diff --git a/default.nix b/default.nix
index 08e46d06..9036aecf 100644
--- a/default.nix
+++ b/default.nix
@@ -11,9 +11,4 @@ pkgs.mkShell {
 
   LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath nativeBuildInputs;
   TMPDIR = "/tmp";
-
-  shellHook = ''
-    set -e
-    uv venv .venv --python=3.12
-  '';
 }
diff --git a/tests/test_ext_types_msgspec.py b/tests/test_ext_types_msgspec.py
index b334b64f..d82759d6 100644
--- a/tests/test_ext_types_msgspec.py
+++ b/tests/test_ext_types_msgspec.py
@@ -5,6 +5,7 @@ Low-level functional audits for our
 B~)
 
 '''
+from __future__ import annotations
 from contextlib import (
     contextmanager as cm,
     # nullcontext,
@@ -20,7 +21,7 @@ from msgspec import (
     # structs,
     # msgpack,
     Raw,
-    # Struct,
+    Struct,
     ValidationError,
 )
 import pytest
@@ -46,6 +47,11 @@ from tractor.msg import (
     apply_codec,
     current_codec,
 )
+from tractor.msg._codec import (
+    default_builtins,
+    mk_dec_hook,
+    mk_codec_from_spec,
+)
 from tractor.msg.types import (
     log,
     Started,
@@ -743,6 +749,143 @@ def test_ext_types_over_ipc(
         assert exc.boxed_type is TypeError
 
 
+'''
+Test the auto enc & dec hooks
+
+Create a codec which will work for:
+    - builtins
+    - custom types
+    - lists of custom types
+'''
+
+
+class TestBytesClass(Struct, tag=True):
+    raw: bytes
+
+    def encode(self) -> bytes:
+        return self.raw
+
+    @classmethod
+    def from_bytes(self, raw: bytes) -> TestBytesClass:
+        return TestBytesClass(raw=raw)
+
+
+class TestStrClass(Struct, tag=True):
+    s: str
+
+    def encode(self) -> str:
+        return self.s
+
+    @classmethod
+    def from_str(self, s: str) -> TestStrClass:
+        return TestStrClass(s=s)
+
+
+class TestIntClass(Struct, tag=True):
+    num: int
+
+    def encode(self) -> int:
+        return self.num
+
+    @classmethod
+    def from_int(self, num: int) -> TestIntClass:
+        return TestIntClass(num=num)
+
+
+builtins = tuple((
+    builtin
+    for builtin in default_builtins
+    if builtin is not list
+))
+
+TestClasses = (TestBytesClass, TestStrClass, TestIntClass)
+
+
+TestSpec = (
+    *TestClasses, list[Union[*TestClasses]]
+)
+
+
+test_codec = mk_codec_from_spec(
+    spec=TestSpec
+)
+
+
+@tractor.context
+async def child_custom_codec(
+    ctx: tractor.Context,
+    msgs: list[Union[*TestSpec]],
+):
+    '''
+    Apply codec and send all msgs passed through stream
+
+    '''
+    with (
+        apply_codec(test_codec),
+        limit_plds(
+            test_codec.pld_spec,
+            dec_hook=mk_dec_hook(TestSpec),
+            ext_types=TestSpec + builtins
+        ),
+    ):
+        await ctx.started(None)
+        async with ctx.open_stream() as stream:
+            for msg in msgs:
+                await stream.send(msg)
+
+
+def test_multi_custom_codec():
+    '''
+    Open subactor setup codec and pld_rx and wait to receive & assert from
+    stream
+
+    '''
+    msgs = [
+        None,
+        True, False,
+        0xdeadbeef,
+        .42069,
+        b'deadbeef',
+        TestBytesClass(raw=b'deadbeef'),
+        TestStrClass(s='deadbeef'),
+        TestIntClass(num=0xdeadbeef),
+        [
+            TestBytesClass(raw=b'deadbeef'),
+            TestStrClass(s='deadbeef'),
+            TestIntClass(num=0xdeadbeef),
+        ]
+    ]
+
+    async def main():
+        async with tractor.open_nursery() as an:
+            p: tractor.Portal = await an.start_actor(
+                'child',
+                enable_modules=[__name__],
+            )
+            async with (
+                p.open_context(
+                    child_custom_codec,
+                    msgs=msgs,
+                ) as (ctx, _),
+                ctx.open_stream() as ipc
+            ):
+                with (
+                    apply_codec(test_codec),
+                    limit_plds(
+                        test_codec.pld_spec,
+                        dec_hook=mk_dec_hook(TestSpec),
+                        ext_types=TestSpec + builtins
+                    )
+                ):
+                    msg_iter = iter(msgs)
+                    async for recv_msg in ipc:
+                        assert recv_msg == next(msg_iter)
+
+            await p.cancel_actor()
+
+    trio.run(main)
+
+
 # def chk_pld_type(
 #     payload_spec: Type[Struct]|Any,
 #     pld: Any,
diff --git a/tractor/msg/_codec.py b/tractor/msg/_codec.py
index 1e9623af..f8bc3aa6 100644
--- a/tractor/msg/_codec.py
+++ b/tractor/msg/_codec.py
@@ -39,13 +39,11 @@ from contextvars import (
 )
 import textwrap
 from typing import (
-    Any,
-    Callable,
-    Protocol,
-    Type,
     TYPE_CHECKING,
-    TypeVar,
+    Any,
+    Type,
     Union,
+    Callable,
 )
 from types import ModuleType
 
@@ -54,6 +52,13 @@ from msgspec import (
     msgpack,
     Raw,
 )
+from msgspec.inspect import (
+    CustomType,
+    UnionType,
+    SetType,
+    ListType,
+    TupleType
+)
 # TODO: see notes below from @mikenerone..
 # from tricycle import TreeVar
 
@@ -81,7 +86,7 @@ class MsgDec(Struct):
 
     '''
     _dec: msgpack.Decoder
-    # _ext_types_box: Struct|None = None
+    _ext_types_boxes: dict[Type, Struct] = {}
 
     @property
     def dec(self) -> msgpack.Decoder:
@@ -226,6 +231,8 @@ def mk_dec(
             f'ext_types = {ext_types!r}\n'
         )
 
+    _boxed_structs: dict[Type, Struct] = {}
+
     if dec_hook:
         if ext_types is None:
             raise TypeError(
@@ -237,17 +244,15 @@ def mk_dec(
                 f'ext_types = {ext_types!r}\n'
             )
 
-        # XXX, i *thought* we would require a boxing struct as per docs,
-        # https://jcristharif.com/msgspec/extending.html#mapping-to-from-native-types
-        # |_ see comment,
-        #  > Note that typed deserialization is required for
-        #  > successful roundtripping here, so we pass `MyMessage` to
-        #  > `Decoder`.
-        #
-        # BUT, turns out as long as you spec a union with `Raw` it
-        # will work? kk B)
-        #
-        # maybe_box_struct = mk_boxed_ext_struct(ext_types)
+        if len(ext_types) > 1:
+            _boxed_structs = mk_boxed_ext_structs(ext_types)
+            ext_types = [
+                etype
+                for etype in ext_types
+                if etype not in _boxed_structs
+            ]
+            ext_types += list(_boxed_structs.values())
+
         spec = Raw | Union[*ext_types]
 
     return MsgDec(
@@ -255,29 +260,26 @@ def mk_dec(
             type=spec,  # like `MsgType[Any]`
             dec_hook=dec_hook,
         ),
+        _ext_types_boxes=_boxed_structs
     )
 
 
-# TODO? remove since didn't end up needing this?
-def mk_boxed_ext_struct(
+def mk_boxed_ext_structs(
     ext_types: list[Type],
 ) -> Struct:
-    # NOTE, originally was to wrap non-msgpack-supported "extension
-    # types" in a field-typed boxing struct, see notes around the
-    # `dec_hook()` branch in `mk_dec()`.
-    ext_types_union = Union[*ext_types]
-    repr_ext_types_union: str = (
-        str(ext_types_union)
-        or
-        "|".join(ext_types)
-    )
-    BoxedExtType = msgspec.defstruct(
-        f'BoxedExts[{repr_ext_types_union}]',
-        fields=[
-            ('boxed', ext_types_union),
-        ],
-    )
-    return BoxedExtType
+    box_types: dict[Type, Struct] = {}
+    for ext_type in ext_types:
+        info = msgspec.inspect.type_info(ext_type)
+        if isinstance(info, CustomType):
+            box_types[ext_type] = msgspec.defstruct(
+                f'Box{ext_type.__name__}',
+                tag=True,
+                fields=[
+                    ('inner', ext_type),
+                ],
+            )
+
+    return box_types
 
 
 def unpack_spec_types(
@@ -378,7 +380,7 @@ class MsgCodec(Struct):
     _dec: msgpack.Decoder
     _pld_spec: Type[Struct]|Raw|Any
 
-    # _ext_types_box: Struct|None = None
+    _ext_types_boxes: dict[Type, Struct] = {}
 
     def __repr__(self) -> str:
         speclines: str = textwrap.indent(
@@ -465,45 +467,29 @@ class MsgCodec(Struct):
 
         '''
         __tracebackhide__: bool = hide_tb
-        if use_buf:
-            self._enc.encode_into(py_obj, self._buf)
-            return self._buf
 
-        return self._enc.encode(py_obj)
-        # try:
-        #     return self._enc.encode(py_obj)
-        # except TypeError as typerr:
-        #     typerr.add_note(
-        #         '|_src error from `msgspec`'
-        #         # f'|_{self._enc.encode!r}'
-        #     )
-        #     raise typerr
+        try:
 
-        # TODO! REMOVE once i'm confident we won't ever need it!
-        #
-        # box: Struct = self._ext_types_box
-        # if (
-        #     as_ext_type
-        #     or
-        #     (
-        #         # XXX NOTE, auto-detect if the input type
-        #         box
-        #         and
-        #         (ext_types := unpack_spec_types(
-        #             spec=box.__annotations__['boxed'])
-        #         )
-        #     )
-        # ):
-        #     match py_obj:
-        #         # case PayloadMsg(pld=pld) if (
-        #         #     type(pld) in ext_types
-        #         # ):
-        #         #     py_obj.pld = box(boxed=py_obj)
-        #         #     breakpoint()
-        #         case _ if (
-        #             type(py_obj) in ext_types
-        #         ):
-        #             py_obj = box(boxed=py_obj)
+            box: Struct|None = self._ext_types_boxes.get(type(py_obj), None)
+            if (
+                as_ext_type
+                or
+                box
+            ):
+                py_obj = box(inner=py_obj)
+
+            if use_buf:
+                self._enc.encode_into(py_obj, self._buf)
+                return self._buf
+
+            return self._enc.encode(py_obj)
+
+        except TypeError as typerr:
+            typerr.add_note(
+                '|_src error from `msgspec`'
+                # f'|_{self._enc.encode!r}'
+            )
+            raise typerr
 
     @property
     def dec(self) -> msgpack.Decoder:
@@ -565,11 +551,6 @@ def mk_codec(
     enc_hook: Callable|None = None,
     ext_types: list[Type]|None = None,
 
-    # optionally provided msg-decoder from which we pull its,
-    # |_.dec_hook()
-    # |_.type
-    ext_dec: MsgDec|None = None
-    #
     # ?TODO? other params we might want to support
     # Encoder:
     # write_buffer_size=write_buffer_size,
@@ -597,12 +578,6 @@ def mk_codec(
             )
 
     dec_hook: Callable|None = None
-    if ext_dec:
-        dec: msgspec.Decoder = ext_dec.dec
-        dec_hook = dec.dec_hook
-        pld_spec |= dec.type
-        if ext_types:
-            pld_spec |= Union[*ext_types]
 
     # (manually) generate a msg-spec (how appropes) for all relevant
     # payload-boxing-struct-msg-types, parameterizing the
@@ -630,10 +605,16 @@ def mk_codec(
     enc = msgpack.Encoder(
        enc_hook=enc_hook,
     )
+
+    boxes = {}
+    if ext_types and len(ext_types) > 1:
+        boxes = mk_boxed_ext_structs(ext_types)
+
     codec = MsgCodec(
         _enc=enc,
         _dec=dec,
         _pld_spec=pld_spec,
+        _ext_types_boxes=boxes
     )
     # sanity on expected backend support
     assert codec.lib.__name__ == libname
@@ -809,78 +790,282 @@ def limit_msg_spec(
     assert curr_codec is current_codec()
 
 
-# XXX: msgspec won't allow this with non-struct custom types
-# like `NamespacePath`!@!
-# @cm
-# def extend_msg_spec(
-#     payload_spec: Union[Type[Struct]],
+'''
+Encoder / Decoder generic hook factory
 
-# ) -> MsgCodec:
-#     '''
-#     Extend the current `MsgCodec.pld_spec` (type set) by extending
-#     the payload spec to **include** the types specified by
-#     `payload_spec`.
-
-#     '''
-#     codec: MsgCodec = current_codec()
-#     pld_spec: Union[Type] = codec.pld_spec
-#     extended_spec: Union[Type] = pld_spec|payload_spec
-
-#     with limit_msg_spec(payload_types=extended_spec) as ext_codec:
-#         # import pdbp; pdbp.set_trace()
-#         assert ext_codec.pld_spec == extended_spec
-#         yield ext_codec
-#
-# ^-TODO-^ is it impossible to make something like this orr!?
-
-# TODO: make an auto-custom hook generator from a set of input custom
-# types?
-# -[ ] below is a proto design using a `TypeCodec` idea?
-#
-# type var for the expected interchange-lib's
-# IPC-transport type when not available as a built-in
-# serialization output.
-WireT = TypeVar('WireT')
+'''
 
 
-# TODO: some kinda (decorator) API for built-in subtypes
-# that builds this implicitly by inspecting the `mro()`?
-class TypeCodec(Protocol):
+# builtins we can have in same pld_spec as custom types
+default_builtins = (
+    None,
+    bool,
+    int,
+    float,
+    bytes,
+    list
+)
+
+
+# spec definition type
+TypeSpec = (
+    Type |
+    Union[Type] |
+    list[Type] |
+    tuple[Type] |
+    set[Type]
+)
+
+
+class TypeCodec:
     '''
-    A per-custom-type wire-transport serialization translator
-    description type.
+    This class describes a way of encoding to or decoding from a "wire type",
+    objects that have `encode_fn` and `decode_fn` can be used with
+    `.encode/.decode`.
 
     '''
-    src_type: Type
-    wire_type: WireT
 
-    def encode(obj: Type) -> WireT:
-        ...
+    def __init__(
+        self,
+        wire_type: Type,
+        decode_fn: str,
+        encode_fn: str = 'encode',
+    ):
+        self._encode_fn: str = encode_fn
+        self._decode_fn: str = decode_fn
+        self._wire_type: Type = wire_type
 
-    def decode(
-        obj_type: Type[WireT],
-        obj: WireT,
-    ) -> Type:
-        ...
+    @property
+    def encode_fn(self) -> str:
+        return self._encode_fn
+
+    @property
+    def decode_fn(self) -> str:
+        return self._decode_fn
+
+    @property
+    def wire_type(self) -> str:
+        return self._wire_type
+
+    def is_type_compat(self, obj: any) -> bool:
+        return (
+            hasattr(obj, self._encode_fn)
+            and
+            hasattr(obj, self._decode_fn)
+        )
+
+    def encode(self, obj: any) -> any:
+        return getattr(obj, self._encode_fn)(obj)
+
+    def decode(self, cls: Type, raw: any) -> any:
+        return getattr(cls, self._decode_fn)(raw)
 
 
-class MsgpackTypeCodec(TypeCodec):
-    ...
+'''
+Default codec descriptions for wire types:
+
+    - bytes
+    - str
+    - int
+
+'''
 
 
-def mk_codec_hooks(
-    type_codecs: list[TypeCodec],
+BytesCodec = TypeCodec(
+    decode_fn='from_bytes',
+    wire_type=bytes
+)
 
-) -> tuple[Callable, Callable]:
+
+StrCodec = TypeCodec(
+    decode_fn='from_str',
+    wire_type=str
+)
+
+
+IntCodec = TypeCodec(
+    decode_fn='from_int',
+    wire_type=int
+)
+
+
+default_codecs: dict[Type, TypeCodec] = {
+    bytes: BytesCodec,
+    str: StrCodec,
+    int: IntCodec
+}
+
+
+def mk_spec_set(
+    spec: TypeSpec
+) -> set[Type]:
     '''
-    Deliver a `enc_hook()`/`dec_hook()` pair which handle
-    manual convertion from an input `Type` set such that whenever
-    the `TypeCodec.filter()` predicate matches the
-    `TypeCodec.decode()` is called on the input native object by
-    the `dec_hook()` and whenever the
-    `isiinstance(obj, TypeCodec.type)` matches against an
-    `enc_hook(obj=obj)` the return value is taken from a
-    `TypeCodec.encode(obj)` callback.
+    Given any of the different spec definitions, always return a `set[Type]`
+    with each spec type as an item.
+
+    - When passed list|tuple|set do nothing
+    - When passed a single type we wrap it in tuple
+    - When passed a Union we wrap its inner types in tuple
 
     '''
-    ...
+    if not (
+        isinstance(spec, set)
+        or
+        isinstance(spec, list)
+        or
+        isinstance(spec, tuple)
+    ):
+        spec_info = msgspec.inspect.type_info(spec)
+        match spec_info:
+            case UnionType():
+                return set((
+                    t.cls
+                    for t in spec_info.types
+                ))
+
+            case (
+                SetType() |
+                ListType() |
+                TupleType()
+            ):
+                return set((spec_info.item_type, ))
+
+            case _:
+                return set((spec, ))
+
+    return set(spec)
+
+
+def mk_codec_map_from_spec(
+    spec: TypeSpec,
+    codecs: dict[Type, TypeCodec] = default_codecs
+) -> dict[Type, TypeCodec]:
+    '''
+    Generate a map of spec type -> supported codec
+
+    '''
+
+    spec: set[Type] = mk_spec_set(spec)
+
+    spec_codecs: dict[Type, TypeCodec] = {}
+    for t in spec:
+        for codec in codecs.values():
+            if codec.is_type_compat(t):
+                spec_codecs[t] = codec
+
+    return spec_codecs
+
+
+def mk_enc_hook(
+    spec: TypeSpec,
+    with_builtins: bool = True,
+    builtins: set[Type] = default_builtins,
+    codecs: dict[Type, TypeCodec] = default_codecs
+) -> Callable:
+    '''
+    Given a type specification return a msgspec enc_hook fn
+
+    '''
+    spec_codecs = mk_codec_map_from_spec(spec)
+
+    def enc_hook(obj: any) -> any:
+        t = type(obj)
+        maybe_codec = spec_codecs.get(t, None)
+        if maybe_codec:
+            return maybe_codec.encode(obj)
+
+        # passthrough built ins
+        if builtins and t in builtins:
+            return obj
+
+        raise NotImplementedError(
+            f"Objects of type {type(obj)} are not supported:\n{obj}"
+        )
+
+    return enc_hook
+
+
+def mk_dec_hook(
+    spec: TypeSpec,
+    with_builtins: bool = True,
+    builtins: set[Type] = default_builtins,
+    codecs: dict[Type, TypeCodec] = default_codecs
+) -> Callable:
+    '''
+    Given a type specification return a msgspec dec_hook fn
+
+    '''
+    spec_codecs = mk_codec_map_from_spec(spec)
+
+    def dec_hook(t: Type, obj: any) -> any:
+        maybe_codec = spec_codecs.get(t, None)
+        if maybe_codec:
+            return maybe_codec.decode(t, obj)
+
+        # passthrough builtins
+        if builtins and type in builtins:
+            return obj
+
+        raise NotImplementedError(
+            f"Objects of type {type} are not supported from {obj}"
+        )
+
+    return dec_hook
+
+
+def mk_codec_hooks(*args, **kwargs) -> tuple[Callable, Callable]:
+    '''
+    Given a type specification return a msgspec enc & dec hook fn pair
+
+    '''
+    return (
+        mk_enc_hook(*args, **kwargs),
+
+        mk_dec_hook(*args, **kwargs)
+    )
+
+
+def mk_codec_from_spec(
+    spec: TypeSpec,
+    with_builtins: bool = True,
+    builtins: set[Type] = default_builtins,
+    codecs: dict[Type, TypeCodec] = default_codecs
+) -> MsgCodec:
+    '''
+    Given a type specification return a MsgCodec
+
+    '''
+    spec: set[Type] = mk_spec_set(spec)
+
+    return mk_codec(
+        enc_hook=mk_enc_hook(
+            spec,
+            with_builtins=with_builtins,
+            builtins=builtins,
+            codecs=codecs
+        ),
+        ext_types=spec
+    )
+
+
+def mk_msgpack_codec(
+    spec: TypeSpec,
+    with_builtins: bool = True,
+    builtins: set[Type] = default_builtins,
+    codecs: dict[Type, TypeCodec] = default_codecs
+) -> tuple[msgpack.Encoder, msgpack.Decoder]:
+    '''
+    Get a msgpack Encoder, Decoder pair for a given type spec
+
+    '''
+    spec: set[Type] = mk_spec_set(spec)
+
+    enc_hook, dec_hook = mk_codec_hooks(
+        spec,
+        with_builtins=with_builtins,
+        builtins=builtins,
+        codecs=codecs
+    )
+    encoder = msgpack.Encoder(enc_hook=enc_hook)
+    decoder = msgpack.Decoder(spec, dec_hook=dec_hook)
+    return encoder, decoder