-
-            # cancel result waiter that may have been spawned in
-            # tandem if not done already
-            log.cancel(
-                'Cancelling portal result reaper task\n'
-                f'c)> {subactor.aid.reprol()!r}\n'
-            )
-            nursery.cancel_scope.cancel()
+        # This is a "soft" (cancellable) join/reap which
+        # will remote cancel the actor on a ``trio.Cancelled``
+        # condition.
+        await soft_kill(
+            proc,
+            trio.Process.wait,  # XXX, uses `pidfd_open()` below.
+            portal
+        )
 
     finally:
         # XXX NOTE XXX: The "hard" reap since no actor zombies are

tractor/to_actor/__init__.py

@@ -0,0 +1,33 @@
+# tractor: distributed structured concurrency.
+# Copyright 2018-eternity Tyler Goodlet.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+'''
+`tractor.to_actor`: high-level "one-shot" remote-task APIs.
+
+Adopts the "run it over there" parlance from analogous
+(sibling-library) APIs like `trio.to_thread` and
+`anyio.to_process` but for SC-supervised actors: spawn (or
+reuse) a subactor, schedule a single remote task, wait on
+its result and (when the call owns the subactor) reap it.
+
+The "spiritual successor" to (and replacement of) the removed
+legacy `ActorNursery.run_in_actor()` API; see
+https://github.com/goodboy/tractor/issues/477
+
+'''
+from ._api import (
+    run as run,
+)

tractor/to_actor/_api.py

@@ -0,0 +1,226 @@
+# tractor: distributed structured concurrency.
+# Copyright 2018-eternity Tyler Goodlet.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+'''
+One-shot remote-task invocation built on spawn-and-portal
+primitives.
+
+Implemented (as prescribed by #477) entirely "on top of"
+the lower level daemon-actor spawn + portal APIs,
+
+- `ActorNursery.start_actor()` for (daemon-style) subactor
+  spawning,
+- `Portal.run()` for scheduling the lone remote task and
+  waiting on its result,
+- `Portal.cancel_actor()` for reaping the subactor once
+  that result (or error) arrives,
+
+such that error collection and propagation happens in the
+*caller's task* (and thus whatever `trio` nursery/scope
+encloses it) instead of inside the actor-nursery's
+spawn-machinery nurseries as with the (now removed) legacy
+`ActorNursery.run_in_actor()` API.
+
+'''
+from __future__ import annotations
+import inspect
+from typing import (
+    Any,
+    Callable,
+    TYPE_CHECKING,
+)
+
+from ..runtime._supervise import (
+    ActorNursery,
+    open_nursery,
+)
+
+if TYPE_CHECKING:
+    from ..discovery._addr import UnwrappedAddress
+    from ..runtime._portal import Portal
+
+
+def _validate_one_shot_fn(
+    fn: Callable,
+) -> None:
+    '''
+    Ensure `fn` is a non-streaming async function, raise
+    a `TypeError` otherwise.
+
+    The same constraint enforced by `Portal.run()` but
+    checked up-front, BEFORE any subactor is spawned.
+
+    '''
+    if not (
+        inspect.iscoroutinefunction(fn)
+        and
+        not getattr(
+            fn,
+            '_tractor_stream_function',
+            False,
+        )
+    ):
+        raise TypeError(
+            f'{fn!r} must be a non-streaming async '
+            f'function!'
+        )
+
+
+async def _invoke_in_subactor(
+    an: ActorNursery,
+    fn: Callable,
+    name: str,
+    spawn_kwargs: dict[str, Any],
+    fn_kwargs: dict[str, Any],
+) -> Any:
+    '''
+    Spawn a (daemon) subactor via `an.start_actor()`,
+    schedule `fn` as its lone remote task via
+    `Portal.run()` and, ALWAYS, reap the subactor once
+    that task's result (or error) has been delivered.
+
+    '''
+    portal: Portal = await an.start_actor(
+        name,
+        **spawn_kwargs,
+    )
+    try:
+        return await portal.run(
+            fn,
+            **fn_kwargs,
+        )
+    finally:
+        # one-shot semantics: the subactor's lifetime is
+        # bound to its lone task's completion; the
+        # cancel-req's bounded wait is shielded
+        # internally (see `Portal.cancel_actor()`) so
+        # this reap also runs when the caller's scope
+        # was itself cancelled.
+        await portal.cancel_actor()
+
+
+async def run(
+    fn: Callable,
+    *,
+
+    # actor "placement": reuse an already-running peer
+    # via its `portal`, spawn a fresh subactor from
+    # a caller-managed `an: ActorNursery`, or, when
+    # neither is provided, open a private actor-nursery
+    # (implicitly booting the actor-runtime as needed)
+    # scoped to just this call.
+    portal: Portal|None = None,
+    an: ActorNursery|None = None,
+
+    # subactor spawn opts passed (mostly) verbatim to
+    # `ActorNursery.start_actor()`; unused when `portal`
+    # is provided.
+    name: str|None = None,
+    bind_addrs: list[UnwrappedAddress]|None = None,
+    enable_modules: list[str]|None = None,
+    loglevel: str|None = None,
+    debug_mode: bool|None = None,
+    infect_asyncio: bool = False,
+    inherit_parent_main: bool = True,
+    proc_kwargs: dict[str, Any]|None = None,
+
+    # passed verbatim to the private `open_nursery()`
+    # (and in turn any implicit `open_root_actor()`)
+    # when NO `an`/`portal` is provided.
+    runtime_kwargs: dict[str, Any]|None = None,
+
+    **fn_kwargs,  # explicit (keyword) args to `fn`
+
+) -> Any:
+    '''
+    Run the async `fn` as the lone task in a (new)
+    subactor, block waiting on its result and return it;
+    the distributed-parallelism equivalent of
+    `trio.to_thread.run_sync()`.
+
+    Unlike the removed legacy `.run_in_actor()` (which
+    returned a `Portal` whose result was only collected
+    at actor-nursery teardown) this is a plain "call and
+    wait" primitive: any remote error is raised HERE, in
+    the caller's task. Concurrency is composed the usual
+    `trio` way by scheduling multiple `run()` calls in
+    a local task nursery, ideally against a shared
+    caller-managed `an: ActorNursery` (see the test
+    suite for the canonical worker-pool-ish pattern).
+
+    '''
+    __runtimeframe__: int = 1  # noqa
+    _validate_one_shot_fn(fn)
+
+    if (
+        runtime_kwargs
+        and
+        (
+            an is not None
+            or
+            portal is not None
+        )
+    ):
+        raise ValueError(
+            '`runtime_kwargs` only applies when this '
+            'call opens its own private actor-nursery '
+            '(no `an`/`portal` provided)!'
+        )
+
+    if portal is not None:
+        if an is not None:
+            raise ValueError(
+                'Pass at most ONE of `portal` or `an`, '
+                'not both!'
+            )
+        return await portal.run(
+            fn,
+            **fn_kwargs,
+        )
+
+    name: str = name or fn.__name__
+    spawn_kwargs: dict[str, Any] = dict(
+        enable_modules=(
+            [fn.__module__]
+            +
+            (enable_modules or [])
+        ),
+        bind_addrs=bind_addrs,
+        loglevel=loglevel,
+        debug_mode=debug_mode,
+        infect_asyncio=infect_asyncio,
+        inherit_parent_main=inherit_parent_main,
+        proc_kwargs=proc_kwargs,
+    )
+    if an is not None:
+        return await _invoke_in_subactor(
+            an,
+            fn,
+            name,
+            spawn_kwargs,
+            fn_kwargs,
+        )
+
+    async with open_nursery(
+        **(runtime_kwargs or {}),
+    ) as an:
+        return await _invoke_in_subactor(
+            an,
+            fn,
+            name,
+            spawn_kwargs,
+            fn_kwargs,
+        )