Add post-mortem catch around failed transport addr binds to aid with runtime debugging

tractor/_root.py

@@ -260,10 +260,14 @@ async def open_root_actor(
         # start the actor runtime in a new task
         async with trio.open_nursery() as nursery:
 
-            # ``_runtime.async_main()`` creates an internal nursery and
+            # ``_runtime.async_main()`` creates an internal nursery
-            # thus blocks here until the entire underlying actor tree has
+            # and blocks here until any underlying actor(-process)
-            # terminated thereby conducting structured concurrency.
+            # tree has terminated thereby conducting so called
-
+            # "end-to-end" structured concurrency throughout an
+            # entire hierarchical python sub-process set; all
+            # "actor runtime" primitives are SC-compat and thus all
+            # transitively spawned actors/processes must be as
+            # well.
             await nursery.start(
                 partial(
                     async_main,

tractor/_runtime.py

@@ -1405,6 +1405,7 @@ async def async_main(
                 # - root actor: the ``accept_addr`` passed to this method
                 assert accept_addrs
 
+                try:
                     actor._server_n = await service_nursery.start(
                         partial(
                             actor._serve_forever,
@@ -1412,6 +1413,14 @@ async def async_main(
                             listen_sockaddrs=accept_addrs,
                         )
                     )
+                except OSError as oserr:
+                    # NOTE: always allow runtime hackers to debug
+                    # tranport address bind errors - normally it's
+                    # something silly like the wrong socket-address
+                    # passed via a config or CLI Bo
+                    entered_debug = await _debug._maybe_enter_pm(oserr)
+                    raise
+
                 accept_addrs: list[tuple[str, int]] = actor.accept_addrs
 
                 # NOTE: only set the loopback addr for the