Skip Linux netns tests on other platforms

Keep platform-independent spawn coverage active while avoiding Linux
`/proc` and `os.setns()` assumptions on macOS and Windows.

Deats,
- define one reusable Linux netns test mark
- apply it only to tests requiring real Linux namespace APIs
- preserve cross-platform bootstrap and transport unit coverage

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

ai/prompt-io/claude/20260813T001102Z_27c34aeb_prompt_io.md

@@ -3,8 +3,8 @@ model: claude-opus-5
 service: claude
 session: 7b9c97c4-fff7-4ac4-97fb-35720453308e
 timestamp: 2026-08-13T00:11:02Z
-git_ref: 27c34aeb
-scope: docs+code
+git_ref: 27c34aebb615c30d4039fa399f4ce2766ed7ba2c
+scope: code
 substantive: true
 raw_file: 20260813T001102Z_27c34aeb_prompt_io.raw.md
 ---

ai/prompt-io/claude/20260813T001102Z_27c34aeb_prompt_io.raw.md

@@ -2,15 +2,15 @@
 model: claude-opus-5
 service: claude
 timestamp: 2026-08-13T00:11:02Z
-git_ref: 27c34aeb
-diff_cmd: git diff main..ng_tpts_planning
+git_ref: 27c34aebb615c30d4039fa399f4ce2766ed7ba2c
+diff_cmd: git diff 3ad7e7e5dc28aa336499725a03744fc10c6c0026..27c34aebb615c30d4039fa399f4ce2766ed7ba2c
 ---
 
 # Raw output — next-gen tpt-backend implementation plans
 
 ## Generated planning docs
 
-> `git diff main..ng_tpts_planning -- ai/tpt-backends/`
+> `git diff 3ad7e7e5dc28aa336499725a03744fc10c6c0026..27c34aebb615c30d4039fa399f4ce2766ed7ba2c -- ai/tpt-backends/`
 
 Five markdown docs. `00_shared_backend_contract.md` is normative
 and the other three are written against it so they can be worked
@@ -43,7 +43,7 @@ independently:
 
 ## Generated example code
 
-> `git diff main..ng_tpts_planning -- examples/multihost/wg_lan/`
+> `git diff 3ad7e7e5dc28aa336499725a03744fc10c6c0026..27c34aebb615c30d4039fa399f4ce2766ed7ba2c -- examples/multihost/wg_lan/`
 
 - `wg_maddr.py` — `WGTunnelledAddr(msgspec.Struct, frozen=True)`
   carrying `bearer: tuple[str, int]`, `peer_pubkey: str`,

ai/prompt-io/opencode/20260831T022317Z_768b5316_prompt_io.md

@@ -0,0 +1,72 @@
+---
+model: gpt-5.6-sol
+service: opencode
+session: f3a5eef0-9695-48ab-a336-861187473f8a
+timestamp: 2026-08-31T02:23:17Z
+git_ref: ng_tpts_planning
+diff_cmd: git diff 768b531662a88037e3988885102d2ff24a7ce34e..HEAD
+scope: code
+substantive: true
+raw_file: 20260831T022317Z_768b5316_prompt_io.raw.md
+---
+
+## Prompt
+
+The human asked to continue the retained PR landing sequence and
+selected "Repair all blockers" after a read-only review of PR #492.
+They then corrected the TIPC assessment:
+
+> oh one thing on the tipc findings, they may have already been
+> addressed in the downstream patch branch no?
+
+The repair therefore had to use downstream #493 as implementation
+evidence, avoid duplicating solved TIPC work, preserve the dirty
+downstream worktree, and repair the remaining shared, QUIC,
+WireGuard, lock, and provenance defects without committing,
+pushing, or publishing.
+
+## Response summary
+
+Reworked PR #492's plans and executable WireGuard example into a
+consistent landing candidate. The shared and TIPC documents now
+match current runtime/downstream behavior while naming remaining
+risks. The QUIC plan now defines transport ownership across the
+whole actor lifecycle. The WireGuard example validates keys and
+binds both hosts and the service actor correctly without elevating
+Tractor. The dependency lock and historical provenance pointers
+are synchronized.
+
+## Files changed
+
+- `ai/tpt-backends/00_shared_backend_contract.md` - current backend
+  contract, dispatch, capability, and locality rules.
+- `ai/tpt-backends/01_tipc_backend.md` - #493 reconciliation and
+  bounded unresolved work.
+- `ai/tpt-backends/02_quic_iroh_backend.md` - lifecycle-safe QUIC
+  and UniFFI implementation plan.
+- `ai/tpt-backends/03_wg_tunnel_bindspace.md` - corrected address
+  registry and privilege semantics.
+- `ai/tpt-backends/README.md` - refreshed plan summaries.
+- `examples/multihost/wg_lan/README.md` - unprivileged two-host
+  setup and accurate verification limits.
+- `examples/multihost/wg_lan/host_a_srv.py` - local key check,
+  overlay child bind, and stable RPC exposure.
+- `examples/multihost/wg_lan/host_b_client.py` - peer key check,
+  host-B bind, and explicit missing-service failure.
+- `examples/multihost/wg_lan/wg_maddr.py` - strict parsing and
+  asynchronous role-specific key inspection.
+- `uv.lock` - exact `py-multiaddr` Git source resolution.
+- `ai/prompt-io/claude/20260813T001102Z_27c34aeb_prompt_io.md` -
+  valid scope and immutable Git reference.
+- `ai/prompt-io/claude/20260813T001102Z_27c34aeb_prompt_io.raw.md`
+  - immutable historical diff pointers.
+
+## Human edits
+
+The human chose the full repair path rather than reducing the PR
+to planning documents or publishing the initial review. They also
+identified that the initial TIPC review had not accounted for the
+downstream implementation branch. That correction materially
+changed the work: solved TIPC items were backported into the plan,
+remaining defects were separated from implemented behavior, and
+the dirty downstream worktree was kept read-only.

ai/prompt-io/opencode/20260831T022317Z_768b5316_prompt_io.raw.md

@@ -0,0 +1,60 @@
+---
+model: gpt-5.6-sol
+service: opencode
+timestamp: 2026-08-31T02:23:17Z
+git_ref: ng_tpts_planning
+diff_cmd: git diff 768b531662a88037e3988885102d2ff24a7ce34e..HEAD
+---
+
+# Raw output - repair PR #492 for landing
+
+## Generated changes
+
+> `git diff 768b531662a88037e3988885102d2ff24a7ce34e..HEAD -- ai/tpt-backends/`
+
+- Reconciled the shared backend contract with current address,
+  dispatch, capability, locality, and listener-rebind APIs.
+- Updated the TIPC plan from downstream #493 implementation and
+  tests, preserving unresolved registrar election, collision,
+  locality, and socket-cleanup work as explicit follow-ups.
+- Reworked the QUIC plan around a launch-time transport bootstrap,
+  one actor-owned endpoint, a transport nursery spanning parent
+  dial through deregistration, supervised UniFFI cleanup, complete
+  routable addresses, connection leases, and listener-owned tasks.
+- Corrected the WireGuard bindspace plan to distinguish the
+  build-registered address registry from runtime capability.
+
+> `git diff 768b531662a88037e3988885102d2ff24a7ce34e..HEAD -- examples/multihost/wg_lan/`
+
+- Hardened WireGuard key conversion and parsing with strict
+  32-byte validation, lazy protocol lookup, and explicit rejection
+  of unsupported nested tunnel descriptors.
+- Made interface inspection asynchronous, bounded at its
+  cancellation request, role-specific, and separable from
+  privileged preflight commands.
+- Corrected host-local binds, subactor overlay publication, stable
+  RPC module exposure, and missing-actor handling in the two-host
+  example.
+- Updated the README so Tractor remains unprivileged and the local
+  versus remote overlay roles are explicit.
+
+> `git diff 768b531662a88037e3988885102d2ff24a7ce34e..HEAD -- pyproject.toml uv.lock ai/prompt-io/`
+
+- Regenerated `uv.lock` for the exact merged `py-multiaddr` WireGuard
+  codec revision.
+- Replaced mutable historical prompt diff pointers with immutable
+  refs and normalized the substantive scope without rewriting the
+  historical raw response.
+
+## Verification output
+
+- `git diff --check`: passed.
+- `uv lock --check`: passed.
+- Ruff on the WireGuard example directory: passed.
+- Python compilation of the WireGuard example directory: passed.
+- Tractor imported from the PR worktree's existing environment.
+- WireGuard address round-trip, local/peer role checks, malformed
+  base64 rejection, and nested-tunnel rejection: passed.
+- Three independent final re-reviews reported no actionable
+  findings in the shared/TIPC, QUIC, or WireGuard slices.
+- No live TIPC, iroh/UniFFI, or WireGuard network test was run.

ai/tpt-backends/00_shared_backend_contract.md

@@ -33,19 +33,35 @@ 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).
+A transport backend is **one module** under `tractor/ipc/`.
+There is no ABC to subclass and no plugin entrypoint; wiring is by
+explicit table registration (§2) plus one piece of reflection
+(§1.3).
+
+Keep two contracts distinct:
+
+- `tractor.discovery._addr.Address` is a static `Protocol`. It
+  declares address-wrapper members including `namespace`,
+  `open_listener()` and `close_listener()`.
+- the runtime's empirical contract is what `_tcp.py`, `_uds.py`
+  and `_server.py` actually call. The current address classes do
+  not implement every declared `Address` member: listener
+  lifecycle is module-level, `def_bindspace` is used despite not
+  being declared by the `Protocol`, and `namespace` remains
+  aspirational.
+
+Until those surfaces are deliberately reconciled, implement the
+empirical module contract below and update the static `Protocol`
+only when the runtime really consumes the new member. Do not claim
+that structural conformance alone defines a backend.
 
 ### 1.1 `class <Proto>Address(msgspec.Struct, frozen=True)`
 
-Structurally conforms to the `Address` `Protocol` in
-`tractor/discovery/_addr.py:82`. Required surface:
+The runtime-consumed address-wrapper surface is:
 
 | member | kind | notes |
 | --- | --- | --- |
-| `proto_key` | `ClassVar[str]` | the wire/registry key, e.g. `'tcp'`, `'uds'` |
+| `proto_key` | `ClassVar[str]` | internal transport 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" |
@@ -81,22 +97,32 @@ Hard constraints learned from the existing two:
   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.
+  backends: make the unwrapped form carry an explicit internal
+  proto-key** — `('tcp', host, port)`,
+  `('uds', filedir, filename)`, `('tipc', stype, inst, scope)`.
+  The tag must be a `TransportProtocolKey`/registry key. In
+  particular it is **`'uds'`, not the external multiaddr spelling
+  `'unix'`**. If a wire or display format uses a different name,
+  name that translation explicitly; today `_multiaddr.py` maps
+  internal `uds` to external `/unix/`. Then `wrap_address()` can
+  dispatch through `_address_types[addr[0]]` without an
+  order-sensitive shape match.
 
   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 a **wire-format change**. Widen and keep synchronized
+    `discovery._addr.UnwrappedAddress` and the duplicate wire
+    alias in `msg.types`; change `SpawnSpec.reg_addrs` and
+    `.bind_addrs`, not only `_root_mailbox` and
+    `_registry_addrs`. Audit the related `RuntimeVars`
+    `_root_mailbox`/`_root_addrs` annotations, `Actor.reg_addrs`
+    and accept-address annotations, channel/spawn signatures,
+    fixtures, and downstream config (`piker`'s `[network]`
+    table). `msgspec` rejects a union containing multiple
+    array-like tuple shapes, so #493 used
+    `tuple[str|int, ...]` as the truthful transitional wire type;
+    the complete proto-key migration can restore per-proto
+    validation. This 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
@@ -104,8 +130,8 @@ Hard constraints learned from the existing two:
     `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
+- **`.get_random()` must not deterministically alias 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.
@@ -168,10 +194,11 @@ if (unwrapped := lstnr.socket.getsockname()) != self.addr.unwrap():
 ```
 
 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.
+return value is a valid `from_addr()` input. That is false for
+TIPC, whose listener sockname is an undialable port ID, and for
+non-socket iroh. Both plans must use the explicit backend rebind
+policy added at this integration point rather than pretending a
+sockname is always an address replacement.
 
 ### 1.4 `class Msgpack<Proto>Stream(MsgpackTransport)`
 
@@ -230,20 +257,26 @@ path.** This is why plan 01 is small and plan 02 is not.
 
 ---
 
-## 2. Registration tables (the full wiring checklist)
+## 2. Registration and policy wiring
 
-Adding a backend touches these and only these:
+Adding a backend requires this complete audit. Not every item
+changes for every backend, but none may be assumed from the others:
 
 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.
+   internal key. This `Literal` is the **declared protocol-key
+   set**, not proof that a backend is usable on this host.
+2. `tractor/discovery/_addr.py` `_address_protos` and
+   `_address_types: dict[str, Type[Address]]` — register
+   `'<key>': <Proto>Address`. `_address_types` is a plain
+   **`dict`, not a `bidict`**, and represents the backends this
+   build registers for import and dispatch. UDS is conditional on
+   `HAS_UDS`, while TIPC can remain registered on a host where its
+   kernel support is unavailable. An importable backend with a
+   runtime capability requirement therefore needs a separate
+   availability check. Never conflate this dispatch registry with
+   either host usability or the declared `TransportProtocolKey`
+   universe.
 3. `tractor/discovery/_addr.py:181` `_default_lo_addrs` —
    `'<key>': <Proto>Address.get_root().unwrap()`.
    ⚠️ this dict is built at **import time**, so
@@ -256,7 +289,7 @@ Adding a backend touches these and only these:
    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`.
+    `_address_types` lookup 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]`.
@@ -268,9 +301,17 @@ Adding a backend touches these and only these:
    `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
+9. `tractor/discovery/_api.py::_is_local_addr()` and
+   `prefer_addr()` — define and test the backend's locality and
+   selection tier. The current order is UDS, local TCP, then
+   remote. A new backend must not silently fall into `remote` by
+   accident: for example TIPC node scope is local, cluster scope
+   is not known-local, and an observed address with unknown scope
+   must not be promoted. Preserve the last-registered tie-break
+   unless intentionally changing policy.
+10. `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
+11. `pyproject.toml` — new deps go in an **optional extra**, never
     in `[project].dependencies`. See §5.
 
 ## 3. Where the `trio.SocketListener` assumption is load-bearing
@@ -345,7 +386,10 @@ dep-free, or make that table lazy.
   `_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).
+  asserts the lookup). Thus CLI acceptance follows the
+   build-registered `_address_types`, while type-level declarations
+   follow `TransportProtocolKey` and host usability follows each
+   backend's capability probe; test all three layers separately.
 - 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
@@ -359,8 +403,11 @@ dep-free, or make that table lazy.
   `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).
+- New pytest marks must be registered in
+  `_testing/pytest.py::pytest_configure()` with
+  `config.addinivalue_line()`, alongside the existing custom
+  marks. The repo has no `pyproject.toml` marker table. This is
+  still part of the fix-warnings-at-source rule (gh #469).
 
 ## 7. Code style (non-negotiable, matches the repo)
 

ai/tpt-backends/01_tipc_backend.md

@@ -4,13 +4,18 @@ 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.
+gives us kernel-native service-name publication, known-address
+dialling, and topology events. Those are primitives for reducing
+registrar traffic; they do **not** by themselves replace
+`tractor.discovery`, derive an actor's address from its name, or
+elect one registrar. It is stdlib-only: zero new dependencies.
+
+This plan is reconciled against downstream PR [#493]'s code and
+tests. Treat that implementation as prior art without mistaking
+implemented transport primitives for completed discovery policy.
 
 [#378]: https://github.com/goodboy/tractor/issues/378
+[#493]: https://github.com/goodboy/tractor/pull/493
 
 ---
 
@@ -74,10 +79,12 @@ The design decision that makes this backend coherent:
 > 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.
+This is the "leverage the built-in discovery machinery" part of
+#378: publishing a bind is kernel name-table registration and
+`connect()` on an already-known name is a kernel lookup, with no
+registrar actor on that **dial** path. Mapping an application name
+to that address and maintaining Tractor's actor registry remain
+separate work (§5).
 
 ### 2.2 the struct
 
@@ -89,12 +96,12 @@ class TIPCAddress(
     _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
+    # observed-only, excluded from the unwrapped service identity
     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]
+    unwrapped_type: ClassVar[type] = tuple[str, int, int, int]
     def_bindspace: ClassVar[int] = TIPC_CLUSTER_SCOPE
 ```
 
@@ -106,8 +113,8 @@ 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.**
+> **make the unwrapped form carry the explicit internal
+> `TransportProtocolKey`.**
 
 ```python
 def unwrap(self) -> tuple[str, int, int, int]:
@@ -115,11 +122,31 @@ def unwrap(self) -> tuple[str, int, int, int]:
 ```
 
 `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.
+the collision class disappears. The complete all-backend change
+is a prerequisite migration; #493 necessarily carried the
+transitional `UnwrappedAddress`/`SpawnSpec.reg_addrs`/
+`.bind_addrs` widening needed for TIPC. See contract §1.1 for the
+remaining runtime annotations, fixtures and `piker` config. Here
+`tipc` is both the internal and external spelling; UDS remains
+internally `uds` and translates explicitly to external `/unix/`.
+
+`msgpack` decodes tuples as lists, so both forms are part of the
+round-trip contract. Match only the exact three- or four-element
+tagged shapes and test all four routes:
+
+```python
+case (
+    ('tipc', int() as stype, int() as inst, int() as scope)
+    |
+    ['tipc', int() as stype, int() as inst, int() as scope]
+):
+    ...
+```
+
+Also test the scope-defaulted three-element form through
+`TIPCAddress.from_addr()`, and tuple/list forms through the global
+`wrap_address()`. A normal two-element TCP/UDS address whose first
+element happens to be `'tipc'` must retain its classic dispatch.
 
 ⚠️ an earlier revision of this plan proposed a self-tagging
 `('tipc:<stype>:<scope>', instance)` string-prefix hack with an
@@ -150,25 +177,28 @@ treatment (`_uds.py:242`).
 - `_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:
+  reproducible and well-distributed, **not collision-free**:
   ```python
-  # 32-bit instance derived from the actor's uuid4 (+ pid when
-  # there's no live runtime, per the UDS precedent).
+  # 32-bit instance derived from the actor's Aid.uid, or from a
+  # per-call token + pid when there is no live runtime.
   inst: int = int.from_bytes(
       blake2b(seed.encode(), digest_size=4).digest(),
       'big',
   )
   ```
-  where `seed = f'{actor.aid.name}@{pid}'` if
+  where `seed = '.'.join(actor.aid.uid)` 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))`.
+  The UUID is load-bearing because TIPC names are cluster-wide
+  while PIDs are only host-local: `(actor name, pid)` can alias on
+  different hosts.
   ⚠️ *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.
+  a statistical test and §9 records the unresolved recovery work
+  in [#501].
 - `_scope`: `TIPC_NODE_SCOPE` for a same-host-only actor (the
   UDS-equivalent), `TIPC_CLUSTER_SCOPE` (default) for
   cluster-visible. **This is `.bindspace`**:
@@ -189,7 +219,9 @@ treatment (`_uds.py:242`).
 @property
 def is_valid(self) -> bool:
     return (
-        self._instance != 0
+        self._instance > 0
+        and
+        self._stype > 0
         and
         self._stype not in _tipc_reserved_stypes  # {0, 1, ...}
         and
@@ -236,10 +268,11 @@ Notes / hazards:
 - **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.
+- `SocketListener.__init__` calls
+  `getsockopt(SOL_SOCKET, SO_ACCEPTCONN)`. The live-kernel probe
+  used by #493 answers `1`; retain the unit test so a kernel-side
+  change is visible rather than relying on trio's suppressed-
+  `OSError` carve-out.
 - 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
@@ -258,33 +291,31 @@ 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`:
+`TIPCAddress.from_addr()` must accept only proto-keyed service
+names. It must reject a bare port ID because no conversion can
+recover `(stype, instance)`:
 
 ```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))
+        # our proto-keyed tuple or decoded-list wire form
+        case (
+            ('tipc', int() as stype, int() as inst, int() as scope)
+            |
+            ['tipc', int() as stype, int() as inst, int() as scope]
+        ):
+            return TIPCAddress(stype, inst, _norm_scope(scope))
 
-        # a kernel-observed TIPC_ADDR_ID 5-tuple: keep the
-        # *service* identity we already know and only annotate
-        # the observed port-id.
+        # a bare kernel-observed TIPC_ADDR_ID 5-tuple has no
+        # service identity to annotate.
         case (int() as atype, *rest) if atype == socket.TIPC_ADDR_ID:
-            ...
+            raise ValueError(...)
 ```
 
-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`:
+The `TIPC_ADDR_ID` case cannot reconstruct `(stype, instance)`.
+The resolution is the explicit listener-rebind policy added ahead
+of the backend in #493:
 
 ```python
 if (
@@ -300,12 +331,13 @@ 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.
+hack. Keep the guard 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.
+Do **not** annotate `Endpoint.addr` from `getsockname()`: the
+listener endpoint must remain the dialable service name. Port IDs
+are observed only on connected streams and may annotate a copy via
+`with_port_id()` purely for logging/repr.
 
 ### 3.3 `MsgpackTIPCStream`
 
@@ -340,8 +372,9 @@ class MsgpackTIPCStream(MsgpackTransport):
                 0,              # domain: 0 == "anywhere in scope"
                 destaddr._scope,
             ))
+            stream = trio.SocketStream(sock)
             return cls(
-            trio.SocketStream(sock),
+                stream,
                 prefix_size=prefix_size,
                 codec=codec,
             )
@@ -363,11 +396,11 @@ class MsgpackTIPCStream(MsgpackTransport):
     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).
+- **`connect_to()` on a name with no publisher**: the live-kernel
+  result is immediate `EHOSTUNREACH`. Python exposes that as a
+  bare `OSError`, not a `ConnectionError` subtype, so
+  `_reraise_as_connerr()` is load-bearing for contract §4. Keep
+  the exact errno and normalization under test.
 
 ### 3.4 `get_stream_addrs()`
 
@@ -385,29 +418,27 @@ 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()`).
+- `get_stream_addrs()` converts both socket results into
+  **observed-only** addresses: `_stype`/`_instance` use the
+  `TIPC_NAME_UNKNOWN = -1` sentinel and `maybe_node`/`maybe_ref`
+  carry the port ID. Such addresses are invalid for dialling.
+- the **connecting** side knows the service name it dialled, so
+  `connect_to()` replaces `_raddr` after construction with that
+  known `TIPCAddress` while retaining the constructor's one
+  tolerant port-ID observation. Do not call `getpeername()` a
+  second time: the peer can withdraw between the two calls.
+- the **accepting** side genuinely cannot recover the peer's
+  service name from a port ID. Keep the observed-only `raddr`;
+  the handshake's `Aid` supplies logical identity. Piggybacking a
+  bound name in the handshake is outside this backend.
+- `laddr` is observed-only as well. It is used for repr/logging,
+  not to replace the endpoint's known service name.
+- unlike TCP/UDS, TIPC can answer `ENOTCONN` from
+  `getpeername()` after a connect-then-drop. This lookup happens
+  during `MsgpackTransport` construction, before handshake error
+  tolerance. Wrap `getsockname()` and `getpeername()` in a
+  tolerant helper and degrade to a port-ID-less observed address;
+  a dropped peer must cost an observation, not kill the actor.
 
 ---
 
@@ -444,43 +475,47 @@ the maddr stays 2-segment like `/unix/...`.
 
 ---
 
-## 5. Discovery: the actually-interesting part
+## 5. Discovery primitives and explicit limits
 
-Two independently-shippable layers. **Layer A is in scope for
-the first PR; layer B is a fast-follow.**
+The backend provides independently-shippable kernel primitives.
+Neither primitive alone implements Tractor's actor-name discovery,
+registry ownership, or registrar election.
 
 ### 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:
+`connect(TIPC_ADDR_NAME)` resolves, a caller that **already knows**
+a TIPC service address can dial it without a registrar lookup.
+This is narrower than registrar-less `find_actor(name)`:
 
-- `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.
+- `tractor.discovery._api.find_actor()` and peers still query a
+  registrar; #493 does not change them.
+- deriving a stable service address from `(name, uuid)` and
+  dialling it directly is follow-up [#499]. The mapping must be
+  documented and cross-language stable.
+- `registry_addrs` still identify registrars. Connecting to a
+  known registrar by TIPC name removes no registrar bookkeeping
+  or ownership semantics.
 
-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.
+There is also an unresolved **split-brain election** problem.
+Duplicate TIPC name publication succeeds and round-robins, so two
+roots can both probe an unoccupied registrar name, both bind it,
+and both believe they won. The backend provides no atomic
+compare-and-publish, lease, quorum, or deterministic winner. A
+topology subscription can reveal multiple publisher port IDs but
+does not elect or fence one. Do not describe registrar election as
+solved until a separate protocol closes this race.
 
 ### 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()`.
+This is the push primitive behind #378's "end game cluster proto"
+direction: a subscription to kernel name-table publish/withdraw
+events. #493 implements `open_topology_events()`; consuming that
+feed in `discovery._registry` is follow-up [#496]. Until then it
+does not replace registrar state or `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):
+Mechanics, verified against `linux/include/uapi/linux/tipc.h`,
+`net/tipc/topsrv.c` and #493's live-kernel probe:
 
 ```python
 # SOCK_SEQPACKET connected to the topology server
@@ -498,22 +533,25 @@ await sock.connect((
 #   __u32 filter;              /* TIPC_SUB_{PORTS,SERVICE,CANCEL} */
 #   char  usr_handle[8];
 # }                            /* == 28 bytes */
-_SUBSCR_FMT: str = '=IIIII8s'   # ⚠ 5*I is 20 -> use '=5I8s'
+_SUBSCR_FMT: str = '=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.
+- **byte order**: #493's live-kernel probe verified native
+  standard-size (`'='`) packing for publish and withdraw events.
+  Use `'=5I8s'` for the 28-byte subscription. Do not retain the
+  speculative `'>'` retry/probe as if it were required. Preserve
+  the earlier `# ?TODO` to verify the deterministic rule directly
+  against `net/tipc/topsrv.c`; it is source-audit work, not a
+  runtime retry requirement.
 - **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}`.
+  echo: **48 bytes** (`4 + 4 + 4 + 8 + 28`), not 40. Use
+  `'=10I8s'` and assert `struct.calcsize(...) == 48`.
+  `event ∈ {TIPC_PUBLISHED, TIPC_WITHDRAWN,
+  TIPC_SUBSCR_TIMEOUT}`. Python exposes `TIPC_WAIT_FOREVER` as
+  `-1`, so mask it with `& 0xFFFF_FFFF` before packing an
+  unsigned `I`.
 - **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:
@@ -538,14 +576,22 @@ async def open_topology_events(
   `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.
+  task doing `await sock.recv(48)` in a loop. The feed is
+  authoritative and may neither block the socket reader nor drop
+  transitions silently. Use `send_nowait()` and, on
+  `trio.WouldBlock`, raise a dedicated
+  `TIPCNameEventOverflow` that aborts the subscription and tells
+  the consumer to resubscribe and rebuild its view. A timeout
+  event is delivered once and then closes the channel. The
+  `@acm` cancels its reader before closing the fd so teardown
+  cannot race a retried `recv()` into `EBADF`.
+- **scope**: topology events carry no publication scope. Use an
+  explicit unknown-scope sentinel and keep the resulting address
+  non-dialable; never copy caller/subscription context into
+  supposedly observed data.
+- **consumer**: [#496] owns the optional watch mode and the
+  decision whether the feed subsumes or merely accelerates
+  existing registrar bookkeeping.
 - **`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"
@@ -561,14 +607,16 @@ async def open_topology_events(
 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`
+   `get_random()` distribution, 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) +
+4. registration tables (contract §2 items 1-8 and 10) +
    `pyproject.toml` mark/extra. Test: full suite under
-   `--tpt-proto tipc` (§7.3).
+   `--tpt-proto tipc` (§7.3). Keep TIPC in the conservative remote
+   preference tier until a follow-up implements and tests contract
+   item 9's node-scope locality policy.
 5. maddr support (`str` form + prefix special-case) + docs.
 6. `open_topology_events()` @acm + its tests (layer B).
 7. docs page + `docs/` example.
@@ -589,6 +637,8 @@ def is_tipc_available() -> bool:
     the `tipc` module is loaded.
 
     '''
+    if sys.platform != 'linux':
+        return False
     try:
         socket.socket(socket.AF_TIPC, socket.SOCK_STREAM).close()
         return True
@@ -596,17 +646,22 @@ def is_tipc_available() -> bool:
         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.
+Do not permanently memoize the result: `modprobe tipc` and module
+removal can change it during a long-lived process. Probe once per
+runtime startup, or use an explicitly refreshable cache whose
+owner invalidates it after module-management operations. The
+predicate itself remains side-effect-free and silent.
 
 ### 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`.
+- `pytest.mark.tipc` registered in
+  `_testing/pytest.py::pytest_configure()` via
+  `config.addinivalue_line()`, where this repo declares its other
+  custom marks. Do not invent a `pyproject.toml` marker table.
+- keep pure address, serialization, and topology-codec tests
+  runnable on every host. Apply a shared `requires_tipc` marker
+  only to tests that create sockets or otherwise touch the kernel;
+  do not module-skip `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
@@ -622,23 +677,29 @@ side effects, no logging.
   `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.
+  throwaway workflow before wiring the matrix. #493's TIPC leg
+  is now blocking. If runners cease permitting the module load,
+  fix the environment or use a suitable container rather than
+  silently restoring `continue-on-error`.
 - 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
+- **known-name publication/resolution**: 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.)
+- **`get_random()` distribution**: 10k `get_random()` calls with
+  no live runtime. Do **not** assert 10k distinct values: the
+  no-runtime seeds and outputs are both only 32 bits. Including
+  duplicate seeds plus distinct-seed hash collisions puts the
+  modeled chance of at least one duplicate near 2.3% for 10k
+  calls. #493 uses `>= n - 2` (modeled probability of more than
+  two collisions around `2e-6`) and separately proves
+  `instance_from_seed()` is a pure function. Also hold actor
+  name/PID fixed while varying only `Aid.uuid` to prove live
+  actors seed from `Aid.uid`.
 - **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
@@ -678,14 +739,61 @@ 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) |
+- **Instance collision / silent crosstalk remains unresolved.**
+  `Aid.uid` seeding and §7.4 tests reduce and measure risk, but
+  the instance field is still a hard 32 bits. [#501] owns
+  post-bind verification and recovery. Do not fold bits into
+  `_stype`: topology can watch only one service type.
+- **Concurrent registrar startup can split brain.** Topology can
+  observe duplicate publisher port IDs but cannot elect or fence
+  a winner; a separate election protocol is required (§5.1).
+- **Kernel/module availability is opt-in.** Keep the hard gate in
+  §7.2; TIPC is never the default transport.
+- **A listener sockname is a port ID, not its service name.** Keep
+  the `rebind_from_sockname` opt-out (§3.2).
+- **`/tipc` is not yet a registered multiaddr protocol.** Keep
+  the interim `str` maddr fallback (§4) and upstream gh #483.
+- **The public TIPC docs can be stale.** Treat
+  `include/uapi/linux/tipc.h` and `net/tipc/` as normative and
+  cite file/symbol names in code comments.
+- **A slow topology consumer loses continuity.** Fail fast with
+  `TIPCNameEventOverflow`; resubscribe and rebuild rather than
+  block the reader or retain stale state (§5.2).
+- **TIPC locality preference is not implemented.** Current
+  `_is_local_addr()` handles only UDS and TCP, so node- and
+  cluster-scope TIPC both remain in the conservative remote tier.
+  Add explicit scope-aware policy and multihomed selection tests
+  before claiming node-scope preference (contract §2.9).
+
+### 9.1 remaining constructor/error cleanup
+
+#493 closes the peer-withdrawal race in transport construction,
+but it is not a blanket error-path cleanup. Keep these gaps
+explicit rather than reporting the backend as fully hardened:
+
+- direct `TIPCAddress(...)` construction bypasses
+  `from_addr()` scope normalization; `is_valid` is queried later
+  rather than enforcing validity at construction. Decide whether
+  constructors should reject bad service types/instances/scopes
+  or document direct construction as trusted-internal.
+- `maybe_node`/`maybe_ref` are excluded from `.unwrap()` but, as
+  `msgspec.Struct` fields, still participate in structural
+  equality/hash. If service-name identity must ignore observation
+  metadata, represent or compare it explicitly instead of relying
+  on the current "observed-only" description.
+- `start_listener()` must keep ownership of the raw socket through
+  `bind()`, `listen()` and `SocketListener(...)`. The downstream
+  implementation normalizes bind errors but does not yet wrap the
+  complete listener-construction sequence in close-on-error, so a
+  later setup failure can leak the fd.
+- `_maybe_sockaddr()` currently degrades every `OSError` to an
+  unknown observed address. Narrow that tolerance to expected
+  peer-withdrawal errors (notably `ENOTCONN`) so unrelated bad-fd
+  or programming failures remain visible.
+- error normalization is intentionally required for an
+  unpublished-name `EHOSTUNREACH`, but setup `setsockopt`,
+  listener-constructor, and topology setup failures still need a
+  consistent policy and focused regression tests.
 
 ## 10. Follow-up issue seeds
 
@@ -695,9 +803,11 @@ single best demo this backend has; lead with it.
   `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)
+- registrar-less discovery fast path via name derivation ([#499],
+  §5.1)
 - `TIPC_TOP_SRV`-driven push registry in
-  `discovery/_registry.py` (§5.2)
+  `discovery/_registry.py` ([#496], §5.2)
+- post-bind collision verification and recovery ([#501], §9)
 - `TIPC_IMPORTANCE` for the parent<->child lifetime channel
   (§3.3) — genuinely novel supervision QoS, no other backend
   can do it
@@ -705,3 +815,7 @@ single best demo this backend has; lead with it.
   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
+
+[#496]: https://github.com/goodboy/tractor/issues/496
+[#499]: https://github.com/goodboy/tractor/issues/499
+[#501]: https://github.com/goodboy/tractor/issues/501

ai/tpt-backends/02_quic_iroh_backend.md

@@ -3,6 +3,12 @@
 Tracks gh [#353]. Prereq reading:
 [`00_shared_backend_contract.md`](./00_shared_backend_contract.md).
 
+**External-fact rule**: every claim here about `iroh`, UniFFI,
+generated bindings, QUIC wire/security behavior, or multiaddr
+support is provisional until the step-0 API-truth pass records a
+source or probe. Tractor/Trio behavior read from this checkout is
+the only locally proven basis for the plan.
+
 **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
@@ -49,20 +55,22 @@ relitigate:
   **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.
+Version pinning: treat API stability across `iroh` minors as an
+**unverified external constraint** until step 0. Pin the version
+exercised by the spike to `iroh>=X.Y,<X.Y+1` in a `quic` extra,
+and **write down the exact resolved version + 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.
+pinned `iroh`, inspect both its generated Python and loaded FFI
+symbols, and run the throwaway two-process spike. Record in
+§1.1 the real names and observed contracts. Every statement
+below about `iroh`, UniFFI, Rust callbacks, or generated symbols
+is a **step-0 hypothesis**, not a locally proven fact, unless it
+is copied into the completed API-truth table with a source or
+probe. Tractor and Trio behavior cited from this checkout is not
+subject to that qualifier.
 
 ### 1.1 API-truth table (fill in during step 0)
 
@@ -79,122 +87,120 @@ from memory.
 | send | `await send_stream.write_all(b)` | |
 | recv | `await recv_stream.read(n) -> bytes\|None` | |
 | half-close | `await send_stream.finish()` | |
+| endpoint close + completion | `close()` / `await closed()` | |
+| resolved node address | relay URL + direct socket addrs | |
+| future start/poll callback ABI | generated symbols + args | |
+| future cancel/complete/free | generated symbols + ordering | |
+| callback quiescence guarantee | after poll/complete/free? | |
+| cancellation terminal poll code | generated enum/value | |
+| iroh exception/status taxonomy | per operation | |
 
 ---
 
 ## 2. The `trio`-native uniffi future bridge (`tractor/ipc/_uniffi_trio.py`)
 
-### 2.1 what uniffi actually generates
+### 2.1 Step-0 generated-ABI gate
 
-`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:
+The expected generated shape is: start an opaque Rust future,
+poll it with a C callback, cancel through a generated cancel
+symbol, consume its terminal value/status through `complete`,
+then call `free`. The expected callback may arrive on a foreign
+Rust thread. **All of that is external and provisional.** Step 0
+must identify the exact generated driver and prove, from its
+template/source plus probes:
 
-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)`.
+1. the start, poll, cancel, complete, and free signatures for
+   every return-type family used by `iroh`;
+2. poll result values and whether callbacks can be synchronous,
+   concurrent, repeated, or late;
+3. which terminal state permits `complete`, when `free` is
+   legal, and when no callback can still reference Python;
+4. whether generated callback-data and call-status objects must
+   remain alive, and how generated lifting/errors are applied;
+5. whether one narrow generated async-driver entrypoint can be
+   replaced without importing or requiring an asyncio loop.
 
-**The asyncio dependency is confined to step 3.** That is the
-whole insight: the bridge is ~40 lines.
+Do not implement from a remembered UniFFI version. If cancel
+does not have a documented path to a terminal, safely freeable
+state, the native Trio bridge fails the spike gate and the first
+backend uses the infected-asyncio fallback.
 
-### 2.2 the trio version
+### 2.2 Cancellation-safe ownership
 
-```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()`.
+Do not let the caller task own a raw handle across an `await`.
+Introduce an actor-scoped `UniffiFutureSupervisor` running in the
+dedicated transport nursery specified in §3.2.1. That nursery
+must span parent bootstrap, the service nurseries, and final
+deregistration. For each call, its operation task owns the
+**entire** generated lifecycle:
 
-    '''
-    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)
+```text
+create handle -> poll/callback loop -> complete -> lift/status
+              -> free -> publish result
+                 ^
+                 cancel request uses generated cancel, then follows
+                 the verified terminal poll/complete/free protocol
 ```
 
-Critical details, each a real bug if missed:
+The operation task, not the awaiting caller, creates the handle.
+Creation and insertion in the supervisor's live-operation set
+must have no cancellation checkpoint between them. The operation
+retains strong references to the C callback trampoline, callback
+data, wake state, call status, and handle until step 0 proves all
+callbacks are quiescent and `free` has returned. Use one stable
+callback per operation unless the verified ABI requires a fresh
+one per poll; in either case, retain every potentially callable
+trampoline. Capture `current_trio_token()` in the Trio owner and
+schedule the wake into Trio with `token.run_sync_soon(...)`; the
+foreign callback only stores its poll result and schedules that
+wake.
 
-- **`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).
+Caller cancellation is a request, not handle ownership transfer:
+
+1. the caller sends an idempotent cancel request and waits under
+   a short shield for the operation to acknowledge it;
+2. the owner invokes the generated cancel function exactly once
+   and continues the **verified** poll/complete/free sequence;
+3. once caller cancellation is observed, cleanup completion never
+   wins the race by returning a value. After acknowledgement the
+   caller continues propagating its original Trio cancellation;
+   if cleanup outlives the grace period it first abandons its
+   result channel while the actor supervisor keeps ownership;
+4. actor endpoint teardown stops accepting new calls, requests
+   cancellation of all live operations, and joins the supervisor
+   before destroying endpoint/key state.
+
+There is deliberately no `move_on_after(...): free(handle)`
+path. A timeout proves only that cleanup is slow; it does not
+prove that callbacks are quiescent or that `free` is legal. A
+wedged operation therefore remains visible in the supervisor and
+can delay graceful actor shutdown; process-level termination is
+the final escalation, not an unsafe FFI free.
+
+Structured-concurrency race to test: caller cancellation may land
+after handle creation, after each poll, during callback delivery,
+after terminal readiness, during `complete`, and before result
+publication. At every checkpoint exactly one operation task owns
+the handle, exactly one `free` is possible, and the supervisor
+cannot exit while that task or a callable trampoline remains.
 
 ### 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:
+Do **not** fork/vendor the generated `iroh` Python. Subject to the
+step-0 gate, 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.
+- write `tractor/ipc/_uniffi_trio.py` with the supervisor and a
+  `@cm patch_uniffi_for_trio()` that patches only the generated
+  async-driver entrypoint recorded in §1.1;
 - 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.
+- treat every `iroh`/UniFFI upgrade as requiring the step-0 ABI
+  gate again. Keep a test that drives one trivial call under bare
+  `trio.run()`, asserts no asyncio loop, and injects cancellation
+  at every lifecycle checkpoint. Point the module docstring at
+  the exact generated template/revision mirrored by the shim.
 
 If step 0 reveals the generated code is *structurally* hostile
 to this (e.g. `asyncio` imported and used at module scope for
@@ -228,18 +234,52 @@ iroh bi-stream     ==  one `Channel`/`MsgTransport`  -> 1:1
 - `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.
+**Connection pooling** is actor-endpoint state, never module
+state. Its key is exactly
+`(local_endpoint_identity, remote_node_id, alpn)`, where local
+endpoint identity is the local NodeId derived from the actor key.
+Remote NodeId alone would incorrectly share connections across
+local keys or protocol epochs. Build it over the codebase's
+`maybe_open_context()` idiom only after a concurrency review of
+its actual last-user teardown behavior in the implementation
+revision. Do not assume an issue reference proves the required
+ordering.
+
+`acquire_connection()` returns a `ConnectionLease`, not a bare
+connection. An outgoing `QuicMsgStream` owns that entered lease
+for its whole lifetime; `connect_to()` must not exit the cached
+context immediately after `open_bi()`. Exact transfer paths:
+
+- dial/acquire or `open_bi()` failure releases the lease in a
+  shielded `finally` before raising;
+- successful stream construction atomically transfers the lease
+  to `QuicMsgStream` before the first cancellation checkpoint;
+- `send_eof()` closes only the send half and does not release;
+- clean receive EOF closes only the receive half and does not
+  release while the send half remains usable;
+- one guarded terminal-state transition releases exactly once
+  when both halves have become terminal, in either order;
+- `aclose()`, reset, or terminal connection failure closes both
+  halves as applicable and idempotently releases exactly once;
+- a stream queued by `QuicListener` already owns its lease; if
+  never accepted, listener draining closes it and releases it.
+
+After `accept()` returns, the server dispatch path owns the stream
+until a handler task starts and must close it if task start fails.
+The handler then takes ownership, with an outer `finally` that
+calls `stream.aclose()` on normal return, handshake failure, and
+cancellation. Lease release itself is an idempotent pool state
+transition; if last-user connection teardown awaits FFI, the actor
+endpoint's pool supervisor owns that await so cancellation of the
+handler cannot strand the lease.
+
+For inbound connections, the connection-feeder owns a base lease
+while accepting streams and each queued/returned stream gets a
+child lease. The base lease is released only after the accept
+loop ends; the pool closes the connection after the base and all
+stream leases are gone. Reject or deterministically reconcile a
+simultaneous inbound/outbound duplicate for the same full key;
+record the chosen iroh-compatible rule during step 0.
 
 ### 3.2 `IrohAddress`
 
@@ -248,29 +288,29 @@ 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, ...] = ()
+    _node_id: str
+    _alpn: str
+    _relay_url: str|None
+    _direct_addrs: tuple[str, ...]
 
-    proto_key: ClassVar[str] = 'iroh'   # ?or 'quic'; see §3.2.1
-    unwrapped_type: ClassVar[type] = tuple[str, str]
+    proto_key: ClassVar[str] = 'quic'
+    unwrapped_type: ClassVar[type] = tuple
     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.
+- **`.unwrap()` is the complete, tagged wire descriptor**:
+  `('quic', node_id, alpn, relay_url, direct_addrs)`. All values
+  are msgpack-native and `direct_addrs` is canonicalized to a
+  tuple. `from_addr()` requires that exact tag and shape; never
+  infer QUIC from a `(str, str)` pair. This depends on the shared
+  contract's tagged-address migration and removes the UDS
+  collision rather than ordering around it.
+- The descriptor always carries NodeId, ALPN, and both route-hint
+  fields. For this discovery-free first backend, `.is_valid`
+  requires a parseable NodeId, non-empty ALPN, and at least one
+  relay URL or direct address. Whether NodeId-only dialing works
+  through optional iroh discovery is a step-0 API check and is
+  not part of the first implementation.
 - `.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
@@ -278,39 +318,80 @@ class IrohAddress(
   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'`
+### 3.2.1 One actor endpoint and key
+
+Add an actor-scoped `QuicActorEndpoint` resource containing the
+secret key, one bound iroh endpoint, the UniFFI supervisor, the
+connection pool, and its latest resolved `IrohAddress`. It cannot
+live in `_service_tn`: a child dials its parent before that nursery
+opens, while final deregistration may dial after it closes.
+
+Add a dedicated `transport_tn` around the complete actor runtime:
+the task that opens this nursery must start the complete
+`async_main` sequence as a **child** of it and wait for that child.
+That makes `transport_tn` an ancestor of every parent-dial,
+service, and deregistration caller, satisfying
+`maybe_open_context(tn=transport_tn)` rather than asking the
+nursery-opening task to use its own child nursery. The child keeps
+the nursery around `_root_tn` and `_service_tn`, performs final
+deregistration while it remains open, then returns so the owner can
+close the transport resource and nursery. Root startup needs the
+equivalent outer owner around actor construction, service, and
+teardown. If this shape cannot be preserved, the connection pool
+must stop depending on `maybe_open_context()`'s ancestor-nursery
+contract. No path creates a second endpoint for the actor.
+
+The child currently receives transport configuration only in the
+`SpawnSpec` sent over its already-open parent channel. QUIC cannot
+derive its local key, ALPN, or requested bind policy from that late
+message. Add a small msgpack/pickle-native
+`ChildTransportBootstrap` to every process-launch path. It carries
+the selected protocol and the QUIC-local key reference/generation
+policy, ALPN, relay policy, and requested bind constraints. It is
+available before `_from_parent()`; the later `SpawnSpec` repeats
+the public configuration and startup rejects any mismatch. Root
+actors derive the same bootstrap record directly from
+`open_root_actor()` inputs before address selection.
+
+With that prep in place, the order is:
+
+1. consume the launch-time bootstrap record, select one key
+   (persisted and explicitly provisioned for a registrar, fresh
+   for an ordinary actor), and construct/bind the endpoint in the
+   transport owner task;
+2. await the step-0-verified address-ready API and build a valid
+   descriptor from the endpoint's NodeId, ALPN, relay URL, and
+   direct addresses;
+3. only then dial `_from_parent()` through this endpoint;
+4. start `QuicListener` over this endpoint's accept API;
+5. publish the resolved descriptor as `Endpoint.addr` and
+   `Actor.accept_addrs` before parent/registrar registration;
+6. after service nurseries close, keep the endpoint available for
+   deregistration; then close listeners and streams, drain
+   connection leases and FFI operations, close/join the endpoint,
+   and release key state.
+
+`IrohAddress.get_random()` is therefore a descriptor lookup on
+the active actor transport resource, not key generation. Broaden
+the shared `get_random()` contract for resource-backed transports
+and make root/subactor address selection consume the bootstrap
+resource instead of calling it before that resource exists. Do not
+hide a secret in a module-level side table. Calls without an active
+resource fail clearly rather than allocating an unowned key.
+
+`get_root()` never returns an empty/sentinel NodeId. Make default
+addresses lazy, and have QUIC load a provisioned public registrar
+descriptor. Registrar provisioning writes its secret separately
+with mode 0600 and writes the matching complete public descriptor
+atomically; endpoint startup verifies the derived NodeId. If no
+descriptor exists, default QUIC registrar discovery fails with an
+actionable configuration error. Automatic first-process election
+is deferred until a safe key-file locking and endpoint-binding
+protocol is proven; key generation never occurs in the listen
+path.
+
+#### 3.2.2 `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*.
@@ -357,7 +438,7 @@ class QuicMsgStream(trio.abc.HalfCloseableStream):
     '''
     tpt_key: ClassVar[MsgTransportKey] = ('msgpack', 'quic')
 
-    def __init__(self, conn, send, recv) -> None: ...
+    def __init__(self, conn, send, recv, lease) -> 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: ...
@@ -379,17 +460,38 @@ already exists in `_transport.py` and must keep working):
   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.
+- honour Trio's one-task-per-direction rule with public,
+  implementation-local guards that raise
+  `trio.BusyResourceError`; do not depend on `trio._util`.
+  `MsgpackTransport` already serializes sends, while receives 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.
 
+Centralize exception translation at every iroh/UniFFI boundary;
+no generated exception may escape into `Channel` or server code.
+Step 0 must record actual exception classes/status payloads and
+build an exhaustive operation-specific mapping:
+
+| observed condition | adapter result |
+| --- | --- |
+| receive clean EOF | `b''` |
+| local stream/listener/endpoint already closed | `trio.ClosedResourceError` |
+| concurrent same-direction operation | `trio.BusyResourceError` |
+| peer reset, stopped stream, lost connection | `trio.BrokenResourceError` |
+| dial rejected or no usable route | `ConnectionRefusedError` or `ConnectionError` |
+| caller's Trio deadline/cancellation | preserve Trio cancellation semantics |
+| unexpected FFI status/panic | chained `RuntimeError` identifying operation and pinned version |
+
+Preserve the original exception as `__cause__`, but sanitize
+messages so `_transport.py` sees stable Trio/Tractor categories,
+not version-specific iroh text. Endpoint accept failure becomes a
+listener `BrokenResourceError`; normal endpoint shutdown becomes
+`ClosedResourceError`. Add one test per observed step-0 status.
+
 ```python
 class QuicListener(trio.abc.Listener):
     '''
@@ -402,41 +504,63 @@ class QuicListener(trio.abc.Listener):
     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.
+The accept-side subtlety is fan-out: one actor transport accepts
+connections and each connection accepts streams, while
+`Listener.accept()` returns one stream. Give **each** listener a
+supervisor task started with
+`await server_ep.listen_tn.start(...)`.
+That task creates and owns a cancel scope, a child nursery for the
+endpoint feeder plus per-connection feeders, a guarded stream
+queue, and a completion event.
+`start_listener(addr=, server_ep=, actor_tpt=)` does not return
+until the supervisor has reported all of those ready.
+Do not borrow an implicit parent nursery or spawn feeders lazily
+from `accept()`.
 
-⚠️ 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.
+The queue is a guarded `deque`, not an unowned memory-channel
+buffer. A feeder transfers a fully constructed, lease-owning
+stream into it only while the listener is open; if close wins the
+race, the feeder closes the stream itself. `accept()` atomically
+pops one item or waits on the queue condition. Once close is
+marked and the queue is empty, it raises
+`trio.ClosedResourceError`.
 
-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.
+`QuicListener.aclose()` is idempotent and has this exact order:
+
+1. under the queue guard, mark closed and wake all `accept()`
+   waiters without a checkpoint between the state change and
+   notification;
+2. cancel the listener-owned supervisor scope;
+3. the supervisor's shielded `finally` joins the endpoint and all
+   connection feeders, atomically detaches the queue, closes every
+   queued stream, releases their leases, and closes the queue;
+4. only after that finalizer finishes, the supervisor sets its
+   completion event;
+5. `aclose()` waits under a shield for that event and returns;
+   concurrent closers wait for the same event.
+
+The same supervisor finalizer runs if its parent nursery is
+cancelled before someone calls `aclose()`. This makes the
+supervisor, not an arbitrarily cancelled caller, the sole final
+cleanup owner. Test cancellation at feeder accept, stream
+construction, queue transfer, `accept()` wakeup, and each close
+checkpoint; no feeder may outlive the listener and no queued
+lease may survive completion.
+
+This needs two explicit, typed references in the module-level
+listener call: `server_ep=` is the IPC server `Endpoint` that owns
+`listen_tn`, while `actor_tpt=` is the already-open
+`QuicActorEndpoint` whose iroh accept API supplies connections.
+Store `actor_tpt` on the server endpoint during actor transport
+bootstrap and pass both keyword-only arguments; socket backends
+ignore `actor_tpt`. `Endpoint.start_listener()` then stores the
+listener's already-resolved address instead of calling
+`getsockname()`.
 
 ### 3.4 `maddr`
 
-Multiaddr already standardizes the pieces:
+Expected multiaddr spellings for direct QUIC and relay routes are
+**step-0 verification items**, not assumptions:
 
 ```
 /ip4/<h>/udp/<p>/quic-v1                     # direct
@@ -444,19 +568,16 @@ Multiaddr already standardizes the pieces:
 /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`).
+- Do not emit NodeId alone in the first backend: without enabled
+  discovery it would discard the route required by the complete
+  `IrohAddress`. `mk_maddr()` must preserve NodeId, ALPN, relay
+  URL, and all direct addresses, or return a canonical Tractor
+  string form that does until a multiaddr grammar can round-trip
+  every field.
+- Verify whether an iroh NodeId can losslessly map to `/p2p/`.
+  If not, use a tractor-local `/iroh/<node-id>` segment rather
+  than pretending to be a libp2p peer-id. This needs upstream
+  registration, on the same track as `wg`/`tipc` (gh #483).
 - 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
@@ -466,24 +587,25 @@ Multiaddr already standardizes the pieces:
 
 ## 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.
+- The registrar stores the complete `IrohAddress`, not only a
+  NodeId. Registration is forbidden until endpoint address
+  resolution has produced that descriptor. If route hints change
+  later, dynamic re-registration is a follow-up; the spike uses
+  the pre-registration snapshot.
+- Optional iroh discovery mechanisms and their names/capabilities
+  are step-0 verification items and out of scope for the first
+  backend. No NodeId-only reachability claim is made.
+- Relay configuration belongs to `QuicActorEndpoint` creation,
+  not `start_listener()`, because dialing and listening reuse the
+  same endpoint. The demo's relay choice and self-hosted option
+  are selected only after step 0 verifies the pinned API.
 
 ## 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:
+The transport-security and NodeId-authentication properties of the
+pinned iroh stack are **step-0 documentation-verification items**.
+Claim only the properties supported by that version's source and
+docs. Two design consequences remain:
 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
@@ -497,59 +619,72 @@ transport security and peer authentication. Two things follow:
 
 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).
+   bi-stream between two processes. Fill §1.1 with generated ABI,
+   endpoint resolution, close/join, and error observations. Probe
+   cancel at every generated lifecycle phase. Timebox it and use
+   the fallback if any mandatory ownership fact stays unknown.
+1. prep PR: tagged address migration, annotation widening,
+   non-socket listener reconciliation, `tpt_key` dispatch,
+   typed `server_ep=`/`actor_tpt=` listener inputs, and lazy
+   default addresses. **No new backend.** Keep tcp and uds
+   behavior unchanged.
+2. bootstrap prep: pass `ChildTransportBootstrap` through every
+   process-launch path and add the transport nursery around child
+   parent-dial, service, deregistration, and teardown. Resolve the
+   endpoint address before registration. Add no iroh-specific
+   global state.
+3. `_uniffi_trio.py` supervisor + lifecycle fault-injection tests:
+   no asyncio loop, one owner/complete/free, callback retention,
+   bounded caller handoff, and joined durable cleanup.
+4. `QuicActorEndpoint` + provisioned registrar descriptor +
+   loopback direct-address tests; prove one endpoint handles dial,
+   listen, address lookup, and ordered teardown.
+5. `QuicMsgStream` + exhaustive error-normalization and lease
+   release tests against the loopback endpoint pair.
+6. `QuicListener` supervisor + cancellation-at-every-checkpoint
+   tests, including queued-stream draining and feeder joins.
+7. `MsgpackQuicStream`, full-key connection pooling, registration
+   tables, and `--tpt-proto quic`; then run the full suite.
+8. routable maddr/string form + 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.
+  *and* every step-0-recorded 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).
+- Measure endpoint bind and first-connect latency in step 0; do
+  not assume a multiplier. Before changing a deadline, rule out
+  the project's CPU-throttle false-positive, then prefer one
+  per-proto harness multiplier over individual-test edits.
+- Use the step-0-verified relay-disable configuration with direct
+  loopback addresses for default CI. Mark separately verified
+  relay tests `pytest.mark.net` and keep them out of default CI.
+- leak checks: assert the actor has one key/endpoint, every FFI
+  operation completed/freed once, all listener feeders joined,
+  all queued streams closed, every connection lease released,
+  and endpoint close completion observed before actor teardown.
+- address-ordering check: block registration until a descriptor
+  with NodeId, ALPN, and at least one route is published; reject
+  sentinel, NodeId-only, and post-registration mutation cases.
 
 ## 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 |
+| callback wakeup/lifetime semantics differ from the hypothesis | step-0 source + probe gate; retain callback/data through verified quiescence; durable owner; never timeout-free |
+| cancelled foreign future never reaches a freeable state | bounded caller handoff to visible actor supervisor; joined graceful shutdown or process-level escalation; never speculative free |
 | `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) |
+| endpoint or route resolution is not ready before parent dial/registration | actor endpoint bootstrap barrier; publish only a complete resolved descriptor |
+| connection closes while a stream still uses it | full-key pool + stream-held leases + exact-once release tests |
+| listener close strands feeder tasks or queued streams | listener-owned scope/completion event; cancel, join, drain, then return |
+| QUIC latency/jitter destabilizes suite timing assumptions | measure first; per-proto multiplier only if demonstrated; relay-less CI mode |
+| address tuple collides with another backend | required `'quic'` tag and exact-shape dispatch |
 | 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

ai/tpt-backends/03_wg_tunnel_bindspace.md

@@ -19,7 +19,7 @@ onto `trio` as the library's sans-io layer allows.
 
 ---
 
-## 1. What exists today (verified, per #482)
+## 1. What exists today (derived from #482)
 
 - `wrap_address()` accepts maddr `str`s (leading-`/` dispatch,
   `_addr.py:262`). `parse_maddr()` and `mk_maddr()` support plain
@@ -32,9 +32,12 @@ onto `trio` as the library's sans-io layer allows.
   by multiformats/py-multiaddr#107 and gh #483.
 - **today's deployable story remains declarative**: run `wg-quick`
   out-of-band, parse the maddr, strip its wrapper to the overlay
-  `(host, port)`, verify the pubkey against the live tunnel,
-  hand the overlay addr to `registry_addrs=`/`tpt_bind_addrs=`.
-  #482 already contains working example code for exactly this.
+  `(host, port)`, explicitly verify the declared pubkey against the
+  local interface key or configured peers with async
+  `verify_wg_peer()`, then hand the overlay addr to
+  `registry_addrs=`/`tpt_bind_addrs=`.
+  The repaired `examples/multihost/wg_lan/` implementation derives
+  from and supersedes #482's original example.
 - `Address.namespace` exists in the Protocol
   (`_addr.py:94-101`, "the if-available OS-specific network
   namespace key"). `TunnelledAddress` implements it from its spec;
@@ -44,9 +47,9 @@ onto `trio` as the library's sans-io layer allows.
 
 | layer | what | dep | ships |
 | --- | --- | --- | --- |
-| **A. declarative** | commit #482's examples; `parse_maddr()` learns `/wg/u<key>` → overlay `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 |
+| **A. declarative** | land repaired examples derived from #482; `parse_maddr()` learns `/wg/u<key>` → `TunnelledAddress` wrappers carrying overlay `Address` values and declared WG pubkeys | `multiaddr`, `py-multibase`, `wg(8)` CLI | first |
+| **B. `pyroute2` read/verify** | replace the example-local, role-aware async `wg(8)` verification probe with netlink queries | `pyroute2` extra | second |
+| **C. `@acm` lifecycle** | create/configure/tear down wg ifaces + netns *from the runtime*, consume `Address.namespace` for nested bindspaces, and implement explicit `None` on concrete transports | `pyroute2` + `CAP_NET_ADMIN` + `CAP_SYS_ADMIN` or a userns/helper equivalent | third |
 
 Each is independently valuable and independently reviewable.
 **Do not attempt C first** — the interesting design (nested
@@ -72,28 +75,24 @@ does not create a new address type.** Two candidate encodings;
       overlay: Address         # e.g. TCPAddress
       tunnel: WGTunnelSpec     # proto-specific, frozen
   ```
-  with `.proto_key` **delegating to `overlay.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 `overlay.unwrap()` so **nothing new
-  crosses the wire**. `.namespace` and `.bindspace` come from
-  the tunnel spec. The wrapper is stripped (`→ .overlay`) 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.
+  with `.proto_key`, `.bindspace`, and `.unwrap()` delegating to
+  the overlay so transport guards retain their existing meaning
+  and **nothing new crosses the wire**. `.namespace` derives from
+  the tunnel spec. Exact-type dispatch through
+  `_addr_to_transport`/`transport_from_addr()` still requires the
+  wrapper to be stripped (`→ .overlay`) at bind/connect time.
+  - ⚠️ `is_wrapped_addr()` explicitly recognizes
+    `TunnelledAddress` even though the wrapper is deliberately not
+    in `_address_types`: it has no `MsgTransport` of its own and
+    therefore gets no build-registered proto-key entry.
   - 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.
+    the bindspace `@acm` (layer C) or explicitly via `.overlay`
+    or `strip_tunnels()` at each bind/dial boundary (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()`.
 
@@ -103,10 +102,10 @@ class WGTunnelSpec(
     frozen=True,
 ):
     peer_pubkey: str          # std-base64 `wg(8)` form
+    bearer: tuple[str, int]|None = None
     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, ...] = ()
 ```
 
@@ -136,9 +135,8 @@ 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/multihost/wg_lan/` now rejects it with an actionable
-error.
+no overlay endpoint at all. `tractor.net.parse_wg_maddr()`
+now rejects it with an actionable error.
 Observed protocol-name lists, for writing the `match`:
 
 | maddr | `[p.name for p in m.protocols()]` |
@@ -167,7 +165,7 @@ Observed protocol-name lists, for writing the `match`:
 
   | need | API |
   | --- | --- |
-  | isolate the bearer | `ma.decapsulate_code(P_WG)` |
+  | isolate the bearer | `ma.decapsulate_code(_wg_proto_code())` |
   | drop the overlay, keep bearer+key | `ma.decapsulate(overlay_ma)` |
   | per-seg maddrs | `ma.split()` |
   | rejoin a seg tail | `Multiaddr.join(*segs)` |
@@ -183,16 +181,12 @@ Observed protocol-name lists, for writing the `match`:
   silently returns the **first** match, i.e. the bearer's host.
   Always call it on a peeled sub-maddr, never the whole stack.
 
-- `parse_maddr()` gains a case on
-  `[('ip4'|'ip6'), 'udp', 'wg', ('ip4'|'ip6'), <overlay-l4>]` →
-  peel w/ the API above, decode the multibase key to std-base64,
-  and return `TunnelledAddress(overlay=..., tunnel=WGTunnelSpec(
-  ...))` w/ the bearer recorded in the spec.
-- keep the existing 2-proto cases byte-identical; add the new
-  case *after* them.
-- nesting (wg-in-wg) falls out of `.decapsulate_code()` cutting
-  at the *last* occurrence — peel repeatedly rather than
-  recursing through a bespoke splitter.
+- keep the existing 2-proto cases byte-identical; add
+  `case _ if 'wg' in proto_names:` after them.
+- that case delegates to `parse_wg_maddr()`, which repeatedly
+  peels the last `/wg/`, decodes its key to std-base64, records
+  its bearer in `WGTunnelSpec`, and wraps the overlay in one
+  `TunnelledAddress` per segment.
 - `mk_maddr()` inverse for `TunnelledAddress` is just
   `.encapsulate()` composition; don't rebuild `str`s by hand.
 - **pending an upstream release**: py-multiaddr#108 is merged, so
@@ -206,21 +200,27 @@ Observed protocol-name lists, for writing the `match`:
   **not** hand-roll a `wg` parser in `tractor` — the whole point
   of #429 was dropping the NIH parser.
 
-### 3.3 pure codecs + explicit verification
+### 3.3 pure parser helpers + explicit verification
 
-Port #482 §2's pure helpers into
-`tractor/net/_tunnel.py`, keeping the impure probe cleanly
-separated until layer B:
+The parser/key-codec helpers and async production verifier live in
+`tractor/net/_tunnel.py`; parsing remains pure while verification
+is an explicit, impure caller step:
 
 ```python
-def parse_wg_maddr(maddr: str) -> TunnelledAddress: ...   # pure
-def wg8_pubkey(multibase_key: str) -> str: ...            # pure
+def parse_wg_maddr(maddr: str|Multiaddr) -> TunnelledAddress: ...
+def mb_pubkey(wg8_key: str) -> str: ...
+def wg8_pubkey(multibase_key: str) -> str: ...
 async def verify_wg_peer(spec: WGTunnelSpec) -> bool: ... # layer B
 ```
 
-Layer A's example-local `verify_wg_peer()` may shell out (`wg show
-<if> peers`), but layer B replaces that probe with one explicit async
-function backed by pyroute2. Never call it implicitly from
+Layer A's example-local `verify_wg_key()` used role-specific
+`wg show <if> public-key|peers` queries. Layer B replaces it with
+`verify_wg_peer()`, backed by one pyroute2 key snapshot selected by
+`spec.iface` and `spec.netns`. It validates the declared key before
+I/O and accepts either the interface's own public key or a configured
+peer key. It does not enforce a host-specific role and verifies key
+presence only, not `Endpoint`, `AllowedIPs`, handshake state, or
+routing. 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).
@@ -281,13 +281,13 @@ Three integration options, in increasing trio-nativeness:
 - (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).
+reviewable replacement of the example-local verification probe with
+production `verify_wg_peer()`; 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 or infect
 every wg-using actor merely to service one-shot netlink calls. A
@@ -535,12 +535,11 @@ omitted endpoint only for the selected maddr peer.
 
 The composition driver folds a list of specs into nested contexts with
 `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|TunnelledAddress]]` 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.
+`parse_endpoints()` API (`_multiaddr.py:189`) is the front door:
+its `ParsedEndpoints` values already contain
+`Address|TunnelledAddress` declarations and preserve each tunnel
+stack for the eventual bindspace handler. It carries declarations;
+it does not *enter* their bindspaces.
 
 `open_wg_bindspace()` is the initial driver for one bindspace and an
 ordered sequence of `(WGTunnelSpec, WGInterfaceConfig)` layers. It
@@ -635,8 +634,8 @@ server bound in the old namespace.
     the parent/supervisor's `Bindspace` context.
   - document the constraint rather than hiding it; a
     `RuntimeError` if namespace entry is attempted after bootstrap.
-- capabilities: iface/netns creation/config needs `CAP_NET_ADMIN`;
-  entering an existing Linux namespace normally requires
+- capabilities: iface/route/WG configuration needs `CAP_NET_ADMIN`;
+  creating or entering a Linux network namespace normally requires
   `CAP_SYS_ADMIN` in the owning user namespace. Never `sudo` from
   inside the runtime. A privileged parent/helper should provision the
   stack and open the namespace FD; the child receives only the scoped
@@ -674,12 +673,13 @@ server bound in the old namespace.
 
 - 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.
+- integration, gated on `CAP_NET_ADMIN` plus `CAP_SYS_ADMIN` in the
+  owning user namespace (or a tested userns/helper equivalent; skip
+  otherwise). In CI, grant both capabilities explicitly. Create two
+  netns + a wg pair entirely in-process, boot a `tractor` root in one
+  and a subactor in the other, then `find_actor()` across the tunnel.
+  This is fully self-contained — no second host and no `sudo` in the
+  test body.
 - the `to_thread`-netns-mismatch regression from §5.4, written
   **first** (red), then the fix (green), per project convention.
 - bootstrap ordering: assert the child reports the expected namespace

ai/tpt-backends/README.md

@@ -7,9 +7,9 @@ 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.
+duck-type, registration and address-selection wiring, the
+test-harness plumbing, the code-style rules). The three plans
+assume it and document only their own deltas.
 
 | plan | issue | dep | size | lands |
 | --- | --- | --- | --- | --- |
@@ -23,10 +23,12 @@ Headline conclusions:
   `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.)
+  contract boilerplate, zero new deps, and it buys kernel-native
+  service primitives: `bind()` publishes, known-address
+  `connect()` resolves, and topology events report publication
+  changes. Actor-name lookup, registrar state and split-brain-safe
+  election remain separate work. (`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 —

examples/multihost/wg_lan/README.md

@@ -50,7 +50,8 @@ uv sync --extra wg
 
 gets you a `wg`-aware `multiaddr` plus pyroute2's Linux netlink API.
 The multiaddr pin goes away once a release carries the codec.
-`py-multibase` is a direct dependency.
+`py-multibase` is a direct project dependency, so no separate install
+command is needed.
 
 Without the codec `parse_wg_maddr()` raises immediately with an
 actionable message — there is deliberately **no** degraded
@@ -62,8 +63,8 @@ tunnel API (`.decapsulate_code()`, `.split()`, `.join()`,
 `.encapsulate()`, `.value_for_protocol()`) rather than any
 bespoke segment slicing — see its README "En/decapsulate" and
 "Tunneling" sections. gh #429 was about *dropping* our NIH
-parser, and that applies to peeling a tunnel stack just as much
-as to decoding one proto.
+parser, and that applies to peeling nested tunnel stacks just as
+much as to decoding one proto.
 
 ## 0. tunnel setup (out-of-band, both hosts)
 
@@ -104,8 +105,11 @@ 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.
+This example configures host A's `ListenPort` and host B's
+`Endpoint` from the maddr bearer, and configures host A's
+`[Interface] Address` from its overlay host. The verification
+step below checks keys only; it does not inspect those fields or
+either peer's `AllowedIPs`.
 
 ```bash
 sudo wg-quick up wg0   # both hosts
@@ -116,16 +120,34 @@ ping -c1 10.0.11.1     # from B
 
 ```bash
 python -c "
- from tractor.net import mb_pubkey
- key = open('wg_pub.key').read().strip()
- print(mb_pubkey(key))
+from tractor.net import mb_pubkey
+key = open('wg_pub.key').read().strip()
+print(mb_pubkey(key))
 "
 ```
 
 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
+## 2. verify the keys
+
+Both scripts explicitly call `await verify_wg_peer(addr.tunnel)`
+before starting `tractor`. The helper validates the maddr's declared
+key, reads one `wg0` key snapshot through pyroute2's Linux
+generic-netlink API, and accepts the key when it is either the
+interface's own public key or one of its configured peers.
+
+This establishes key presence only. It does not enforce a
+host-specific local/peer role and does not verify `Endpoint`,
+`AllowedIPs`, a recent handshake, or routing.
+
+Interface inspection commonly requires `CAP_NET_ADMIN` in the user
+namespace that owns the target network namespace. Run each program in
+a security context that already has the required inspection authority.
+The helper never invokes `sudo` or `wg(8)`, escalates privileges, or
+creates a namespace.
+
+## 3. run
 
 ```bash
 # host A
@@ -135,6 +157,16 @@ python host_a_srv.py
 python host_b_client.py
 ```
 
+Run both `tractor` programs as the normal application account in a
+security context with the inspection authority described above. No
+`WG_KEY_INSPECTION` export or subprocess preflight is used; tunnel
+setup remains out-of-band. Do not run the applications as root.
+
+The client binds its own actor listener to `10.0.11.2:0`, while
+the service actor binds to host A's `10.0.11.1` overlay host with
+a random port. Keep `LOCAL_OVERLAY_BIND` aligned with host B's
+WireGuard interface address if adapting this example.
+
 `host_a_srv.py` must be importable on host B too, since
 `portal.run()` refs the fn by module path — standard `tractor`
 RPC semantics.
@@ -156,13 +188,15 @@ Four corrections, all from
    kernel inspection from a parser is a nasty surprise.
 3. **no `sudo` or subprocess.** #482 ran `sudo wg show`; tractor's
    helper reads generic netlink through pyroute2 and never attempts
-   privilege escalation or namespace creation.
+   privilege escalation or namespace creation. The caller must
+   already have the required inspection authority.
 4. **no new `Address` proto-type.** The tunnel rides *beside* the
    overlay addr in a frozen `TunnelledAddress`, and only `.overlay`
    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.
+   registered in `_address_types` — that registry maps available
+   transport keys to concrete address types, and
+   `_addr_to_transport` wants a `MsgTransport` per addr-type,
+   which `wg` doesn't have.
 
 ## root composition
 

examples/multihost/wg_lan/host_a_srv.py

@@ -34,8 +34,9 @@ async def echo(msg: str) -> str:
 
 async def main():
     addr: TunnelledAddress = parse_wg_maddr(WG_MADDR)
-    assert await verify_wg_peer(addr.tunnel), (
-        f'wg pubkey from maddr not active on wg0 !\n'
+    if not await verify_wg_peer(addr.tunnel):
+        raise RuntimeError(
+            f'Maddr key is not wg0 local public key!\n'
             f'maddr: {WG_MADDR}\n'
             f'key: {addr.tunnel.peer_pubkey}\n'
         )
@@ -49,9 +50,12 @@ async def main():
         registry_addrs=[addr.overlay],
         enable_transports=[addr.overlay.proto_key],
     ) as an:
+        overlay_host, _ = addr.unwrap()
         await an.start_actor(
             'echo_srv',
-            enable_modules=[__name__],
+            bind_addrs=[(overlay_host, 0)],
+            enable_transports=[addr.overlay.proto_key],
+            enable_modules=['host_a_srv'],
         )
         print(f'echo_srv up on\n  {mk_maddr(addr)}\n')
         await trio.sleep_forever()

examples/multihost/wg_lan/host_b_client.py

@@ -15,29 +15,35 @@ from tractor.net import (
 )
 
 from host_a_srv import echo  # noqa: F401  (RPC refs it by mod path)
+
 # 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'
 )
+LOCAL_OVERLAY_BIND: tuple[str, int] = ('10.0.11.2', 0)
 
 
 async def main():
     addr: TunnelledAddress = parse_wg_maddr(WG_MADDR)
-    assert await verify_wg_peer(addr.tunnel), (
-        f'wg pubkey from maddr not a peer on wg0 !\n'
+    if not await verify_wg_peer(addr.tunnel):
+        raise RuntimeError(
+            f'Maddr key is not a configured wg0 peer!\n'
             f'maddr: {WG_MADDR}\n'
+            f'key: {addr.tunnel.peer_pubkey}\n'
         )
     async with (
         tractor.open_root_actor(
             name='wg_client',
+            tpt_bind_addrs=[LOCAL_OVERLAY_BIND],
             registry_addrs=[addr.overlay],
             enable_transports=[addr.overlay.proto_key],
         ),
         tractor.find_actor(
             'echo_srv',
             registry_addrs=[addr.overlay],
+            raise_on_none=True,
         ) as portal,
     ):
         res: str = await portal.run(

uv.lock

@@ -273,9 +273,9 @@ name = "greenback"
 version = "1.2.1"
 source = { registry = "https://pypi.org/simple" }
 dependencies = [
-    { name = "greenlet", marker = "python_full_version < '3.14'" },
-    { name = "outcome", marker = "python_full_version < '3.14'" },
-    { name = "sniffio", marker = "python_full_version < '3.14'" },
+    { name = "greenlet" },
+    { name = "outcome" },
+    { name = "sniffio" },
 ]
 sdist = { url = "https://files.pythonhosted.org/packages/dc/c1/ab3a42c0f3ed56df9cd33de1539b3198d98c6ccbaf88a73d6be0b72d85e0/greenback-1.2.1.tar.gz", hash = "sha256:de3ca656885c03b96dab36079f3de74bb5ba061da9bfe3bb69dccc866ef95ea3", size = 42597, upload-time = "2024-02-20T21:23:13.239Z" }
 wheels = [
@@ -762,15 +762,6 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/5a/dc/491b7661614ab97483abf2056be1deee4dc2490ecbf7bff9ab5cdbac86e1/pyreadline3-3.5.4-py3-none-any.whl", hash = "sha256:eaf8e6cc3c49bcccf145fc6067ba8643d1df34d604a1ec0eccbf7a18e6d3fae6", size = 83178, upload-time = "2024-09-19T02:40:08.598Z" },
 ]
 
-[[package]]
-name = "pyroute2"
-version = "0.9.6"
-source = { registry = "https://pypi.org/simple" }
-sdist = { url = "https://files.pythonhosted.org/packages/9b/3c/cae3aa8a07522d4fd625958f690ab6eb4ffbd9c94e30e2995f585fded630/pyroute2-0.9.6.tar.gz", hash = "sha256:6bc5e2ea9a372ded682b4ede4028ba00236bd6e35b42d833f39a96b219ef1db2", size = 478486, upload-time = "2026-04-15T18:26:07.408Z" }
-wheels = [
-    { url = "https://files.pythonhosted.org/packages/14/f5/77292e847cb2bcd94f0e7be214ad09972de5db6a6914e47117293ed0f4a8/pyroute2-0.9.6-py3-none-any.whl", hash = "sha256:3334091326e560a506635449af03b26920d22d4e5a7996aed354363d106fcef8", size = 483440, upload-time = "2026-04-15T18:26:03.14Z" },
-]
-
 [[package]]
 name = "pytest"
 version = "9.1.0"
@@ -1135,18 +1126,12 @@ dependencies = [
     { name = "multiaddr" },
     { name = "pdbp" },
     { name = "platformdirs" },
-    { name = "py-multibase" },
     { name = "setproctitle" },
     { name = "tricycle" },
     { name = "trio" },
     { name = "wrapt" },
 ]
 
-[package.optional-dependencies]
-wg = [
-    { name = "pyroute2", marker = "sys_platform == 'linux'" },
-]
-
 [package.dev-dependencies]
 dev = [
     { name = "greenback", marker = "python_full_version < '3.14'" },
@@ -1207,14 +1192,11 @@ requires-dist = [
     { name = "multiaddr", git = "https://github.com/multiformats/py-multiaddr.git?rev=f86519daaa21699023d0037c58cdff600313dd09" },
     { name = "pdbp", specifier = ">=1.8.2,<2" },
     { name = "platformdirs", specifier = ">=4.4.0" },
-    { name = "py-multibase", specifier = ">=2.0.0,<3" },
-    { name = "pyroute2", marker = "sys_platform == 'linux' and extra == 'wg'", specifier = ">=0.9.6,<0.10" },
     { name = "setproctitle", specifier = ">=1.3,<2" },
     { name = "tricycle", specifier = ">=0.4.1,<0.5" },
     { name = "trio", specifier = ">0.27" },
     { name = "wrapt", specifier = ">=1.16.0,<2" },
 ]
-provides-extras = ["wg"]
 
 [package.metadata.requires-dev]
 dev = [