Another cancel-req-invalid log msg fmt tweak

tractor/_runtime.py

@@ -715,10 +715,12 @@ class Actor:
                         f'|_{chan}\n'
                     )
                     try:
-                        # send a msg loop terminate sentinel
+                        # send msg loop terminate sentinel which
+                        # triggers cancellation of all remotely
+                        # started tasks.
                         await chan.send(None)
 
-                        # XXX: do we want this?
+                        # XXX: do we want this? no right?
                         # causes "[104] connection reset by peer" on other end
                         # await chan.aclose()
 
@@ -1208,10 +1210,10 @@ class Actor:
             # - callee self raises ctxc before caller send request,
             # - callee errors prior to cancel req.
             log.cancel(
-                'Cancel request invalid, RPC task already completed?\n'
+                'Cancel request invalid, RPC task already completed?\n\n'
                 f'<= canceller: {requesting_uid}\n\n'
-                f'=>{parent_chan}\n'
-                f'  |_ctx-id: {cid}\n'
+                f'=> {cid}@{parent_chan.uid}\n'
+                f'  |_{parent_chan}\n'
             )
             return True
 
@@ -1510,7 +1512,6 @@ async def async_main(
             ):
                 accept_addrs = set_accept_addr_says_rent
 
-
         # The "root" nursery ensures the channel with the immediate
         # parent is kept alive as a resilient service until
         # cancellation steps have (mostly) occurred in