Add masked crash-handler cm for debugging wonky inter-actor comms (teardowns)

Unmask the CRE case block for peer-closed socket errors which already
had a TODO about reproducing the condition. It appears this case can
happen during inter-actor comms teardowns in `piker`, but i haven't been
able to figure out exactly what reproduces it yet..

So activate the block again for that 'socket already closed'-msg case,
and add a TODO questioning how to reproduce it.

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

tractor/ipc/_chan.py

@@ -497,6 +497,9 @@ async def _connect_chan(
     teardown.
 
     '''
+    # XXX, ONLY uncomment for tracing lowlevel connection issues.
+    # from tractor.devx import open_crash_handler
+    # with open_crash_handler():
     chan = await Channel.from_addr(addr)
     yield chan
     with trio.CancelScope(shield=True):

tractor/ipc/_transport.py

@@ -459,21 +459,23 @@ class MsgpackTransport(MsgTransport):
                         )
                         raise tpt_closed from trans_err
 
-                    # case trio.ClosedResourceError() if (
+                    # ??TODO??, what case in piker does this and HOW
-                    #     'this socket was already closed'
+                    # CAN WE RE-PRODUCE IT?!?!?
-                    #     in
+                    case trio.ClosedResourceError() if (
-                    #     trans_err.args[0]
+                        'this socket was already closed'
-                    # ):
+                        in
-                    #     tpt_closed = TransportClosed.from_src_exc(
+                        trans_err.args[0]
-                    #         message=(
+                    ):
-                    #             f'{tpt_name} already closed by peer\n'
+                        tpt_closed = TransportClosed.from_src_exc(
-                    #         ),
+                            message=(
-                    #         body=f'{self}\n',
+                                f'{tpt_name} already closed by peer\n'
-                    #         src_exc=trans_err,
+                            ),
-                    #         raise_on_report=True,
+                            body=f'{self}\n',
-                    #         loglevel='transport',
+                            src_exc=trans_err,
-                    #     )
+                            raise_on_report=True,
-                    #     raise tpt_closed from trans_err
+                            loglevel='transport',
+                        )
+                        raise tpt_closed from trans_err
 
                     # unless the disconnect condition falls under "a
                     # normal operation breakage" we usualy console warn