Add `Address.rebind_from_sockname` opt-out

Gate `Endpoint.start_listener()`s `getsockname()`-vs-`.addr`
reconciliation on a new per-addr-type `ClassVar[bool]`, set
`True` on both `TCPAddress` and `UDSAddress` so existing
behaviour is bit-for-bit unchanged.

That reconciliation exists ONLY to learn a kernel-assigned
port from a `port=0` tcp bind (its own comment says so). The
incoming `tipc` backend (gh #378) has no late-binding
analogue AND its `getsockname()` answers a `TIPC_ADDR_ID`
port-id rather than the name-seq it published — rebinding
from that would swap a dialable service name for an
un-dialable, un-reconstructable port id.

So opting out is semantically right rather than a hack.

(this patch was generated in some part by `claude-code` using `claude-opus-5` (`anthropic`))

tractor/discovery/_addr.py

@@ -82,6 +82,16 @@ UnwrappedAddress = (
 class Address(Protocol):
     proto_key: ClassVar[str]
     unwrapped_type: ClassVar[UnwrappedAddress]
+    # whether `.ipc._server.Endpoint.start_listener()` should
+    # reconcile a bound `.addr` against its listener's
+    # `socket.getsockname()`.
+    #
+    # XXX NOTE, that reconciliation exists ONLY to learn the
+    # kernel-*assigned* port from a `port=0` tcp bind; a backend
+    # whose `getsockname()` reports a categorically different thing
+    # than what was `.bind()`ed must opt out with `False`, else the
+    # ep's addr gets clobbered by an un-dialable one.
+    rebind_from_sockname: ClassVar[bool]
 
     # TODO, i feel like an `.is_bound()` is a better thing to
     # support?

tractor/ipc/_server.py

@@ -661,7 +661,16 @@ class Endpoint(Struct):
 
         # NOTE, for handling the resolved non-0 port for
         # TCP/UDP network sockets.
+        #
+        # XXX, gated on the addr-type's opt-in since for some
+        # backends `getsockname()` does NOT answer "the addr you
+        # bound"; `tipc` reports a `TIPC_ADDR_ID` port-id instead
+        # of the published name-seq, so rebinding from it would
+        # replace a dialable service-name with an un-dialable
+        # (and un-reconstructable) port-id.
         if (
+            self.addr.rebind_from_sockname
+            and
             (unwrapped := lstnr.socket.getsockname())
             !=
             self.addr.unwrap()

tractor/ipc/_tcp.py

@@ -65,6 +65,10 @@ class TCPAddress(
     unwrapped_type: ClassVar[type] = tuple[str, int]
     def_bindspace: ClassVar[str] = '127.0.0.1'
 
+    # XXX, REQUIRED here since a `port=0` bind means the kernel
+    # picks and `getsockname()` is the only way we learn it.
+    rebind_from_sockname: ClassVar[bool] = True
+
     # ?TODO, actually validate ipv4/6 with stdlib's `ipaddress`
     @property
     def is_valid(self) -> bool:

tractor/ipc/_uds.py

@@ -117,6 +117,12 @@ class UDSAddress(
     unwrapped_type: ClassVar[type] = tuple[str, int]
     def_bindspace: ClassVar[Path] = get_rt_dir()
 
+    # NOTE, `getsockname()` answers the sock-file path as a `str`
+    # which never `==` our 2-tuple `.unwrap()`, so the round-trip
+    # always fires; it's a no-op modulo `.maybe_pid` and is kept
+    # `True` to preserve pre-existing behaviour exactly.
+    rebind_from_sockname: ClassVar[bool] = True
+
     @property
     def bindspace(self) -> Path:
         '''