Polish `to_actor` examples and references

Remaining review threads requested clearer scheduling intent, result
ownership and Portal RPC usage across the migrated examples, plus a
more descriptive concurrent-primes filename.

Explain the relevant example boundaries, fix the transport typo, expand
the local helper signature and rename the live primes example and guide
reference while preserving historical Prompt-IO paths.

Review: PR #481 (goodboy)
https://github.com/goodboy/tractor/pull/481#pullrequestreview-5012942328

(this patch was generated in some part by `opencode` using `gpt-5.6-sol` (`openai`))

docs/guide/rpc.rst

@@ -100,7 +100,7 @@ Semantics worth knowing:
 - it blocks until the remote task returns, re-raising any
   remote error in the usual boxed form right in the calling
   task.
-- placement also determines process ownership: ``an=`` spawns and
+- lifetime mode also determines process ownership: ``an=`` spawns and
   reaps a fresh child in an existing actor nursery, while passing
   neither does the same in a private call-scoped nursery (booting
   the runtime if needed). ``portal=`` instead runs one linked task
@@ -108,7 +108,7 @@ Semantics worth knowing:
   the portal's owner remains responsible for its lifetime.
 - concurrency composes the plain ``trio`` way: schedule
   multiple ``run()`` calls into a local task nursery (see
-  ``examples/parallelism/to_actor_one_shots.py``).
+  ``examples/parallelism/concurrent_toactor_primes.py``).
 
 A reused actor must expose both the target module and the
 ``to_actor`` context trampoline:

examples/a_trynamic_first_scene.py

@@ -35,8 +35,12 @@ async def main():
             for name in ('donny', 'gretchen')
         }
 
-        async def run_and_print(name: str, other_actor: str):
+        async def run_and_print(
+            name: str,
+            other_actor: str,
+        ) -> None:
             print(
+                # RPC through an existing actor's `Portal`.
                 await portals[name].run(
                     say_hello,
                     other_actor=other_actor,

examples/debugging/multi_nested_subactors_error_up_through_nurseries.py

@@ -37,6 +37,8 @@ async def spawn_until(depth=0):
                 )
             )
 
+            # Let the background one-shot enter `breakpoint_forever()`
+            # before its sibling raises and cancellation propagates.
             await trio.sleep(0.5)
             # rx and propagate error from child
             await tractor.to_actor.run(

examples/debugging/root_cancelled_but_child_is_in_tty_lock.py

@@ -44,7 +44,7 @@ async def main():
     async with (
         tractor.open_nursery(
             debug_mode=True,
-            enable_transports=['uds'],  # TODO, apss this via osenv?
+            enable_transports=['uds'],  # TODO, pass this via osenv?
             loglevel='devx',  # XXX, required for test!
         ) as an,
         trio.open_nursery() as tn,

examples/parallelism/concurrent_toactor_primes.py

@@ -1,5 +1,5 @@
 '''
-`tractor.to_actor.run()`: one-shot single-task subactor
+`tractor.to_actor.run()`: concurrent one-shot prime checks
 invocation, the SC-parallelism sibling of
 `trio.to_thread.run_sync()` (and `anyio.to_process`).
 

examples/parallelism/single_func.py

@@ -31,7 +31,7 @@ async def main():
         tn.start_soon(burn_cpu)
 
         # run the same func as the lone task in a subactor,
-        # block on (and collect) its result
+        # block on and collect its PID as the caller-side result
         pid = await tractor.to_actor.run(burn_cpu)
 
     print(f"Collected subproc {pid}")