Support nested `wg` maddrs

Teach discovery to preserve WireGuard bearer and identity metadata
around a bindable TCP overlay.

Deats,
- encode `wg(8)` keys as strict 32-byte multibase values
- peel nested stacks with `Multiaddr.decapsulate_code()` and compose
  them with `.encapsulate()` instead of splitting strings
- integrate wrappers with `parse_maddr()`, `mk_maddr()`,
  `wrap_address()` and `parse_endpoints()`
- pin the unreleased py-multiaddr#108 codec in package metadata
- cover exact round trips, nesting, bad grammar and missing codecs

Prompt-IO: ai/prompt-io/opencode/20260818T075031Z_dd02c7c0_prompt_io.md

(this patch was generated in some part by `opencode` using `gpt-5.6-sol` (`openai`))

ai/prompt-io/opencode/20260818T021729Z_d9a6e2e9_prompt_io.md

@@ -0,0 +1,69 @@
+---
+model: gpt-5.6-sol
+service: opencode
+session: intercepted-claude-7b9c97c4-fff7-4ac4-97fb-35720453308e
+timestamp: 2026-08-18T02:17:29Z
+git_ref: d9a6e2e9
+scope: code
+substantive: true
+raw_file: 20260818T021729Z_d9a6e2e9_prompt_io.raw.md
+---
+
+## Prompt
+
+> Intercept Claude session
+> `7b9c97c4-fff7-4ac4-97fb-35720453308e`, pick up where it
+> stopped in its open worktree, finish the tunnelled-address change
+> and commit plan, and prepare any outstanding context for another
+> provider.
+
+The recovered final prompt specifically called out the `uds` versus
+`unix` boundary decision, absent concrete `Address.namespace`
+implementations, the corrected namespace test, and the passing
+focused and wider suites.
+
+During review, the human further required that tunnelled-maddr work
+delegate to `multiaddr`'s encapsulation APIs, challenged the premature
+transport-shaped listener hooks and directed their removal, corrected
+the long-term bearer provisioning model, and confirmed the intended
+split between discovery metadata and bindspace lifecycle code.
+
+## Response summary
+
+Recovered the transcript and matched it to `wkts/addr_unpacking`,
+audited the staged implementation, and completed the interrupted
+verification and commit-plan work. The audit removed premature
+transport-shaped listener hooks, widened the namespace identifier
+type, updated stale import documentation, and removed an
+invalid-escape warning from the maddr diagram. It also preserved the
+layer-C design where tractor provisions the kernel-owned tunnel
+bearer without treating it as a message transport.
+
+## Files changed
+
+- `tractor/discovery/_tunnel.py` - tunnel specs, address wrapper, and
+  peeling helpers.
+- `tractor/discovery/_addr.py` - wrapped-address recognition and
+  namespace typing.
+- `tractor/discovery/__init__.py` - public tunnel API exports.
+- `tests/discovery/test_tunnelled_addr.py` - delegation and boundary
+  regression coverage.
+- `ai/tpt-backends/03_wg_tunnel_bindspace.md` - distinguish
+  tractor-owned bindspace provisioning from kernel socket ownership.
+
+## Human edits
+
+Substantial human-directed editing occurred over several review turns:
+
+- required use of `multiaddr`'s `.encapsulate()`/`.decapsulate()`
+  family rather than a hand-rolled tunnel peeler
+- rejected the premature `start_listener()`/`close_listener()` hooks
+  and directed their removal from this foundational change
+- corrected the documentation so tractor retains ownership of future
+  bindspace provisioning while the kernel owns the bearer socket
+- reviewed and accepted the placement of declarative tunnel metadata
+  under `tractor.discovery`, with lifecycle code kept separate
+
+The final source lines were applied through the coding agents, but
+these design corrections and deletion decisions came from the human
+review and materially shaped the patch.

ai/prompt-io/opencode/20260818T021729Z_d9a6e2e9_prompt_io.raw.md

@@ -0,0 +1,66 @@
+---
+model: gpt-5.6-sol
+service: opencode
+timestamp: 2026-08-18T02:17:29Z
+git_ref: d9a6e2e9
+diff_cmd: git diff HEAD~1..HEAD
+---
+
+# Raw output - tunnelled-address handoff completion
+
+Recovered Claude Code session
+`7b9c97c4-fff7-4ac4-97fb-35720453308e` and continued its
+interrupted `wkts/addr_unpacking` changes.
+
+## Generated code
+
+> `git diff HEAD~1..HEAD -- tractor/discovery/_tunnel.py`
+
+Added frozen `WGTunnelSpec` and `TunnelledAddress` structs. The
+wrapper delegates transport identity, validity, bindspace, and wire
+serialization to its overlay while retaining tunnel metadata locally.
+Added pure helpers to peel nested wrappers and enumerate their tunnel
+specs. The module documents why wrappers must be peeled before
+`Endpoint` selects the overlay transport backend.
+
+> `git diff HEAD~1..HEAD -- tractor/discovery/_addr.py`
+
+Extended `is_wrapped_addr()` to recognize `TunnelledAddress` without
+registering tunnels as message transports, and widened the namespace
+identifier type to cover named network namespaces.
+
+> `git diff HEAD~1..HEAD -- tractor/discovery/__init__.py`
+
+Exported the tunnel address API from `tractor.discovery` and updated
+the eager-import documentation.
+
+> `git diff HEAD~1..HEAD -- tests/discovery/test_tunnelled_addr.py`
+
+Added focused coverage for delegation, serialization, rewrapping,
+namespace fallback, nested peeling order, and frozen structs.
+
+> `git diff HEAD~1..HEAD -- ai/tpt-backends/03_wg_tunnel_bindspace.md`
+
+Clarified that tractor owns the eventual bindspace lifecycle and may
+provision the WireGuard iface, routes, and kernel UDP listener through
+netlink/`pyroute2`. Kernel socket ownership does not make the bearer an
+application `MsgTransport` endpoint.
+
+## Verification
+
+Focused tests:
+
+```text
+9 passed in 0.03s
+```
+
+Discovery and IPC suites:
+
+```text
+67 passed, 2 xpassed
+```
+
+The audit removed premature module-level listener hooks. Runtime
+integration must peel the wrapper explicitly at bind and dial
+boundaries rather than make `._tunnel` impersonate a transport
+backend.

ai/prompt-io/opencode/20260818T075031Z_dd02c7c0_prompt_io.md

@@ -0,0 +1,50 @@
+---
+model: gpt-5.6-sol
+service: opencode
+session: tractor-addr-unpacking-followup
+timestamp: 2026-08-18T07:50:31Z
+git_ref: dd02c7c0
+scope: code
+substantive: true
+raw_file: 20260818T075031Z_dd02c7c0_prompt_io.raw.md
+---
+
+## Prompt
+
+The human requested the complete tunnelled-maddr parsing/composition
+slice as an unattended batch, with every numbered requirement finished
+and atomic commit plans prepared at the end. Existing human decisions
+required native `multiaddr` encapsulation APIs, no hand-written peeler,
+and preservation of tractor's future bindspace lifecycle ownership.
+
+## Response summary
+
+Implemented strict WG key codecs and native single/nested tunnel maddr
+parsing and composition, integrated them into discovery APIs, migrated
+the multihost example off its duplicate parser, corrected package
+dependency metadata, and added focused and end-to-end parser
+regressions. Verified the complete tractor suite and built both package
+artifacts.
+
+## Files changed
+
+- `tractor/discovery/` - WG codecs, parser/composer, wrapper typing,
+  public exports, and discovery dispatch.
+- `tests/discovery/` - key, grammar, nesting, round-trip, and public
+  boundary regressions.
+- `examples/multihost/wg_lan/` - production parser migration and
+  updated usage documentation.
+- `pyproject.toml`, `uv.lock` - reproducible WG codec and multibase
+  dependencies for checkout and package installs.
+- `ai/tpt-backends/03_wg_tunnel_bindspace.md` - current layer-A state
+  and future bindspace ownership.
+
+## Human edits
+
+The human selected the five-step scope and batch execution model,
+required delegation to `multiaddr`'s encapsulation APIs, rejected
+transport-shaped listener placeholders in the prerequisite commit, and
+clarified that tractor will eventually provision the kernel-owned
+bearer through its bindspace layer. The agent implemented and tested
+those decisions; no direct manual source edits were observed during
+this batch.

ai/prompt-io/opencode/20260818T075031Z_dd02c7c0_prompt_io.raw.md

@@ -0,0 +1,61 @@
+---
+model: gpt-5.6-sol
+service: opencode
+timestamp: 2026-08-18T07:50:31Z
+git_ref: dd02c7c0
+diff_cmd: git diff HEAD~1..HEAD
+---
+
+# Raw output - native WireGuard maddr integration
+
+The human requested completion of the five-step tunnelled-maddr slice:
+port the proven WireGuard parser, delegate to `py-multiaddr`'s native
+tunnel APIs, integrate public parse and composition entry points, add
+regressions, and return atomic commit plans after completing the batch.
+
+## Generated code
+
+> `git diff HEAD~1..HEAD -- tractor/discovery/_tunnel.py tractor/discovery/_multiaddr.py tractor/discovery/_addr.py tractor/discovery/__init__.py`
+
+Added strict WireGuard standard-base64/multibase key codecs and native
+WG maddr parsing/composition. Nested stacks peel the last `/wg/`
+repeatedly with `.decapsulate_code()`, isolate segments through
+`.split()`/`.join()`, and compose recursively with `.encapsulate()`.
+Public discovery parsing, wrapping, endpoint-table parsing, and maddr
+composition now preserve `TunnelledAddress` metadata locally.
+
+> `git diff HEAD~1..HEAD -- pyproject.toml uv.lock`
+
+Declared `py-multibase` directly and pinned the unreleased
+py-multiaddr#108 WG codec revision in distribution metadata. Enabled
+Hatch direct-reference metadata so editable, wheel, and sdist builds
+use the same dependency contract.
+
+> `git diff HEAD~1..HEAD -- tests/discovery/test_multiaddr.py tests/discovery/test_tunnelled_addr.py`
+
+Added key-codec, single/nested WG round-trip, malformed key, invalid
+bearer/overlay, missing codec, missing bearer, `wrap_address()`, and
+`parse_endpoints()` coverage while retaining plain TCP/UDS regressions.
+
+> `git diff HEAD~1..HEAD -- examples/multihost/wg_lan ai/tpt-backends/03_wg_tunnel_bindspace.md`
+
+Removed the duplicate example parser, migrated callers to production
+`TunnelledAddress`, retained only explicit `wg(8)` verification, and
+updated dependency and future bindspace ownership documentation.
+
+## Verification
+
+- focused discovery files: `45 passed`
+- discovery and IPC suites: `81 passed, 2 xpassed`
+- full suite: `443 passed, 9 skipped, 7 xfailed, 4 xpassed`
+- collection: `462 tests`
+- Ruff: clean
+- sdist and wheel builds: successful
+
+## Review corrections
+
+A review caught that `[tool.uv.sources]` alone would not constrain
+built-package consumers to a WG-capable py-multiaddr revision. The
+dependency was moved into PEP 621 metadata and the parser now converts
+missing-codec failures into an actionable tractor error without
+misclassifying Unix paths containing a `wg` directory.

ai/tpt-backends/03_wg_tunnel_bindspace.md

@@ -123,7 +123,7 @@ that the key decodes to exactly 32 bytes, so a truncated key is a
 ```
 /ip4/192.168.1.50/udp/51820/wg/u<A_pub>/ip4/10.0.11.1/tcp/1616
 \_______ bearer __________/\__ key __/\______ overlay ______/
- underlay, wg `ListenPort`             the ONLY part we bind
+ underlay, wg `ListenPort`             the `MsgTransport` bind
 ```
 
 The `/wg/` segment is **infix, not suffix** — the segments
@@ -150,11 +150,11 @@ Observed protocol-name lists, for writing the `match`:
 - so the three parts have **three different owners**, and only the
   third is an `Endpoint`:
 
-  | part | bound by | in the runtime? |
+  | part | socket owner / provisioner | runtime role |
   | --- | --- | --- |
-  | bearer | kernel, via `wg-quick`/`pyroute2` | no |
-  | `/wg/u<key>` | nothing — it's an identity | no, verified out-of-band |
-  | overlay | `tractor`'s `IPCServer` | **yes**, as `.overlay` |
+  | bearer | kernel-owned; externally provisioned in layer A, tractor bindspace-provisioned in layer C | control-plane metadata, never an `Endpoint` |
+  | `/wg/u<key>` | nothing — it's an identity | parsed and explicitly verified |
+  | overlay | `tractor`'s `IPCServer` | application `MsgTransport`, as `.overlay` |
 
   This owner-split is the real axis of the design, *not* whether
   the maddr stack is "composed" (it is).
@@ -319,6 +319,14 @@ data-structure which can easily be passed to nested `@acm`s
 which consecutively setup nested net bindspaces for binding the
 endpoint addrs"*.
 
+Layer C is where tractor takes ownership of bindspace orchestration.
+For a fully bootstrapped deployment it may create the netns and wg
+iface, configure peers/routes, and ask the kernel to establish the
+bearer's UDP `ListenPort` through netlink/`pyroute2`. "Kernel-owned"
+describes the data-plane socket, not who provisions it: tractor owns
+the lifecycle while `Endpoint`/`MsgTransport` remain responsible only
+for the overlay application socket.
+
 ### 5.1 the composition
 
 ```python

pyproject.toml

@@ -48,7 +48,10 @@ dependencies = [
   # typed IPC msging
   "msgspec>=0.20.0",
   "bidict>=0.23.1",
-  "multiaddr>=0.2.0",
+  # unreleased `/wg/` codec from py-multiaddr#108
+  "multiaddr @ git+https://github.com/multiformats/py-multiaddr.git@f86519daaa21699023d0037c58cdff600313dd09",
+  # encode/decode `wg` pubkeys carried by multiaddrs
+  "py-multibase>=2.0.0,<3",
   "platformdirs>=4.4.0",
   # per-actor `argv[0]` proc-title for OS-level diag tools
   # (`ps`, `top`, `psutil`-backed tooling like `acli.pytree`).
@@ -166,17 +169,6 @@ sync_pause = {requires-python = ">=3.13, <3.14"}
 # linux kernel networking
 # 'pyroute2
 
-# XXX TEMP, the `/wg/u<key>` maddr proto is MERGED upstream (in
-# py-multiaddr#108, 2026-07-28) but is in NO release yet; the
-# latest `0.2.0` (2026-03-17) predates the merge by ~4 months.
-# Pinned by `rev` (not `branch`) so CI stays reproducible.
-#
-# Drop this pin (and bump the `multiaddr` dep floor above) the
-# moment a release carries the `wg` codec; the only consumer is
-# `examples/multihost/wg_lan/`.
-# |_https://github.com/multiformats/py-multiaddr/pull/108
-multiaddr = { git = 'https://github.com/multiformats/py-multiaddr.git', rev = 'f86519daaa21699023d0037c58cdff600313dd09' }
-
 # ------ tool.uv.sources ------
 
 [tool.uv]
@@ -191,6 +183,9 @@ python-preference = 'system'
 
 # ------ tool.uv ------
 
+[tool.hatch.metadata]
+allow-direct-references = true
+
 [tool.hatch.build.targets.sdist]
 include = ["tractor"]
 

tests/discovery/test_multiaddr.py

@@ -10,6 +10,14 @@ from types import SimpleNamespace
 import pytest
 from multiaddr import Multiaddr
 
+from tractor.discovery import (
+    TunnelledAddress,
+    WGTunnelSpec,
+    mb_pubkey,
+    mk_wg_maddr,
+    parse_wg_maddr,
+    tunnels_of,
+)
 from tractor.ipc._tcp import TCPAddress
 from tractor.ipc._uds import UDSAddress
 from tractor.discovery._multiaddr import (
@@ -22,6 +30,19 @@ from tractor.discovery._multiaddr import (
 from tractor.discovery._addr import wrap_address
 
 
+_WG_PUBKEY: str = (
+    'g3x7z0AdV1rM6UQU22CC7IL3/ivn4DzrE7ikDhCZ/Dc='
+)
+_WG_PUBKEY_2: str = (
+    'AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8='
+)
+_WG_MADDR: str = (
+    f'/ip4/192.168.1.50/udp/51820'
+    f'/wg/{mb_pubkey(_WG_PUBKEY)}'
+    f'/ip4/10.0.11.1/tcp/1616'
+)
+
+
 def test_tpt_proto_to_maddr_mapping():
     '''
     `_tpt_proto_to_maddr` maps all supported `proto_key`
@@ -210,6 +231,181 @@ def test_parse_maddr_unsupported():
         parse_maddr('/ip4/127.0.0.1/udp/1234')
 
 
+def test_parse_wg_maddr():
+    '''
+    `parse_maddr()` previously rejected the canonical infix `/wg/`
+    grammar even though `py-multiaddr` parsed it. Feed a bearer,
+    identity, and TCP overlay through both the WG-specific and public
+    parsers, then prove they produce the same local-only tunnel
+    annotation without changing the bindable overlay.
+
+    '''
+    parsed = parse_wg_maddr(_WG_MADDR)
+
+    assert parse_maddr(_WG_MADDR) == parsed
+    assert isinstance(parsed, TunnelledAddress)
+    assert parsed.tunnel == WGTunnelSpec(
+        peer_pubkey=_WG_PUBKEY,
+        bearer=('192.168.1.50', 51820),
+    )
+    assert isinstance(parsed.overlay, TCPAddress)
+    assert parsed.overlay.unwrap() == ('10.0.11.1', 1616)
+
+
+def test_mk_wg_maddr_roundtrip():
+    '''
+    `mk_maddr()` previously saw only the wrapper's delegated TCP
+    proto-key and silently dropped all tunnel metadata. Parse the
+    canonical maddr, compose it through both public entry points, and
+    prove bearer, key, and overlay survive byte-for-byte.
+
+    '''
+    parsed = parse_wg_maddr(_WG_MADDR)
+
+    assert str(mk_wg_maddr(parsed)) == _WG_MADDR
+    assert str(mk_maddr(parsed)) == _WG_MADDR
+
+
+def test_nested_wg_maddr_roundtrip():
+    '''
+    A single first-match lookup confuses nested WG keys and bearers.
+    Arrange an IPv4 outer bearer around an IPv6 inner bearer, parse
+    from the last `/wg/` outward, and assert tunnel ordering plus an
+    exact re-composition of the original stack.
+
+    '''
+    nested_maddr: str = (
+        f'/ip4/192.168.1.50/udp/51820'
+        f'/wg/{mb_pubkey(_WG_PUBKEY)}'
+        f'/ip6/2001:db8::2/udp/51821'
+        f'/wg/{mb_pubkey(_WG_PUBKEY_2)}'
+        f'/ip4/10.0.11.1/tcp/1616'
+    )
+
+    parsed = parse_maddr(nested_maddr)
+    specs = tunnels_of(parsed)
+
+    assert len(specs) == 2
+    assert specs[0].peer_pubkey == _WG_PUBKEY
+    assert specs[0].bearer == ('192.168.1.50', 51820)
+    assert specs[1].peer_pubkey == _WG_PUBKEY_2
+    assert specs[1].bearer == ('2001:db8::2', 51821)
+    assert str(mk_maddr(parsed)) == nested_maddr
+
+
+@pytest.mark.parametrize(
+    'maddr, match',
+    [
+        pytest.param(
+            (
+                f'/ip4/192.168.1.50/tcp/51820'
+                f'/wg/{mb_pubkey(_WG_PUBKEY)}'
+                f'/ip4/10.0.11.1/tcp/1616'
+            ),
+            'Bad `wg` bearer',
+            id='non-udp-bearer',
+        ),
+        pytest.param(
+            (
+                f'/ip4/192.168.1.50/udp/51820'
+                f'/wg/{mb_pubkey(_WG_PUBKEY)}'
+            ),
+            'no overlay endpoint',
+            id='missing-overlay',
+        ),
+        pytest.param(
+            (
+                f'/ip4/192.168.1.50/udp/51820'
+                f'/wg/{mb_pubkey(_WG_PUBKEY)}'
+                f'/ip4/10.0.11.1/udp/1616'
+            ),
+            'Unsupported `wg` overlay',
+            id='non-tcp-overlay',
+        ),
+    ],
+)
+def test_parse_wg_maddr_rejects_bad_grammar(
+    maddr: str,
+    match: str,
+):
+    '''
+    Accepting an invalid bearer or overlay assigns an endpoint to the
+    wrong runtime owner. Exercise parseable but unsupported protocol
+    combinations and prove each fails before constructing a wrapper,
+    with an error identifying the violated WG grammar boundary.
+
+    '''
+    with pytest.raises(ValueError, match=match):
+        parse_maddr(maddr)
+
+
+def test_parse_wg_maddr_rejects_malformed_key():
+    '''
+    A truncated multibase key used to be vulnerable to silent
+    identity corruption in hand-written parsers. Give the upstream
+    `/wg/` codec a short key and prove `Multiaddr()` rejects it
+    before tractor's wrapper parser runs.
+
+    '''
+    maddr: str = (
+        '/ip4/192.168.1.50/udp/51820'
+        '/wg/udG9vIHNob3J0'
+        '/ip4/10.0.11.1/tcp/1616'
+    )
+    with pytest.raises(ValueError):
+        parse_maddr(maddr)
+
+
+def test_parse_wg_maddr_reports_missing_codec(
+    monkeypatch,
+):
+    '''
+    Released `multiaddr==0.2.0` does not know `/wg/` and emits an
+    opaque unknown-protocol parse error. Simulate that registry and
+    prove an actual WG stack reports the dependency action while a
+    Unix path containing a `wg` directory remains ordinary UDS data.
+
+    '''
+    from multiaddr.exceptions import ProtocolNotFoundError
+    from tractor.discovery import _tunnel
+
+    def no_wg_proto(name: str):
+        raise ProtocolNotFoundError(name)
+
+    monkeypatch.setattr(
+        _tunnel,
+        'protocol_with_name',
+        no_wg_proto,
+    )
+    uds = parse_maddr('/unix/tmp/wg/service.sock')
+    assert isinstance(uds, UDSAddress)
+
+    with pytest.raises(
+        RuntimeError,
+        match='py-multiaddr#108',
+    ):
+        parse_maddr(_WG_MADDR)
+
+
+def test_mk_wg_maddr_requires_bearer():
+    '''
+    A key-only tunnel spec relies on local configuration and cannot
+    be reconstructed as the canonical bearer-first maddr. Build that
+    incomplete annotation and prove composition raises instead of
+    emitting a misleading overlay-only address.
+
+    '''
+    addr = TunnelledAddress(
+        overlay=TCPAddress('10.0.11.1', 1616),
+        tunnel=WGTunnelSpec(peer_pubkey=_WG_PUBKEY),
+    )
+    with pytest.raises(
+        ValueError,
+        match='without a bearer',
+    ):
+        mk_maddr(addr)
+
+
 @pytest.mark.parametrize(
     'addr',
     [
@@ -252,6 +448,21 @@ def test_wrap_address_maddr_str():
     assert result.unwrap() == ('127.0.0.1', 9999)
 
 
+def test_wrap_address_wg_maddr_str():
+    '''
+    `wrap_address()` delegates slash-prefixed strings to
+    `parse_maddr()`. Pass a canonical WG maddr through that public
+    boundary and prove it preserves the tunnel annotation rather than
+    rejecting the protocol stack or returning only its TCP overlay.
+
+    '''
+    result = wrap_address(_WG_MADDR)
+
+    assert isinstance(result, TunnelledAddress)
+    assert result.tunnel.peer_pubkey == _WG_PUBKEY
+    assert result.overlay.unwrap() == ('10.0.11.1', 1616)
+
+
 # ------ parse_endpoints() tests ------
 
 def test_parse_endpoints_tcp_only():
@@ -302,6 +513,30 @@ def test_parse_endpoints_mixed_tpts():
     assert str(filedir) == '/tmp/tractor'
 
 
+def test_parse_endpoints_wg_maddr():
+    '''
+    Service endpoint tables previously rejected WG protocol stacks.
+    Put a tunnelled maddr beside a plain TCP address and prove
+    `parse_endpoints()` retains input order while delivering the
+    wrapper needed by the future bindspace lifecycle.
+
+    '''
+    table = {
+        'registry': [
+            _WG_MADDR,
+            '/ip4/127.0.0.1/tcp/1616',
+        ],
+    }
+    addrs = parse_endpoints(table)['registry']
+
+    assert isinstance(addrs[0], TunnelledAddress)
+    assert addrs[0].tunnel.bearer == (
+        '192.168.1.50',
+        51820,
+    )
+    assert isinstance(addrs[1], TCPAddress)
+
+
 def test_parse_endpoints_unwrapped_tuples():
     '''
     `parse_endpoints()` accept raw `(host, port)` tuples

tests/discovery/test_tunnelled_addr.py

@@ -0,0 +1,234 @@
+'''
+`TunnelledAddress` delegation + peeling semantics.
+
+A tunnel annotates an existing L4 addr rather than being its own
+transport, so the contract under test is mostly *delegation*: the
+runtime must not be able to tell a tunnelled addr from its
+overlay, and **nothing** about the tunnel may cross the wire.
+
+See `ai/tpt-backends/03_wg_tunnel_bindspace.md` §3.1/§3.4.
+
+'''
+from __future__ import annotations
+
+import msgspec
+import pytest
+
+from tractor.discovery import (
+    TunnelledAddress,
+    WGTunnelSpec,
+    mb_pubkey,
+    strip_tunnels,
+    tunnels_of,
+    wg8_pubkey,
+)
+from tractor.discovery._addr import (
+    is_wrapped_addr,
+    wrap_address,
+)
+from tractor.ipc._tcp import TCPAddress
+
+
+# a valid-looking std-base64 `wg(8)` pubkey (32B -> 44 chars)
+_PUBKEY: str = 'g3x7z0AdV1rM6UQU22CC7IL3/ivn4DzrE7ikDhCZ/Dc='
+
+
+@pytest.fixture
+def overlay() -> TCPAddress:
+    return TCPAddress('10.0.11.1', 1616)
+
+
+@pytest.fixture
+def spec() -> WGTunnelSpec:
+    return WGTunnelSpec(
+        peer_pubkey=_PUBKEY,
+        bearer=('192.168.1.50', 51820),
+    )
+
+
+@pytest.fixture
+def tunnelled(
+    overlay: TCPAddress,
+    spec: WGTunnelSpec,
+) -> TunnelledAddress:
+    return TunnelledAddress(overlay=overlay, tunnel=spec)
+
+
+def test_wg_pubkey_codec_roundtrip():
+    '''
+    Standard `wg(8)` base64 keys can contain `/`, which cannot be
+    embedded unchanged in a slash-delimited maddr. Prove the helper
+    emits `u`-prefixed multibase base64url without `/` and decodes
+    it back to the exact original 32-byte key.
+
+    '''
+    mb_key: str = mb_pubkey(_PUBKEY)
+
+    assert mb_key.startswith('u')
+    assert '/' not in mb_key
+    assert wg8_pubkey(mb_key) == _PUBKEY
+
+
+@pytest.mark.parametrize(
+    'key, converter',
+    [
+        pytest.param(
+            'dG9vIHNob3J0',
+            mb_pubkey,
+            id='wg8-base64',
+        ),
+        pytest.param(
+            'udG9vIHNob3J0',
+            wg8_pubkey,
+            id='multibase',
+        ),
+    ],
+)
+def test_wg_pubkey_codec_rejects_wrong_size(
+    key: str,
+    converter,
+):
+    '''
+    WireGuard silently-corrupt key handling would let an invalid
+    identity reach peer verification. Exercise both input encodings
+    with a short payload and prove conversion rejects it before a
+    tunnel spec or maddr can be constructed.
+
+    '''
+    with pytest.raises(
+        ValueError,
+        match='must decode to 32 bytes',
+    ):
+        converter(key)
+
+
+def test_proto_key_delegates(
+    tunnelled: TunnelledAddress,
+    overlay: TCPAddress,
+):
+    '''
+    A tunnel has no transport of its own, so every table lookup
+    must see the *overlay's* proto-key.
+
+    '''
+    assert tunnelled.proto_key == overlay.proto_key == 'tcp'
+
+
+def test_unwrap_is_identical_to_overlay(
+    tunnelled: TunnelledAddress,
+    overlay: TCPAddress,
+):
+    '''
+    The whole point: nothing new crosses the wire, so a peer
+    never has to understand tunnels.
+
+    '''
+    assert tunnelled.unwrap() == overlay.unwrap()
+
+    # and it must survive msgpack as-is
+    enc: bytes = msgspec.msgpack.encode(tunnelled.unwrap())
+    assert msgspec.msgpack.decode(enc) == list(overlay.unwrap())
+
+
+def test_unwrap_roundtrips_back_to_plain_overlay(
+    tunnelled: TunnelledAddress,
+    overlay: TCPAddress,
+):
+    '''
+    `wrap_address()` on a tunnelled addr's unwrapped form yields
+    the *plain* overlay type — the tunnel is simply absent, which
+    is correct: it was never on the wire.
+
+    '''
+    rewrapped = wrap_address(tunnelled.unwrap())
+    assert type(rewrapped) is TCPAddress
+    assert rewrapped == overlay
+    assert not isinstance(rewrapped, TunnelledAddress)
+
+
+def test_bindspace_and_validity_delegate(
+    tunnelled: TunnelledAddress,
+    overlay: TCPAddress,
+):
+    assert tunnelled.bindspace == overlay.bindspace
+    assert tunnelled.is_valid == overlay.is_valid
+
+
+def test_is_wrapped_addr_accepts_tunnelled(
+    tunnelled: TunnelledAddress,
+    overlay: TCPAddress,
+):
+    '''
+    `TunnelledAddress` is deliberately absent from
+    `_address_types`, so `is_wrapped_addr()` needs its own
+    clause.
+
+    '''
+    assert is_wrapped_addr(overlay)
+    assert is_wrapped_addr(tunnelled)
+    # the unwrapped form is NOT a wrapped addr
+    assert not is_wrapped_addr(tunnelled.unwrap())
+
+
+def test_namespace_comes_from_the_tunnel(
+    overlay: TCPAddress,
+):
+    '''
+    First real consumer of `Address.namespace`, spec'd in the
+    protocol since day one and implemented by no backend.
+
+    '''
+    # XXX, "no backend implements it" is literal — the member
+    # isn't even declared, so this is `AttributeError` not `None`.
+    # This assert is the guard: when a backend finally declares
+    # `.namespace`, it fails and the `getattr()` fallback in
+    # `TunnelledAddress.namespace` can go.
+    assert not hasattr(overlay, 'namespace')
+
+    no_ns = TunnelledAddress(
+        overlay=overlay,
+        tunnel=WGTunnelSpec(peer_pubkey=_PUBKEY),
+    )
+    assert no_ns.namespace is None
+
+    in_ns = TunnelledAddress(
+        overlay=overlay,
+        tunnel=WGTunnelSpec(peer_pubkey=_PUBKEY, netns='wg-test'),
+    )
+    assert in_ns.namespace == ('netns', 'wg-test')
+
+
+def test_strip_tunnels(
+    tunnelled: TunnelledAddress,
+    overlay: TCPAddress,
+    spec: WGTunnelSpec,
+):
+    # idempotent on a plain addr
+    assert strip_tunnels(overlay) is overlay
+    # peels one
+    assert strip_tunnels(tunnelled) is overlay
+    # and collapses a nested stack in one call
+    nested = TunnelledAddress(overlay=tunnelled, tunnel=spec)
+    assert strip_tunnels(nested) is overlay
+
+
+def test_tunnels_of_is_outermost_first(
+    tunnelled: TunnelledAddress,
+    overlay: TCPAddress,
+):
+    assert tunnels_of(overlay) == ()
+    assert tunnels_of(tunnelled) == (tunnelled.tunnel,)
+
+    inner_spec = WGTunnelSpec(peer_pubkey=_PUBKEY, iface='wg1')
+    nested = TunnelledAddress(
+        overlay=tunnelled,
+        tunnel=inner_spec,
+    )
+    assert tunnels_of(nested) == (inner_spec, tunnelled.tunnel)
+
+
+def test_frozen(
+    tunnelled: TunnelledAddress,
+):
+    with pytest.raises(AttributeError):
+        tunnelled.overlay = TCPAddress('127.0.0.1', 1)

tractor/discovery/__init__.py

@@ -18,11 +18,10 @@
 Discovery (protocols) API for automatic addressing
 and location management of (service) actors.
 
-NOTE: this ``__init__`` only eagerly imports the
-``._multiaddr`` submodule (for public re-exports).
-Heavier submodules like ``._addr`` and ``._api``
-are NOT imported here to avoid circular imports;
-use direct module paths for those.
+NOTE: this ``__init__`` only eagerly imports the lightweight
+``._multiaddr`` and ``._tunnel`` submodules for public re-exports.
+Heavier submodules like ``._addr`` and ``._api`` are NOT imported
+here to avoid circular imports; use direct module paths for those.
 
 '''
 from ._multiaddr import (
@@ -30,3 +29,14 @@ from ._multiaddr import (
     parse_maddr as parse_maddr,
     mk_maddr as mk_maddr,
 )
+from ._tunnel import (
+    TunnelledAddress as TunnelledAddress,
+    TunnelSpec as TunnelSpec,
+    WGTunnelSpec as WGTunnelSpec,
+    mb_pubkey as mb_pubkey,
+    mk_wg_maddr as mk_wg_maddr,
+    parse_wg_maddr as parse_wg_maddr,
+    strip_tunnels as strip_tunnels,
+    tunnels_of as tunnels_of,
+    wg8_pubkey as wg8_pubkey,
+)

tractor/discovery/_addr.py

@@ -35,6 +35,7 @@ from ..ipc._tcp import TCPAddress
 from ..ipc._uds import UDSAddress
 
 if TYPE_CHECKING:
+    from ._tunnel import TunnelledAddress
     from ..runtime._runtime import Actor
 
 log = get_logger()
@@ -93,7 +94,7 @@ class Address(Protocol):
 
     # TODO, maybe `.netns` is a better name?
     @property
-    def namespace(self) -> tuple[str, int]|None:
+    def namespace(self) -> tuple[str, str|int]|None:
         '''
         The if-available, OS-specific "network namespace" key.
 
@@ -192,7 +193,16 @@ def get_address_cls(name: str) -> Type[Address]:
 
 
 def is_wrapped_addr(addr: any) -> bool:
-    return type(addr) in _address_types.values()
+    # XXX NOTE, a `TunnelledAddress` is genuinely "wrapped" but is
+    # deliberately NOT in `_address_types`: it has no
+    # `MsgTransport` of its own (a tunnel is transparent to
+    # `socket(2)`), so it gets no proto-key entry. See `._tunnel`.
+    from ._tunnel import TunnelledAddress
+    return (
+        type(addr) in _address_types.values()
+        or
+        isinstance(addr, TunnelledAddress)
+    )
 
 
 def mk_uuid() -> str:
@@ -206,8 +216,8 @@ def mk_uuid() -> str:
 
 
 def wrap_address(
-    addr: UnwrappedAddress|str,
-) -> Address:
+    addr: UnwrappedAddress|str|Address|TunnelledAddress,
+) -> Address|TunnelledAddress:
     '''
     Wrap an `UnwrappedAddress` as an `Address`-type based
     on matching builtin python data-structures which we adhoc

tractor/discovery/_multiaddr.py

@@ -32,6 +32,7 @@ from multiaddr import Multiaddr
 
 if TYPE_CHECKING:
     from tractor.discovery._addr import Address
+    from tractor.discovery._tunnel import TunnelledAddress
 
 # map from tractor-internal `proto_key` identifiers
 # to the standard multiaddr protocol name strings.
@@ -48,7 +49,7 @@ _maddr_to_tpt_proto: dict[str, str] = {
 
 
 def mk_maddr(
-    addr: 'Address',
+    addr: 'Address|TunnelledAddress',
 ) -> Multiaddr:
     '''
     Construct a `Multiaddr` from a tractor `Address` instance,
@@ -56,6 +57,13 @@ def mk_maddr(
     multiaddr-spec-compliant protocol path.
 
     '''
+    from ._tunnel import (
+        TunnelledAddress,
+        mk_wg_maddr,
+    )
+    if isinstance(addr, TunnelledAddress):
+        return mk_wg_maddr(addr)
+
     proto_key: str = addr.proto_key
     maddr_proto: str|None = _tpt_proto_to_maddr.get(proto_key)
     if maddr_proto is None:
@@ -90,7 +98,7 @@ def mk_maddr(
 
 def parse_maddr(
     maddr_str: str,
-) -> 'Address':
+) -> 'Address|TunnelledAddress':
     '''
     Parse a multiaddr string into a tractor `Address`.
 
@@ -101,7 +109,16 @@ def parse_maddr(
     from tractor.ipc._tcp import TCPAddress
     from tractor.ipc._uds import UDSAddress
 
+    try:
         maddr = Multiaddr(maddr_str)
+    except ValueError:
+        # Diagnose an unavailable WG codec after upstream parsing
+        # fails. Pre-checking the raw string would misclassify valid
+        # values such as `/unix/tmp/wg/service.sock`.
+        if '/wg/' in maddr_str:
+            from ._tunnel import _wg_proto_code
+            _wg_proto_code()
+        raise
     proto_names: list[str] = [
         p.name for p in maddr.protocols()
     ]
@@ -124,6 +141,10 @@ def parse_maddr(
                 filename=sockpath.name,
             )
 
+        case _ if 'wg' in proto_names:
+            from ._tunnel import parse_wg_maddr
+            return parse_wg_maddr(maddr)
+
         case _:
             raise ValueError(
                 f'Unsupported multiaddr protocol combo: '
@@ -142,11 +163,11 @@ EndpointsTable = dict[
     list[str|tuple],        # maddr strs or UnwrappedAddress
 ]
 
-# output table: actor/service name -> list of wrapped
-# `Address` instances ready for transport binding.
+# output table: actor/service name -> list of wrapped address
+# declarations ready for bindspace handling.
 ParsedEndpoints = dict[
     str,                    # actor/service name
-    list['Address'],
+    list['Address|TunnelledAddress'],
 ]
 
 
@@ -155,7 +176,7 @@ def parse_endpoints(
 ) -> ParsedEndpoints:
     '''
     Parse a service-endpoint config table into wrapped
-    `Address` instances suitable for transport binding.
+    address declarations suitable for bindspace handling.
 
     Each key is an actor/service name and each value is
     a list of addresses in any format accepted by
@@ -167,6 +188,8 @@ def parse_endpoints(
       ``/uds/`` proto_key)
     - raw unwrapped tuples: ``('127.0.0.1', 1616)``
     - pre-wrapped `Address` objects (passed through)
+    - `wg` maddrs, returned as `TunnelledAddress` wrappers which
+      must be peeled at the eventual bind/dial boundary
 
     Returns a new `dict` with the same keys, where each
     value list contains the corresponding `Address`

tractor/discovery/_tunnel.py

@@ -0,0 +1,491 @@
+# tractor: structured concurrent "actors".
+# Copyright 2018-eternity Tyler Goodlet.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+r'''
+Tunnelled addresses: an `Address` that rides *inside* a tunnel.
+
+A tunnel (`wg`, and later plain ip-in-udp, `veth`-in-netns, ..) is
+**not** a `MsgTransport`. Its data plane is transparent to the
+application's `socket(2)`, so it never gets its own entry in
+`._addr._address_types` nor a `MsgpackTransport` impl. Instead it
+*annotates* an existing L4 addr, and this module carries that
+annotation beside it.
+
+That does not mean tractor can never provision the tunnel. Layer A
+assumes an externally configured iface; a later bindspace lifecycle
+may create its iface, netns, routes, and kernel-owned UDP listener
+through netlink/`pyroute2`. The distinction is that this
+control-plane work does not turn the bearer into an application
+`Endpoint`.
+
+Naming follows `py-multiaddr`'s encapsulation model, where earlier
+maddr segs wrap later ones (`.encapsulate()` appends):
+
+    /ip4/192.168.1.50/udp/51820/wg/u<key>/ip4/10.0.11.1/tcp/1616
+    \_______ bearer __________/\__ key __/\______ overlay ______/
+
+- **bearer**: the underlay ep the tunnel iface listens on
+  (`wg(8)`'s `ListenPort`). The kernel owns this data-plane socket;
+  tractor may later provision it through a bindspace lifecycle but
+  never treats it as a `MsgTransport` listener.
+- **overlay**: the ep `tractor` actually binds/dials, i.e. the
+  application IPC endpoint handled by `Endpoint`/`MsgTransport`.
+
+We avoid `inner`/`outer` deliberately: in a *call* stack "inner"
+reads as higher-up and later-called, whereas here the
+encapsulated addr is bound *first* and sits deeper in the maddr.
+
+XXX XXX READ THIS BEFORE USING XXX XXX
+--------------------------------------
+A `TunnelledAddress` **must be unwrapped to `.overlay` before it
+reaches `Endpoint`**. `Endpoint.start_listener()` resolves its
+listener fns by `inspect.getmodule(self.addr)`, so a wrapper
+would resolve to *this* module rather than the transport's and
+silently fail to find `start_listener()`.
+
+If a wrapper reaches `Endpoint`, its backend lookup resolves this
+module instead of the overlay transport module:
+
+    tpt_mod = inspect.getmodule(self.addr)
+    await tpt_mod.start_listener(addr=self.addr)
+
+This module intentionally does not impersonate that transport API.
+Unwrap at the parse or bindspace boundary; see `.overlay` and
+`strip_tunnels()`.
+
+'''
+from __future__ import annotations
+import base64
+import ipaddress
+from typing import (
+    ClassVar,
+    TYPE_CHECKING,
+)
+
+import msgspec
+import multibase
+from multiaddr import Multiaddr
+from multiaddr.exceptions import ProtocolNotFoundError
+from multiaddr.protocols import protocol_with_name
+
+if TYPE_CHECKING:
+    from ._addr import (
+        Address,
+        UnwrappedAddress,
+    )
+
+
+class WGTunnelSpec(
+    msgspec.Struct,
+    frozen=True,
+):
+    '''
+    The `wg`-specific half of a tunnel annotation.
+
+    Everything here is an *interface-layer* concern owned by
+    `wg(8)`/the kernel. A later tractor bindspace lifecycle may
+    provision it through netlink, but it is never an application
+    `MsgTransport` endpoint.
+
+    '''
+    # tunnel peer pubkey in the std-base64 `wg(8)` form, i.e.
+    # directly comparable to `wg show <if> peers` output
+    peer_pubkey: str
+
+    # the underlay `(ip, udp-port)` the wg iface listens on, i.e.
+    # wg's `ListenPort`. The kernel owns the socket even when a
+    # tractor bindspace lifecycle provisions it. `None` when the
+    # maddr declared only a key (identity) and the bearer is
+    # implied by local cfg.
+    bearer: tuple[str, int]|None = None
+
+    iface: str = 'wg0'
+    netns: str|None = None
+
+    # layer-C-only fields, unset in layer A
+    maybe_allowed_ips: tuple[str, ...] = ()
+
+    # the `multiaddr` proto name for this tunnel kind
+    tunnel_key: ClassVar[str] = 'wg'
+
+
+# the tunnel-spec union; grows as new tunnel kinds land
+# (plain ip-in-udp, `veth`-in-netns, ..)
+TunnelSpec = WGTunnelSpec
+
+
+def mb_pubkey(
+    wg8_key: str,
+) -> str:
+    '''
+    Encode a `wg(8)` public key as multibase base64url.
+
+    WireGuard public keys are exactly 32 bytes. Enforce that here
+    before handing the `u`-prefixed result to `py-multiaddr`'s
+    `/wg/` codec.
+
+    '''
+    raw: bytes = base64.b64decode(
+        wg8_key,
+        validate=True,
+    )
+    if (nbytes := len(raw)) != 32:
+        raise ValueError(
+            f'A `wg` public key must decode to 32 bytes, '
+            f'not {nbytes}!'
+        )
+
+    return multibase.encode(
+        'base64url',
+        raw,
+    ).decode('ascii')
+
+
+def wg8_pubkey(
+    mb_key: str,
+) -> str:
+    '''
+    Decode a multibase public key to `wg(8)` standard base64.
+
+    '''
+    raw: bytes = multibase.decode(mb_key)
+    if (nbytes := len(raw)) != 32:
+        raise ValueError(
+            f'A `wg` public key must decode to 32 bytes, '
+            f'not {nbytes}!'
+        )
+
+    return base64.b64encode(raw).decode('ascii')
+
+
+def _wg_proto_code() -> int:
+    '''
+    Deliver the installed `py-multiaddr` `/wg/` protocol code.
+
+    `wg` support is merged upstream but not yet in a release, so
+    fail clearly when tractor was installed without the pinned rev.
+
+    '''
+    try:
+        return protocol_with_name('wg').code
+    except ProtocolNotFoundError as exc:
+        raise RuntimeError(
+            'Installed `py-multiaddr` has no `/wg/` protocol!\n'
+            'Install py-multiaddr#108 or use tractor\'s pinned '
+            'dependency revision.\n'
+        ) from exc
+
+
+class TunnelledAddress(
+    msgspec.Struct,
+    frozen=True,
+):
+    '''
+    An `Address` annotated with the tunnel it must be reached
+    *through*.
+
+    Address-level properties delegate to `.overlay`, so proto-key
+    guards and `.unwrap()` retain their existing meaning and
+    **nothing new crosses the wire**. Transport boundaries which
+    dispatch on exact type or declaring module must first call
+    `strip_tunnels()`.
+
+    '''
+    overlay: Address|TunnelledAddress
+    tunnel: TunnelSpec
+
+    # ---- delegated, so the runtime can't tell the difference ----
+
+    @property
+    def proto_key(self) -> str:
+        '''
+        The *overlay's* proto-key — a tunnel has no transport of
+        its own.
+
+        NOTE, this is a property whereas `Address.proto_key` is
+        spec'd as a `ClassVar`. That's deliberate: the value is
+        only knowable per-instance here, and this type is never
+        registered in `_address_types`, so no class-level access
+        of it should ever occur.
+
+        '''
+        return self.overlay.proto_key
+
+    @property
+    def is_valid(self) -> bool:
+        return self.overlay.is_valid
+
+    @property
+    def bindspace(self) -> str:
+        return self.overlay.bindspace
+
+    def unwrap(self) -> UnwrappedAddress:
+        '''
+        Delegate to `.overlay`, so the tunnel annotation is
+        **not** serialized and no peer needs to understand it.
+
+        '''
+        return self.overlay.unwrap()
+
+    # ---- the tunnel's own contribution ----
+
+    @property
+    def namespace(self) -> tuple[str, str|int]|None:
+        '''
+        The tunnel's netns, when it declares one.
+
+        This is the first real consumer of `Address.namespace`,
+        spec'd in the `Address` protocol since day one and
+        implemented by no backend.
+
+        XXX NOTE, "implemented by no backend" is literal: neither
+        `TCPAddress` nor `UDSAddress` defines `.namespace` at all,
+        so a plain attr access on an overlay raises
+        `AttributeError` rather than yielding `None`. Hence the
+        `getattr()` — drop it once the backends actually declare
+        the member.
+
+        '''
+        if (netns := self.tunnel.netns) is None:
+            return getattr(self.overlay, 'namespace', None)
+
+        return ('netns', netns)
+
+    def __repr__(self) -> str:
+        return (
+            f'{type(self).__name__}(\n'
+            f'  overlay={self.overlay!r},\n'
+            f'  via={self.tunnel.tunnel_key!r} '
+            f'iface={self.tunnel.iface!r},\n'
+            f')'
+        )
+
+
+def _wg_bearer(
+    bearer_ma: Multiaddr,
+    source_ma: Multiaddr,
+) -> tuple[str, int]:
+    '''
+    Parse one kernel-owned `wg` bearer endpoint.
+
+    '''
+    proto_names: list[str] = [
+        proto.name
+        for proto in bearer_ma.protocols()
+    ]
+    match proto_names:
+        case [('ip4' | 'ip6') as ip_proto, 'udp']:
+            return (
+                bearer_ma.value_for_protocol(ip_proto),
+                int(bearer_ma.value_for_protocol('udp')),
+            )
+
+        case _:
+            raise ValueError(
+                f'Bad `wg` bearer, expected '
+                f'`/ip4|ip6/<host>/udp/<port>`\n'
+                f'got: {bearer_ma}\n'
+                f'from maddr: {source_ma}\n'
+            )
+
+
+def parse_wg_maddr(
+    maddr: str|Multiaddr,
+) -> TunnelledAddress:
+    '''
+    Parse a `wg` maddr stack into nested tunnel annotations.
+
+    Pure: every segment operation delegates to `py-multiaddr`.
+    Repeated `.decapsulate_code()` calls peel the last `/wg/`
+    first, while `.split()` and `.join()` isolate that tunnel's
+    bearer without parsing slash-delimited strings ourselves.
+
+    '''
+    ma: Multiaddr = (
+        maddr
+        if isinstance(maddr, Multiaddr)
+        else Multiaddr(maddr)
+    )
+    wg_code: int = _wg_proto_code()
+    segs: list[Multiaddr] = ma.split()
+    proto_names: list[str] = [
+        proto.name
+        for seg in segs
+        for proto in seg.protocols()
+    ]
+    if 'wg' not in proto_names:
+        raise ValueError(
+            f'Not a `wg`-tunnelled maddr; no `/wg/` segment!\n'
+            f'maddr: {ma}\n'
+        )
+
+    final_wg_i: int = len(proto_names) - 1
+    final_wg_i -= proto_names[::-1].index('wg')
+    overlay_ma: Multiaddr = Multiaddr.join(
+        *segs[final_wg_i + 1:]
+    )
+    overlay_names: list[str] = [
+        proto.name
+        for proto in overlay_ma.protocols()
+    ]
+    match overlay_names:
+        case [('ip4' | 'ip6'), 'tcp']:
+            from ._multiaddr import parse_maddr
+            overlay: Address|TunnelledAddress = parse_maddr(
+                str(overlay_ma)
+            )
+
+        case []:
+            raise ValueError(
+                f'`wg` maddr declares no overlay endpoint!\n'
+                f'Append the endpoint tractor should bind.\n'
+                f'maddr: {ma}\n'
+            )
+
+        case _:
+            raise ValueError(
+                f'Unsupported `wg` overlay protocol combo: '
+                f'{overlay_names!r}\n'
+                f'overlay: {overlay_ma}\n'
+                f'from maddr: {ma}\n'
+            )
+
+    cursor: Multiaddr = ma
+    while any(
+        proto.name == 'wg'
+        for proto in cursor.protocols()
+    ):
+        cursor_segs: list[Multiaddr] = cursor.split()
+        cursor_names: list[str] = [
+            proto.name
+            for seg in cursor_segs
+            for proto in seg.protocols()
+        ]
+        wg_i: int = len(cursor_names) - 1
+        wg_i -= cursor_names[::-1].index('wg')
+        mb_key: str = cursor_segs[wg_i].value_for_protocol('wg')
+
+        bearer_prefix: Multiaddr = cursor.decapsulate_code(
+            wg_code
+        )
+        prefix_segs: list[Multiaddr] = bearer_prefix.split()
+        prefix_names: list[str] = [
+            proto.name
+            for seg in prefix_segs
+            for proto in seg.protocols()
+        ]
+        prior_wg_i: int = (
+            len(prefix_names) - 1
+            - prefix_names[::-1].index('wg')
+            if 'wg' in prefix_names
+            else -1
+        )
+        bearer_ma: Multiaddr = Multiaddr.join(
+            *prefix_segs[prior_wg_i + 1:]
+        )
+        overlay = TunnelledAddress(
+            overlay=overlay,
+            tunnel=WGTunnelSpec(
+                peer_pubkey=wg8_pubkey(mb_key),
+                bearer=_wg_bearer(bearer_ma, ma),
+            ),
+        )
+        cursor = bearer_prefix
+
+    return overlay
+
+
+def mk_wg_maddr(
+    addr: TunnelledAddress,
+) -> Multiaddr:
+    '''
+    Compose nested tunnel annotations as a canonical `wg` maddr.
+
+    Only the peer key and bearer have maddr representations. Local
+    interface, namespace, and allowed-IP config remains local.
+
+    '''
+    _wg_proto_code()
+    if (bearer := addr.tunnel.bearer) is None:
+        raise ValueError(
+            f'Can not compose a `wg` maddr without a bearer!\n'
+            f'tunnel: {addr.tunnel!r}\n'
+        )
+
+    bindable: Address = strip_tunnels(addr)
+    if bindable.proto_key != 'tcp':
+        raise ValueError(
+            f'Unsupported `wg` overlay proto-key: '
+            f'{bindable.proto_key!r}\n'
+            f'overlay: {bindable!r}\n'
+        )
+
+    host, port = bearer
+    ip = ipaddress.ip_address(host)
+    ip_proto: str = (
+        'ip4'
+        if ip.version == 4
+        else 'ip6'
+    )
+    bearer_ma = Multiaddr(
+        f'/{ip_proto}/{host}/udp/{port}'
+    )
+    key_ma = Multiaddr(
+        f'/wg/{mb_pubkey(addr.tunnel.peer_pubkey)}'
+    )
+
+    from ._multiaddr import mk_maddr
+    overlay_ma: Multiaddr = mk_maddr(addr.overlay)
+    return (
+        bearer_ma
+        .encapsulate(key_ma)
+        .encapsulate(overlay_ma)
+    )
+
+
+def strip_tunnels(
+    addr: Address|TunnelledAddress,
+) -> Address:
+    '''
+    Deliver the bindable `Address`, peeling any tunnel
+    annotation(s).
+
+    Pure. Idempotent on an un-tunnelled `Address`, and loops so
+    a nested (tunnel-in-tunnel) stack collapses in one call.
+
+    Call this at every bind/dial boundary.
+
+    '''
+    while isinstance(addr, TunnelledAddress):
+        addr = addr.overlay
+
+    return addr
+
+
+def tunnels_of(
+    addr: Address|TunnelledAddress,
+) -> tuple[TunnelSpec, ...]:
+    '''
+    Deliver every tunnel spec wrapping `addr`, outermost first.
+
+    Pure; empty for an un-tunnelled `Address`.
+
+    '''
+    specs: list[TunnelSpec] = []
+    while isinstance(addr, TunnelledAddress):
+        specs.append(addr.tunnel)
+        addr = addr.overlay
+
+    return tuple(specs)

uv.lock

@@ -1113,6 +1113,7 @@ dependencies = [
     { name = "multiaddr" },
     { name = "pdbp" },
     { name = "platformdirs" },
+    { name = "py-multibase" },
     { name = "setproctitle" },
     { name = "tricycle" },
     { name = "trio" },
@@ -1177,6 +1178,7 @@ requires-dist = [
     { name = "multiaddr", git = "https://github.com/multiformats/py-multiaddr.git?rev=f86519daaa21699023d0037c58cdff600313dd09" },
     { name = "pdbp", specifier = ">=1.8.2,<2" },
     { name = "platformdirs", specifier = ">=4.4.0" },
+    { name = "py-multibase", specifier = ">=2.0.0,<3" },
     { name = "setproctitle", specifier = ">=1.3,<2" },
     { name = "tricycle", specifier = ">=0.4.1,<0.5" },
     { name = "trio", specifier = ">0.27" },