# ADR-001: ALPN, Open Op, and Trivial Params

## Status

Accepted (2026-09-20, Phase 1)

## Context

The crate rides alkcall channels: a produced SOCKS5 resource is an
openable ALPN-op, opened by consumers via `ChannelClient` (alkcall
ADR-037/043). The ALPN string is wire-stable once published
(AGENTS.md conventions 5/16: decide via ADR before the first
consumer). Phase 0's POCs (#1, #2, #5) all ran one ALPN
(`alk/socks5`), one open op (`channels/socks5/sub`), with trivially
empty params, the natural reading of "the RFC conversation is the
data plane": the SOCKS5 target is unknown at open time (it arrives
in-stream post-negotiation), so there is nothing for params to carry
(`poc-connect-wasm-findings.md` §Wire/API notes).

## Decision

- **ALPN: `alk/socks5`** (provisional → stable on first publish;
  the alk/ prefix per the alkcall ADR-004 ALPN-string convention;
  AGENTS.md convention 16's "ADR-004/ADR-006" shorthand cites the
  naming family, of which ADR-004 is the operative one). One ALPN
  per protocol.
- **One open op: `channels/socks5/sub`**: the SOCKS5 session op,
  flavor-form like alktunnels' (`…/sub`; alkcall ADR-047: openable
  ALPNs are operations). All three RFC 1928 commands (CONNECT,
  BIND, UDP ASSOCIATE) ride this one op, selected in-stream at
  command dispatch (the command is an RFC-1928 wire fact, not a
  wire-format choice of ours).
- **Params: the trivial object** `{}` (schema `{type: object}`,
  additionalProperties false). Nothing else is needed at open time
  (the establisher is a session gate, not a dial; the target is
  unknown). Extensibility: if a later need surfaces per-session
  options (e.g. a requested local bind hint), that is an
  **additive** params schema change while no params were ever
  required; consumers that send `{}` stay valid. Params are a
  self-contained JSON object identifying the produced resource
  (alkcall ADR-039's shape, following alktunnels ADR-001's template).
- **Reply: `{"channel_id": <u32>}`**: the Sub-typed operation
  reply, as with alktunnels. No extra reply fields in v1 (the
  establishment phase is a session gate and has nothing to project;
  the alkcall 0.8.0 `with_reply_field` seam remains available
  additively if a future need appears).

## Consequences

- The wire surface is minimal and stable: one ALPN + one op + empty
  params + one reply field. The one-way-door surface is the ALPN
  string, the op id, and the (trivial) params shape, all frozen at
  first publish.
- Command-level differentiation (CONNECT vs ASSOCIATE vs BIND)
  lives in the RFC 1928 stream and in the ACL scope check at
  command dispatch (see ADR-006), not in the op set. No
  per-command ops: that would re-encode the RFC's own command byte
  in our wire format for no benefit.
- POC-validated: all three POCs served CONNECT/ASSOCIATE/BIND on
  the same registration (`connect_still_served_on_the_same_
  registration`, POC #2; test 7, POC #5).

## References

- OQ-SK-01 (params context), OQ-SK-03 (the handle swap, why no
  correlation params), OQ-SK-08 (BIND rides the same op)
- POC #1 `poc-connect-wasm-findings.md` (the trivial-params finding),
  POC #2 `poc-udp-associate-findings.md` (one-op regression guard),
  POC #5 `poc-bind-findings.md` (one-registration-three-commands)
- Upstream: alkcall ADR-037 (channel open ops), ADR-039
  (params is ALPN-specific), ADR-047 (flavor-form op ids)
- Sibling template: alktunnels ADR-001/ADR-002