alksocks/tasks/implementation/composed-accept.md

---
id: implementation/composed-accept
name: Composed — the bind-first accept (the listener on a listen resource)
status: pending
depends_on: [implementation/composed-egress]
scope: moderate
risk: medium
impact: component
level: implementation
---

## Description

The `composed` feature's accept provider (ADR-008's composed
variants; ADR-007 variant 2): the BIND accept whose listener lives on
an alktunnels 0.2.0 bind-first listen resource
(`register_tunnel_bindfirst_openable` + `BindFirstInjections`) —
per-listener ACL for free, hub-relayable. **Vanilla-fidelity with no
stand-ins since the graduation** (ADR-007): reply#1 advertises the
real OS-chosen `bound` (the open-op reply's `bound` field, alkcall
0.8.0 reply projection); reply#2 carries the real peer (the forwarded
op's `peer` param).

Deliverables:

1. **`src/composed/` additions** (feature `composed`) — the composed
   accept, named per producer.md §Wiring:
   - `bindfirst_accept(...)` → `BindAcceptFactory`: the POC #5
     `composed_bind_accept` shape **updated to the graduation** —
     the POC's pinned workaround (reply#1 first, the tunnel open
     rides the accept future; the factory carries an expected
     `bind_addr`) is **retired** (ADR-007 §Consequences). The landed
     shape: the factory opens the bind-first listen channel
     (`TunnelListener::open` — the reply projection surfaces
     `bound`), reply#1 advertises the real `bound`, and the accept
     future correlates the forwarded sessions (the `listen` token →
     the adopted forwarded sessions the assembly correlates; the
     forwarded op's `peer` param is reply#2's peer).
   - **The correlation shape is the design center** (the POC's
     upstream-ask ledger retired by the graduation): the factory
     returns `BindAccept` whose accept future waits for the ONE
     forwarded session matching the listener's token. The
     correlation registry is assembly-side bookkeeping (the
     alktunnels `TunnelListener` docs: "forwarded sessions arrive as
     ordinary adopted sessions on the manager; the listener does not
     own the receipt queue"). The provider owns: the
     `register_tunnel_forwarded_openable` serving side (the opener
     half — the SOCKS5 producer's connection must serve the
     forwarded op), the token→waiter map, and the per-forwarded
     pump. Design the wait shape against the landed alkcall 0.8.0
     adopt surface (`manager.adopt_channel`) and record it in Notes.
   - **The Sync-bound wrinkle** (shared with composed-egress): the
     accepted halves must be `Box<dyn AsyncRead + Send + Sync +
     Unpin>` (`BindTargetHandle`'s payloads); alktunnels' `Taken
     Halves` yields `Send + Unpin` only. The owner-wrapper rides
     **inside the handle payloads** (egress.rs's documented posture)
     — the wrapper owns the adopted channel session so dropping the
     handle drops everything (the teardown-at-birth discipline,
     compiler-enforced). This is the load-bearing wrapper: design it
     once (with composed-egress's needs), pin it with a test.
   - **Peer-address fidelity**: the forwarded op's `peer` param is
     reply#2's real peer (the graduation's win); the wrapper-aware
     sentinel (`0.0.0.0:0`) is the in-band default's shape, not this
     variant's.
   - **The establishment bound covers only the open-op round trip**
     (ADR-007): the accept wait lives in the teardown-governed pump
     phase — the quiet wait's `select!` drop of the accept future IS
     the client-gone teardown; the listener (inside the future)
     closes with it. The forwarded-op correlation must survive a
     client-gone drop without leaking the listener (the accept
     future owns it end-to-end — the seam contract).
   - Module doc: names the ADRs (007/008), the graduation's
     vanilla-fidelity win, the correlation shape, the owner-wrapper.
2. **Tests** (`tests/composed-accept.rs`): the full composed BIND
   story over channels — a bind-first tunnel producer
   (`register_tunnel_bindfirst_openable` + injections), the SOCKS5
   producer with `composed::bindfirst_accept(...)`, a consumer BIND
   session: reply#1 carries the real `bound`, an app server dials
   the far listener, reply#2 carries the real peer, the pass-through
   data plane round-trips; the client-gone teardown releases the
   listener (drop-witness); two concurrent BIND sessions get
   distinct tokens; a forwarded-open failure is per-accept isolated.

## Acceptance Criteria

- [ ] `cargo test` passes; `cargo test --all-features` passes
- [ ] `cargo check --features composed --target wasm32-unknown-
      unknown` clean (hard gate)
- [ ] `cargo clippy --all-targets --all-features -- -D warnings`
      clean; `cargo fmt --check` clean
- [ ] The graduation's shape lands (reply#1 = the real `bound`;
      reply#2 = the forwarded op's real `peer`) — no expected-addr
      stand-in — pinned by test
- [ ] The owner-wrapper rides inside the handle payloads (Sync
      halves; teardown structural) — pinned by test
- [ ] The client-gone teardown releases the listener (the accept
      future owns it end-to-end) — pinned by drop-witness test
- [ ] The forwarded-op serving side + correlation land; per-accept
      isolation — pinned by tests

## References

- docs/architecture/decisions/007-bind-in-base.md (variant 2 + the
  graduation), 008-provider-defaults.md, 004 (the accept seam's
  contracts), 006 (the command gate)
- docs/architecture/producer.md §Wiring
  (`composed::bindfirst_accept`), §The Three Seams
- POC reference: `/workspace/alksocks-bind-poc/src/accept.rs`
  (`composed_bind_accept` — the superseded-in-shape workaround, the
  owner-wrapper's first witness)
- Landed surfaces: `src/egress.rs` (`BindAccept`/`BindTargetHandle`
  — the contracts), alktunnels 0.2.0 (`register_tunnel_bindfirst_
  openable`, `BindFirstInjections`, `TunnelListener`,
  `register_tunnel_forwarded_openable`, `ForwardedHandler`)

## Notes

> To be filled by implementation agent

## Summary

> To be filled on completion