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glm-5.3-flash bd7d1ad8ec docs: Phase 1 architecture spec — ADRs 001..006, spec docs, OQ promotion

The Phase 0 OQ ledger (OQ-TN-01..10) promoted into
docs/architecture/open-questions.md (now OQ-TN-01..14, with four
new Phase 1 residues). Six ADRs and four spec docs, all Draft, all
decision-shaped per the SDD process (ADRs carry the WHY; specs carry
the WHAT and reference by number):

ADRs:
- 001 open-params-layout: params = {resource, substrate} — the
  producer's stable name, not an address; wire-stable from the first
  consumer; unknown substrates fail loudly at schema time
- 002 alpn-strategy: single alk/tunnel ALPN (option A); substrate in
  params selects the framing; prior art (SSH/SOCKS5/udpgw) gives no
  reason for the split
- 003 codec-and-udp-framing: raw pass-through (stream) / mandatory
  [len: u16 BE] (UDP) — F-2 mandate recorded (the codec is mandatory
  for correctness, not cosmetics); len=0 = legal empty datagram;
  OQ-TN-13 resolved fail-loud (truncation)
- 004 no-backend-trait: halves functions at the assembly layer;
  listen is an establisher shape; hub re-produce deferred(OQ-TN-12);
  trait re-evaluated at the alknet ADR-078 convergence threshold
- 005 consumer-session-owns-teardown: TunnelSession with
  open/adopt/stream_halves/take_halves/pump_against/close/join/Drop —
  the W3 adopter gap closes structurally; Drop is the best-effort
  fallback
- 006 access-control-posture: the open gate is the boundary;
  TUNNEL_OPEN_SCOPE = tunnel:open (stable once published); op-level
  ACL; ownership seam; no allowlists in v1; identity = 0.7.0's
  precedence chain

Spec docs:
- overview.md: purpose, resource model, deps (alkcall 0.7.0,
  wasm-clean default, local feature), module map
- wire.md: the open op (params/reply/typed errors), the data plane
  by substrate, sentinels + half-close, byte diagrams
- producer.md: spec, establisher (dial + listen shapes), pump
  handler (pump_bidi inline, R-02), registration API, ACL posture
- consumer.md: TunnelSession (forward open + reverse adopt
  construction), data plane, teardown API (close/join/Drop incl.
  pump-less join semantics)
- bast.md: the BAST doc for the UDP codec (convention 12's trigger
  fired — the framing IS binary beyond pass-through)
- open-questions.md: OQ-TN-01..14; 01..10 promoted (faithful to the
  phase-0 ledger's final states), 11 partially resolved (collision
  domain = per-producer registry per ADR-001; lifecycle open),
  12 deferred(scope), 13 resolved fail-loud (ADR-003), 14 open

Verified by an architecture-reviewer pass (2 criticals, 6 majors,
10 minors — all fixed: ADR-001/003-vs-OQ decision-state contradictions
resolved; the Layer-2 mislabel corrected to the ADR-047 §4 per-session
fork; alktty/alknet ADR misattributions fixed; codec placement pinned
to the establisher (pump stays substrate-agnostic); reverse-path
construction named (TunnelSession::adopt + pump_against); security
posture promoted to ADR-006; BAST doc written; F-2 rationale deduped;
README tables completed; channel_id > 0; MTU wording fixed; ADR-047 §5
attributions corrected; impacts lines added to unresolved OQs; review/
ledger pointer paths added to README references).

Verification: doc set internal cross-refs all resolve; cargo test,
fmt --check, doc --no-deps clean

2026-09-07 18:36:44 +00:00

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status, last_updated

status	last_updated
draft	2026-09-07

alktunnels — Architecture

Arbitrary bidirectional tunnels over alkcall channels: the alk/tunnel-family producer/consumer protocol crate. This directory holds the architecture spec docs and the ADRs. It is the sibling of alktty's architecture (/workspace/@alkdev/alktty/docs/architecture/) — same substrate (alkcall channels), same shape (a producer open-handler + a typed consumer session), different service (tunnels: raw byte/datagram transport, not terminal sessions).

Documents

Document	Status	Description
overview.md	draft	Crate purpose, the resource model in brief, dependencies, ALPN, feature gates, module map
wire.md	draft	The wire format: open-op params JSON (ADR-001), the data-plane codec (raw pass-through for stream substrates; mandatory `[len: u16 BE]` framing for UDP — ADR-003), sentinels, half-close semantics
producer.md	draft	The producer half: the `channels/tunnel/sub` open op, the establisher (dial + listen variants), the pump handler, registration, scope gating
consumer.md	draft	The consumer half: `TunnelSession` (stream + datagram variants), the reverse-flow initiator, teardown ownership (ADR-005)
bast.md	draft	The BAST (Binary Abstract Syntax Tree) document for the data-plane's binary framing (the UDP `[len: u16 BE]` codec — ADR-003); the stream pass-through has no binary framing to describe
open-questions.md	draft	Centralized OQ tracker (OQ-TN-01..14; the Phase 0 ledger promoted)

Applicable ADRs

alktunnels-native ADRs (001..005). Upstream ADRs (alkcall/alknet) are referenced by their own numbers and are NOT ported — the alkcall originals at /workspace/@alkdev/alkcall/docs/architecture/decisions/ remain authoritative for the shared surfaces (establishment, channels wire format, pump_bidi, identity seam).

ADR	Title	Status
001	Open-Op Params Layout: Resource + Substrate	Accepted
002	Single `alk/tunnel` ALPN (Option A)	Accepted
003	Data-Plane Codec: Raw Pass-Through (Stream) / Mandatory Length Framing (UDP)	Accepted
004	No TunnelBackend Trait — Halves Functions at the Assembly Layer	Accepted
005	The Consumer Session Type Owns Teardown	Accepted
006	Access-Control Posture — the Open Gate Is the Security Boundary	Accepted

Key Design Principles

A tunnel is a resource, not an address. params identify a produced resource + substrate discriminator; the producer owns the backing (local port, docker container, in-process service, unix socket). No URL-style general addressing in the wire — rich addressing enters only through -D/dynamic composition, which speaks its protocol inside the tunnel payload. See ADR-001 and wire.md.
Role follows the resource; connection direction is independent. Whoever can reach the target is the producer (registers openable channels); whoever wants the bytes is the consumer. -L and -R are the same open op with the entry point on different machines — no protocol-level direction (the hub-owns-the-connection model, OQ-TN-03). Validated by the reverse-flow POC: the worker serves on the connect side; the hub initiates per accept. See producer.md and consumer.md.
Raw pass-through for stream substrates; mandatory length framing for UDP. A tunnel has one data stream per direction — no sub-demux key, no tunnel-level header on stream substrates (0 B tunnel overhead; the channels 8-byte header is the only cost). UDP rides [len: u16 BE] framing — mandatory for correctness (F-2; the rationale and the executable pin live in ADR-003). See ADR-003 and wire.md.
The two-pump shape is alkcall::channels::pump_bidi — never hand-rolled. The producer's pump handler and the consumer-side pump both consume the upstream helper (ADR-050); each pump shuts down the opposite sink on completion (half-close semantics fall out). The OpenHandler's returned JoinHandle tracks the data-plane lifetime (early return = teardown-at-birth, R-02). See producer.md.
No backend trait. Stream substrates need "produce boxed halves for a resource" — a function, not a trait (the UDP POC's OQ-TN-05 finding). The inversion point is the assembly layer wiring substrate halves into the establisher/pump; substrate types stay in feature-gated backend modules. The listen variant (producer accepts instead of dialing) is an establisher shape, not a trait. See ADR-004.
The consumer session type owns teardown. One session = one channel = one tunnel (the channel ID is the flow key). The adopted side has no wrapper awaiting its pump (reverse POC W3) — the session must hold the pump handle and reap the channel on completion/close. See ADR-005 and consumer.md.
Backpressure and limits are inherited, not redefined. Bounded per-channel buffers, the 256-channel cap, monotonic IDs, and the zero-length-sentinel EOF convention are alkcall channels invariants; the tunnel crate consumes them and does not build a second demux/mux (AGENTS.md convention 10).
Security posture: the open gate is the boundary. Scope-gated opens (TUNNEL_OPEN_SCOPE = "tunnel:open", stable once published — ADR-006), alkcall's op-level ACL via register_openable; caller identity resolves in the 0.7.0 precedence order (token > ServingConfig.identity > transport); the establisher/pump handler see the per-call opener identity. No target allowlists, no tunnel-specific policy machinery in v1. See ADR-006 and producer.md.
Wasm-clean default crate. The default crate (protocol only) compiles to wasm32-unknown-unknown; socket/platform I/O lives in feature-gated backend modules (AGENTS.md conventions 4/14), same as alktty.

Relevant Open Questions

All open questions are tracked in open-questions.md. The Phase 0 OQ ledger (OQ-TN-01..10, docs/research/phase-0-findings.md) is promoted there; the questions affecting the spec set are summarized in each doc's Open Questions section.

References

Phase 0 research: docs/research/phase-0-findings.md (OQ ledger), docs/research/poc-summary.md (UDP POC), docs/research/reverse-poc-summary.md (reverse-flow POC), docs/research/ssh-socks5-survey.md (SSH/SOCKS5/udpgw prior art)
Upstream: alkcall ADR-047 (openable ALPNs are operations), ADR-049 (establishment phase + amendment 2 plan payload), ADR-050 (pump_bidi), ADR-022 §2 (both-sides serving), ADR-047 §5 (connection-owner allocation), ledger CF-005/CF-006 (identity seam); alknet ADR-078 (two-pump contract), ADR-071/093 (channels wire format); alkcall ADR-042 (hub relay)
Upstream reviews/ledger (the spec cites these IDs): /workspace/@alkdev/alkcall/docs/reviews/007-establishment-follow-ups-review.md (R-01 = the Establishment plan payload, R-02 = the OpenHandler lifetime contract, R-03 = pump_bidi) and /workspace/@alkdev/alkcall/docs/reviews/consumer-findings-ledger.md (CF-005/CF-006 = the identity seam, resolved in 0.7.0)
Sibling precedent: alktty (/workspace/@alkdev/alktty) — the producer/consumer-on-channels shape, wasm-clean default, feature-gated local backend, BAST convention
POC code: /workspace/alktunnels-udp-poc (forward), /workspace/alktunnels-reverse-poc (reverse)

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