Rework landing example onto the `Context` API

`run_in_actor()` is slated to become a hilevel wrapper
(`runtime/_supervise.py` "TODO: DEPRECATE THIS"), so the showcase
`we_are_processes.py` shouldn't lead with it. Move it to the modern
API: each `worker_<i>` subactor runs a `@tractor.context`
`endpoint()` that `started()`-hands its name + pid back over
`Portal.open_context()` and parks; the root sleeps then raises on
purpose so the runtime reaps the whole tree (zero zombies).

The subs spawn concurrently from bg `trio.Task`s so each child's
cold `import tractor` (~0.4s, see #470) overlaps instead of
stacking; a comment flags the coming `main_thread_forkserver`
backend (#463) which'll make serial spawns cheap enough to just
loop.

Match the landing prose to the snippet — name the `Context` +
`started()` handshake it now leads with.

Also, document `--watch examples` on the `sphinx-autobuild` cmds so
edits to `literalinclude`-d example scripts (which live outside
`docs/`) live-reload too.

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

docs/index.rst

@@ -24,8 +24,10 @@ Sixty seconds of why
    you can read a ``trio`` program you can read a
    ``tractor`` one — that's the whole pitch.
 
-Spawn one actor per core, crash the root on purpose,
-and watch the runtime contain the blast: errors
+Spawn one actor per core, open a ``Context`` into
+each — the child ``started()``-handshakes its name
+and pid back — then crash the root on purpose and
+watch the runtime contain the blast: errors
 propagate, *every* child is reaped, zero zombies —
 guaranteed (it's a bug otherwise).
 

examples/parallelism/we_are_processes.py

@@ -1,11 +1,11 @@
-"""
+'''
 Run with a process monitor from a terminal using::
 
     $TERM -e watch -n 0.1  "pstree -a $$" \
         & python examples/parallelism/we_are_processes.py \
         && kill $!
 
-"""
+'''
 from multiprocessing import cpu_count
 import os
 
@@ -13,26 +13,70 @@ import tractor
 import trio
 
 
-async def target():
-    print(
-        f"Yo, i'm '{tractor.current_actor().name}' "
-        f"running in pid {os.getpid()}"
-    )
-
+@tractor.context
+async def endpoint(
+    ctx: tractor.Context,
+):
+    actor_name: str = tractor.current_actor().name
+    pid: int = os.getpid()
+    await ctx.started((actor_name, pid))
     await trio.sleep_forever()
 
 
+async def spawn_and_open_ep(
+    an: tractor.ActorNursery,
+    i: int,
+) -> None:
+    '''
+    Spawn a subactor, start a remote `endpoint()`-task in it.
+
+    '''
+    ptl: tractor.Portal = await an.start_actor(
+        name=f'worker_{i}',
+        enable_modules=[__name__],
+    )
+    ctx: tractor.Context
+    async with ptl.open_context(endpoint) as (
+        ctx,
+        (sub_name, sub_pid),
+    ):
+        print(
+            f'Started ep-task in subactor,\n'
+            f'{i}::{sub_name!r}@{sub_pid}\n'
+        )
+        await ctx.wait_for_result()
+
+
 async def main():
+    '''
+    Spawn a subactor-per-CPU then self-destruct the cluster.
 
-    async with tractor.open_nursery() as n:
-
+    '''
+    tn: trio.Nursery
+    an: tractor.ActorNursery
+    async with (
+        tractor.open_nursery(
+            # XXX coming soon!
+            # https://github.com/goodboy/tractor/pull/463
+            # start_method='main_thread_forkserver',
+        ) as an,
+        # spawn subs concurrently (in bg `trio.Task`s) so each
+        # actor's cold `import tractor` (~0.4s, see #470) overlaps
+        # instead of stacking; once forkserver (#463) lands, spawn
+        # is cheap enough to just loop sequentially.
+        trio.open_nursery() as tn,
+    ):
         for i in range(cpu_count()):
-            await n.run_in_actor(target, name=f'worker_{i}')
-
-        print('This process tree will self-destruct in 1 sec...')
-        await trio.sleep(1)
-
-        # you could have done this yourself
+            tn.start_soon(
+                spawn_and_open_ep,
+                an,
+                i,
+            )
+        destruct_in: int = 2
+        print(
+            f'This tree will self-destruct in {destruct_in}s..\n'
+        )
+        await trio.sleep(destruct_in)
         raise Exception('Self Destructed')
 
 

notes_to_self/howtodocs.md

@@ -38,10 +38,15 @@ Rebuilds + refreshes the browser on every save:
 
 ```
 nix develop .#docs -c uv run --with sphinx-autobuild \
-    --group docs sphinx-autobuild docs docs/_build/html
+    --group docs sphinx-autobuild docs docs/_build/html \
+    --watch examples
 # then open http://127.0.0.1:8000
 ```
 
+The `--watch examples` is what makes edits to ``literalinclude``-d
+example scripts live-reload too: those files live *outside* `docs/`,
+so autobuild won't notice them changing without it.
+
 ## Share it on your LAN
 
 To let someone on your subnet view the docs, bind the server to
@@ -52,7 +57,8 @@ Live-reload, LAN-visible:
 
 ```
 nix develop .#docs -c uv run --with sphinx-autobuild --group docs \
-    sphinx-autobuild docs docs/_build/html --host 0.0.0.0 --port 8000
+    sphinx-autobuild docs docs/_build/html --host 0.0.0.0 --port 8000 \
+    --watch examples
 ```
 
 Or just statically serve an already-built `docs/_build/html` (no