Port non-debugging examples off `run_in_actor`

4 example scripts of the #477 removal sweep, each exercised by
`test_docs_examples.py`,

- `actor_spawning_and_causality.py`: the simplest possible
  `to_actor.run()` demo — private call-scoped nursery, block on
  and print the one-shot's result.
- `remote_error_propagation.py`: blocking `to_actor.run(an=n)`
  raises the boxed `AssertionError` in the caller's task,
  cancelling the sibling daemons.
- `parallelism/single_func.py`: bg-burn a core in the parent via
  a local task-nursery while the one-shot burns (and returns
  from) a subactor.
- `a_trynamic_first_scene.py`: donny + gretchen wait on each
  *other* so their one-shots run concurrently in a local
  task-nursery against a shared `an` (mirrors the migrated
  `test_trynamic_trio`).

Gate: all 4 green via the example-runner suite.

(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

examples/a_trynamic_first_scene.py

@@ -17,27 +17,38 @@ async def say_hello(other_actor):
         return await portal.run(hi)
 
 
+async def run_and_print(
+    an: tractor.ActorNursery,
+    name: str,
+    other_actor: str,
+):
+    print(
+        await tractor.to_actor.run(
+            say_hello,
+            an=an,
+            name=name,
+            # arguments are always named
+            other_actor=other_actor,
+        )
+    )
+
+
 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,
+        trio.open_nursery() as tn,
+    ):
         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 the *other* to register so their
+        # one-shots must run concurrently.
+        tn.start_soon(run_and_print, an, 'donny', 'gretchen')
+        tn.start_soon(run_and_print, an, 'gretchen', 'donny')
+
+    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/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/remote_error_propagation.py

@@ -15,11 +15,12 @@ async def main():
                 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=n)
 
-    # 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__':