Derive transport registries from one list

The five transport/address lookup maps each hand-guarded `uds`
with its own `if HAS_UDS:` block (3 in `ipc/_types`, 2 in
`discovery/_addr`) — easy to let drift so a backend half-registers
(known by address but not by key, listed but unroutable, &c).

- build one `_msg_transports` / `_address_protos` list per module
  (TCP always, UDS only when `HAS_UDS`), then DERIVE every map
  from it via each backend's ClassVars (`codec_key`,
  `address_type`, `proto_key`). Adding a backend now touches one
  list, and the maps can't disagree.

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

tractor/discovery/_addr.py

@@ -172,24 +172,36 @@ class Address(Protocol):
         ...
 
 
-_address_types: bidict[str, Type[Address]] = {
-    'tcp': TCPAddress,
-}
+# the address types available on this host: TCP always, UDS only
+# where usable (`HAS_UDS`). Both registries derive from this single
+# list via each type's `proto_key`.
+_address_protos: list[Type[Address]] = [TCPAddress]
 if HAS_UDS:
-    _address_types['uds'] = UDSAddress
+    _address_protos.append(UDSAddress)
+
+_address_types: bidict[str, Type[Address]] = bidict({
+    cls.proto_key: cls
+    for cls in _address_protos
+})
 
 
 # TODO! really these are discovery sys default addrs ONLY useful for
 # when none is provided to a root actor on first boot.
 _default_lo_addrs: dict[str, UnwrappedAddress] = {
-    'tcp': TCPAddress.get_root().unwrap(),
+    cls.proto_key: cls.get_root().unwrap()
+    for cls in _address_protos
 }
-if HAS_UDS:
-    _default_lo_addrs['uds'] = UDSAddress.get_root().unwrap()
 
 
 def get_address_cls(name: str) -> Type[Address]:
-    return _address_types[name]
+    try:
+        return _address_types[name]
+    except KeyError:
+        raise NotImplementedError(
+            f'No IPC transport backend for {name!r} on this '
+            f'platform!\n'
+            f'(available: {list(_address_types)})\n'
+        )
 
 
 def is_wrapped_addr(addr: any) -> bool:
@@ -287,7 +299,14 @@ def default_lo_addrs(
     for an input transport key set.
 
     '''
-    return [
-        _default_lo_addrs[transport]
-        for transport in transports
-    ]
+    lo_addrs: list[UnwrappedAddress] = []
+    for transport in transports:
+        try:
+            lo_addrs.append(_default_lo_addrs[transport])
+        except KeyError:
+            raise NotImplementedError(
+                f'No default loopback addr for transport '
+                f'{transport!r} on this platform!\n'
+                f'(available: {list(_default_lo_addrs)})\n'
+            )
+    return lo_addrs

tractor/ipc/_types.py

@@ -41,26 +41,28 @@ from tractor.ipc._uds import (
 # hosts `HAS_UDS` is `False` and the runtime registers TCP only.
 Address = TCPAddress|UDSAddress
 
-# manually updated list of all supported msg transport types
+# the available msg-transport backends on this host: TCP always,
+# UDS only where usable (`HAS_UDS`). The lookup maps below are all
+# DERIVED from this single list via each backend's ClassVars
+# (`codec_key`, `address_type`) — register a backend here and every
+# map picks it up; no per-map `if HAS_UDS` to keep in sync.
 _msg_transports: list[Type[MsgTransport]] = [
     MsgpackTCPStream,
 ]
 if HAS_UDS:
     _msg_transports.append(MsgpackUDSStream)
 
-# map a `MsgTransportKey` to its `MsgTransport` type
+# map a `MsgTransportKey` -> `MsgTransport` type
 _key_to_transport: dict[MsgTransportKey, Type[MsgTransport]] = {
-    ('msgpack', 'tcp'): MsgpackTCPStream,
+    (t.codec_key, t.address_type.proto_key): t
+    for t in _msg_transports
 }
-if HAS_UDS:
-    _key_to_transport[('msgpack', 'uds')] = MsgpackUDSStream
 
-# map an `Address`-wrapper to its `MsgTransport` type
+# map an `Address`-wrapper -> `MsgTransport` type
 _addr_to_transport: dict[Type[Address], Type[MsgTransport]] = {
-    TCPAddress: MsgpackTCPStream,
+    t.address_type: t
+    for t in _msg_transports
 }
-if HAS_UDS:
-    _addr_to_transport[UDSAddress] = MsgpackUDSStream
 
 
 # ------------------------------------------------------------