feat: consumer-session — TunnelSession (open/adopt, data planes, teardown)

- TunnelSession (src/consumer.rs): open (ChannelClient::open_channel)
  + adopt (ChannelManager::adopt_channel) construction, substrate-
  shaped data planes (raw halves for stream; ADR-003 codec + pending
  frame queue for UDP), pump_against (session-owned pump_bidi handle),
  and teardown ownership per ADR-005: close (abort + ungraceful reap),
  join (await + reap + copy counts, pump-less (0,0,reaped)), Drop
  (abort + sync reap, never leaks). No Clone (compile_fail doc-test).
- open_reverse_channel on the CallConnection (the reverse path's
  two-step: call then adopt — the POC's honest shape).
- Error surfaces (src/error.rs): TunnelOpenError (typed ADR-049 §4
  surface via open_ref/establishment_reason), TunnelIoError (wrong-
  substrate, TruncatedDatagram fail-loud, ChannelTaken), ReverseOpenError.
- Tests: tests/consumer_session.rs (12) over two harness topologies —
  forward (wire_forward/ForwardTopology: consumer connect-side pure
  client, producer serving via adapter) and reverse (the POC shape);
  teardown matrix, W4 half-close, out-of-band close + self-reap (W3),
  F-2 empty datagram, AdoptFailed-on-collision (bogus-id adopt parks
  by design — documented), concurrent sessions. Harness: all_substrate_dial.
- Adopt takes substrate (task-note deviation: the data plane shape
  rode the open call; cannot be inferred from the ID).

Verified: cargo test green (38), clippy -D warnings (native + wasm32),
fmt clean, cargo check --target wasm32-unknown-unknown passes.

tests/consumer_session.rs

@@ -0,0 +1,597 @@
+//! Integration tests for the consumer half — `TunnelSession` per
+//! consumer.md + ADR-005, over the duplex harness. Ported from the
+//! reverse POC's `ReverseTunnel` suite (the W3/W4 probes) plus the
+//! forward POC's session shapes, generalized to the spec's session
+//! type.
+//!
+//! Covered: forward open (session halves drive a duplex round-trip),
+//! reverse open+adopt+pump_against (round-trip, W4 half-close, join
+//! copy counts, out-of-band close + self-reaping, pump-less join),
+//! datagram variant (round-trip incl. the empty datagram — the F-2
+//! layering), wrong-substrate errors, and the teardown matrix
+//! (close/join/Drop — no leaked channel entries via `channel_ids()`).
+
+mod harness;
+
+use alktunnels::params::{Substrate, TunnelParams};
+use alktunnels::producer::ResourceRegistry;
+use alktunnels::{open_reverse_channel, TunnelSession};
+
+use harness::{all_substrate_dial, echo_dial, framed_udp_echo_dial, wire, wire_forward, Topology};
+
+fn params(resource: &str, substrate: Substrate) -> TunnelParams {
+    TunnelParams {
+        resource: resource.to_string(),
+        substrate,
+    }
+}
+
+/// Both managers hold only channel 0 (the phantom-channel property,
+/// asserted from both topologies).
+trait LeakCheck {
+    fn no_data_channels(&self) -> bool;
+}
+
+impl LeakCheck for Topology {
+    fn no_data_channels(&self) -> bool {
+        self.consumer_manager
+            .channel_ids()
+            .iter()
+            .all(|&id| id == 0)
+            && self
+                .producer
+                .manager()
+                .channel_ids()
+                .iter()
+                .all(|&id| id == 0)
+    }
+}
+
+impl LeakCheck for harness::ForwardTopology {
+    fn no_data_channels(&self) -> bool {
+        self.consumer
+            .manager()
+            .channel_ids()
+            .iter()
+            .all(|&id| id == 0)
+            && self
+                .producer_manager
+                .channel_ids()
+                .iter()
+                .all(|&id| id == 0)
+    }
+}
+
+fn only_channel_0<T: LeakCheck>(topo: &T) -> bool {
+    topo.no_data_channels()
+}
+
+#[tokio::test]
+async fn forward_open_session_halves_round_trip() {
+    let registry = ResourceRegistry::new();
+    registry
+        .register("echo", Substrate::Tcp, "in-process")
+        .await;
+    let topo = wire_forward(registry, echo_dial()).await;
+
+    let mut session = TunnelSession::open(&topo.consumer, params("echo", Substrate::Tcp))
+        .await
+        .expect("open");
+    assert!(topo.producer_manager.has_channel(session.channel_id));
+
+    use tokio::io::{AsyncReadExt, AsyncWriteExt};
+    let (read, write) = session.stream_halves().expect("stream session has halves");
+    write.write_all(b"ping").await.expect("write");
+    write.flush().await.expect("flush");
+    let mut buf = vec![0u8; 4];
+    tokio::time::timeout(std::time::Duration::from_secs(5), read.read_exact(&mut buf))
+        .await
+        .expect("round trip")
+        .expect("read");
+    assert_eq!(&buf, b"ping");
+
+    // Teardown: the session reaps its adopted entry (ADR-005).
+    let channel_id = session.channel_id;
+    let reaped = session.close().await;
+    assert!(reaped, "close reaped the adopted entry");
+    tokio::time::sleep(std::time::Duration::from_millis(100)).await;
+    assert!(!topo.producer_manager.has_channel(channel_id));
+    assert!(only_channel_0(&topo), "no leaked entries after close");
+}
+
+#[tokio::test]
+async fn forward_open_take_halves_then_pumpless_join() {
+    // consumer.md's pinned semantics: after take_halves the session is
+    // pump-less — join completes immediately, reaps only, (0, 0, reaped).
+    let registry = ResourceRegistry::new();
+    registry
+        .register("echo", Substrate::Tcp, "in-process")
+        .await;
+    let topo = wire_forward(registry, echo_dial()).await;
+
+    let session = TunnelSession::open(&topo.consumer, params("echo", Substrate::Tcp))
+        .await
+        .expect("open");
+    let taken = session.take_halves();
+
+    use tokio::io::{AsyncReadExt, AsyncWriteExt};
+    let mut read = taken.read;
+    let mut write = taken.write;
+    write.write_all(b"echo-me").await.expect("write");
+    write.flush().await.expect("flush");
+    let mut buf = vec![0u8; 7];
+    tokio::time::timeout(std::time::Duration::from_secs(5), read.read_exact(&mut buf))
+        .await
+        .expect("round trip through taken halves")
+        .expect("read");
+    assert_eq!(&buf, b"echo-me");
+
+    let session = taken.session;
+    // Drop the halves BEFORE joining: EOF propagates through the mux,
+    // the producer-side wrapper reaps, and the pump-less session reaps
+    // its own adopted entry on join (nothing to await).
+    drop(read);
+    drop(write);
+    let (c2p, p2c, reaped) = session.join().await;
+    assert_eq!((c2p, p2c), (0, 0), "pump-less join: no pump to await");
+    assert!(reaped, "pump-less join reaps the adopted entry");
+    tokio::time::sleep(std::time::Duration::from_millis(200)).await;
+    assert!(only_channel_0(&topo));
+}
+
+#[tokio::test]
+async fn datagram_round_trip_including_empty() {
+    // The datagram variant over the codec (ADR-003): round-trip incl.
+    // the F-2 empty datagram — `len=0` is a legal datagram, never EOF.
+    let registry = ResourceRegistry::new();
+    registry.register("dns", Substrate::Udp, "in-process").await;
+    let topo = wire_forward(registry, framed_udp_echo_dial()).await;
+
+    let mut session = TunnelSession::open(&topo.consumer, params("dns", Substrate::Udp))
+        .await
+        .expect("udp open");
+    assert!(
+        session.stream_halves().is_none(),
+        "stream_halves is stream-substrate-only"
+    );
+
+    session
+        .send_datagram(b"query-1")
+        .await
+        .expect("send datagram");
+    session
+        .send_datagram(b"")
+        .await
+        .expect("send empty datagram");
+
+    let dg1 = tokio::time::timeout(std::time::Duration::from_secs(5), session.recv_datagram())
+        .await
+        .expect("recv timed out")
+        .expect("no io error")
+        .expect("first datagram");
+    assert_eq!(&dg1[..], b"query-1");
+    let dg2 = tokio::time::timeout(std::time::Duration::from_secs(5), session.recv_datagram())
+        .await
+        .expect("recv timed out")
+        .expect("no io error")
+        .expect("second datagram (empty round-trips — F-2)");
+    assert!(dg2.is_empty(), "the empty datagram round-trips (F-2)");
+
+    let reaped = session.close().await;
+    assert!(reaped);
+    // The producer-side wrapper reap is async (the pump task exits,
+    // the wrapper reaps) — settle before asserting both managers.
+    tokio::time::sleep(std::time::Duration::from_millis(200)).await;
+    assert!(only_channel_0(&topo));
+}
+
+#[tokio::test]
+async fn wrong_substrate_operations_are_typed() {
+    // The POC's WrongSubstrate shape: substrate-shaped operations fail
+    // typed on the wrong plane.
+    let registry = ResourceRegistry::new();
+    registry
+        .register("echo", Substrate::Tcp, "in-process")
+        .await;
+    registry.register("dns", Substrate::Udp, "in-process").await;
+    let topo = wire_forward(registry, all_substrate_dial()).await;
+
+    let mut stream_session = TunnelSession::open(&topo.consumer, params("echo", Substrate::Tcp))
+        .await
+        .expect("tcp open");
+    let err = stream_session
+        .send_datagram(b"nope")
+        .await
+        .expect_err("send_datagram on a stream session");
+    assert!(matches!(err, alktunnels::TunnelIoError::WrongSubstrate));
+    let err = stream_session
+        .recv_datagram()
+        .await
+        .expect_err("recv_datagram on a stream session");
+    assert!(matches!(err, alktunnels::TunnelIoError::WrongSubstrate));
+    stream_session.close().await;
+
+    let mut dg_session =
+        match TunnelSession::open(&topo.consumer, params("dns", Substrate::Udp)).await {
+            Err(_) => panic!("setup: udp dial must succeed in the framed harness"),
+            Ok(mut s) => {
+                assert!(
+                    s.stream_halves().is_none(),
+                    "stream_halves is stream-substrate-only"
+                );
+                s
+            }
+        };
+    dg_session.send_datagram(b"late").await.expect("send works");
+    dg_session.close().await;
+    tokio::time::sleep(std::time::Duration::from_millis(200)).await;
+    assert!(only_channel_0(&topo));
+}
+
+#[tokio::test]
+async fn reverse_open_adopt_pump_round_trip() {
+    // The reverse flow (the POC's ReverseTunnel shape, generalized):
+    // open_reverse_channel → adopt → pump_against → round-trip →
+    // join (copy counts + reap).
+    let registry = ResourceRegistry::new();
+    registry
+        .register("echo", Substrate::Tcp, "in-process")
+        .await;
+    let topo = wire(registry, echo_dial()).await;
+
+    let channel_id =
+        open_reverse_channel(&topo.consumer_call, &params("echo", Substrate::Tcp), None)
+            .await
+            .expect("reverse open call");
+
+    let session = TunnelSession::adopt(
+        &topo.consumer_manager,
+        channel_id,
+        Substrate::Tcp,
+        alktunnels::TUNNEL_ALPN,
+    )
+    .await
+    .expect("adopt");
+    assert_eq!(session.channel_id, channel_id);
+
+    let (accepted_end, local_end) = tokio::io::duplex(64 * 1024);
+    let session = session.pump_against(accepted_end).await;
+
+    use tokio::io::{AsyncReadExt, AsyncWriteExt};
+    let (mut l_read, mut l_write) = tokio::io::split(local_end);
+    l_write.write_all(b"reverse").await.expect("write");
+    l_write.flush().await.expect("flush");
+    let mut buf = vec![0u8; 7];
+    tokio::time::timeout(
+        std::time::Duration::from_secs(5),
+        l_read.read_exact(&mut buf),
+    )
+    .await
+    .expect("round trip")
+    .expect("read");
+    assert_eq!(&buf, b"reverse");
+
+    // EOF propagates through the two pumps (the two-pump contract).
+    drop(l_write);
+    drop(l_read);
+    let (c2p, p2c, reaped) =
+        tokio::time::timeout(std::time::Duration::from_secs(5), session.join())
+            .await
+            .expect("join timed out");
+    assert!(c2p > 0 && p2c > 0, "both pumps moved bytes: {c2p}, {p2c}");
+    assert!(reaped, "join reaps after pump completion");
+    tokio::time::sleep(std::time::Duration::from_millis(100)).await;
+    assert!(
+        !topo.producer.manager().has_channel(channel_id),
+        "producer-side channel reaped (wrapper-managed)"
+    );
+    assert!(only_channel_0(&topo), "no leaked entries after join");
+}
+
+#[tokio::test]
+async fn reverse_half_close_semantics_w4() {
+    // W4's shape: the local side half-closes (shutdown write); the
+    // target sees EOF on its read side while the reverse direction
+    // stays pumpable, and the target's final reply still flows back.
+    let registry = ResourceRegistry::new();
+    registry
+        .register("echo", Substrate::Tcp, "in-process")
+        .await;
+    let topo = wire(registry, echo_dial()).await;
+
+    let channel_id =
+        open_reverse_channel(&topo.consumer_call, &params("echo", Substrate::Tcp), None)
+            .await
+            .expect("reverse open call");
+    let session = TunnelSession::adopt(
+        &topo.consumer_manager,
+        channel_id,
+        Substrate::Tcp,
+        alktunnels::TUNNEL_ALPN,
+    )
+    .await
+    .expect("adopt");
+
+    let (accepted_end, local_end) = tokio::io::duplex(64 * 1024);
+    let session = session.pump_against(accepted_end).await;
+
+    use tokio::io::{AsyncReadExt, AsyncWriteExt};
+    let (mut l_read, mut l_write) = tokio::io::split(local_end);
+    l_write.write_all(b"half").await.expect("write");
+    l_write.flush().await.expect("flush");
+    l_write.shutdown().await.expect("half close");
+
+    let mut buf = vec![0u8; 4];
+    tokio::time::timeout(
+        std::time::Duration::from_secs(5),
+        l_read.read_exact(&mut buf),
+    )
+    .await
+    .expect("echo after half close")
+    .expect("read echo");
+    assert_eq!(&buf, b"half");
+
+    let _ = tokio::time::timeout(std::time::Duration::from_secs(5), session.join())
+        .await
+        .expect("join after half close");
+    assert!(only_channel_0(&topo));
+}
+
+#[tokio::test]
+async fn out_of_band_close_then_session_self_reap() {
+    // The POC's reverse_channel_close_out_of_band shape: a peer-initiated
+    // `channel/close` tears the SERVING side down; the consumer's session
+    // still owns its adopted entry — close/join reaps it (W3 split).
+    let registry = ResourceRegistry::new();
+    registry
+        .register("echo", Substrate::Tcp, "in-process")
+        .await;
+    let topo = wire(registry, echo_dial()).await;
+
+    let channel_id =
+        open_reverse_channel(&topo.consumer_call, &params("echo", Substrate::Tcp), None)
+            .await
+            .expect("reverse open call");
+    let session = TunnelSession::adopt(
+        &topo.consumer_manager,
+        channel_id,
+        Substrate::Tcp,
+        alktunnels::TUNNEL_ALPN,
+    )
+    .await
+    .expect("adopt");
+    let session = session.pump_against(tokio::io::duplex(1024).0).await;
+
+    let response = topo
+        .consumer_call
+        .call_with_payload(serde_json::json!({
+            "operationId": "channel/close",
+            "input": { "channel_id": channel_id, "reason": "out-of-band" }
+        }))
+        .await;
+    assert!(response.result.is_ok(), "channel/close resolved");
+
+    // The close ran on the PRODUCER side; the consumer's entry remains.
+    tokio::time::sleep(std::time::Duration::from_millis(200)).await;
+    assert!(
+        !topo.producer.manager().has_channel(channel_id),
+        "producer-side channel reaped by the out-of-band close"
+    );
+    assert!(topo.consumer_manager.has_channel(channel_id));
+    let reaped = session.close().await;
+    assert!(reaped, "session reaped its adopted entry");
+    assert!(only_channel_0(&topo));
+}
+
+#[tokio::test]
+async fn drop_never_leaks_the_channel_entry() {
+    // ADR-005: Drop = abort + sync reap (best-effort). Dropping a live
+    // session without close/join never leaks the entry.
+    let registry = ResourceRegistry::new();
+    registry
+        .register("echo", Substrate::Tcp, "in-process")
+        .await;
+    let ftopo = wire_forward(registry.clone(), echo_dial()).await;
+
+    let session = TunnelSession::open(&ftopo.consumer, params("echo", Substrate::Tcp))
+        .await
+        .expect("open");
+    let channel_id = session.channel_id;
+    assert!(ftopo.consumer.manager().has_channel(channel_id));
+    drop(session);
+    assert!(
+        !ftopo.consumer.manager().has_channel(channel_id),
+        "Drop reaped the adopted entry"
+    );
+
+    // Drop with a session-owned pump: the pump aborts too (the reverse
+    // topology — pump_against is the reverse-flow use).
+    let topo = wire(registry, echo_dial()).await;
+    let channel_id =
+        open_reverse_channel(&topo.consumer_call, &params("echo", Substrate::Tcp), None)
+            .await
+            .expect("second reverse open");
+    let session = TunnelSession::adopt(
+        &topo.consumer_manager,
+        channel_id,
+        Substrate::Tcp,
+        alktunnels::TUNNEL_ALPN,
+    )
+    .await
+    .expect("adopt");
+    let session = session.pump_against(tokio::io::duplex(1024).0).await;
+    assert!(topo.consumer_manager.has_channel(channel_id));
+    drop(session);
+    assert!(!topo.consumer_manager.has_channel(channel_id));
+}
+
+#[tokio::test]
+async fn oversize_datagram_rejected_at_frame_time() {
+    // ADR-003: a >65535-byte send is rejected at frame time (`Oversize`),
+    // never a wire overflow.
+    let registry = ResourceRegistry::new();
+    registry.register("dns", Substrate::Udp, "in-process").await;
+    let topo = wire_forward(registry, framed_udp_echo_dial()).await;
+
+    let mut session = TunnelSession::open(&topo.consumer, params("dns", Substrate::Udp))
+        .await
+        .expect("udp open");
+    let err = session
+        .send_datagram(&vec![0u8; alktunnels::MAX_DATAGRAM_LEN + 1])
+        .await
+        .expect_err("oversize must fail");
+    assert!(
+        matches!(
+            err,
+            alktunnels::TunnelIoError::Codec(alktunnels::wire::DatagramCodecError::Oversize(_, _))
+        ),
+        "oversize is a codec error at frame time: {err:?}"
+    );
+    session.close().await;
+}
+
+#[tokio::test]
+async fn failed_open_never_yields_a_session() {
+    // No phantom session: unknown resource → typed error, no channel
+    // anywhere, and `open_ref()` exposes the typed surface.
+    let registry = ResourceRegistry::new();
+    registry
+        .register("echo", Substrate::Tcp, "in-process")
+        .await;
+    let topo = wire_forward(registry, echo_dial()).await;
+
+    let err = match TunnelSession::open(&topo.consumer, params("ghost", Substrate::Tcp)).await {
+        Ok(_) => panic!("unknown resource must not open"),
+        Err(e) => e,
+    };
+    assert_eq!(
+        err.open_ref().establishment_reason(),
+        Some("unknown_resource")
+    );
+    assert!(only_channel_0(&topo));
+
+    // Reverse path on the reverse topology: the call fails typed;
+    // adopt is never reached.
+    let registry = ResourceRegistry::new();
+    registry
+        .register("echo", Substrate::Tcp, "in-process")
+        .await;
+    let topo = wire(registry, echo_dial()).await;
+    let err =
+        match open_reverse_channel(&topo.consumer_call, &params("ghost", Substrate::Tcp), None)
+            .await
+        {
+            Ok(_) => panic!("reverse open of unknown resource must fail"),
+            Err(e) => e,
+        };
+    assert!(matches!(err, alktunnels::ReverseOpenError::Call(_)));
+    assert!(only_channel_0(&topo));
+}
+
+#[tokio::test]
+async fn adopt_failure_is_typed_not_establishment() {
+    // An adopt failure is `AdoptFailed`-class (post-reply local
+    // failure: ID collision), not an establishment error. A bogus-id
+    // adopt SUCCEEDS by design — the manager parks early arrivals for
+    // any not-yet-seen ID (the adoption race cover, ADR-047 §5) — so
+    // the collision path is the honest probe: adopt the same ID twice.
+    let registry = ResourceRegistry::new();
+    registry
+        .register("echo", Substrate::Tcp, "in-process")
+        .await;
+    let topo = wire(registry, echo_dial()).await;
+
+    let channel_id =
+        open_reverse_channel(&topo.consumer_call, &params("echo", Substrate::Tcp), None)
+            .await
+            .expect("reverse open");
+
+    let first = TunnelSession::adopt(
+        &topo.consumer_manager,
+        channel_id,
+        Substrate::Tcp,
+        alktunnels::TUNNEL_ALPN,
+    )
+    .await
+    .expect("first adopt");
+
+    let err = match TunnelSession::adopt(
+        &topo.consumer_manager,
+        channel_id,
+        Substrate::Tcp,
+        alktunnels::TUNNEL_ALPN,
+    )
+    .await
+    {
+        Ok(_) => panic!("adopting a live id twice must fail"),
+        Err(e) => e,
+    };
+    match err.open_ref() {
+        alkcall::channels::client::ChannelOpenError::AdoptFailed(
+            alkcall::channels::manager::ManagerError::ChannelExists(_),
+        ) => {}
+        other => panic!("expected AdoptFailed(ChannelExists), got {other:?}"),
+    }
+
+    first.close().await;
+    tokio::time::sleep(std::time::Duration::from_millis(200)).await;
+    assert!(only_channel_0(&topo));
+}
+
+#[tokio::test]
+async fn concurrent_reverse_sessions_independent() {
+    // Two reverse sessions on one connection: independent channels,
+    // each round-trips its own marker, both reaped.
+    let registry = ResourceRegistry::new();
+    registry
+        .register("echo", Substrate::Tcp, "in-process")
+        .await;
+    let topo = wire(registry, echo_dial()).await;
+
+    use tokio::io::{AsyncReadExt, AsyncWriteExt};
+    let mut sessions = Vec::new();
+    for i in 0..2 {
+        let channel_id =
+            open_reverse_channel(&topo.consumer_call, &params("echo", Substrate::Tcp), None)
+                .await
+                .expect("reverse open");
+        let session = TunnelSession::adopt(
+            &topo.consumer_manager,
+            channel_id,
+            Substrate::Tcp,
+            alktunnels::TUNNEL_ALPN,
+        )
+        .await
+        .expect("adopt");
+        let (accepted_end, local_end) = tokio::io::duplex(64 * 1024);
+        let session = session.pump_against(accepted_end).await;
+        let (mut l_read, mut l_write) = tokio::io::split(local_end);
+        let msg = format!("marker {i}");
+        l_write.write_all(msg.as_bytes()).await.expect("write");
+        l_write.flush().await.expect("flush");
+        let mut buf = vec![0u8; msg.len()];
+        tokio::time::timeout(
+            std::time::Duration::from_secs(5),
+            l_read.read_exact(&mut buf),
+        )
+        .await
+        .expect("round trip")
+        .expect("read");
+        assert_eq!(buf, msg.as_bytes());
+        sessions.push(session);
+    }
+    assert_ne!(sessions[0].channel_id, sessions[1].channel_id);
+
+    for session in sessions {
+        let (_, _, reaped) = session.join().await;
+        assert!(reaped);
+    }
+    assert!(only_channel_0(&topo));
+}
+
+#[allow(dead_code)]
+fn type_assertions() {
+    // The `compile_fail` doc-test in consumer.rs is the no-Clone gate;
+    // this parity stub keeps the type in the test's namespace.
+    let _ = std::mem::size_of::<TunnelSession>();
+}

tests/harness.rs

@@ -1,5 +1,6 @@
 //! Test harness — the producer↔consumer wiring over a
 //! `tokio::io::duplex` carrying the channels 8-byte chunk format.
+#![allow(dead_code)]
 //!
 //! Topology (the reverse POC's shape, mirrored for both directions):
 //! - **producer** (connect side of the channels connection — it runs
@@ -222,6 +223,133 @@ pub async fn wire(registry: ResourceRegistry, dial: alktunnels::producer::DialFn
     .await
 }
 
+/// The forward topology (the `-L` direction): the consumer dials the
+/// transport (connect side — `ChannelClient::from_connection`, a pure
+/// consumer serving nothing) and the producer accepts (the adapter +
+/// an install hook that registers the channel ops + the tunnel
+/// openable on the producer's serving registry). This is the topology
+/// `TunnelSession::open(&channel_client, params)` is normative for:
+/// the consumer's own client calls the open op on the producer's
+/// channel 0.
+///
+/// Identity on the accept-side serving path (the mTLS posture): the
+/// transport authenticated the dialer; the hook attaches the resolved
+/// identity to channel 0 so the serving dispatch sees the caller
+/// (the accept-side analogue of CF-005 (b)'s propagation).
+pub struct ForwardTopology {
+    /// The consumer's own client (connect side, pure consumer). Its
+    /// manager adopted the producer-allocated channel IDs; the
+    /// session reaps via this manager.
+    pub consumer: Arc<ChannelClient>,
+    /// The producer's manager (accept side, serving) — for asserting
+    /// wrapper-managed reaping.
+    pub producer_manager: ChannelManager,
+    /// What the establisher's per-call auth carried (the CF-006 probe).
+    pub identity_witness: Arc<tokio::sync::Mutex<Option<String>>>,
+}
+
+pub async fn wire_forward(
+    registry: ResourceRegistry,
+    dial: alktunnels::producer::DialFn,
+) -> ForwardTopology {
+    let producer_op_registry = Arc::new(OperationRegistry::new());
+    let (producer_manager_tx, mut producer_manager_rx) =
+        tokio::sync::mpsc::channel::<ChannelManager>(1);
+    let identity_witness = Arc::new(tokio::sync::Mutex::new(None::<String>));
+    let dial_witness = Arc::clone(&identity_witness);
+
+    // --- producer (accept side, serving): adapter + install hook ------
+    let install_hook: InstallChannelZero = Arc::new(move |manager, channel0_conn, _auth| {
+        let registry_arc = Arc::clone(&producer_op_registry);
+        let resource_registry = registry.clone();
+        let dial = Arc::clone(&dial);
+        let witness = Arc::clone(&dial_witness);
+        let manager_tx = producer_manager_tx.clone();
+        tokio::spawn(async move {
+            let channel0_bidi = match channel0_conn.accept_bi().await {
+                Ok(s) => s,
+                Err(_) => return,
+            };
+            let (writer, reader) = split_single_stream(channel0_bidi);
+            // The accept-side transport-identity posture: the transport
+            // authenticated the dialer; attach the resolved identity to
+            // channel 0 (the dispatch reads it as the caller identity).
+            let _ = channel0_conn.set_identity(consumer_identity());
+            let call_connection = Arc::new(CallConnection::new_single_stream(
+                channel0_conn,
+                Arc::clone(&writer),
+            ));
+
+            // Register the generic channel ops + the tunnel openable
+            // (the producer.md recipe) before the dispatch loop runs.
+            let core = alkcall::channels::operations::ChannelCore::new(
+                manager.clone(),
+                alkcall::channels::policy::default_policy(),
+            );
+            let ops = ChannelOperations::with_default_policy(manager.clone());
+            ops.register_on(&registry_arc)
+                .expect("register channel ops on producer");
+            register_tunnel_openable(
+                &core,
+                &resource_registry,
+                &registry_arc,
+                AuthContext::anonymous(b"alk/tunnel"),
+                dial,
+                Some(witness),
+            )
+            .expect("register tunnel openable");
+            let _ = manager_tx.send(manager).await;
+
+            let dp = Dispatcher::new(
+                registry_arc,
+                Arc::new(alkcall::core::auth::NoopIdentityProvider),
+            );
+            dp.serve_single_stream(call_connection, reader, writer)
+                .await;
+        })
+    });
+
+    // --- transport ------------------------------------------------------
+    let (consumer_end, producer_end) = tokio::io::duplex(64 * 1024);
+    let consumer_conn = CoreConnection::from_bidi(consumer_end, b"alk/channels".to_vec(), None);
+    let producer_conn = CoreConnection::from_bidi(producer_end, b"alk/channels".to_vec(), None);
+
+    // The dialer's transport identity (the mTLS/QUIC posture) — set
+    // before from_connection. The accept side resolves it out-of-band
+    // (modeled in the hook above).
+    consumer_conn
+        .set_identity(consumer_identity())
+        .expect("transport identity set once");
+
+    let adapter = ChannelsAdapter::new(install_hook, Arc::new(alkcall::channels::policy::NoCap));
+    let producer_transport_auth = AuthContext::anonymous(b"alk/channels");
+    let _adapter_task = tokio::spawn(async move {
+        let _ = alkcall::core::types::ProtocolHandler::handle(
+            &adapter,
+            producer_conn,
+            &producer_transport_auth,
+        )
+        .await;
+    });
+
+    // --- consumer (connect side): pure client ---------------------------
+    let consumer_client = ChannelClient::from_connection(consumer_conn)
+        .await
+        .expect("consumer channel client init");
+    let consumer_client = Arc::new(consumer_client);
+
+    let producer_manager = producer_manager_rx
+        .recv()
+        .await
+        .expect("producer manager captured");
+
+    ForwardTopology {
+        consumer: consumer_client,
+        producer_manager,
+        identity_witness,
+    }
+}
+
 /// An echo dial closure (the ADR-004 injection point under test): an
 /// in-process pipe per dial — the "target" echoes bytes until EOF.
 /// The consumer side gets split `DuplexStream` halves; a spawned task
@@ -263,6 +391,17 @@ pub fn echo_dial() -> alktunnels::producer::DialFn {
     })
 }
 
+/// A both-substrates dial: stream substrates echo via pipes, UDP
+/// echoes via the framed codec (the datagram tests' single dial).
+pub fn all_substrate_dial() -> alktunnels::producer::DialFn {
+    let echo = echo_dial();
+    let udp = framed_udp_echo_dial();
+    Arc::new(move |substrate: Substrate, backing: &str| match substrate {
+        Substrate::Udp => udp(substrate, backing),
+        Substrate::Tcp | Substrate::Unix => echo(substrate, backing),
+    })
+}
+
 /// A failing dial closure (the `dial_failed` stand-in).
 pub fn failing_dial(message: &'static str) -> alktunnels::producer::DialFn {
     Arc::new(move |_substrate: Substrate, _backing: &str| {
@@ -273,3 +412,60 @@ pub fn failing_dial(message: &'static str) -> alktunnels::producer::DialFn {
         })
     })
 }
+
+/// A framed UDP echo dial (the ADR-003 codec at the target boundary —
+/// the in-process stand-in for the real `local` UDP adapter): the
+/// dial's halves carry the `[len: u16 BE]` wire framing; a spawned
+/// echo task decodes frames from the channel side and re-frames the
+/// echoed payloads back. The producer pump copies raw bytes; the
+/// codec lives at this boundary (the pump never sees UDP specifics).
+pub fn framed_udp_echo_dial() -> alktunnels::producer::DialFn {
+    Arc::new(move |substrate: Substrate, backing: &str| {
+        let backing = backing.to_string();
+        Box::pin(async move {
+            match substrate {
+                Substrate::Udp => {
+                    let (consumer_side, target_side) = tokio::io::duplex(64 * 1024);
+                    tokio::spawn(async move {
+                        use alktunnels::wire::DatagramReader;
+                        use tokio::io::{AsyncReadExt, AsyncWriteExt};
+                        let (mut t_read, mut t_write) = tokio::io::split(target_side);
+                        let mut reader = DatagramReader::new();
+                        let mut buf = vec![0u8; 16 * 1024];
+                        loop {
+                            let n = match t_read.read(&mut buf).await {
+                                Ok(0) | Err(_) => return,
+                                Ok(n) => n,
+                            };
+                            let dgs = match reader.feed(&buf[..n]) {
+                                Ok(dgs) => dgs,
+                                Err(_) => return,
+                            };
+                            for dg in dgs {
+                                let framed = match alktunnels::wire::frame_datagram(&dg) {
+                                    Ok(f) => f,
+                                    Err(_) => return,
+                                };
+                                if t_write.write_all(&framed).await.is_err() {
+                                    return;
+                                }
+                                let _ = t_write.flush().await;
+                            }
+                        }
+                    });
+                    let _ = &backing;
+                    let (c_read, c_write) = tokio::io::split(consumer_side);
+                    Ok(alktunnels::producer::TargetHandle {
+                        read: Box::new(c_read),
+                        write: Box::new(c_write),
+                    })
+                }
+                Substrate::Tcp | Substrate::Unix => {
+                    Err(alktunnels::producer::TunnelEstablishError::DialFailed(
+                        format!("stream dial not wired in the udp harness: {backing}"),
+                    ))
+                }
+            }
+        })
+    })
+}