Retain realized `BindspaceRef` metadata

Add `TunnelledAddress.with_bindspace_ref()` to annotate frozen tunnel
declarations with stable, serializable namespace metadata.

Deats,
- omit absent refs from the existing msgspec shape
- reject declared and realized namespace-name mismatches
- report the declared key before realization and inode afterward
- keep transport peeling free of live bindspace capability state
- expose realized refs through real listener diagnostics

Prompt-IO: ai/prompt-io/opencode/20260826T030534Z_d130431c_prompt_io.md

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

ai/prompt-io/opencode/20260826T030534Z_d130431c_prompt_io.md

@@ -0,0 +1,54 @@
+---
+model: gpt-5.6-sol
+service: opencode
+session: tractor-addr-unpacking
+timestamp: 2026-08-26T03:05:34Z
+git_ref: d130431c
+scope: code
+substantive: true
+raw_file: 20260826T030534Z_d130431c_prompt_io.raw.md
+---
+
+## Prompt
+
+After committing the reviewed bindspace/interface stack, the human
+asked to continue with the next established Layer C step.
+
+## Response summary
+
+Retained a serializable realized `BindspaceRef` on frozen tunnelled
+address declarations without carrying the process-local `Bindspace`
+capability. The namespace API remains tuple-shaped, using the declared
+key before realization and stable inode afterward. Existing transport
+peeling and unrealized serialization remain unchanged.
+
+## Files changed
+
+- `tractor/discovery/_tunnel.py` - realized bindspace-ref retention and
+  immutable annotation method.
+- `tests/discovery/test_tunnelled_addr.py` - ref, compatibility and
+  mismatch coverage.
+- `tests/ipc/test_server_tunnel_boundary.py` - real listener diagnostic
+  coverage for the realized inode.
+- `ai/tpt-backends/03_wg_tunnel_bindspace.md` - realized namespace
+  visibility contract.
+
+## Human edits
+
+The human accepted and committed the preceding reviewed composition
+boundary, then requested the next step. Their stated preference for
+end-to-end tests informed use of the existing real TCP listener path to
+verify endpoint/server diagnostics, while focused unit coverage handles
+metadata invariants without pyroute2 overhead. During review, the human
+chose the final unshipped terminology: `BindspaceRef` for the
+serializable non-owning reference, `Bindspace` for the live
+process-local capability, `.ref` for that capability's reference, and
+`bindspace_ref` at the tunnel declaration API.
+They then requested the prerequisite model rename as a separate commit
+before this feature. The human also replaced the module-level helper
+with `TunnelledAddress.with_bindspace_ref()` and requested inline
+msgspec encode/decode expressions in the serialization assertions. The
+human chose not to add a second typed `.namespace` projection, and
+requested native tagged `TunnelledAddress` decoding remain as a separate
+design-plan follow-up. The agent applied those human-directed changes;
+no direct manual source edits were observed.

ai/prompt-io/opencode/20260826T030534Z_d130431c_prompt_io.raw.md

@@ -0,0 +1,31 @@
+---
+model: gpt-5.6-sol
+service: opencode
+timestamp: 2026-08-26T03:05:34Z
+git_ref: d130431c
+diff_cmd: git diff HEAD~1..HEAD
+---
+
+# Raw output - retain realized bindspace identity
+
+After committing WireGuard bindspace composition, the human requested
+the next incremental Layer C change.
+
+> `git diff HEAD~1..HEAD -- tractor/discovery/_tunnel.py tractor/discovery/__init__.py tests/discovery/test_tunnelled_addr.py tests/ipc/test_server_tunnel_boundary.py ai/tpt-backends/03_wg_tunnel_bindspace.md`
+
+Added optional `BindspaceIdentity` metadata to frozen
+`TunnelledAddress` declarations and a pure
+`with_bindspace_identity()` annotation helper. Unrealized declarations
+retain their prior serialized shape. Realized declarations retain only
+serializable key/inode identity, never the FD-bearing capability.
+
+The existing `.namespace` tuple contract remains compatible:
+unrealized declarations report `(kind, key)`, while realized
+declarations report the stable `(kind, inode)`. Name mismatches between
+the tunnel declaration and realized bindspace are rejected.
+
+Unit coverage verifies immutability, serialization, delegation and
+mismatch handling. The existing real TCP listener test proves endpoint
+and server diagnostics expose the retained inode without implying that
+the process entered that namespace. Ruff passed and focused tunnel,
+listener and bindspace coverage passed 30 tests.

ai/tpt-backends/03_wg_tunnel_bindspace.md

@@ -557,8 +557,12 @@ composed maddr can name a server source or client destination (§5.4).
 
 ### 5.3 `Address.namespace`, at last
 
-- `TunnelledAddress.namespace` → `(kind, id)` e.g.
+- an unrealized `TunnelledAddress.namespace` reports its declared name
-  `('netns', 'tractor-wg0')`.
+  as `(kind, key)`, e.g. `('netns', 'tractor-wg0')`;
+- `TunnelledAddress.with_bindspace_ref()` returns a frozen declaration
+  annotated with `bindspace.ref`, never the FD-bearing `Bindspace`.
+  Its `.namespace` reports `(kind, inode)` so the
+  realized ref remains stable across rename or unlink;
 - existing plain backends implement it explicitly as `None`, so the
   Protocol does not lie and tunnel delegation needs no `getattr()`
   fallback.

tests/discovery/test_tunnelled_addr.py

@@ -15,6 +15,7 @@ import msgspec
 import pytest
 
 from tractor.discovery import (
+    BindspaceRef,
     TunnelledAddress,
     WGTunnelSpec,
     mb_pubkey,
@@ -196,6 +197,71 @@ def test_namespace_comes_from_the_tunnel(
     assert in_ns.namespace == ('netns', 'wg-test')
 
 
+def test_realized_namespace_uses_stable_ref(
+    overlay: TCPAddress,
+) -> None:
+    '''
+    Realization must retain a stable ref without mutating the maddr.
+
+    Build an unrealized named declaration, annotate it with the
+    matching realized key and inode, and prove the frozen original is
+    unchanged. The annotated copy must preserve transport delegation
+    and expose the stable inode through `.namespace`. Direct msgspec
+    encoding also proves only serializable ref metadata was retained.
+
+    '''
+    declared: TunnelledAddress = TunnelledAddress(
+        overlay=overlay,
+        tunnel=WGTunnelSpec(
+            peer_pubkey=_PUBKEY,
+            netns='wg-test',
+        ),
+    )
+    ref: BindspaceRef = BindspaceRef(
+        kind='netns',
+        key='wg-test',
+        inode=1234,
+    )
+    realized: TunnelledAddress = declared.with_bindspace_ref(
+        ref,
+    )
+
+    assert declared.bindspace_ref is None
+    assert realized.bindspace_ref is ref
+    assert realized.namespace == ('netns', 1234)
+    assert realized.overlay is declared.overlay
+    assert realized.tunnel is declared.tunnel
+    assert realized.unwrap() == declared.unwrap()
+    assert realized.bindspace == declared.bindspace
+
+    declared_payload: dict[str, object] = msgspec.msgpack.decode(
+        msgspec.msgpack.encode(declared)
+    )
+    assert 'bindspace_ref' not in declared_payload
+
+    decoded: dict[str, object] = msgspec.msgpack.decode(
+        msgspec.msgpack.encode(realized)
+    )
+    assert decoded['bindspace_ref'] == {
+        'kind': 'netns',
+        'key': 'wg-test',
+        'inode': 1234,
+    }
+
+    mismatched: BindspaceRef = BindspaceRef(
+        kind='netns',
+        key='other-netns',
+        inode=5678,
+    )
+    with pytest.raises(
+        ValueError,
+        match='wg-test.*other-netns',
+    ):
+        declared.with_bindspace_ref(
+            mismatched,
+        )
+
+
 def test_strip_tunnels(
     tunnelled: TunnelledAddress,
     overlay: TCPAddress,

tests/ipc/test_server_tunnel_boundary.py

@@ -7,6 +7,7 @@ from __future__ import annotations
 import trio
 
 from tractor.discovery import (
+    BindspaceRef,
     TunnelledAddress,
     WGTunnelSpec,
     tunnels_of,
@@ -25,8 +26,9 @@ def test_server_peels_before_endpoint_construction() -> None:
     instead of the TCP backend. Start a real listener from the
     wrapper, assert the resulting `Endpoint` contains only a resolved
     `TCPAddress`. Prove `Endpoint.declared_addr` still retains the
-    original tunnel namespace for diagnostics and the future
+    original declaration and realized bindspace ref for
-    bindspace lifecycle.
+    diagnostics. This retained metadata does not claim the listener
+    process entered that namespace.
 
     '''
     overlay = TCPAddress('127.0.0.1', 0)
@@ -38,11 +40,19 @@ def test_server_peels_before_endpoint_construction() -> None:
             netns='actor-net',
         ),
     )
+    ref: BindspaceRef = BindspaceRef(
+        kind='netns',
+        key='actor-net',
+        inode=1234,
+    )
+    declared: TunnelledAddress = tunnelled.with_bindspace_ref(
+        ref,
+    )
 
     async def main() -> None:
         async with open_ipc_server() as server:
             eps = await server.listen_on(
-                accept_addrs=[tunnelled],
+                accept_addrs=[declared],
             )
             assert len(eps) == 1
             endpoint = eps[0]
@@ -51,9 +61,9 @@ def test_server_peels_before_endpoint_construction() -> None:
             _, host, port = endpoint.addr.unwrap()
             assert host == overlay.unwrap()[1]
             assert port > 0
-            assert endpoint.addr is not tunnelled
+            assert endpoint.addr is not declared
-            assert endpoint.declared_addr is tunnelled
+            assert endpoint.declared_addr is declared
-            namespace: tuple[str, str] = ('netns', 'actor-net')
+            namespace: tuple[str, int] = ('netns', 1234)
             assert endpoint.namespace == namespace
             endpoint_repr: str = endpoint.pformat()
             server_repr: str = server.pformat()
@@ -61,9 +71,9 @@ def test_server_peels_before_endpoint_construction() -> None:
             assert expected_namespace in endpoint_repr
             assert ' |_namespaces:' in server_repr
             assert 'netns' in server_repr
-            assert 'actor-net' in server_repr
+            assert '1234' in server_repr
-            assert tunnels_of(tunnelled) == (
+            assert tunnels_of(declared) == (
-                tunnelled.tunnel,
+                declared.tunnel,
             )
 
             server.cancel()

tractor/discovery/_tunnel.py

@@ -94,6 +94,7 @@ import trio
 from ..msg._local import ProcessLocal
 from ._bindspace import (
     Bindspace,
+    BindspaceRef,
     BindspaceSpec,
     open_bindspace,
 )
@@ -864,6 +865,7 @@ def _wg_proto_code() -> int:
 class TunnelledAddress(
     msgspec.Struct,
     frozen=True,
+    omit_defaults=True,
 ):
     '''
     An `Address` annotated with the tunnel it must be reached
@@ -878,6 +880,32 @@ class TunnelledAddress(
     '''
     overlay: Address|TunnelledAddress
     tunnel: TunnelSpec
+    bindspace_ref: BindspaceRef|None = None
+
+    def __post_init__(self) -> None:
+        '''
+        Validate the retained ref against the tunnel declaration.
+
+        '''
+        ref: BindspaceRef|None = self.bindspace_ref
+        if ref is None:
+            return
+        if not isinstance(ref, BindspaceRef):
+            raise TypeError(
+                '`TunnelledAddress.bindspace_ref` must be a '
+                '`BindspaceRef` or `None`!'
+            )
+
+        declared_netns: str|None = self.tunnel.netns
+        if (
+            declared_netns is not None
+            and
+            ref.key != declared_netns
+        ):
+            raise ValueError(
+                f'Declared netns {declared_netns!r} does not match '
+                f'realized bindspace key {ref.key!r}!'
+            )
 
     # ---- delegated, so the runtime can't tell the difference ----
 
@@ -917,14 +945,35 @@ class TunnelledAddress(
     @property
     def namespace(self) -> tuple[str, str|int]|None:
         '''
-        The tunnel's netns, when it declares one.
+        Return the realized ref or declared tunnel netns.
 
         '''
+        ref: BindspaceRef|None = self.bindspace_ref
+        if ref is not None:
+            return (
+                ref.kind,
+                ref.inode,
+            )
+
         if (netns := self.tunnel.netns) is None:
             return self.overlay.namespace
 
         return ('netns', netns)
 
+    def with_bindspace_ref(
+        self,
+        ref: BindspaceRef,
+    ) -> TunnelledAddress:
+        '''
+        Return a copy retaining one realized bindspace ref.
+
+        '''
+        realized: TunnelledAddress = msgspec.structs.replace(
+            self,
+            bindspace_ref=ref,
+        )
+        return realized
+
     def __repr__(self) -> str:
         return (
             f'{type(self).__name__}(\n'