Only cancel/get-result from a ctx if transport is up

There's no point in sending a cancel message to the remote linked task
and especially no reason to block waiting on a result from that task if
the transport layer is detected to be disconnected. We expect that the
transport shouldn't go down at the layer of the message loop
(reconnection logic should be handled in the transport layer itself) so
if we detect the channel is not connected we don't bother requesting
cancels nor waiting on a final result message.

Why?

- if the connection goes down in error the caller side won't have a way
  to know "how long" it should block to wait for a cancel ack or result
  and causes a potential hang that may require an additional ctrl-c from
  the user especially if using the debugger or if the traceback is not
  seen on console.
- obviously there's no point in waiting for messages when there's no
  transport to deliver them XD

Further, add some more detailed cancel logging detailing the task and
actor ids.

tractor/_portal.py

@@ -442,6 +442,10 @@ class Portal:
         _err: Optional[BaseException] = None
         ctx._portal = self
 
+        uid = self.channel.uid
+        cid = ctx.cid
+        etype: Optional[Exception] = None
+
         # deliver context instance and .started() msg value in open tuple.
         try:
             async with trio.open_nursery() as scope_nursery:
@@ -477,13 +481,24 @@ class Portal:
             # KeyboardInterrupt,
 
         ) as err:
-            _err = err
+            etype = type(err)
             # the context cancels itself on any cancel
             # causing error.
-            log.cancel(
-                f'Context to {self.channel.uid} sending cancel request..')
 
-            await ctx.cancel()
+            if ctx.chan.connected():
+                log.cancel(
+                    'Context cancelled for task, sending cancel request..\n'
+                    f'task:{cid}\n'
+                    f'actor:{uid}'
+                )
+                await ctx.cancel()
+            else:
+                log.warning(
+                    'IPC connection for context is broken?\n'
+                    f'task:{cid}\n'
+                    f'actor:{uid}'
+                )
+
             raise
 
         finally:
@@ -492,7 +507,13 @@ class Portal:
             # sure we get the error the underlying feeder mem chan.
             # if it's not raised here it *should* be raised from the
             # msg loop nursery right?
-            result = await ctx.result()
+            if ctx.chan.connected():
+                log.info(
+                    'Waiting on final context-task result for\n'
+                    f'task:{cid}\n'
+                    f'actor:{uid}'
+                )
+                result = await ctx.result()
 
             # though it should be impossible for any tasks
             # operating *in* this scope to have survived
@@ -502,14 +523,17 @@ class Portal:
                 # should we encapsulate this in the context api?
                 await ctx._recv_chan.aclose()
 
-            if _err:
+            if etype:
                 if ctx._cancel_called:
                     log.cancel(
-                        f'Context {fn_name} cancelled by caller with\n{_err}'
+                        f'Context {fn_name} cancelled by caller with\n{etype}'
                     )
                 elif _err is not None:
                     log.cancel(
-                        f'Context {fn_name} cancelled by callee with\n{_err}'
+                        f'Context for task cancelled by callee with {etype}\n'
+                        f'target: `{fn_name}`\n'
+                        f'task:{cid}\n'
+                        f'actor:{uid}'
                     )
             else:
                 log.runtime(

tractor/_streaming.py

@@ -604,7 +604,8 @@ class Context:
                     self._portal._streams.remove(rchan)
 
     async def result(self) -> Any:
-        '''From a caller side, wait for and return the final result from
+        '''
+        From a caller side, wait for and return the final result from
         the callee side task.
 
         '''