Add a `wg`-tunnelled 2-host example set

Re-renders gh #482's examples w/ the corrected (infix) maddr
grammar, as the "layer A" slice of the wg plan: declarative
maddrs only, tunnel pre-provisioned out-of-band, zero runtime
changes.

- `wg_maddr.py`: a `frozen=True` `msgspec.Struct` addr carrying
  `bearer`/`peer_pubkey`/`inner` (+ `inner_proto`), a `.maddr`
  property that re-renders the canonical form, and pure
  `mb_pubkey()`/`wg8_pubkey()`/`parse_wg_maddr()`. The parser
  rejects #482's inverted suffix form w/ an actionable error and
  stays **side-effect free** — `verify_wg_peer()` is a separate,
  explicitly impure step the caller composes, never something a
  parse path shells out to.
- `host_a_srv.py`/`host_b_client.py`: the two-host runs, passing
  only `addr.inner` into `open_nursery()`/`open_root_actor()`,
  which is the whole point — the bearer + key layers are already
  established before any bind happens.
- `README.md`: the grammar + the 3-owners table, the `#108`
  branch install line, tunnel setup, and a "what changed vs
  #482" section enumerating the corrections.

Runnable-shaped but **not yet run against a live tunnel**; that's
next, and the reason these sit on the planning branch rather than
in `examples/` proper. `_segments()` marks its stopgap for when
the `wg` codec isn't installed.

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

ai/tpt-backends/00_shared_backend_contract.md

@@ -0,0 +1,403 @@
+# `tractor.ipc` next-gen transport backends: the shared contract
+
+Status: design doc / implementation spec.
+Audience: any model or human implementing one of the three
+sibling plans in this directory.
+
+- [`01_tipc_backend.md`](./01_tipc_backend.md) — `AF_TIPC`
+  (gh #378)
+- [`02_quic_iroh_backend.md`](./02_quic_iroh_backend.md) — QUIC
+  via `iroh` FFI, uniffi-async rewritten onto `trio` (gh #353)
+- [`03_wg_tunnel_bindspace.md`](./03_wg_tunnel_bindspace.md) —
+  WireGuard (and other shuttle-able) tunnels as a *nested
+  bindspace* layer via `pyroute2` (gh #482, #443)
+
+This doc is the **normative** description of what a `tractor`
+transport backend *is* as of `main@83b34884`. Each sibling plan
+assumes it and only documents its own deltas. Read this first;
+do not re-derive it from the code.
+
+---
+
+## 0. Why a shared contract doc
+
+The three plans are meant to be implementable *independently and
+concurrently* by different models/providers without design
+drift. Everything they share — the backend duck-type, the
+registration tables, the test harness plumbing, the naming and
+code-style rules — lives here exactly once. If an implementer
+finds this doc disagrees with `main`, **the code wins**; fix this
+doc in the same PR.
+
+---
+
+## 1. The backend duck-type (empirical, from `_tcp.py`/`_uds.py`)
+
+A transport backend is **one module** under `tractor/ipc/`
+exposing exactly four things. There is no ABC to subclass and no
+plugin entrypoint; wiring is by explicit table registration
+(§2) plus one piece of reflection (§1.3).
+
+### 1.1 `class <Proto>Address(msgspec.Struct, frozen=True)`
+
+Structurally conforms to the `Address` `Protocol` in
+`tractor/discovery/_addr.py:82`. Required surface:
+
+| member | kind | notes |
+| --- | --- | --- |
+| `proto_key` | `ClassVar[str]` | the wire/registry key, e.g. `'tcp'`, `'uds'` |
+| `unwrapped_type` | `ClassVar[type]` | the primitive tuple shape |
+| `def_bindspace` | `ClassVar` | default bindspace value |
+| `is_valid` | `@property -> bool` | "is this a *dialable/bindable* addr" |
+| `bindspace` | `@property` | the "set of hosts"-ish scope (see below) |
+| `from_addr(cls, addr)` | `@classmethod` | primitive -> wrapped, `match`-based |
+| `unwrap(self)` | method | wrapped -> primitive (must be msgpack-native!) |
+| `get_random(cls, bindspace=...)` | `@classmethod` | per-subactor ephemeral addr |
+| `get_root(cls)` | `@classmethod` | host-singleton default registrar addr |
+| `__repr__` | method | `f'{type(self).__name__}[{...}]'` house style |
+
+Hard constraints learned from the existing two:
+
+- **`frozen=True`.** Addresses are dict keys
+  (`Server.epsdict()`, `Endpoint.peer_tpts`) and are compared by
+  value all over the runtime.
+- **`.unwrap()` output must round-trip through `msgspec` and
+  through `wrap_address()`.** It is what actually crosses the
+  wire in `SpawnSpec`/`_root_mailbox`/`_registry_addrs`, and it
+  is what `Actor.reg_addrs` and every test compares against. If
+  your unwrapped form is not *uniquely* pattern-matchable
+  against the other backends' forms in
+  `wrap_address()` (`_addr.py:230`), you have a bug that
+  manifests as the wrong transport being loaded — the file's own
+  `XXX NOTE` warns about precisely this.
+
+  ⚠️ **and shape-matching does not survive 4 backends.** Adding
+  TIPC and iroh breaks it outright: TIPC's natural form is a
+  `(str, int)` — indistinguishable from `TCPAddress` — and
+  iroh's is a `(str, str)`, which the *existing* UDS case
+  (`case (_, filename) if type(filename) is str`) already
+  swallows. Ordering hacks and prefix-tagging (an earlier
+  revision of plan 01 proposed `('tipc:<stype>:<scope>', inst)`)
+  paper over it at best.
+
+  **The fix, and the recommended prerequisite for all three
+  backends: make the unwrapped form carry an explicit
+  proto-key, using the `multiaddr` protocol name as the
+  canonical spelling** — `('tcp', host, port)`,
+  `('unix', path)`, `('udp', ...)`, `('tipc', stype, inst,
+  scope)`. Then `wrap_address()` collapses from an
+  order-sensitive `match` to `_address_types[addr[0]]`, and the
+  whole collision class stops existing. Note this *also* aligns
+  the on-wire form with `mk_maddr()`/`parse_maddr()`, so the two
+  representations stop being independent inventions.
+
+  Two consequences to plan for:
+  - it's a **wire-format change** (`SpawnSpec`,
+    `_root_mailbox`, `_registry_addrs`) plus every test fixture
+    and downstream config (`piker`'s `[network]` table). It
+    wants its **own migration commit, landed before any new
+    backend**, not smuggled into one.
+  - it's the moment to **stop handing raw unwrapped tuples to
+    users at all.** The long-term shape is: `Address` subtypes
+    are the public currency and `UnwrappedAddress` becomes an
+    internal serialization detail — the same discipline
+    `ipaddress` uses (you pass `IPv4Address`, not a 4-tuple).
+    Public API should accept `Address|maddr-str` and treat bare
+    tuples as legacy-tolerated input, ideally deprecated.
+- **`.get_random()` must be collision-free without a live
+  runtime.** See the `UDSAddress.get_random()` uuid-token
+  comment (`_uds.py:207-220`): with no `current_actor()` the
+  sockname degenerates to a pure fn of `(prefix, pid)` and two
+  calls in one proc alias. Mix in a `uuid4().hex[:8]` token.
+- **`.bindspace` semantics**: "the address' bindable space" —
+  ip/host for `tcp`, the socket-file *directory* for `uds`. For
+  the new backends: the TIPC *scope* (§1 of plan 01), the iroh
+  *ALPN + relay/discovery realm* (plan 02), the netns (plan 03).
+  `Address.namespace` is already spec'd in the Protocol as
+  "the if-available OS-specific network namespace key" and is
+  currently unimplemented by both backends — plan 03 is the
+  first real consumer.
+
+### 1.2 module-level listener lifecycle
+
+```python
+async def start_listener(
+    addr: <Proto>Address,
+    **kwargs,
+) -> trio.SocketListener   # or a trio.abc.Listener, see §3
+    ...
+
+def close_listener(          # OPTIONAL
+    addr: <Proto>Address,
+    lstnr: trio.abc.Listener,
+) -> None:
+    ...
+```
+
+`close_listener()` is optional; `Endpoint.close_listener()`
+(`_server.py:674`) `getattr`s it and treats absence as "closing
+is implicit". `uds` needs it (unlinks the sock-file), `tcp`
+does not.
+
+### 1.3 the ONE piece of reflection you must not break
+
+`Endpoint.start_listener()` (`_server.py:656`):
+
+```python
+tpt_mod: ModuleType = inspect.getmodule(self.addr)
+lstnr = await tpt_mod.start_listener(addr=self.addr)
+```
+
+The transport module is found by `inspect.getmodule()` **on the
+`Address` instance**. Therefore: *the `Address` class and its
+`start_listener()`/`close_listener()` MUST live in the same
+module.* Do not define the address type in `_types.py` or a
+`_addrs.py` and the listener elsewhere.
+
+Immediately after, the same method does:
+
+```python
+if (unwrapped := lstnr.socket.getsockname()) != self.addr.unwrap():
+    self.addr = self.addr.from_addr(unwrapped)
+```
+
+i.e. it assumes `lstnr.socket.getsockname()` exists and that its
+return value is a valid `from_addr()` input. This is fine for
+TIPC (§3 of plan 01) and **is the main integration hazard for
+iroh** (§3 of plan 02) — plans that break it must say so
+explicitly and propose the upstream `_server.py` patch.
+
+### 1.4 `class Msgpack<Proto>Stream(MsgpackTransport)`
+
+Subclass `tractor.ipc._transport.MsgpackTransport`. You inherit
+all framing (`<I` 4-byte little-endian length prefix),
+`msgspec` codec ctx-var lookup, `TransportClosed` normalization,
+`.drain()`, `__aiter__`. You implement only:
+
+| member | notes |
+| --- | --- |
+| `address_type` | the `<Proto>Address` class |
+| `layer_key: int` | OSI-ish layer, `4` for both current backends |
+| `maddr` `@property` | `-> Multiaddr\|str`, via `mk_maddr(self.raddr)` |
+| `connected(self) -> bool` | `tcp`/`uds` both use `self.stream.socket.fileno() != -1` |
+| `connect_to(cls, addr, prefix_size=4, codec=None, **kw)` | `@classmethod`, returns an instance |
+| `get_stream_addrs(cls, stream) -> (laddr, raddr)` | `@classmethod`, called from `MsgpackTransport.__init__` |
+
+`MsgpackTransport.__init__` requires the object passed as
+`stream` to satisfy:
+
+- `await stream.send_all(bytes)`
+- usable as `tricycle.BufferedReceiveStream(transport_stream=stream)`,
+  i.e. `await stream.receive_some(n)`
+- `trio.BrokenResourceError` / `trio.ClosedResourceError` /
+  `ValueError('...unclean EOF...')` on the failure paths that
+  `_iter_packets()` and `send()` already `match` on
+  (`_transport.py:221-304`, `:436-499`).
+
+That is **`trio.abc.Stream`, not `trio.SocketStream`**. The
+`MsgTransport` Protocol's `stream: trio.SocketStream`
+annotation (`_transport.py:83`) is a lie of convenience — the
+actual `MsgpackTransport.__init__` param is typed
+`trio.abc.Stream` and nothing in the msg path touches
+`.socket`. Only `connected()` (which each backend defines) and
+`Endpoint.start_listener()`'s `getsockname()` do.
+
+### 1.5 verified-good news for socket-family backends
+
+Both `trio.SocketStream` and `trio.SocketListener` are
+**address-family agnostic**. Verified against the installed
+`trio` (`trio/_highlevel_socket.py`): the only constructor
+checks are
+
+- `isinstance(socket, trio.socket.SocketType)`
+- `socket.type == SOCK_STREAM`
+- (listener) `getsockopt(SOL_SOCKET, SO_ACCEPTCONN)` is truthy,
+  with `OSError` **suppressed** (the macOS carve-out, which
+  also covers exotic families that reject the opt)
+
+There is no `AF_*` check and no `IPPROTO_TCP` hard dependency
+(`TCP_NODELAY`/`TCP_NOTSENT_LOWAT` are set under
+`suppress(OSError)`). Consequence: **any `SOCK_STREAM` family
+CPython can create — including `AF_TIPC` — drops straight into
+the existing `trio.SocketStream` + `trio.serve_listeners()`
+path.** This is why plan 01 is small and plan 02 is not.
+
+---
+
+## 2. Registration tables (the full wiring checklist)
+
+Adding a backend touches these and only these:
+
+1. `tractor/runtime/_state.py:46`
+   `TransportProtocolKey = Literal['tcp', 'uds', ...]` — add the
+   key. This `Literal` is the canonical set; `_testing/pytest.py`
+   drives `--tpt-proto` validation off `_addr._address_types`,
+   and the spawn-backend fixture already models the
+   "drive-the-set-from-the-Literal" pattern
+   (`pytest.py:870-880`) — do the same rather than hardcoding.
+2. `tractor/discovery/_addr.py:173` `_address_types: bidict` —
+   `{'<key>': <Proto>Address}`. Note it is a **`bidict`**, so
+   the mapping must stay 1:1.
+3. `tractor/discovery/_addr.py:181` `_default_lo_addrs` —
+   `'<key>': <Proto>Address.get_root().unwrap()`.
+   ⚠️ this dict is built at **import time**, so
+   `get_root()` must not require a live runtime, a loaded kernel
+   module, or network I/O. (`UDSAddress.def_bindspace =
+   get_rt_dir()` is the precedent for "cheap, pure, filesystem-
+   ish".) A backend whose root addr needs I/O must make this
+   entry lazy — propose that refactor explicitly.
+4. `tractor/discovery/_addr.py:230` `wrap_address()` `match` —
+   add a case iff your `unwrapped_type` isn't already uniquely
+   matched. **Preferably do the proto-key migration in §1.1
+   first**, after which this step becomes a one-line
+   `_address_types` entry instead of an order-sensitive `case`.
+5. `tractor/ipc/_types.py` — `Address` union alias,
+   `_msg_transports` list, `_key_to_transport[('msgpack', key)]`,
+   `_addr_to_transport[<Proto>Address]`.
+6. `tractor/ipc/_types.py:92` `transport_from_stream()` — the
+   `sock.family` `match`. For a non-socket stream type (iroh)
+   this needs a different discriminator; see plan 02 §3.3.
+7. `tractor/discovery/_multiaddr.py` —
+   `_tpt_proto_to_maddr`, and a `case` in both `mk_maddr()` and
+   `parse_maddr()`.
+8. `tractor/ipc/__init__.py` — re-export if the backend has a
+   public surface.
+9. `tractor/_testing/addr.py::get_rando_addr()` — per-proto
+   branch so the whole suite can run under `--tpt-proto <key>`.
+10. `pyproject.toml` — new deps go in an **optional extra**, never
+    in `[project].dependencies`. See §5.
+
+## 3. Where the `trio.SocketListener` assumption is load-bearing
+
+`_serve_ipc_eps()` (`_server.py:1041`) annotates
+`listener: trio.abc.Listener` and hands the list to
+`trio.serve_listeners(handler=handle_stream_from_peer,
+listeners=..., handler_nursery=stream_handler_tn)`.
+`trio.serve_listeners` itself is generic over
+`trio.abc.Listener`. So the *only* `SocketListener`-specific
+code in the server path is the `getsockname()` reconciliation in
+`Endpoint.start_listener()` (§1.3) and the type annotations.
+
+`handle_stream_from_peer()` (`_server.py:298`) then does
+`Channel.from_stream(stream)` →
+`transport_from_stream(stream)` → `sock.family` match (§2.6).
+
+**Therefore**: a non-socket backend needs (a) a
+`trio.abc.Listener` subclass, (b) a change to
+`Endpoint.start_listener()` to not blindly `getsockname()`, and
+(c) a change to `transport_from_stream()`'s discrimination.
+All three are small, upstream-able, and *should be landed as
+their own prep PR* before the backend itself — see plan 02 §3.
+
+## 4. Handshake / discovery invariants you inherit
+
+- Every accepted stream immediately does
+  `chan._do_handshake(aid=actor.aid)`; a peer that fails it is
+  logged at `runtime` and dropped, **not** raised
+  (`_server.py:334-365`). Discovery-sys "pings" rely on this,
+  so your `connect_to()` must raise something that normalizes
+  to `TransportClosed`/`ConnectionError` on a dead peer, never
+  a novel exception type.
+- `_root.py:381-406` fail-fasts when a `registry_addrs` entry's
+  `proto_key` is not in `enable_transports`. Your key must be
+  spellable in both.
+- `_root.py:256` currently enforces `len(enable_transports) == 1`.
+  Multi-tpt actors are a separate work item; none of these three
+  plans may depend on lifting it.
+- Sub-actor bind addrs come from
+  `_runtime.py:1600-1610`: for each key in the parent-supplied
+  `enable_transports`, `get_address_cls(key).get_random()`.
+  So `get_random()` runs *in the child, post-fork, pre-listen*.
+  Anything it needs (kernel module, netns membership, an iroh
+  secret key) must already be true at that moment.
+
+## 5. Dependency policy
+
+`[project].dependencies` stays lean (see the boot-latency work,
+gh #470: `import tractor` is budgeted at ~0.145s). Every new
+backend dep is an extra:
+
+```toml
+[project.optional-dependencies]
+tipc = []                       # stdlib-only!
+quic = ["iroh>=0.35"]           # pin per plan 02 §1
+wg   = ["pyroute2>=0.9"]        # pin per plan 03 §1
+```
+
+and every backend module must be **import-lazy**: a
+`tractor/ipc/_<proto>.py` that imports its 3rd-party dep at
+module scope must not be imported by `tractor/__init__.py`,
+`tractor/ipc/__init__.py`, or `tractor/discovery/_addr.py`'s
+import-time table construction. The `_addr._default_lo_addrs`
+eager-dict (§2.3) is the trap: keep the backend's `get_root()`
+dep-free, or make that table lazy.
+
+## 6. Test-harness plumbing (identical for all three)
+
+- `--tpt-proto <key>` (`_testing/pytest.py:409`) selects the
+  session-wide proto; the `tpt_proto` fixture mutates
+  `_state._def_tpt_proto` + `_runtime_vars['_enable_tpts']`
+  (`pytest.py:807-835`). Adding the key to `_address_types` is
+  what makes `--tpt-proto <key>` legal (`pytest.py:795-800`
+  asserts the lookup).
+- The **acceptance bar** for every backend is: the *entire*
+  existing suite passes under `--tpt-proto <key>`, unmodified.
+  That is the whole point of the abstraction. Backend-specific
+  unit tests go in `tests/ipc/test_each_tpt.py` (the existing
+  `test_uds_bindspace_created_implicitly` /
+  `test_uds_double_listen_raises_connerr` are the model).
+- Capability gating: each backend needs a **cheap, pure
+  predicate** + a `pytest.mark.skipif`, because these are all
+  environment-dependent. Verified example: on this dev box
+  `socket.socket(AF_TIPC, SOCK_STREAM)` raises
+  `OSError(97, 'Address family not supported by protocol')`
+  because the `tipc` module isn't loaded. Put the predicate in
+  the backend module (so apps can use it too), not in the test.
+- New pytest marks must be registered in `pyproject.toml`, per
+  the project's fix-warnings-at-source rule (gh #469).
+
+## 7. Code style (non-negotiable, matches the repo)
+
+- module header tagline: `# tractor: distributed structured
+  concurrency.` for **new** files (not the legacy
+  `structured concurrent "actors".` form the existing `_tcp.py`
+  carries).
+- AGPL header block copied verbatim from `_tcp.py`.
+- `from __future__ import annotations` first.
+- annotate *everything*, including locals:
+  `sockpath: Path = addr.sockpath`.
+- `match`/`case` over `isinstance` chains for address and
+  error dispatch.
+- multi-line call/`import` style with trailing commas.
+- never emit a whitespace-only line.
+- error messages are multi-line f-strings ending in `\n`, with
+  the `f'...\n' f'...\n'` implicit-concat layout and the
+  `>[`/`[>`/`<=(` nested-op sigils where a `nest_from_op()` is
+  in play.
+- prefer pure functions + module-level helpers over methods;
+  keep `Address` types data-only. Where a helper needs
+  scoped setup/teardown, it's an `@acm` — not a class with
+  `.start()`/`.stop()`.
+- pure getters: no `get_*(..., mutate=True)` flags; split into
+  a read-only getter and an explicit sibling setter.
+
+---
+
+## 8. Cross-plan sequencing
+
+The three are independent *except*:
+
+- plan 02 (iroh) needs the `_server.py` /
+  `transport_from_stream()` generalization (§3) — plan 01 does
+  **not**, and should therefore land first as the cheap proof
+  that the table-registration story works for a genuinely new
+  proto.
+- plan 03 (wg) composes *under* whatever L4 tpt is in use and
+  its netns work is what finally implements
+  `Address.namespace`. It can land before or after 02, but its
+  `TunnelledAddress` design must be reviewed against plan 02's
+  address shape so the "tunnelled maddr" grammar (gh #443)
+  covers `/…/quic-v1/p2p/…` inner addrs too.
+- All three want first-class `wg`/`quic`/`tipc` protos in
+  `py-multiaddr`; that upstream track is gh #483 and
+  multiformats/py-multiaddr#107/#108.

ai/tpt-backends/01_tipc_backend.md

@@ -0,0 +1,707 @@
+# Plan 01 — `TIPC` transport backend (`tractor/ipc/_tipc.py`)
+
+Tracks gh [#378]. Prereq reading:
+[`00_shared_backend_contract.md`](./00_shared_backend_contract.md).
+
+**Thesis**: TIPC is the *cheapest* new backend we can add and
+simultaneously the only one that gives us cluster-wide service
+discovery **for free, in the kernel**, replacing (for
+TIPC-capable deployments) the whole `tractor.discovery`
+registrar round-trip with a `bind()`/`connect()` on a
+*service name*. It is stdlib-only: zero new dependencies.
+
+[#378]: https://github.com/goodboy/tractor/issues/378
+
+---
+
+## 1. Why this is small: three verified facts
+
+1. **CPython already speaks TIPC.** `socket.AF_TIPC` plus 23
+   `TIPC_*` constants are present in the stdlib on Linux
+   (verified on the dev box, py3.13):
+   `AF_TIPC, SOL_TIPC, TIPC_ADDR_ID, TIPC_ADDR_NAME,
+   TIPC_ADDR_NAMESEQ, TIPC_CFG_SRV, TIPC_CLUSTER_SCOPE,
+   TIPC_CONN_TIMEOUT, TIPC_{CRITICAL,HIGH,MEDIUM,LOW}_IMPORTANCE,
+   TIPC_DEST_DROPPABLE, TIPC_IMPORTANCE, TIPC_NODE_SCOPE,
+   TIPC_PUBLISHED, TIPC_SRC_DROPPABLE, TIPC_SUBSCR_TIMEOUT,
+   TIPC_SUB_CANCEL, TIPC_SUB_PORTS, TIPC_SUB_SERVICE,
+   TIPC_TOP_SRV, TIPC_WAIT_FOREVER, TIPC_WITHDRAWN,
+   TIPC_ZONE_SCOPE`.
+   `sock.bind()/connect()/getsockname()` take/return the
+   5-tuple `(addr_type, v1, v2, v3, scope)` — the last element
+   is optional on input and defaults to `0`.
+2. **`trio` doesn't care about the address family.** Per
+   contract §1.5, `trio.SocketStream` and `trio.SocketListener`
+   only require a trio socket object of type `SOCK_STREAM`.
+   TIPC's `SOCK_STREAM` is a real connection-oriented reliable
+   byte stream. So we reuse `trio.SocketStream`,
+   `trio.SocketListener`, `trio.serve_listeners()`,
+   `MsgpackTransport`'s framing — *all of it*.
+3. **It is not available by default.** On this box
+   `socket.socket(AF_TIPC, SOCK_STREAM)` →
+   `OSError(97, 'Address family not supported by protocol')`
+   with no `tipc` in `/proc/modules`. `modprobe tipc` is
+   required; cross-node needs a bearer
+   (`tipc bearer enable media eth device <if>` or
+   `media udp name <n> localip <ip>`). Everything about this
+   plan's testability hinges on gating (§7).
+
+Non-goals: `SOCK_RDM`/`SOCK_DGRAM`/`SOCK_SEQPACKET` message
+modes, multicast fan-out, and TIPC group messaging. They are
+genuinely interesting for a future `tractor` broadcast/pubsub
+transport but they do **not** fit `MsgTransport`'s
+stream-of-length-prefixed-msgs shape. Note them in the
+follow-up issue, do not build them here.
+
+---
+
+## 2. `TIPCAddress`
+
+### 2.1 the three TIPC address flavours, and which we use
+
+| flavour | tuple | meaning |
+| --- | --- | --- |
+| `TIPC_ADDR_NAMESEQ` | `(type, lower, upper, scope)` | a *published range* — what a server `bind()`s |
+| `TIPC_ADDR_NAME` | `(type, instance, domain, scope)` | a *lookup* — what a client `connect()`s |
+| `TIPC_ADDR_ID` | `(node, ref, 0, scope)` | a concrete port id — the "physical" address |
+
+The design decision that makes this backend coherent:
+
+> **A `tractor` actor's TIPC address is a *service name*
+> `(type, instance)`; `bind()` publishes the singleton range
+> `(type, instance, instance)`; peers `connect()` by name and
+> the kernel resolves + load-balances. `TIPC_ADDR_ID` is only
+> ever an *observed* address (`getpeername()`), never a
+> user-facing one.**
+
+This is exactly the "leverage the built-in discovery machinery"
+ask in #378: publishing a bind *is* registration, and
+`connect()` on a name *is* a lookup, with no registrar actor in
+the loop.
+
+### 2.2 the struct
+
+```python
+class TIPCAddress(
+    msgspec.Struct,
+    frozen=True,
+):
+    _stype: int                    # TIPC "type" == service class
+    _instance: int                 # service instance within the type
+    _scope: int = TIPC_CLUSTER_SCOPE
+    # observed-only, never part of identity/equality-by-intent
+    maybe_node: int|None = None    # from TIPC_ADDR_ID getpeername()
+    maybe_ref: int|None = None
+
+    proto_key: ClassVar[str] = 'tipc'
+    unwrapped_type: ClassVar[type] = tuple[str, int]
+    def_bindspace: ClassVar[int] = TIPC_CLUSTER_SCOPE
+```
+
+**Unwrapped form** (the wire/`SpawnSpec` shape).
+
+TIPC's natural form is `(stype, instance, scope)` — but a
+2-tuple squeeze of it is a `(str, int)`, i.e. *the same coarse
+shape as `TCPAddress`*, so `wrap_address()`'s
+`case (str(), int())` steals it. This backend is therefore the
+forcing function for the contract-doc's conclusion (§1.1):
+
+> **make the unwrapped form carry an explicit proto-key, spelled
+> with the `multiaddr` protocol name.**
+
+```python
+def unwrap(self) -> tuple[str, int, int, int]:
+    return ('tipc', self._stype, self._instance, self._scope)
+```
+
+`wrap_address()` then dispatches `_address_types[addr[0]]` and
+the collision class disappears. **This is a prerequisite
+migration commit, not part of this backend** — see contract §1.1
+for its blast radius (wire format + every fixture + `piker`
+config) and for the follow-on "stop handing raw tuples to users
+at all, à la `ipaddress`" direction.
+
+⚠️ an earlier revision of this plan proposed a self-tagging
+`('tipc:<stype>:<scope>', instance)` string-prefix hack with an
+ordered `case` guard. **Dropped** — it papers over the problem,
+keeps `wrap_address()` order-sensitive, and doesn't help iroh's
+`(str, str)`-vs-UDS collision at all. Do not resurrect it.
+
+Note `TIPCAddress` is the first backend where `.unwrap()` is
+**not** a lossless view of the live socket — `maybe_node`/
+`maybe_ref` are observed metadata, exactly like
+`UDSAddress.maybe_pid` (which is likewise excluded from
+`.unwrap()`). Follow that precedent, including its `__repr__`
+treatment (`_uds.py:242`).
+
+### 2.3 how to pick `_stype` and `_instance`
+
+- `_stype` = a `tractor`-reserved service class. TIPC reserves
+  0..63 for internal use (`TIPC_TOP_SRV == 1`,
+  `TIPC_CFG_SRV == 0`). Use a module constant
+  `TRACTOR_STYPE: int = 0x74_72_00_00` ("tr\0\0") as the default
+  and make it overridable via `TIPCAddress._stype` so an app
+  can partition service classes. Document that two `tractor`
+  trees sharing a cluster **and** a `_stype` share a namespace.
+- `_instance` for `get_root()`: `1616` — mirrors the
+  `TCPAddress.get_root()` port and the `registry@1616.sock`
+  UDS filename, so the "1616 is tractor's registrar" idiom
+  holds across all backends.
+- `_instance` for `get_random()`: TIPC gives us no
+  kernel-assigned-instance analogue of `port=0`, so we must
+  choose. Use a *pure* fn of the actor identity so it is
+  reproducible and collision-free:
+  ```python
+  # 32-bit instance derived from the actor's uuid4 (+ pid when
+  # there's no live runtime, per the UDS precedent).
+  inst: int = int.from_bytes(
+      blake2b(seed.encode(), digest_size=4).digest(),
+      'big',
+  )
+  ```
+  where `seed = f'{actor.aid.name}@{pid}'` if
+  `current_actor(err_on_no_runtime=False)` else
+  `f'{prefix}.{uuid4().hex[:8]}@{pid}'`. Must avoid the reserved
+  low range: `inst = 64 + (inst % (2**32 - 64))`.
+  ⚠️ *unlike* `port=0`, a collision here surfaces as a
+  successful-but-shared publication (TIPC allows multiple
+  binders on the same name and round-robins!) rather than
+  `EADDRINUSE`. That is a silent-crosstalk failure mode; §7 has
+  the test that proves the 4-byte digest is enough and §9 has
+  the mitigation if it isn't.
+- `_scope`: `TIPC_NODE_SCOPE` for a same-host-only actor (the
+  UDS-equivalent), `TIPC_CLUSTER_SCOPE` (default) for
+  cluster-visible. **This is `.bindspace`**:
+  ```python
+  @property
+  def bindspace(self) -> int:
+      return self._scope
+  ```
+  It is the honest analogue of "the set of hosts this bind is
+  reachable from", which is precisely the docstring in
+  `Address.bindspace`. (`TIPC_ZONE_SCOPE` is deprecated/aliased
+  to cluster in modern kernels — accept it on input, normalize
+  to cluster, log at `transport` level.)
+
+### 2.4 `is_valid`
+
+```python
+@property
+def is_valid(self) -> bool:
+    return (
+        self._instance != 0
+        and
+        self._stype not in _tipc_reserved_stypes  # {0, 1, ...}
+        and
+        self._scope in (TIPC_NODE_SCOPE, TIPC_CLUSTER_SCOPE)
+    )
+```
+
+---
+
+## 3. Listener + stream
+
+### 3.1 `start_listener()`
+
+```python
+async def start_listener(
+    addr: TIPCAddress,
+    backlog: int = 128,
+    **kwargs,
+) -> SocketListener:
+    sock = trio.socket.socket(
+        socket.AF_TIPC,
+        socket.SOCK_STREAM,
+    )
+    # publish the singleton name-range == "register the service"
+    await sock.bind((
+        socket.TIPC_ADDR_NAMESEQ,
+        addr._stype,
+        addr._instance,
+        addr._instance,
+        addr._scope,
+    ))
+    sock.listen(backlog)
+    return SocketListener(sock)
+```
+
+Notes / hazards:
+
+- `bind()` on `AF_TIPC` is **not** a filesystem or port-table
+  operation and can't block on DNS, but keep it `await`ed
+  through `trio.socket` anyway for uniformity.
+- `backlog=128` matching `_uds.start_listener()`'s hard-won
+  value (see its comment at `_uds.py:317-331` re: concurrent
+  deregistration storms). Do not use `1`.
+- **no `close_listener()` needed** — nothing to unlink. Omit the
+  function entirely (contract §1.2: absence means implicit).
+  Withdrawal of the published name happens on socket close.
+- ⚠️ `SocketListener.__init__` will try
+  `getsockopt(SOL_SOCKET, SO_ACCEPTCONN)`. If TIPC rejects it,
+  trio's `except OSError: pass` covers us. Assert this in a
+  unit test rather than assuming.
+- Wrap the bind in a `_reraise_as_connerr()`-style `@cm` (copy
+  the `_uds.py:256` pattern) so `EADDRINUSE`-ish and
+  `EAFNOSUPPORT` become `ConnectionError` with the addr in the
+  message. `EAFNOSUPPORT` here means "kernel module not
+  loaded" and deserves a *specifically actionable* message:
+  `'TIPC unavailable — try `sudo modprobe tipc`\n'`.
+
+### 3.2 the `getsockname()` reconciliation
+
+`Endpoint.start_listener()` does
+`if lstnr.socket.getsockname() != self.addr.unwrap(): self.addr =
+self.addr.from_addr(unwrapped)`.
+
+For TIPC, `getsockname()` on a bound-but-listening socket
+returns a `TIPC_ADDR_ID`-flavoured 5-tuple (the port id), *not*
+the name-seq we bound. So the `!=` is **always true** and
+`from_addr()` will be handed a 5-tuple.
+
+Handle it inside `TIPCAddress.from_addr()` — do **not** patch
+`_server.py`:
+
+```python
+@classmethod
+def from_addr(cls, addr) -> TIPCAddress:
+    match addr:
+        # our own unwrapped form
+        case (str() as tag, int() as inst) if tag.startswith('tipc:'):
+            _, stype, scope = tag.split(':')
+            return TIPCAddress(int(stype), inst, int(scope))
+
+        # a kernel-observed TIPC_ADDR_ID 5-tuple: keep the
+        # *service* identity we already know and only annotate
+        # the observed port-id.
+        case (int() as atype, *rest) if atype == socket.TIPC_ADDR_ID:
+            ...
+```
+
+The `TIPC_ADDR_ID` case cannot reconstruct `(stype, instance)`
+— that info isn't in a port id. So `from_addr()` alone is
+insufficient for the reconciliation path. **Resolution**: make
+`from_addr()` raise a clear `ValueError` for the bare
+`TIPC_ADDR_ID` case, and instead prevent the reconciliation
+from firing by having `start_listener()` return a listener
+whose `getsockname()` we never need — i.e. land this two-line
+upstream fix in `_server.py:664`:
+
+```python
+if (
+    (unwrapped := lstnr.socket.getsockname()) != self.addr.unwrap()
+    and
+    self.addr.rebind_from_sockname   # ClassVar[bool] = True on tcp/uds
+):
+```
+
+with `TIPCAddress.rebind_from_sockname: ClassVar[bool] = False`
+(and `True` on `TCPAddress`/`UDSAddress`, preserving today's
+behaviour exactly). Rationale: the reconciliation exists *only*
+to learn the kernel-assigned port for `port=0` TCP binds (its
+own comment says so, `_server.py:662`); TIPC has no such
+late-binding, so opting out is semantically right rather than a
+hack. **Land this as its own commit, ahead of the backend**,
+with a test that `tcp`'s `port=0` behaviour is unchanged.
+
+Keep the observed port-id available anyway: annotate
+`ep.addr = ep.addr.with_port_id(*getsockname()[1:3])` (a pure
+`msgspec.structs.replace()` helper) purely for logging/repr.
+
+### 3.3 `MsgpackTIPCStream`
+
+```python
+class MsgpackTIPCStream(MsgpackTransport):
+    address_type = TIPCAddress
+    layer_key: int = 4
+
+    @property
+    def maddr(self) -> Multiaddr|str:
+        return mk_maddr(self.raddr)
+
+    def connected(self) -> bool:
+        return self.stream.socket.fileno() != -1
+
+    @classmethod
+    async def connect_to(
+        cls,
+        destaddr: TIPCAddress,
+        prefix_size: int = 4,
+        codec: MsgCodec|None = None,
+        **kwargs,
+    ) -> MsgpackTIPCStream:
+        sock = trio.socket.socket(AF_TIPC, SOCK_STREAM)
+        with close_on_error(sock):
+            # NOTE: connect by *name* -> kernel does the lookup,
+            # so this is our "discovery" call.
+            await sock.connect((
+                socket.TIPC_ADDR_NAME,
+                destaddr._stype,
+                destaddr._instance,
+                0,              # domain: 0 == "anywhere in scope"
+                destaddr._scope,
+            ))
+        return cls(
+            trio.SocketStream(sock),
+            prefix_size=prefix_size,
+            codec=codec,
+        )
+```
+
+- reuse `trio._highlevel_open_unix_stream.close_on_error` (the
+  UDS backend already imports it) or inline the equivalent
+  `try/except: sock.close(); raise`.
+- `SO_/TIPC_` opts worth setting and documenting:
+  - `setsockopt(SOL_TIPC, TIPC_IMPORTANCE, TIPC_HIGH_IMPORTANCE)`
+    for the *parent<->child* lifetime channel — this is a real
+    win TIPC gives us that TCP can't: the runtime's
+    supervision channel can outrank bulk app traffic under
+    congestion. Wire it as a `connect_to(..., importance=...)`
+    kwarg defaulted from a module constant, and have
+    `_runtime.py`'s parent-chan path pass the high value **in a
+    follow-up** (don't couple it to this PR).
+  - `TIPC_CONN_TIMEOUT` — the kernel-side connect timeout;
+    leave at default, we have `trio` cancel scopes.
+  - `TIPC_DEST_DROPPABLE = 0` on the connection so undeliverable
+    msgs come back as errors rather than being silently dropped.
+- **`connect_to()` on a name with no publisher**: TIPC returns
+  `ECONNREFUSED`/`EHOSTUNREACH` promptly (no SYN-timeout wait),
+  which is *better* discovery-ping behaviour than TCP. Confirm
+  the errno and make sure it surfaces as `ConnectionError`
+  (contract §4 — the registrar ping path depends on it).
+
+### 3.4 `get_stream_addrs()`
+
+```python
+@classmethod
+def get_stream_addrs(cls, stream) -> tuple[TIPCAddress, TIPCAddress]:
+    sock = stream.socket
+    # both return TIPC_ADDR_ID 5-tuples for a connected sock
+    l_id = sock.getsockname()
+    r_id = sock.getpeername()
+    ...
+```
+
+Problem: neither end's port-id tells us the *service name*. The
+`laddr`/`raddr` are used for logging, `Channel.raddr`,
+`Server._peers` keying-adjacent repr, and `maddr`. Design:
+
+- the **connecting** side knows the destaddr it dialled →
+  `connect_to()` overrides `_raddr` after construction with the
+  known-good `TIPCAddress`, exactly as
+  `MsgpackUDSStream.connect_to()` does for the peer-pid case
+  (`_uds.py:539-543`).
+- the **accepting** side does not know the peer's service name
+  from the socket. Two honest options:
+  - **(a) accept it: `raddr` carries only `(node, ref)`** via
+    `maybe_node`/`maybe_ref`, `_stype/_instance` set to a
+    sentinel `-1`, and `__repr__` renders
+    `TIPCAddress[<peer-node:0x...>:<ref>]`. The `Aid` from the
+    handshake already gives us the peer's logical identity, so
+    nothing in the runtime actually *needs* the peer's service
+    name. **Recommended.**
+  - (b) piggyback the peer's own bound name in the handshake.
+    Rejected for this PR: touches `Aid`/msg-spec.
+- `laddr` on the accepting side: the `Endpoint` knows its own
+  `addr`; but `get_stream_addrs()` is a `@classmethod` with only
+  the stream. Use `TIPC_ADDR_ID` for `laddr` too and let
+  `Endpoint.peer_tpts` keying (which is by *peer* addr) still
+  work. Verify nothing asserts `laddr == ep.addr` — grep for
+  `.laddr` uses before committing (`_server.py`'s
+  `con_status` logging, `Channel.pformat()`).
+
+---
+
+## 4. Multiaddr representation
+
+There is no `/tipc` in the multiaddr protocol table. Interim
+grammar, mirroring how `uds` maps to the spec-legal `/unix`:
+
+```
+/tipc/<stype>/<instance>            # scope implied = cluster
+/tipc/<stype>/<instance>/<scope>    # explicit
+```
+
+- `_tpt_proto_to_maddr['tipc'] = 'tipc'` and a `mk_maddr()`
+  `case 'tipc':` building the above.
+- `parse_maddr()` gets `case ['tipc']:` — but note
+  `py-multiaddr` will reject an unregistered protocol name
+  outright, so this **requires an upstream registration** (same
+  track as the `wg` work, gh #483 /
+  multiformats/py-multiaddr#107). Until that lands:
+  - `MsgpackTIPCStream.maddr` returns the **`str`** form (the
+    `MsgTransport.maddr` return type is already
+    `Multiaddr|str`, and `MsgpackUDSStream.maddr` already
+    exercises the `str` branch), and
+  - `parse_maddr()` special-cases the `/tipc/` prefix *before*
+    handing the string to `Multiaddr()`.
+  Document this as the reason gh #443's "standardize on
+  returning `Multiaddr` everywhere" item stays blocked.
+
+Propose `/tipc/` upstream as: name `tipc`, code TBD, size
+variable, value `<stype>:<instance>:<scope>` — or as three
+composed protos. Prefer *one* proto with a structured value so
+the maddr stays 2-segment like `/unix/...`.
+
+---
+
+## 5. Discovery: the actually-interesting part
+
+Two independently-shippable layers. **Layer A is in scope for
+the first PR; layer B is a fast-follow.**
+
+### 5.1 Layer A — "discovery by bind" (free)
+
+Because `bind(TIPC_ADDR_NAMESEQ)` publishes and
+`connect(TIPC_ADDR_NAME)` resolves, a `tractor` tree whose
+`registry_addrs` are TIPC service names needs **no registrar
+liveness at all** for the connect path: `find_actor()`'s
+"connect to the registrar and ask" becomes "connect to the
+service name directly". Concretely:
+
+- `tractor.discovery._api.find_actor()` etc. keep working
+  unchanged (they go through the registrar), *and*
+- a new, TIPC-only fast path becomes possible: derive an actor's
+  service name from its `(name, uuid)` and dial it without any
+  registrar hop.
+
+Do **not** build the fast path in PR 1. Instead, prove the
+property with a test (§7.4) and file the follow-up: it changes
+`discovery` semantics (name→instance derivation must be a
+documented, stable, cross-language-able hash) and deserves its
+own design.
+
+### 5.2 Layer B — the topology service (`TIPC_TOP_SRV`)
+
+This is what makes #378's "end game cluster proto" claim real:
+a *subscription* to name-table events, i.e. push-based
+`register`/`deregister` for free, replacing the registrar's
+polled `find_actor()`.
+
+Mechanics (verify each field against
+`linux/include/uapi/linux/tipc.h` + `net/tipc/topsrv.c` at
+implementation time — the struct layout below is from the uapi
+header and the byte-order caveat is real):
+
+```python
+# SOCK_SEQPACKET connected to the topology server
+sock = trio.socket.socket(AF_TIPC, SOCK_SEQPACKET)
+await sock.connect((
+    socket.TIPC_ADDR_NAME,
+    socket.TIPC_TOP_SRV,   # == 1
+    socket.TIPC_TOP_SRV,
+    0,
+))
+
+# struct tipc_subscr {
+#   struct tipc_name_seq seq;  /* 3 * __u32: type, lower, upper */
+#   __u32 timeout;             /* TIPC_WAIT_FOREVER == ~0 */
+#   __u32 filter;              /* TIPC_SUB_{PORTS,SERVICE,CANCEL} */
+#   char  usr_handle[8];
+# }                            /* == 28 bytes */
+_SUBSCR_FMT: str = '=IIIII8s'   # ⚠ 5*I is 20 -> use '=5I8s'
+```
+
+- **byte order**: the topology server historically accepts both
+  host and swapped order and auto-detects; modern kernels are
+  strict-ish. Pack native (`'='`) first, and if the server
+  closes the connection immediately, retry with `'>'`. Encode
+  that as a one-time probe helper
+  `_detect_topsrv_endianness()` cached at module level — and
+  put a `# ?TODO` pointing at `net/tipc/topsrv.c` for someone
+  to make it deterministic.
+- **events**: `struct tipc_event` is `event: u32`,
+  `found_lower: u32`, `found_upper: u32`,
+  `port: {ref: u32, node: u32}`, then the 28-byte subscription
+  echo → 40 bytes. `event ∈ {TIPC_PUBLISHED, TIPC_WITHDRAWN,
+  TIPC_SUBSCR_TIMEOUT}`.
+- **trio shape** — this is where the "nearly-functional,
+  modern-async" style pays off; expose it as an `@acm` yielding
+  a `trio` receive-channel of typed events, *not* a class:
+
+```python
+@acm
+async def open_topology_events(
+    stype: int = TRACTOR_STYPE,
+    lower: int = 0,
+    upper: int = 0xFFFFFFFF,
+    filter: int = TIPC_SUB_SERVICE,
+    timeout: int = TIPC_WAIT_FOREVER,
+    buf_size: int = 64,
+) -> AsyncGenerator[
+    trio.MemoryReceiveChannel[TIPCNameEvent],
+    None,
+]:
+    ...
+```
+
+  with `TIPCNameEvent(msgspec.Struct, frozen=True)` fields
+  `kind: Literal['published','withdrawn','timeout']`,
+  `addr: TIPCAddress`, `node: int`, `ref: int`. One
+  `trio.lowlevel`-free implementation: a nursery-spawned reader
+  task doing `await sock.recv(40)` in a loop and
+  `send_nowait()`ing decoded events, with the `@acm` closing the
+  socket on exit → reader gets `ClosedResourceError` → cancel
+  scope collapses. Standard `tractor` `@acm` discipline.
+- **consumer**: `tractor/discovery/_registry.py` gains an
+  optional "watch" mode so a registrar (or any actor) can keep
+  a live view of the actor set without polling. Sketch the
+  integration in the follow-up issue; do not wire it in PR 1.
+- **`SOCK_SEQPACKET` is fine here** because this socket never
+  goes through `MsgpackTransport` — it's a plain trio socket
+  used with `recv()`. The contract's "`SOCK_STREAM` only"
+  constraint applies to `MsgTransport` streams, not to this.
+
+---
+
+## 6. Commit sequencing (each independently reviewable + green)
+
+1. `_server.py`: add `Address.rebind_from_sockname:
+   ClassVar[bool]`, gate the `getsockname()` reconciliation on
+   it, `True` for tcp/uds. Test: tcp `port=0` unchanged.
+2. `tractor/ipc/_tipc.py`: `TIPCAddress` + `is_tipc_available()`
+   predicate + `start_listener()`. No transport yet.
+   Tests: address round-trip (`unwrap`/`from_addr`/`wrap_address`),
+   `get_random()` uniqueness, bind/listen + `SO_ACCEPTCONN`
+   tolerance, `EAFNOSUPPORT` → actionable `ConnectionError`.
+3. `MsgpackTIPCStream` + `connect_to()` + `get_stream_addrs()`.
+   Test: two `trio` tasks in one proc exchange a msg over
+   `Msgpack` framing (no `tractor` runtime).
+4. registration tables (contract §2 items 1-6, 9) +
+   `pyproject.toml` mark/extra. Test: full suite under
+   `--tpt-proto tipc` (§7.3).
+5. maddr support (`str` form + prefix special-case) + docs.
+6. `open_topology_events()` @acm + its tests (layer B).
+7. docs page + `docs/` example.
+
+Per project convention, a reproducing/guard test lands in its
+own commit **before** the fix it guards.
+
+---
+
+## 7. Testing
+
+### 7.1 the capability predicate (in `_tipc.py`, public)
+
+```python
+def is_tipc_available() -> bool:
+    '''
+    True iff this kernel can create an `AF_TIPC` socket, i.e.
+    the `tipc` module is loaded.
+
+    '''
+    try:
+        socket.socket(socket.AF_TIPC, socket.SOCK_STREAM).close()
+        return True
+    except OSError:
+        return False
+```
+
+Cache it in a module global (it can't change without a
+`modprobe`, and a cold call costs a syscall). Pure predicate, no
+side effects, no logging.
+
+### 7.2 gating
+
+- `pytest.mark.tipc` registered in `pyproject.toml`.
+- module-level
+  `pytestmark = pytest.mark.skipif(not is_tipc_available(),
+  reason='`tipc` kernel module not loaded (`modprobe tipc`)')`
+  in `tests/ipc/test_tipc.py`.
+- `--tpt-proto tipc` with no module must fail **loudly and
+  early** with the actionable message, not with 400 confusing
+  timeouts. Add the check to the `tpt_protos` fixture's existing
+  per-proto validation loop (`_testing/pytest.py:795`): if the
+  chosen `Address` type exposes an `is_available()`-style
+  classmethod, call it and `pytest.fail()` with its reason.
+  Generalize (don't special-case tipc) — plans 02/03 need the
+  same hook.
+
+### 7.3 CI
+
+- add a job matrix entry `--tpt-proto tipc` that runs
+  `sudo modprobe tipc` in a `before` step. GH's
+  `ubuntu-latest` runners do allow `modprobe tipc` (the module
+  ships with the standard Ubuntu kernel package); verify in a
+  throwaway workflow before wiring the matrix. If it turns out
+  to be unavailable, fall back to a container job with
+  `--privileged`/`--cap-add NET_ADMIN`, and mark the job
+  `continue-on-error` until it's proven stable.
+- cross-node TIPC (bearer) cannot be CI'd; cover it with a
+  documented manual smoke test in the docs page, in the style
+  of gh #482's LAN examples.
+
+### 7.4 backend-specific tests worth writing
+
+- **name-publication is discovery**: bind a listener on
+  `(stype, inst)`, then from a second task `connect()` by name
+  and assert it lands — *without* any `tractor` registrar.
+- **`get_random()` collision resistance**: 10k `get_random()`
+  calls with no live runtime → 10k distinct `_instance`s.
+  (This is the silent-crosstalk risk from §2.3; if the 4-byte
+  digest ever collides in this test, escalate to §9.)
+- **round-robin surprise**: two listeners bound to the *same*
+  `(stype, inst)` both succeed (TIPC allows it) and connects
+  distribute. Assert the observed behaviour and reference it
+  from the `get_random()` docstring so the next reader knows
+  why the hash matters.
+- **scope isolation**: a `TIPC_NODE_SCOPE` bind is not visible
+  to a cluster-scope lookup from another node (manual/marked).
+- **importance opt** round-trips via `getsockopt`.
+- **graceful + abrupt close** produce `TransportClosed` with the
+  same `loglevel` classification as tcp/uds — i.e. re-run the
+  relevant `tests/ipc/test_each_tpt.py` cases parametrized over
+  the new proto rather than writing new ones.
+
+---
+
+## 8. Deployment / docs deliverable
+
+A `docs/` page (and/or an `examples/` script) covering:
+
+```bash
+# single host, node-scope only
+sudo modprobe tipc
+tipc node get addr
+
+# multi-host over ethernet (pairs beautifully with plan 03's wg)
+sudo tipc bearer enable media eth device eth0
+# ...or over UDP when L2 isn't available:
+sudo tipc bearer enable media udp name uc localip 10.0.11.1
+tipc link list
+tipc nametable show          # <- see tractor's published services!
+```
+
+`tipc nametable show` displaying live `tractor` actors is the
+single best demo this backend has; lead with it.
+
+---
+
+## 9. Known risks + escalations
+
+| risk | mitigation |
+| --- | --- |
+| `_instance` hash collision → silent crosstalk (two actors share a service name, TIPC round-robins connects between them) | §7.4 test; if it bites, add a post-bind verification handshake, or bump to a 6-byte digest folded into `(stype_low, instance)` |
+| kernel/module unavailability everywhere (dev boxes, macOS, CI) | hard gating (§7.2); TIPC is explicitly an *opt-in cluster* transport, never a default |
+| `getsockname()` returns port-id not name | the `rebind_from_sockname` opt-out (§3.2), landed first |
+| unregistered `/tipc` multiaddr proto | `str` maddr fallback (§4) + upstream track gh #483 |
+| stale docs (#378 notes tipc.io docs may be out of date) | treat `include/uapi/linux/tipc.h` + `net/tipc/` as the only normative source; cite file+symbol in code comments |
+| `SOCK_SEQPACKET` topology framing byte-order | probe helper + `?TODO` (§5.2) |
+
+## 10. Follow-up issue seeds
+
+- **register `/tipc` in the multiaddr spec**, mirroring the `wg`
+  track (multiformats/py-multiaddr#107/#108 + gh #483). Same
+  shape of work: propose the proto + code, land a codec in
+  `py-multiaddr`, then drop our `str`-maddr fallback (§4). Worth
+  filing *alongside* the `wg` spec-submission issue so both
+  proposals go up together rather than as one-offs.
+- registrar-less discovery fast path via name derivation (§5.1)
+- `TIPC_TOP_SRV`-driven push registry in
+  `discovery/_registry.py` (§5.2)
+- `TIPC_IMPORTANCE` for the parent<->child lifetime channel
+  (§3.3) — genuinely novel supervision QoS, no other backend
+  can do it
+- TIPC multicast / group messaging as a *broadcast* transport
+  for `tractor.trionics` fan-out (explicitly not `MsgTransport`)
+- dual-link resiliency / multi-homing (#378's "hybrid dual link")
+  once bearers are scripted in the docs

ai/tpt-backends/02_quic_iroh_backend.md

@@ -0,0 +1,566 @@
+# Plan 02 — QUIC backend via `iroh` FFI, uniffi-async rewritten onto `trio`
+
+Tracks gh [#353]. Prereq reading:
+[`00_shared_backend_contract.md`](./00_shared_backend_contract.md).
+
+**Thesis**: the value of `iroh` over "just QUIC" is
+`NodeId`-addressed, NAT-traversing, relay-fallback endpoints —
+i.e. a `tractor` actor tree that spans hosts *without* a
+reachable listening socket. The cost is that `iroh`'s python
+surface is `uniffi`-generated **asyncio** and its listener is not
+a socket. This plan spends its complexity budget in exactly two
+places: a `trio`-native uniffi future bridge, and a
+`trio.abc.Listener`/`Stream` adapter pair. Everything else is
+contract boilerplate.
+
+[#353]: https://github.com/goodboy/tractor/issues/353
+
+---
+
+## 1. Library selection (decided, with the rejected alternatives)
+
+**Chosen: `iroh` (PyPI, from `n0-computer/iroh-ffi`), pinned to
+a single minor.** The `iroh` python package is a `uniffi`
+binding over the rust `iroh` crate (QUIC via `quinn`/`noq`).
+
+Rejected, and why — record these so the next implementer doesn't
+relitigate:
+
+- **`aioquic`** (sans-io + asyncio): genuinely trio-portable
+  (`hypercorn` already pairs its sans-io core with a trio UDP
+  server, see the links in #353) and dependency-light. But it
+  gives us *only* QUIC — no NodeId identity, no hole punching,
+  no relay. We'd be reimplementing iroh's whole reason for
+  existing. **Keep as the documented fallback** if the FFI
+  bridge (§2) proves unmaintainable; the `MsgTransport` and
+  `Listener` adapters from §3 are ~90% reusable against an
+  `aioquic` core, which is a deliberate design property of this
+  plan.
+- **`quiche` / `quinn` via a hand-rolled PyO3 ext**: strictly
+  more work than reusing `iroh-ffi`, and puts us in the
+  build-wheels business.
+- **`trio-asyncio`**: viable *shortcut* to run the asyncio-shaped
+  bindings under trio, and `tractor` already ships
+  infected-asyncio machinery (`tractor.to_asyncio`,
+  `tests/test_infected_asyncio.py`). Rejected as the *primary*
+  design because it makes every IPC send/recv cross a
+  loop-boundary shim in the hot path, and because #353 asks
+  explicitly for the asyncio support to be "rewritten for trio".
+  **But**: build it first as the throwaway spike (§6 step 0) to
+  de-risk the iroh API surface before writing the bridge.
+
+Version pinning: `iroh` moves fast and has had breaking
+API renames across minors. Pin `iroh>=X.Y,<X.Y+1` in a `quic`
+extra, and **write down the exact resolved version + the
+generated `iroh/_uniffi*` module layout** in the module
+docstring, because §2 depends on generated-code internals.
+
+**Step 0 of implementation is an API-truth pass**: install the
+pinned `iroh`, `python -c "import iroh; help(iroh)"`, and record
+in this doc's §1.1 the real names of: endpoint builder, secret
+key type, `connect`/`accept`, bi-stream open/accept, the
+send/recv methods and their exact signatures/return types, and
+whether they're `async def`. Everything below uses *provisional*
+names and must be reconciled. Do not skip this; do not guess
+from memory.
+
+### 1.1 API-truth table (fill in during step 0)
+
+| concept | provisional name | actual (fill in) |
+| --- | --- | --- |
+| secret key | `iroh.SecretKey.generate()` | |
+| endpoint builder | `iroh.Endpoint.builder(...).bind()` | |
+| node id | `endpoint.node_id() -> str` | |
+| node addr (relay + direct) | `iroh.NodeAddr` | |
+| dial | `await endpoint.connect(node_addr, alpn)` | |
+| accept conn | `await endpoint.accept()` | |
+| open bi-stream | `await conn.open_bi()` | |
+| accept bi-stream | `await conn.accept_bi()` | |
+| send | `await send_stream.write_all(b)` | |
+| recv | `await recv_stream.read(n) -> bytes\|None` | |
+| half-close | `await send_stream.finish()` | |
+
+---
+
+## 2. The `trio`-native uniffi future bridge (`tractor/ipc/_uniffi_trio.py`)
+
+### 2.1 what uniffi actually generates
+
+`uniffi`'s async support does not use asyncio *semantically* —
+it uses asyncio only as the *executor* for a poll loop. The
+generated python for an `async fn` is, in shape:
+
+1. call `_uniffi_..._<method>(...)` → returns an opaque
+   `RustFuture` handle (a `void*`/`u64`).
+2. loop: call
+   `ffi_..._rust_future_poll_<T>(handle, callback, callback_data)`.
+   The callback is a C-ABI fn pointer invoked **from an
+   arbitrary rust thread** with a poll-result code
+   (`READY`/`MAYBE_READY`).
+3. the generated glue's callback resolves an
+   `asyncio.Future` via `loop.call_soon_threadsafe(...)`; the
+   coroutine awaits it, then re-polls.
+4. on ready: `ffi_..._rust_future_complete_<T>(handle,
+   &call_status)` → the value; then
+   `ffi_..._rust_future_free_<T>(handle)`.
+
+**The asyncio dependency is confined to step 3.** That is the
+whole insight: the bridge is ~40 lines.
+
+### 2.2 the trio version
+
+```python
+async def await_rust_future(
+    poll: Callable,      # ffi_..._rust_future_poll_<T>
+    complete: Callable,  # ffi_..._rust_future_complete_<T>
+    free: Callable,      # ffi_..._rust_future_free_<T>
+    handle: int,
+    lift: Callable[[Any], Any],
+) -> Any:
+    '''
+    Drive a `uniffi` rust-future to completion on the current
+    `trio` task, bridging rust-thread wakeups via
+    `TrioToken.run_sync_soon()`.
+
+    '''
+    token = trio.lowlevel.current_trio_token()
+    while True:
+        wake = trio.Event()
+        # NOTE, invoked from a *rust* thread!
+        def _cb(_data, poll_code):
+            token.run_sync_soon(wake.set)
+
+        cb = _UNIFFI_FUTURE_CALLBACK(_cb)   # keep a strong ref!
+        poll(handle, cb, 0)
+        await wake.wait()
+        if <poll_code was READY>:
+            break
+    try:
+        status = _UniffiRustCallStatus.default()
+        res = complete(handle, status)
+        _uniffi_check_call_status(status)   # reuse generated helper
+        return lift(res)
+    finally:
+        free(handle)
+```
+
+Critical details, each a real bug if missed:
+
+- **`token.run_sync_soon()` is the only trio API callable from a
+  foreign thread**, and it is documented as such. Use it; do
+  *not* use `trio.from_thread.run_sync` (requires a trio thread
+  context) and do not touch the `Event` directly from the
+  callback.
+- **the poll code must reach the trio side.** Capture it in a
+  `nonlocal`/1-slot list written by the callback *before*
+  `run_sync_soon`, since the callback owns the value. Handle
+  `MAYBE_READY` by re-polling (the loop above does).
+- **keep the `ctypes` callback object alive** across the await —
+  a GC'd `CFUNCTYPE` trampoline is a segfault. Bind it to a
+  local *and* make sure the local outlives the `poll()` call
+  window.
+- **cancellation.** `await wake.wait()` is a trio checkpoint, so
+  a `Cancelled` can fire while rust still owns the future. On
+  cancel we must still `free(handle)` — and per uniffi, the
+  correct sequence is to call the generated
+  `ffi_..._rust_future_cancel_<T>(handle)` then continue
+  polling to completion before `free`. Wrap the whole thing so
+  the cancel path does:
+  `with trio.CancelScope(shield=True): cancel(handle); <drain
+  poll loop>; free(handle)`. **Bounded** shield (add a
+  `trio.move_on_after()` with a module-level constant) so a
+  wedged rust future can't make an actor un-cancellable —
+  `tractor` is SC-first and an unbounded shield here would
+  violate that.
+- **`trio.lowlevel.current_trio_token()`** must be captured on
+  the trio side (not in the callback).
+
+### 2.3 how to apply it to the generated bindings
+
+Do **not** fork/vendor the generated `iroh` python. Instead ship
+a *narrow* re-dispatch shim:
+
+- write `tractor/ipc/_uniffi_trio.py` with `await_rust_future()`
+  plus a `@cm patch_uniffi_for_trio()` that monkey-patches the
+  generated module's single async-driver entrypoint (in current
+  uniffi that's `_uniffi_rust_call_async` / `_rust_call_async`,
+  one function) to the trio implementation.
+- verify at import time that the expected symbol exists and
+  raise a clear, actionable error naming the pinned `iroh`
+  version if not. A silent fallback to asyncio would be a
+  nightmare to debug.
+- **plan for this to break on `iroh`/`uniffi` upgrades.** Mitigate
+  with (a) a unit test that drives one trivial `iroh` async call
+  under bare `trio.run()` and asserts no event loop was ever
+  created (`asyncio.get_event_loop_policy()` untouched /
+  `asyncio._get_running_loop() is None`), and (b) a docstring
+  pointing at the uniffi codegen template this mirrors.
+
+If step 0 reveals the generated code is *structurally* hostile
+to this (e.g. `asyncio` imported and used at module scope for
+more than the driver), fall back to option (b): run iroh under
+`tractor.to_asyncio` infected mode and open the follow-up to
+revisit. Say so in the PR rather than fighting it.
+
+---
+
+## 3. Mapping QUIC onto `MsgTransport`
+
+### 3.1 the layering decision
+
+QUIC natively multiplexes streams inside one connection. The
+mapping that preserves *all* existing `tractor` semantics with
+the least new code:
+
+```
+iroh Endpoint      ==  one per actor (process)     -> the "listener"
+iroh Connection    ==  one per peer actor           -> pooled
+iroh bi-stream     ==  one `Channel`/`MsgTransport`  -> 1:1
+```
+
+- keep the 4-byte `<I` length-prefix framing **unchanged**. It's
+  redundant-ish over a QUIC stream but it means
+  `MsgpackTransport` is reused verbatim, and framing is cheap.
+  Revisit only after it works.
+- **one-task-per-stream** falls out naturally, which is exactly
+  the #353 note about QUIC sub-stream QoS/cancellation fitting
+  `trio`.
+- `layer_key: int = 4` still (QUIC is L4-ish); note in a comment
+  that this backend is really 4+security+multiplex.
+
+**Connection pooling** is the one place we add state the other
+backends don't have: dialing the same peer twice should reuse
+the `Connection` and open a second bi-stream. Implement as a
+module-level `dict[NodeId, Connection]` guarded by a
+`trio.Lock`... **no** — that's a per-process cache with
+lifetime/teardown hazards. Instead reuse the codebase's existing
+idiom: `tractor.trionics.maybe_open_context()` keyed on the
+node-id, which already solves exactly this (one-cached-resource-
+per-key, refcounted, teardown-on-last-exit) and whose teardown
+semantics were just hardened (gh #488). Use it; do not hand-roll
+a cache. Anything concurrency-subtle here should get the
+`conc-anal` skill run over it.
+
+### 3.2 `IrohAddress`
+
+```python
+class IrohAddress(
+    msgspec.Struct,
+    frozen=True,
+):
+    _node_id: str                 # 32B ed25519 pubkey, hex or z32
+    _alpn: str = 'tractor/0'      # the bindspace!
+    # optional dial hints; NOT part of identity
+    maybe_relay_url: str|None = None
+    maybe_direct_addrs: tuple[str, ...] = ()
+
+    proto_key: ClassVar[str] = 'iroh'   # ?or 'quic'; see §3.2.1
+    unwrapped_type: ClassVar[type] = tuple[str, str]
+    def_bindspace: ClassVar[str] = 'tractor/0'
+```
+
+- **`.unwrap() -> (node_id_str, alpn_str)`** — a `(str, str)`
+  tuple, which is *unambiguously distinct* from
+  `TCPAddress`'s `(str, int)`. But careful:
+  `wrap_address()`'s UDS case is
+  `case (_, filename) if type(filename) is str` — which
+  **already catches `(str, str)`**. So the iroh `case` MUST be
+  ordered *before* the UDS case and guarded, e.g.
+  `case (str() as nid, str() as alpn) if _is_node_id(nid):`
+  with `_is_node_id()` a cheap length+alphabet check. Add a
+  regression test asserting a UDS `(dir, filename)` pair still
+  wraps to `UDSAddress` — this is the exact "wrong transport
+  loaded" hazard `_addr.py:214` warns about.
+- `.bindspace` → `self._alpn`. This is the honest analogue:
+  the ALPN is the set of endpoints willing to talk to you, and
+  two `tractor` deployments sharing an iroh network are
+  separated by ALPN exactly as two UDS deployments are
+  separated by directory. Include a `tractor` version/proto
+  epoch in the default ALPN so incompatible runtimes can't
+  handshake.
+- `.is_valid` → node-id parses, alpn non-empty.
+- **`get_root()` is the hard one.** There is no
+  well-known-port analogue: an iroh node id is a *keypair*, so
+  "the host's default registrar addr" requires a *persisted
+  secret key*. Design:
+  - the root/registrar's secret key lives at
+    `get_rt_dir() / 'iroh_registrar.key'` (0600), created on
+    first use.
+  - `get_root()` must stay **pure and import-time-safe**
+    (contract §2.3: `_default_lo_addrs` is built at import!).
+    So `get_root()` *reads* the key file if present and
+    otherwise returns an `IrohAddress` with
+    `_node_id=''`/sentinel, and the **generation** happens in
+    an explicit sibling — `ensure_registrar_key() ->
+    IrohAddress` — called from the listen path. Pure getter,
+    explicit setter; do not smuggle key generation into
+    `get_root()`.
+  - this almost certainly means `_default_lo_addrs` must become
+    lazy for this backend. **Land that refactor as its own prep
+    commit** (a `default_lo_addrs()` that computes per-call
+    instead of the import-time dict) — it also unblocks plan
+    03's netns-scoped defaults.
+- `get_random()`: generate a fresh `SecretKey` per subactor and
+  return its node-id. Note this runs post-fork pre-listen
+  (contract §4) and costs an ed25519 keygen (~µs, fine). The
+  *secret* can't live in a frozen `Address`, so it must be
+  stashed where the listen path can find it: a module-level
+  `dict[node_id, SecretKey]` populated by `get_random()` and
+  consumed+popped by `start_listener()`. Ugly but honest;
+  document it and note the alternative (thread the key through
+  `Endpoint`) as a follow-up.
+
+#### 3.2.1 `proto_key`: `'iroh'` vs `'quic'`
+
+Use **`'quic'`** for the `proto_key`/`--tpt-proto` name and
+name the module `_quic.py`, with `iroh` as the *implementation*.
+Rationale: it keeps the door open for the `aioquic` fallback
+(§1) without a user-visible rename, and it matches how `uds` is
+a proto name rather than a lib name. Put `iroh`-specific bits
+behind an internal `_iroh` submodule if the file gets big.
+
+### 3.3 the `trio.abc` adapters — where the real work is
+
+Contract §3 says a non-socket backend needs three upstream
+generalizations. Land them **as a prep PR, before any iroh
+code**, so they can be reviewed on their own merits with
+tcp/uds still the only backends:
+
+1. **`Endpoint.start_listener()` must not assume
+   `.socket.getsockname()`.** Use the same
+   `Address.rebind_from_sockname: ClassVar[bool]` gate that
+   plan 01 §3.2 introduces — coordinate so it lands once. (If
+   plan 01 lands first, this is free.)
+2. **`transport_from_stream()` (`_types.py:92`) must not assume
+   `trio.SocketStream`.** Replace the `sock.family` match with:
+   check `isinstance(stream, trio.SocketStream)` → existing
+   family match; else look for a
+   `stream.tpt_key: ClassVar[MsgTransportKey]` attribute on the
+   adapter and use it. Keeps the existing path byte-identical
+   and makes new stream types self-describing (a much better
+   shape than growing an `isinstance` ladder).
+3. **type annotations**: `handle_stream_from_peer(stream:
+   trio.SocketStream)` → `trio.abc.Stream`; `Endpoint._listener:
+   SocketListener|None` → `trio.abc.Listener|None`;
+   `MsgTransport.stream: trio.SocketStream` →
+   `trio.abc.Stream`. Annotation-only, zero behaviour change.
+
+Then the adapters:
+
+```python
+class QuicMsgStream(trio.abc.HalfCloseableStream):
+    '''
+    A single `iroh` bi-directional QUIC stream presented as
+    a `trio` byte-stream so `MsgpackTransport` can frame over
+    it unmodified.
+
+    '''
+    tpt_key: ClassVar[MsgTransportKey] = ('msgpack', 'quic')
+
+    def __init__(self, conn, send, recv) -> None: ...
+    async def send_all(self, data: bytes) -> None: ...
+    async def wait_send_all_might_not_block(self) -> None: ...
+    async def receive_some(self, max_bytes: int|None = None) -> bytes: ...
+    async def send_eof(self) -> None: ...
+    async def aclose(self) -> None: ...
+```
+
+Non-negotiable behaviours (each maps to a `match` case that
+already exists in `_transport.py` and must keep working):
+
+- `receive_some()` returns `b''` at clean EOF →
+  `MsgpackTransport._iter_packets()` sees `header == b''` and
+  raises `TransportClosed(loglevel='transport')`. **This is the
+  graceful-disconnect path the whole runtime relies on**; get it
+  right first.
+- a reset/aborted stream → raise `trio.BrokenResourceError`.
+- use after local close → raise `trio.ClosedResourceError`
+  (ideally with `'another task closed this fd'`-equivalent text
+  absent, so the `raise_on_report` branch at
+  `_transport.py:290` stays quiet).
+- `send_all()` on a closed peer → `trio.BrokenResourceError`.
+- honour `trio`'s one-task-per-direction rule: guard with
+  `trio._util.ConflictDetector` equivalents (or just document +
+  assert), because `MsgpackTransport` already serializes sends
+  with a `StrictFIFOLock` but recvs are single-task by
+  construction.
+- **buffering**: if iroh's `read()` doesn't support
+  "read up to n", `receive_some()` must maintain an internal
+  leftover buffer. Note `MsgpackTransport` wraps us in
+  `tricycle.BufferedReceiveStream` anyway, so `receive_some()`
+  just needs *some* nonzero-progress contract.
+
+```python
+class QuicListener(trio.abc.Listener):
+    '''
+    Accepts iroh `Connection`s and yields one `QuicMsgStream`
+    per accepted bi-stream, so `trio.serve_listeners()` spawns
+    one `handle_stream_from_peer()` per `Channel`.
+
+    '''
+    async def accept(self) -> QuicMsgStream: ...
+    async def aclose(self) -> None: ...
+```
+
+The accept-side subtlety: `trio.abc.Listener.accept()` yields
+one stream per call, but iroh gives us *connections* which then
+yield *streams*. So `QuicListener` needs an internal
+`trio.MemoryReceiveChannel[QuicMsgStream]` fed by a background
+task-pair (one task accepting connections, one per connection
+accepting bi-streams). `trio.abc.Listener` has no nursery, so:
+make the listener **constructed by an `@acm`** that owns the
+nursery, and have `start_listener()` be that `@acm`'s driver.
+
+⚠️ this collides with `Endpoint.start_listener()` being a plain
+`async def` returning a listener. Two options:
+- **(a)** hang the nursery off the `Endpoint`'s existing
+  `listen_tn` — `_serve_ipc_eps()` already creates `listen_tn`
+  and passes it into every `Endpoint` (`_server.py:1063-1074`),
+  and `Endpoint.listen_tn` is right there. So
+  `start_listener()` can `self.listen_tn.start_soon(...)` the
+  acceptor tasks. **Recommended**: no upstream signature change,
+  correct lifetime (dies with the ep group), and it's why
+  `listen_tn` is on the struct in the first place.
+- (b) change `start_listener()` to a `@acm`. Bigger blast
+  radius; only if (a) proves insufficient.
+
+Since `start_listener()` is called via
+`inspect.getmodule(addr)` with only `addr=` (contract §1.3),
+option (a) needs the `Endpoint` itself. Either add `ep=` to the
+module-level `start_listener()` call signature (all backends
+ignore it except quic → small upstream change, do it as part of
+the prep PR and make it keyword-only with a default) or have
+`QuicListener.accept()` lazily spawn via
+`trio.lowlevel.current_task().parent_nursery` (**rejected** —
+fragile, implicit). Do the explicit `ep=` kwarg.
+
+### 3.4 `maddr`
+
+Multiaddr already standardizes the pieces:
+
+```
+/ip4/<h>/udp/<p>/quic-v1                     # direct
+/ip4/<h>/udp/<p>/quic-v1/p2p/<node-id>       # direct + identity
+/dns/<relay-host>/tcp/443/tls/ws/p2p/<node>  # relay-ish
+```
+
+- primary form: `/p2p/<node-id>` alone is a legal maddr and is
+  the *only* required component for iroh dialling — relay +
+  direct addrs are discovery hints. So `mk_maddr()` emits
+  `/p2p/<node_id>` and, when known, prefixes the direct
+  `/ip4/../udp/../quic-v1/`.
+- `/p2p/` values are multihash-encoded peer ids; an iroh node-id
+  is a raw ed25519 key. Converting requires the identity
+  multihash + libp2p key protobuf wrapper. **Decide**: emit the
+  raw node-id under a *tractor-local* `/iroh/<node-id>` segment
+  (needs upstream registration, same track as `wg`/`tipc`,
+  gh #483) rather than pretending to be a libp2p peer-id we
+  can't round-trip. Return the `str` form until upstream lands
+  (`MsgTransport.maddr` is `Multiaddr|str`).
+- this backend is the strongest argument for gh #443's
+  **tunnelled/composed maddr** item: `/ip4/../udp/../quic-v1/..`
+  *is* a composed stack. Cross-reference plan 03 §5 so the two
+  grammars land compatibly.
+
+---
+
+## 4. Discovery integration
+
+- iroh's node-id addressing means the `tractor` registrar can
+  hold `IrohAddress`es that are **reachable from anywhere** with
+  no port-forwarding — that is the headline feature. The
+  registrar itself works unchanged.
+- iroh has its own discovery (DNS/pkarr/mdns). **Out of scope**;
+  note in the follow-up that `tractor.discovery` could
+  eventually delegate to it, which would be the direct analogue
+  of plan 01's TIPC-topology idea.
+- relay servers: default to n0's public relays for the demo,
+  document self-hosting (docs.iroh.computer's dedicated-infra
+  page is linked from #353), and make the relay set a
+  `start_listener()` kwarg.
+
+## 5. Security note
+
+QUIC is TLS-1.3-always and iroh authenticates by node-id, so
+this backend is the first `tractor` transport with real
+transport security and peer authentication. Two things follow:
+1. an **allowlist hook** — an actor should be able to reject
+   inbound connections from unknown node-ids *before* the
+   `Aid` handshake. Natural home: a predicate kwarg on
+   `start_listener()`, evaluated in `QuicListener`'s connection
+   acceptor task. Sketch it; ship it in PR 1 if cheap (it is).
+2. do **not** claim any security property for the other
+   backends by association. `tcp`/`uds`/`tipc` remain
+   unauthenticated; that's what plan 03 (wg) is for.
+
+## 6. Commit sequencing
+
+0. **spike (throwaway, not committed)**: drive iroh under
+   `trio-asyncio`/`tractor.to_asyncio`, echo bytes over a
+   bi-stream between two procs. Fills in §1.1. Timebox it.
+1. prep PR: annotation widening + `rebind_from_sockname` gate +
+   `transport_from_stream()` `tpt_key` dispatch + `ep=` kwarg on
+   `start_listener()` + lazy `default_lo_addrs()`. **No new
+   backend.** Full suite green on tcp *and* uds.
+2. `_uniffi_trio.py` + its tests (drive one iroh async call
+   under bare `trio.run()`; assert no asyncio loop; assert
+   cancellation frees the future).
+3. `QuicMsgStream` + tests against a *loopback* iroh endpoint
+   pair in one process (no `tractor` runtime): send/recv, clean
+   EOF → `b''`, reset → `BrokenResourceError`, use-after-close
+   → `ClosedResourceError`.
+4. `QuicListener` + `start_listener()` + `IrohAddress` +
+   key-file mgmt.
+5. `MsgpackQuicStream(MsgpackTransport)` + `connect_to()` +
+   `maybe_open_context()` connection pooling.
+6. registration tables + `--tpt-proto quic` + full suite.
+7. maddr + docs + a two-host example (pairs with #482's format).
+
+## 7. Testing
+
+- capability predicate `is_quic_available()` → `iroh` importable
+  *and* the uniffi driver symbol present at the pinned version.
+  Same `pytest.fail`-early hook as plan 01 §7.2.
+- **the acceptance bar is the same**: whole suite green under
+  `--tpt-proto quic`. Expect this to shake out real bugs in the
+  adapters (esp. teardown ordering and `TransportClosed`
+  classification) — that's the point.
+- expect to need **timeout headroom**: iroh endpoint bind +
+  first connect (relay discovery) is orders of magnitude slower
+  than a UDS bind. Before touching any test deadline, rule out
+  the CPU-throttle false-positive (see the project's
+  `env_cpu_throttle_masquerades_as_regression` note); then, if
+  real, add a per-proto timeout multiplier to the test harness
+  rather than editing individual tests.
+- a no-network test mode: iroh with relays disabled +
+  loopback direct addrs only, so CI doesn't depend on n0's
+  infra. **Make this the default in CI**; mark the relay tests
+  `pytest.mark.net` and keep them out of the default run.
+- leak checks: assert every `SecretKey`/`Endpoint` is closed on
+  actor teardown (an `Endpoint` left open holds UDP sockets and
+  relay connections; a leak here shows up as hung tests, not
+  errors).
+
+## 8. Risks
+
+| risk | mitigation |
+| --- | --- |
+| uniffi codegen internals shift on upgrade | pinned minor, symbol assertion at import, the "no asyncio loop" test, documented fallback to `to_asyncio` |
+| rust-thread callback → trio wakeup mishandled (segfault / lost wakeup / un-cancellable task) | strong ref on the ctypes trampoline; `run_sync_soon` only; **bounded** shielded cancel-drain; run the `conc-anal` skill over the bridge |
+| `iroh` wheel availability for 3.13/3.14 on linux+macos | verify in step 0; if missing, that alone may force the `aioquic` fallback |
+| QUIC latency/jitter destabilizes the existing suite's timing assumptions | per-proto timeout multiplier, relay-less CI mode |
+| `(str, str)` unwrapped form collides with UDS in `wrap_address()` | guarded case ordered first + explicit regression test (§3.2) |
+| scope creep into iroh's docs/blobs/gossip crates | this backend is `Endpoint`+`Connection`+bi-streams only; anything else is a separate issue |
+
+## 9. Follow-up issue seeds
+
+- `tractor.discovery` delegating to iroh discovery (DNS/pkarr/mdns)
+- per-`Context` QUIC sub-streams: today one `Channel` == one
+  stream; QUIC would let each `tractor.Context` own its own
+  stream with independent flow-control and cancellation — this
+  is the genuinely novel win #353 gestures at, and it's a
+  runtime-layer change, not a transport one
+- unreliable QUIC datagrams for a lossy-ok broadcast transport
+  (pairs with plan 01's TIPC-multicast seed)
+- node-id allowlist → a real `tractor` authz story
+- `aioquic` sans-io backend reusing §3's adapters

ai/tpt-backends/03_wg_tunnel_bindspace.md

@@ -0,0 +1,449 @@
+# Plan 03 — WireGuard (and other tunnels) as a *nested bindspace* via `pyroute2`
+
+Tracks gh [#482] + the tunnelled-maddr item of [#443].
+Prereq reading:
+[`00_shared_backend_contract.md`](./00_shared_backend_contract.md).
+
+**Thesis**: WireGuard is **not** a `MsgTransport`. It is an
+interface-layer tunnel that is transparent to `socket(2)`, so
+the correct abstraction is a *bindspace* — a scoped,
+`@acm`-managed network context that an existing L4 transport
+(`tcp`, and later `quic`/`tipc`-over-UDP-bearer) binds *inside*.
+This plan implements `Address.namespace` (spec'd but unused
+since day one) and the composed/tunnelled maddr grammar, with
+`pyroute2` as the netlink codec and as much of the I/O moved
+onto `trio` as the library's sans-io layer allows.
+
+[#482]: https://github.com/goodboy/tractor/issues/482
+[#443]: https://github.com/goodboy/tractor/issues/443
+
+---
+
+## 1. What exists today (verified, per #482)
+
+- `wrap_address()` accepts maddr `str`s (leading-`/` dispatch,
+  `_addr.py:262`) but `parse_maddr()` only knows
+  `/ip4|ip6/<h>/tcp/<p>` and `/unix/<p>`; a `.../wg/u<key>`
+  maddr raises `ValueError('Unsupported multiaddr protocol
+  combo')`.
+- there is no `wg` proto in the multiaddr spec; the first-draft
+  upstream PR is multiformats/py-multiaddr#108 with key form
+  `u<base64url>` (commit `8be3a8b`), tracked by
+  multiformats/py-multiaddr#107 and gh #483.
+- so **today's deployable story is declarative**: run `wg-quick`
+  out-of-band, parse the maddr, strip to the inner
+  `(host, port)`, verify the pubkey against the live tunnel,
+  hand the inner addr to `registry_addrs=`/`tpt_bind_addrs=`.
+  #482 already contains working example code for exactly this.
+- `Address.namespace` exists in the Protocol
+  (`_addr.py:94-101`, "the if-available OS-specific network
+  namespace key") and **no backend implements it**. This plan is
+  its first consumer.
+
+## 2. Three layers, three PRs
+
+| layer | what | dep | ships |
+| --- | --- | --- | --- |
+| **A. declarative** | commit #482's examples; `parse_maddr()` learns `/wg/u<key>` → inner `Address` + verified pubkey | `multiaddr` (already), `wg(8)` CLI | first |
+| **B. `pyroute2` read/verify** | replace the `subprocess.run(['sudo','wg','show'])` shelling with netlink queries | `pyroute2` extra | second |
+| **C. `@acm` lifecycle** | create/configure/tear down wg ifaces + netns *from the runtime*, as nested bindspaces; implement `Address.namespace` | `pyroute2` + `CAP_NET_ADMIN` | third |
+
+Each is independently valuable and independently reviewable.
+**Do not attempt C first** — the interesting design (nested
+bindspace `@acm`s) is only well-posed once A has pinned the
+address grammar and B has proven the netlink path under trio.
+
+---
+
+## 3. Layer A — declarative `wg` maddrs
+
+### 3.1 the address shape
+
+The decision: **a wg segment annotates an existing address, it
+does not create a new address type.** Two candidate encodings;
+**pick (a)**:
+
+- **(a) `TunnelledAddress` wrapper** (recommended):
+  ```python
+  class TunnelledAddress(
+      msgspec.Struct,
+      frozen=True,
+  ):
+      inner: Address           # e.g. TCPAddress
+      tunnel: WGTunnelSpec     # proto-specific, frozen
+  ```
+  with `.proto_key` **delegating to `inner.proto_key`** so every
+  existing table lookup (`_addr_to_transport`,
+  `enable_transports` guard at `_root.py:391`,
+  `transport_from_addr()`) keeps working untouched, and
+  `.unwrap()` delegating to `inner.unwrap()` so **nothing new
+  crosses the wire**. `.namespace` and `.bindspace` come from
+  the tunnel spec. The wrapper is stripped (`→ .inner`) at the
+  moment of bind/connect.
+  - ⚠️ `is_wrapped_addr()` (`_addr.py:194`) tests
+    `type(addr) in _address_types.values()` — a `bidict` of
+    proto_key→type. `TunnelledAddress` isn't in it and must not
+    be (it's not 1:1 with a proto). So either add an explicit
+    `isinstance(addr, TunnelledAddress)` clause there, or give
+    the wrapper a marker and test structurally. Do the former;
+    it's two lines and honest.
+  - the reflection in `Endpoint.start_listener()`
+    (`inspect.getmodule(self.addr)`) would resolve to the
+    *wrapper's* module, not the transport's. **So the wrapper
+    must be unwrapped before it reaches `Endpoint`** — i.e. by
+    the bindspace `@acm` (layer C) or by `parse_maddr()`
+    (layer A). State this loudly in the docstring; it's the #1
+    way to get this wrong.
+- (b) add fields to each existing `Address` type. Rejected:
+  duplicates tunnel logic per-backend and pollutes `.unwrap()`.
+
+```python
+class WGTunnelSpec(
+    msgspec.Struct,
+    frozen=True,
+):
+    peer_pubkey: str          # std-base64 `wg(8)` form
+    iface: str = 'wg0'
+    netns: str|None = None
+    # layer-C-only fields, unset in layer A
+    maybe_endpoint: tuple[str, int]|None = None
+    maybe_allowed_ips: tuple[str, ...] = ()
+```
+
+### 3.2 `parse_maddr()`/`mk_maddr()`
+
+Grammar — **verified** against py-multiaddr#108
+(`baudco/py-multiaddr@wg_support`, installed in a throwaway venv;
+all three forms below parse *and* round-trip):
+
+```
+/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
+```
+
+The `/wg/` segment is **infix, not suffix** — the segments
+*before* it are the wg **bearer** (the underlay `(ip, udp-port)`
+that `wg(8)` itself listens on, per the codec docstring's own
+`/ip4/1.2.3.4/udp/51820/wg/{key}` example), and the segments
+*after* are the **overlay** endpoint that `tractor` binds.
+
+⚠️ **CORRECTION** — an earlier revision of this plan (and the
+examples in gh #482) used a *suffix* form
+`/ip4/10.0.11.1/tcp/1616/wg/u<key>`. That parses, but it is
+semantically inverted: it puts the overlay addr where the bearer
+belongs, `tcp` where wg's `udp` `ListenPort` goes, and declares
+no overlay endpoint at all. `parse_wg_maddr()` in
+`examples/wg_lan/` now rejects it with an actionable error.
+Observed protocol-name lists, for writing the `match`:
+
+| maddr | `[p.name for p in m.protocols()]` |
+| --- | --- |
+| `/ip4/1.2.3.4/udp/51820/wg/u<k>` | `['ip4','udp','wg']` |
+| `/ip4/../udp/../wg/u<k>/ip4/../tcp/..` | `['ip4','udp','wg','ip4','tcp']` |
+
+- so the three parts have **three different owners**, and only the
+  third is an `Endpoint`:
+
+  | part | bound by | in the runtime? |
+  | --- | --- | --- |
+  | 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 `.inner` |
+
+  This owner-split is the real axis of the design, *not* whether
+  the maddr stack is "composed" (it is).
+- `parse_maddr()` gains a case on
+  `[('ip4'|'ip6'), 'udp', 'wg', ('ip4'|'ip6'), <inner-l4>]` →
+  build the inner `Address` from the trailing segments, decode
+  the multibase key to std-base64, and return
+  `TunnelledAddress(inner=..., tunnel=WGTunnelSpec(...))` with
+  the bearer recorded in the spec.
+- keep the existing 2-proto cases byte-identical; add the new
+  case *after* them.
+- generalize by **peeling at the tunnel segment**: split
+  `proto_names` at `'wg'`, hand the trailing list to the existing
+  inner-stack logic, and recurse for nested tunnels. Write it as
+  a small pure fn `_peel_tunnel_segs(proto_names) ->
+  (bearer_names, tunnel_specs, inner_names)`. This is also what
+  makes a wg-inside-wg stack fall out for free.
+- `mk_maddr()` inverse for `TunnelledAddress`.
+- **blocked on upstream**: `Multiaddr('/…/wg/u…')` only parses
+  once py-multiaddr#108 lands. Until then: pin the branch in the
+  `wg` extra / dev-group and gate the tests on
+  `_have_wg_maddr_proto()` (a cheap try/except around
+  `Multiaddr('/wg/uAAAA')`). Do **not** hand-roll a `wg` parser
+  in `tractor` — the whole point of #429 was dropping the NIH
+  parser.
+
+### 3.3 verification helper (pure, composable)
+
+Port #482 §2's helpers into `tractor/discovery/_tunnel.py` as
+*pure functions* + one impure probe, cleanly separated:
+
+```python
+def parse_wg_maddr(maddr: str) -> TunnelledAddress: ...   # pure
+def wg8_pubkey(multibase_key: str) -> str: ...            # pure
+def verify_wg_peer(spec: WGTunnelSpec) -> bool: ...       # impure probe
+```
+
+In layer A `verify_wg_peer()` may shell out (`wg show <if>
+peers`), but it must be a *single* function so layer B swaps
+only its body. Never call it implicitly from
+`wrap_address()`/`parse_maddr()` — parsing must stay pure and
+side-effect-free; verification is the *caller's* explicit step
+(and later, the bindspace `@acm`'s).
+
+### 3.4 deliverables
+
+- `examples/` scripts distilled from #482 §§3-5 (this is the
+  unchecked "commit examples from ^" bullet in #443).
+- a `docs/` page: tunnel setup, the maddr form, the two-host
+  run. Keep prose in the docs; keep the examples runnable and
+  minimal.
+- tests: maddr round-trip, `TunnelledAddress` delegation
+  (`proto_key`/`unwrap` identical to inner), `wrap_address()`
+  regression (a tunnelled maddr `str` → `TunnelledAddress`; a
+  plain one → unchanged), and **a real end-to-end over a
+  locally-created wg pair** gated on `CAP_NET_ADMIN` (see §5.3).
+
+---
+
+## 4. Layer B — `pyroute2` under `trio`
+
+### 4.1 the library situation (verify at implementation time)
+
+`pyroute2` ≥0.9 rewrote its core onto **asyncio**
+(`AsyncIPRoute`; the sync `IPRoute` wraps it with its own loop).
+It also ships a `WireGuard` netlink (generic-netlink) module
+supporting `.set(iface, private_key=..., peer={...})` and
+`.info(iface)`, plus `pyroute2.netns` / `NetNS` for namespaces,
+and `IPRoute.link('add', kind='wireguard', ifname=...)`.
+
+Three integration options, in increasing trio-nativeness:
+
+- **(1) `trio.to_thread.run_sync()` around the sync API.**
+  Netlink ops here are one-shot, sub-millisecond, and happen at
+  bind/teardown time only — *not* in the msg hot path. This is
+  the **correct default**: it's ~10 lines, uses a battle-tested
+  API, and costs nothing where it's used.
+- **(2) sans-io: `trio.socket` + pyroute2's message codecs.**
+  `pyroute2`'s message classes
+  (`pyroute2.netlink.rtnl.*`, `pyroute2.netlink.generic.wireguard.wgmsg`)
+  encode/decode independently of its I/O core. So a
+  `tractor/ipc/_netlink.py` with a small trio `NetlinkSocket`
+  (`trio.socket.socket(AF_NETLINK, SOCK_RAW|SOCK_DGRAM, proto)`,
+  `sendto`/`recv`, seq/pid matching, `NLMSG_DONE`/`NLMSG_ERROR`
+  handling) + pyroute2 codecs is very achievable and is the
+  honest reading of "as much trio wrapping as possible where any
+  other async support can be replaced".
+  **Do this for the paths we actually need** (link add/del,
+  addr add, wg get/set, netns bind) and *only* those — a
+  general netlink client is out of scope.
+- (3) reimplement the codecs. Never.
+
+**Recommended split**: ship (1) first so layer B is a small,
+reviewable, behaviour-preserving swap of `verify_wg_peer()`'s
+body; then land (2) as a follow-up commit for the read path
+(`wg get`, `link get`) where the sans-io surface is smallest,
+and keep (1) for the privileged mutating ops. Measure before
+converting anything else — there is no perf argument here, only
+a "no foreign event loop in a trio actor" argument, which (1)
+already satisfies (a thread is not an event loop).
+
+Explicitly **do not** pull in `trio-asyncio` for pyroute2: it
+would be the one place in the runtime where an asyncio loop
+exists for no reason.
+
+### 4.2 API shape
+
+Pure-ish, functional, `@acm` for anything with teardown:
+
+```python
+async def read_wg_peers(
+    iface: str = 'wg0',
+    netns: str|None = None,
+) -> tuple[str, ...]: ...          # base64 pubkeys
+
+async def read_wg_pubkey(iface: str = 'wg0', ...) -> str: ...
+```
+
+and `verify_wg_peer()` becomes a thin composition over the two.
+Note the pure-getter rule: no `read_wg_peers(..., create=True)`.
+
+---
+
+## 5. Layer C — nested bindspace `@acm`s + `Address.namespace`
+
+This is the part #443 and `multiaddr_declare_eps.md` actually
+ask for: *"for any tunneled maddr-`str`-entry we deliver a
+data-structure which can easily be passed to nested `@acm`s
+which consecutively setup nested net bindspaces for binding the
+endpoint addrs"*.
+
+### 5.1 the composition
+
+```python
+@acm
+async def open_bindspace(
+    addr: TunnelledAddress,
+) -> AsyncGenerator[Address, None]:
+    '''
+    Enter the net-bindspace implied by `addr`'s tunnel stack,
+    yielding the *inner* `Address` ready to bind/connect.
+
+    Nests: one `@acm` per tunnel segment, outermost-first, so
+    a 2-deep stack is just two nested `async with`s and the
+    teardown order is guaranteed by `trio`.
+
+    '''
+```
+
+with per-tunnel-kind implementations:
+
+```python
+@acm
+async def open_netns(name: str) -> AsyncGenerator[None, None]: ...
+@acm
+async def open_wg_iface(spec: WGTunnelSpec) -> AsyncGenerator[WGTunnelSpec, None]: ...
+```
+
+and a driver that folds a list of specs into nested contexts
+(`contextlib.AsyncExitStack` for the N-deep case). The
+`parse_endpoints()` API (`_multiaddr.py:153`) is the front door:
+it already returns `dict[name, list[Address]]` and the
+`multiaddr_declare_eps.md` sketch anticipates the recursive
+`dict[str, list[Address]]|dict[...]` return for tunnelled
+entries. Extend it to carry the tunnel stack, not to *enter* it.
+
+### 5.2 `Address.namespace`, at last
+
+- `TunnelledAddress.namespace` → `(kind, id)` e.g.
+  `('netns', 'tractor-wg0')`.
+- **and** the existing backends should implement it as `None`
+  explicitly (they currently just don't define it), so the
+  Protocol stops lying.
+- consumers to audit: nothing reads `.namespace` today — so
+  adding it is safe, but the *point* is that
+  `Endpoint`/`Server.pformat()` should start showing it (there's
+  already a `# !TODO, always be ns aware!` +
+  `f'|_netns: {netns}\n'` placeholder sitting in
+  `Endpoint.pformat()`, `_server.py:645`). Fill that in; it's
+  the cheapest possible proof the layer is wired.
+
+### 5.3 the netns/process reality — read this before designing
+
+**The headline consequence, stated up front**: netns is a
+**runtime-level config API, not an actor-app-code API.** It is
+declared as part of how an actor process is *brought up* — a
+spawn-time/boot-time input alongside `enable_transports` and
+`tpt_bind_addrs` — and it is **not** dynamically re-enterable by
+app code once the actor is live. There is deliberately no
+`await actor.enter_netns(...)`. Two hard reasons, both below:
+`setns(2)` doesn't retroactively move existing sockets, and it's
+per-thread rather than per-process. Anything that *looks* like a
+mid-life API here would be a footgun that silently leaves the IPC
+server bound in the old namespace.
+
+- `setns(2)` with `CLONE_NEWNET` affects **the calling thread
+  only**, and sockets already created keep their original netns.
+  A trio actor is effectively single-threaded for our purposes,
+  so "enter the netns, *then* bind" works — but any
+  `to_thread` worker (§4.1 option 1!) is in the **original**
+  netns unless it also `setns`. Concretely: a wg query issued
+  via `trio.to_thread` will hit the wrong namespace. Either
+  pass `netns=` down to `pyroute2` (which does the
+  fork/setns dance itself) or pin a dedicated worker. **This is
+  the single subtlest bug in this plan — write the test first.**
+- entering a netns is *process-global-ish and irreversible-ish*
+  in practice. Therefore: **netns membership belongs to the
+  actor process, decided before the runtime binds**, not to a
+  mid-life `@acm`. Design:
+  - the root/parent decides the netns for a subactor and passes
+    it in the spawn spec (there's already
+    `enable_transports`/`accept_addrs` plumbing at
+    `_runtime.py:1595-1615` — the netns rides alongside).
+  - the child, in `_runtime.async_main()` **before**
+    `IPCServer.listen_on()`, enters it.
+  - the mid-life `@acm` form is then only for the *root* /
+    single-actor case, and for iface creation (which is
+    genuinely scoped).
+  - document the constraint rather than hiding it; a
+    `RuntimeError` if `open_netns()` is entered after any
+    listener exists.
+- privileges: iface/netns creation needs `CAP_NET_ADMIN`.
+  Never `sudo` from inside the runtime. Two supported modes:
+  (i) pre-provisioned out-of-band (layers A/B — the default,
+  and what #482 documents), (ii) runtime-managed when the
+  process already holds the cap. Detect with a cheap
+  `os.geteuid()==0 or CAP_NET_ADMIN in /proc/self/status`
+  probe and *fail loudly with an actionable message* otherwise.
+- teardown must be idempotent and tolerant: an iface/netns
+  already gone must not strand the rest of the teardown — the
+  exact lesson `_uds.close_listener()`'s `FileNotFoundError`
+  tolerance and `_serve_ipc_eps()`'s per-ep `try/except`
+  encode. Mirror both.
+
+### 5.4 tests for layer C
+
+- unit: fold-N-tunnel-specs-into-nested-`@acm`s, with fakes; assert
+  enter/exit ordering (outermost-last-out) via a trace list.
+- integration, gated on `CAP_NET_ADMIN` (skip otherwise, and in
+  CI run it in a `--cap-add NET_ADMIN` container job): create two
+  netns + a wg pair entirely in-process, boot a `tractor` root in
+  one and a subactor in the other, `find_actor()` across the
+  tunnel. This is a *fantastic* test to have and is fully
+  self-contained — no second host, no `sudo` in the test body.
+- the `to_thread`-netns-mismatch regression from §5.3, written
+  **first** (red), then the fix (green), per project convention.
+
+---
+
+## 6. "Other shuttle-able tpts"
+
+The generalization the #482 follow-up gestures at: once
+`TunnelledAddress` + `open_bindspace()` exist, the same
+machinery covers any iface-layer tunnel `pyroute2` can drive —
+`ipip`/`gre`/`sit`/`vxlan`/`geneve`/`bridge`/`veth`. Keep
+`WGTunnelSpec` as *one* frozen struct among a
+`TunnelSpec = WGTunnelSpec|VxlanTunnelSpec|...` union with a
+`kind: ClassVar[str]`, and dispatch `open_*` by `match` on it.
+Design for it now (union + `match`), implement only `wg` +
+`netns`. `veth`-pairs-in-netns is the natural second one because
+it makes the §5.4 integration test possible without wg at all —
+consider doing it *first* for exactly that reason.
+
+## 7. Non-goals
+
+- no wg userspace implementation, no key exchange, no
+  `wg-quick` reimplementation (config-file parsing is
+  out of scope; take structured input).
+- no persistence of private keys beyond what layer C's iface
+  creation needs (and that stays in `get_rt_dir()`, 0600).
+- macOS/Windows: layers B/C are Linux-only. Layer A (declarative)
+  works anywhere `wg` does. Gate accordingly and say so in the
+  docs — do not silently no-op.
+
+## 8. Risks
+
+| risk | mitigation |
+| --- | --- |
+| `to_thread` worker runs in the wrong netns | §5.3; pass `netns=` to pyroute2 or pin a worker; test-first |
+| py-multiaddr#108 not merged | branch pin + `_have_wg_maddr_proto()` gate; layer A's inner-addr path works regardless |
+| `TunnelledAddress` leaks into `Endpoint` and breaks `inspect.getmodule()` | unwrap at parse/bindspace boundary; assert `not isinstance(ep.addr, TunnelledAddress)` in `Endpoint.__post_init__` |
+| privileged ops in a library | never `sudo`; explicit cap probe + actionable error; pre-provisioned is the default |
+| pyroute2 0.9 asyncio core drags a loop into the actor | option (1) is a *thread*, not a loop; forbid `trio-asyncio` here (§4.1) |
+| netns teardown strands actor teardown | idempotent/tolerant teardown mirroring `_uds.close_listener()` |
+
+## 9. Follow-up issue seeds
+
+- `veth`-in-netns bindspace (unblocks capless-ish integration
+  testing, and is a great local multi-"host" test rig)
+- composed/tunnelled maddr grammar shared with plan 02's
+  `/…/quic-v1/…` stacks (gh #443)
+- `wg` proto into the multiaddr **spec** (gh #483), then flip
+  `MsgTransport.maddr` to always return `Multiaddr` (the third
+  #443 bullet)
+- runtime-managed wg key rotation / peer add-remove as a
+  `tractor` service actor — the natural "actor that owns the
+  network" demo

ai/tpt-backends/README.md

@@ -0,0 +1,54 @@
+# next-gen `tractor.ipc` transport backend plans
+
+Implementation specs for three prospective `.ipc` transport
+backends, written so each can be worked independently (by a
+different model/provider) without design or lib-selection drift.
+
+**Read [`00_shared_backend_contract.md`](./00_shared_backend_contract.md)
+first** — it is the normative description of what a `tractor`
+transport backend *is* as of `main@83b34884` (the backend
+duck-type, the 10-item registration checklist, the test-harness
+plumbing, the code-style rules). The three plans assume it and
+document only their own deltas.
+
+| plan | issue | dep | size | lands |
+| --- | --- | --- | --- | --- |
+| [01 — TIPC](./01_tipc_backend.md) | [#378] | **none** (stdlib) | small | first |
+| [02 — QUIC/`iroh`](./02_quic_iroh_backend.md) | [#353] | `iroh` (uniffi FFI) | large | needs a prep PR |
+| [03 — `wg` bindspace](./03_wg_tunnel_bindspace.md) | [#482], [#443] | `pyroute2` | medium, 3 layers | layer A now |
+
+Headline conclusions:
+
+- **TIPC is the cheap win.** Verified: `trio.SocketStream` and
+  `trio.SocketListener` are address-family agnostic (only
+  `SOCK_STREAM` + a trio socket), and CPython ships `AF_TIPC` +
+  23 `TIPC_*` constants. So the backend is ~one module of
+  contract boilerplate, zero new deps, and it buys
+  *kernel-native* service discovery: `bind()` publishes,
+  `connect()`-by-name resolves — no registrar in the loop.
+  (`modprobe tipc` is required; hard-gate everything.)
+- **QUIC's cost is entirely in two adapters**, not in QUIC. The
+  `iroh` python bindings are `uniffi`-generated asyncio, but the
+  asyncio dependency is confined to *one* future-poll callback —
+  a ~40-line `trio` bridge (`TrioToken.run_sync_soon`) replaces
+  it. The second cost is that an iroh listener isn't a socket,
+  which needs a small, independently-reviewable prep PR to
+  `_server.py`/`_types.py`.
+- **WireGuard is not a transport.** It's an iface-layer tunnel,
+  so it belongs as a *nested bindspace* (`TunnelledAddress` +
+  `open_bindspace()` `@acm`s) wrapping whatever L4 tpt is in
+  use — which is also what finally implements the long-spec'd
+  `Address.namespace`, and what generalizes to
+  `veth`/`vxlan`/`gre`.
+
+Ordering rationale: plan 01 first as the cheap proof the
+table-registration story generalizes to a genuinely new proto;
+plan 03 layer A is already deployable-today doc/example work;
+plan 02 last (and gated on its prep PR). Plans 01 and 02 both
+want the same `Address.rebind_from_sockname` gate — whichever
+lands first ships it.
+
+[#378]: https://github.com/goodboy/tractor/issues/378
+[#353]: https://github.com/goodboy/tractor/issues/353
+[#482]: https://github.com/goodboy/tractor/issues/482
+[#443]: https://github.com/goodboy/tractor/issues/443

examples/wg_lan/README.md

@@ -0,0 +1,153 @@
+# `tractor` over a WireGuard tunnel, declared as one maddr
+
+A two-host LAN setup: a `tractor` actor tree on host A, dialed
+from host B, with the endpoint declared as a single `wg`
+multiaddr.
+
+Supersedes the example set in gh
+[#482](https://github.com/goodboy/tractor/issues/482) — see
+[what changed](#what-changed-vs-482).
+
+## the maddr form
+
+```
+/ip4/192.168.1.50/udp/51820/wg/u<A_pub>/ip4/10.0.11.1/tcp/1616
+\____ wg bearer ___________/\__ key __/\____ tractor ep _____/
+ underlay, wg `ListenPort`              overlay, on the wg iface
+ (kernel/`wg(8)` owns it)               (the ONLY part tractor binds)
+```
+
+Three parts, three different owners:
+
+| part | who binds it | in the runtime? |
+| --- | --- | --- |
+| `/ip4/../udp/51820` bearer | kernel via `wg-quick`/`pyroute2` | no |
+| `/wg/u<key>` | nothing — it's an identity | no, verified out-of-band |
+| `/ip4/../tcp/1616` overlay | `tractor`'s `IPCServer` | **yes**, as `.inner` |
+
+Verified against py-multiaddr
+[#108](https://github.com/multiformats/py-multiaddr/pull/108):
+this composed form parses and round-trips
+(`['ip4','udp','wg','ip4','tcp']`).
+
+## requirements
+
+The `wg` proto isn't in released `py-multiaddr` yet (`0.2.0` has
+no `wg` codec), so until #108 lands:
+
+```bash
+uv pip install 'git+https://github.com/baudco/py-multiaddr.git@wg_support' multibase
+```
+
+`wg_maddr.py` degrades to a plain segment split when the codec is
+absent, so the examples still run — but you lose per-segment
+validation. It deliberately does **not** hand-roll a `wg` codec
+(gh #429 was about *dropping* our NIH parser).
+
+## 0. tunnel setup (out-of-band, both hosts)
+
+Host A is the service host (underlay e.g. `192.168.1.50`), host B
+your workstation. Overlay net `10.0.11.0/24`.
+
+```bash
+umask 077
+wg genkey | tee wg_priv.key | wg pubkey > wg_pub.key
+```
+
+`/etc/wireguard/wg0.conf` on **host A**:
+
+```ini
+[Interface]
+PrivateKey = <A_priv>
+Address = 10.0.11.1/24
+ListenPort = 51820
+```
+```ini
+[Peer]
+PublicKey = <B_pub>
+AllowedIPs = 10.0.11.2/32
+```
+
+on **host B**:
+
+```ini
+[Interface]
+PrivateKey = <B_priv>
+Address = 10.0.11.2/24
+```
+```ini
+[Peer]
+PublicKey = <A_pub>
+Endpoint = 192.168.1.50:51820
+AllowedIPs = 10.0.11.1/32
+PersistentKeepalive = 25
+```
+
+Note how `ListenPort` and `Endpoint` are exactly the maddr's
+bearer segment, and `[Interface] Address` is its overlay host.
+
+```bash
+sudo wg-quick up wg0   # both hosts
+ping -c1 10.0.11.1     # from B
+```
+
+## 1. get your pubkey into the maddr
+
+```bash
+python -c "
+import base64, multibase
+key = open('wg_pub.key').read().strip()
+print(multibase.encode('base64url', base64.b64decode(key)).decode())
+"
+```
+
+Paste the `u...` output into `WG_MADDR` in both scripts (they use
+the same string — A's bearer, A's key, A's overlay ep).
+
+## 2. run
+
+```bash
+# host A
+python host_a_srv.py
+
+# host B
+python host_b_client.py
+```
+
+`host_a_srv.py` must be importable on host B too, since
+`portal.run()` refs the fn by module path — standard `tractor`
+RPC semantics.
+
+## what changed vs #482
+
+Four corrections, all from
+`ai/tpt-backends/03_wg_tunnel_bindspace.md`:
+
+1. **the maddr semantics were inverted.** #482 used
+   `/ip4/10.0.11.1/tcp/1616/wg/u<key>` — that parses, but it puts
+   the *overlay* addr where the bearer belongs and `tcp` where
+   wg's `udp` `ListenPort` goes, and it declares no overlay ep at
+   all. `parse_wg_maddr()` now rejects it with an actionable
+   error.
+2. **parsing is pure.** #482's helper had the key-check adjacent
+   to the parse; `verify_wg_peer()` is now a separate, explicitly
+   composed step that the caller invokes. A parser that shells
+   out is a nasty surprise.
+3. **no `sudo`.** #482 ran `sudo wg show`; a library/example must
+   never escalate. `wg show` works unprivileged for read on most
+   setups; if yours needs root, run the script as root rather
+   than embedding `sudo`.
+4. **no new `Address` proto-type.** The tunnel rides *beside* the
+   inner addr in a frozen `WGTunnelledAddr`, and only `.inner`
+   crosses into `open_nursery()`. #482 §6 floated a `WGAddress`
+   registered in `_address_types` — that table is a `bidict`
+   (1:1 proto-key↔type) and `_addr_to_transport` wants a
+   `MsgTransport` per addr-type, which `wg` doesn't have.
+
+## next
+
+`WGTunnelledAddr` is deliberately example-local. Promoting it to
+`tractor.discovery` as a `TunnelledAddress` whose
+`.proto_key`/`.unwrap()` delegate to `.inner`, plus
+`open_bindspace()` `@acm`s that create/tear down the iface +
+netns via `pyroute2`, is layers A→C of the plan doc.

examples/wg_lan/host_a_srv.py

@@ -0,0 +1,61 @@
+# tractor: distributed structured concurrency.
+'''
+Host A: the service host, reachable over a `wg` tunnel.
+
+Binds `tractor`'s registrar + an `echo_srv` sub-actor on the
+tunnel's *overlay* addr, declared as a single `wg` maddr.
+
+'''
+from __future__ import annotations
+
+import tractor
+import trio
+
+from wg_maddr import (
+    parse_wg_maddr,
+    verify_wg_peer,
+    WGTunnelledAddr,
+)
+
+# bearer = host A's underlay `(ip, wg ListenPort)`
+# key    = host A's OWN tunnel pubkey
+# overlay = the ep `tractor` binds, on the wg iface's addr
+WG_MADDR: str = (
+    '/ip4/192.168.1.50/udp/51820'
+    '/wg/u<A_pub_b64url>'
+    '/ip4/10.0.11.1/tcp/1616'
+)
+
+
+async def echo(msg: str) -> str:
+    actor = tractor.current_actor()
+    return f'{actor.aid.name!r} echoes: {msg}'
+
+
+async def main():
+    addr: WGTunnelledAddr = parse_wg_maddr(WG_MADDR)
+    assert verify_wg_peer(addr), (
+        f'wg pubkey from maddr not active on wg0 !\n'
+        f'maddr: {WG_MADDR}\n'
+        f'key: {addr.peer_pubkey}\n'
+    )
+    print(
+        f'wg bearer (kernel-owned): {addr.bearer}\n'
+        f'tractor overlay ep: {addr.inner}\n'
+    )
+    async with tractor.open_nursery(
+        # XXX only `.inner` crosses into the runtime; the bearer
+        # + key are iface-layer concerns `tractor` never binds.
+        registry_addrs=[addr.inner],
+        enable_transports=[addr.inner_proto],
+    ) as an:
+        await an.start_actor(
+            'echo_srv',
+            enable_modules=[__name__],
+        )
+        print(f'echo_srv up on\n  {addr.maddr}\n')
+        await trio.sleep_forever()
+
+
+if __name__ == '__main__':
+    trio.run(main)

examples/wg_lan/host_b_client.py

@@ -0,0 +1,52 @@
+# tractor: distributed structured concurrency.
+'''
+Host B: workstation dialing host A's actor tree through the
+`wg` tunnel.
+
+'''
+from __future__ import annotations
+
+import tractor
+import trio
+
+from host_a_srv import echo  # noqa: F401  (RPC refs it by mod path)
+from wg_maddr import (
+    parse_wg_maddr,
+    verify_wg_peer,
+    WGTunnelledAddr,
+)
+
+# same maddr as host A: A's bearer, A's key, A's overlay ep
+WG_MADDR: str = (
+    '/ip4/192.168.1.50/udp/51820'
+    '/wg/u<A_pub_b64url>'
+    '/ip4/10.0.11.1/tcp/1616'
+)
+
+
+async def main():
+    addr: WGTunnelledAddr = parse_wg_maddr(WG_MADDR)
+    assert verify_wg_peer(addr), (
+        f'wg pubkey from maddr not a peer on wg0 !\n'
+        f'maddr: {WG_MADDR}\n'
+    )
+    async with (
+        tractor.open_root_actor(
+            name='wg_client',
+            registry_addrs=[addr.inner],
+            enable_transports=[addr.inner_proto],
+        ),
+        tractor.find_actor(
+            'echo_srv',
+            registry_addrs=[addr.inner],
+        ) as portal,
+    ):
+        res: str = await portal.run(
+            echo,
+            msg='hello over wg!',
+        )
+        print(res)
+
+
+if __name__ == '__main__':
+    trio.run(main)

examples/wg_lan/wg_maddr.py

@@ -0,0 +1,215 @@
+# tractor: distributed structured concurrency.
+r'''
+Parse `wg`-tunnelled multiaddrs into `tractor`-ready addrs.
+
+The canonical form (per py-multiaddr PR #108, verified to parse +
+round-trip on that branch) nests the *overlay* endpoint **after**
+the `/wg/` segment:
+
+    /ip4/10.0.0.1/udp/51820/wg/u<key>/ip4/10.0.11.1/tcp/1616
+    \_______ wg bearer ______/\_ key _/\____ tractor ep _____/
+      (underlay, wg
+       `ListenPort`)
+
+- the segments *before* `/wg/` are the **bearer**: the underlay
+  `(ip, udp-port)` that `wg(8)` itself listens on. Nothing in
+  `tractor` ever binds this — the kernel/`wg` iface owns it.
+- `/wg/u<key>` carries the tunnel peer's Curve25519 pubkey as
+  multibase base64url (std base64 from `wg(8)` contains `/` and
+  can't go in a `/`-delimited maddr).
+- the segments *after* are the **overlay** endpoint, i.e. the
+  addr `tractor` actually binds/dials. This is the only part the
+  runtime sees.
+
+XXX NOTE, `tractor`'s own `parse_maddr()` can't parse this yet
+(`ValueError('Unsupported multiaddr protocol combo')`), which is
+why this module exists: parse here, hand `.inner` to the runtime.
+
+Design rules this module follows (see
+`ai/tpt-backends/03_wg_tunnel_bindspace.md`):
+
+- **parsing is pure**. `parse_wg_maddr()` does no I/O, no
+  `subprocess`, no netlink. A parser that shells out is a nasty
+  surprise.
+- **verification is an explicit, separate step**. The caller
+  composes `verify_wg_peer()` when it wants it; nothing implicit.
+- **no new `Address` proto-type**. `wg` gets no entry in
+  `tractor.discovery._addr._address_types` (a `bidict`, so 1:1
+  proto-key<->type) bc it has no `MsgTransport` of its own. The
+  tunnel is a *bindspace*, so we carry it beside the inner addr
+  and strip to `.inner` at bind/dial time.
+
+'''
+from __future__ import annotations
+import base64
+import subprocess
+from typing import Literal
+
+import msgspec
+
+
+class WGTunnelledAddr(
+    msgspec.Struct,
+    frozen=True,
+):
+    '''
+    A `wg`-tunnelled endpoint: the underlay bearer, the tunnel
+    peer key, and the overlay addr `tractor` binds/dials.
+
+    '''
+    # underlay, owned by `wg(8)`/the kernel — NEVER bound by us
+    bearer: tuple[str, int]
+
+    # tunnel peer pubkey in the std-base64 `wg(8)` form, i.e.
+    # directly comparable to `wg show <if> peers` output
+    peer_pubkey: str
+
+    # overlay ep: an `UnwrappedAddress` as accepted by
+    # `tractor.discovery.wrap_address()`
+    inner: tuple[str, int]
+    inner_proto: Literal['tcp'] = 'tcp'
+
+    @property
+    def maddr(self) -> str:
+        '''
+        Re-render the canonical maddr `str` form.
+
+        '''
+        b_host, b_port = self.bearer
+        i_host, i_port = self.inner
+        return (
+            f'/ip4/{b_host}/udp/{b_port}'
+            f'/wg/{mb_pubkey(self.peer_pubkey)}'
+            f'/ip4/{i_host}/{self.inner_proto}/{i_port}'
+        )
+
+
+def mb_pubkey(wg8_key: str) -> str:
+    '''
+    `wg(8)` std-base64 pubkey -> multibase base64url (`u`-prefixed).
+
+    '''
+    import multibase
+    raw: bytes = base64.b64decode(wg8_key)
+    return multibase.encode('base64url', raw).decode('ascii')
+
+
+def wg8_pubkey(mb_key: str) -> str:
+    '''
+    Inverse of `mb_pubkey()`: multibase -> `wg(8)` std-base64.
+
+    '''
+    import multibase
+    raw: bytes = multibase.decode(mb_key)
+    return base64.b64encode(raw).decode('ascii')
+
+
+def parse_wg_maddr(
+    maddr: str,
+) -> WGTunnelledAddr:
+    '''
+    Split a `wg`-tunnelled maddr into its bearer/key/overlay
+    parts. Pure — no I/O.
+
+    Uses `py-multiaddr` when it knows the `wg` proto (PR #108),
+    else falls back to a minimal segment split.
+
+    '''
+    segs: list[str] = _segments(maddr)
+    try:
+        wg_at: int = segs.index('wg')
+    except ValueError:
+        raise ValueError(
+            f'Not a `wg`-tunnelled maddr, no `/wg/` segment ??\n'
+            f'maddr: {maddr!r}\n'
+        )
+
+    bearer_segs: list[str] = segs[:wg_at]
+    mb_key: str = segs[wg_at + 1]
+    inner_segs: list[str] = segs[wg_at + 2:]
+
+    match bearer_segs:
+        case ['ip4'|'ip6', str() as b_host, 'udp', str() as b_port]:
+            bearer = (b_host, int(b_port))
+        case _:
+            raise ValueError(
+                f'Bad `wg` bearer, expected `/ip4|ip6/<h>/udp/<p>`\n'
+                f'got: {"/".join(bearer_segs)!r}\n'
+                f'from maddr: {maddr!r}\n'
+            )
+
+    match inner_segs:
+        case ['ip4'|'ip6', str() as i_host, 'tcp', str() as i_port]:
+            inner = (i_host, int(i_port))
+            inner_proto = 'tcp'
+        case []:
+            raise ValueError(
+                f'`wg` maddr declares no overlay endpoint!\n'
+                f'A bare `/…/wg/<key>` names only the tunnel; '
+                f'append the ep `tractor` should bind, e.g.\n'
+                f'  {maddr}/ip4/10.0.11.1/tcp/1616\n'
+            )
+        case _:
+            raise ValueError(
+                f'Unsupported `wg` overlay proto combo\n'
+                f'got: {"/".join(inner_segs)!r}\n'
+                f'from maddr: {maddr!r}\n'
+            )
+
+    return WGTunnelledAddr(
+        bearer=bearer,
+        peer_pubkey=wg8_pubkey(mb_key),
+        inner=inner,
+        inner_proto=inner_proto,
+    )
+
+
+def _segments(maddr: str) -> list[str]:
+    '''
+    Deliver a maddr's `/`-split segments, preferring the real
+    parser when it supports `wg`.
+
+    '''
+    from multiaddr import Multiaddr
+    try:
+        # the real thing: validates every proto + value
+        Multiaddr(maddr)
+    except Exception:
+        # XXX STOPGAP, only until py-multiaddr#108 lands; then
+        # this branch is dead and `Multiaddr` is authoritative.
+        # We deliberately DON'T hand-roll a `wg` codec (the whole
+        # point of gh #429 was dropping the NIH parser).
+        pass
+    return [s for s in maddr.split('/') if s]
+
+
+def verify_wg_peer(
+    addr: WGTunnelledAddr,
+    iface: str = 'wg0',
+) -> bool:
+    '''
+    True iff `addr.peer_pubkey` is a configured peer (or our own
+    pubkey) on `iface`.
+
+    IMPURE + explicit by design: never called from
+    `parse_wg_maddr()`.
+
+    ?TODO, per plan-03 layer B, swap this body for `pyroute2`
+    (keeping the signature) — and note `setns(2)` is *per-thread*,
+    so a query issued via `trio.to_thread` lands in the ORIGINAL
+    netns unless `netns=` is passed down.
+
+    '''
+    def _wg(*args: str) -> str:
+        return subprocess.run(
+            ['wg', 'show', iface, *args],
+            capture_output=True,
+            text=True,
+            check=True,
+        ).stdout
+
+    return (
+        addr.peer_pubkey in _wg('peers').split()
+        or
+        addr.peer_pubkey == _wg('public-key').strip()
+    )