alktunnels/AGENTS.md

# AGENTS.md

Operating instructions for opencode agents working in this repo. opencode
auto-loads this file as instructions, overriding the built-in defaults for
this project. Custom agents in `.opencode/agents/` inherit these rules
unless their own prompts say otherwise.

## Git Workflow

**Commit and push when reasonable.** When a change is complete and
verified (build + lint + tests pass), commit and push to `origin/main`
without asking. This overrides the built-in default of "only commit when
explicitly asked."

The workflow:

1. Make the change
2. Verify: `cargo test`, `cargo clippy --all-targets -- -D warnings`,
   `cargo fmt --check`, `cargo doc --no-deps` if docs changed
3. Inspect `git status` and `git diff` before staging — stage only the
   intended files, never secrets
4. Write a concise commit message matching the repo style (see `git log
   --oneline -10`). For multi-point changes, use a summary line plus a
   body with bullet points and a verification block.
5. `git push origin main`
6. Report the commit hash and the verification summary

Exceptions — **do not** commit or push without asking:

- The change is exploratory / speculative (you're not sure the user wants
  it kept)
- The user is actively reviewing the diff and may ask for changes
- The change touches the wire format or a trait shape that backends or
  consumers implement (one-way doors — see "Wire formats are stable" and
  "Backend trait shapes are one-way doors" below; once consumers exist,
  those signatures are wire-stable contracts)
- You'd be force-pushing, amending a published commit, creating an empty
  commit, or skipping hooks

Never commit secrets, keys, or credentials. If a commit fails or hooks
reject it, fix the issue and create a new commit — do not amend the
failed one.

Git identity is preconfigured (`glm-5.3-flash <glm-5.3-flash@alk.dev>`). Do
not change `git config`, skip hooks, or use `git commit -i`.

## Project Conventions (Rust / tunnel protocol crate)

This is the tunnels protocol crate — arbitrary bidirectional tunnels in
the `ssh -L` / `ssh -D` sense (TCP, UDP, unix sockets, and other stream
or datagram substrates), riding alkcall channels the same way alktty
does. It is the sibling of alktty (`alk/tty` — terminal sessions) and
alkcall (call + channels — the substrate both build on). Where alktty
multiplexes one service with a fixed five-stream channel structure, this
crate generalizes the tunnel handler shape: the producer side dials or
accepts on some local substrate and pumps bytes to/from a channels data
channel; the consumer side bridges its own substrate onto that channel.
The conventions below apply to all work in `src/` and `tests/`. They
mirror `.opencode/agents/implementation-specialist.md` §Project
Conventions and are repeated here so they apply to every session, not
just spawned implementation agents.

1. **No comments in code** unless the user explicitly asks. This is a
   project-wide convention. Doc comments (`///`, `//!`) are fine and
   expected on public API. Inline `//` comments only when the user asks
   or when a non-obvious safety/correctness constraint would otherwise be
   missed (e.g., "a two-pump tunnel must shut down the opposite sink on
   pump completion — `try_join!` alone deadlocks; see alkcall ADR-050's
   `pump_bidi` / alknet ADR-078").

2. **Error handling** — `thiserror` for library error types
   (`TunnelError`; `HandlerError`/`StreamError` come from
   `alkcall::core`). No panics in library code. No `unwrap()` or
   `expect()` outside tests. If you reach for `unwrap`, the error path
   wasn't specified — stop and decide what should actually happen. For
   poisoned `RwLock`/`Mutex`, use `unwrap_or_else(|e| e.into_inner())`
   so a panic in one operation does not cascade to other operations.

3. **`tokio` is the async runtime** — all I/O is async. The tunnel
   pumps, the channels integration, and the consumer session type are
   all async. Use `tokio::sync` primitives (`oneshot`, `mpsc`) for
   lifecycle correlation and per-direction data flow. Any non-wasm
   backend module (local TCP/UDP sockets, process-spawned listeners)
   lives behind a feature flag like alktty's `local`.

4. **WASM target is load-bearing (by default)** — the default crate
   (protocol-only) should compile to `wasm32-unknown-unknown`, following
   alktty's precedent. This is what keeps the downstream TS/Python
   adapter story viable (a wasm-compiled alktunnels is the protocol
   layer for a sandboxed adapter). Use the wasm-clean tokio subset
   (`rt`, `sync`, `io-util`, `macros`, `time`) — **do NOT use `features
   = ["full"]`** — and keep socket/platform I/O feature-gated. If a
   design decision ever forces the default crate off wasm (e.g. the
   wire format embeds a substrate-specific type), that is an ADR-worthy
   decision, not an accident.

5. **Wire format is stable** — the tunnel wire format is a one-way door
   once consumers exist. Follow the alknet ADR-093/alktty ADR-008
   precedent: the tunnel payload rides inside channels data channels as
   raw bytes (channels strips its 8-byte header transparently; the
   tunnel protocol owns whatever framing it puts inside the
   `BiStream`). If a negotiation/setup frame is needed (like alktty's
   `NegotiateRequest`), make it self-contained per alktty ADR-006 —
   length-prefixed JSON, not alkcall's `EventEnvelope` framing. Any
   wire-format ADR must be written before the first consumer exists;
   after that, changes are additive-only.

6. **Producer/consumer, not server/client** — both sides of a channels
   connection can initiate. A producer exposes tunnels (registers
   openable channels via `ChannelCore::register_openable`); a consumer
   opens tunnel channels (`ChannelClient`). Both sides can be both
   simultaneously — connection direction (who opened it) is independent
   of tunnel direction (who dials the target, who serves it). Avoid
   "server" and "client" framing in docs and API names; use "producer"
   and "consumer," or "accept side" / "connect side" for the
   connection-establishment half specifically. See alkcall ADR-022,
   ADR-037.

7. **Substrate-agnostic by construction** — the protocol layer must not
   know whether the bytes come from TCP, UDP, a Unix socket, or a
   stdio pipe. The handler sees a `Connection`/`BiStream` from alkcall
   core and pumps bytes; the substrate-specific types (`TcpStream`,
   `UdpSocket`, etc.) are confined to backend modules behind feature
   flags, injected at the assembly layer — the same inversion-point
   pattern as alktty's `TtyBackend`. "Arbitrary tunnels" means the
   bookkeeping (target addressing, direction, lifecycle) must not
   hardcode a substrate. See alknet ADR-078 §Where the pattern lives
   and the channels-adapter spec.

8. **Two-pump shutdown-on-completion is a contract** — a tunnel is the
   canonical two-pump handler (one pump per direction). Each pump MUST
   shut down the opposite sink when it completes; `tokio::try_join!`
   alone deadlocks. This was POC-validated in the alknet-channels POC
   (Target 3), pinned as alknet ADR-078, and the helper is pinned
   upstream as alkcall `channels::pump_bidi` (ADR-050, review 007
   R-03) — use it; do not hand-roll the two-pump shape. The channels
   layer drops all per-channel senders on transport EOF — rely on
   that for teardown, and emit EOF sentinels (zero-length chunks) on
   clean sink shutdown. Await `pump_bidi` inline inside the
   `OpenHandler`'s task — the returned `JoinHandle` must track the
   data-plane lifetime (R-02; early return = teardown-at-birth).

9. **No forced local binding** — a tunnel must not require the producer
   (or consumer) to bind a local port. The POC's TCP-tunnel shape
   dialed a target from the handler; SSH `-R` style flows need the
   reverse (the remote side asks the local side to dial or listen).
   The API surface must support both directions and unbound/listen-
   optional flows; the binding decision belongs to the caller
   (assembly layer), not the protocol crate. This is a spec-level
   requirement for the architecture docs, not just an implementation
   preference.

10. **Backpressure and limits are inherited, not redefined** — bounded
    per-channel buffers, the 256-channel per-connection cap, monotonic
    channel IDs, and the zero-length-sentinel EOF convention are
    alkcall channels invariants (see alkcall ADR-040/041/034). The
    tunnel crate consumes them via `ChannelCore`/`ChannelClient`; do
    not build a second demux/mux or re-derive limits. Datagram
    substrates (UDP) map onto the chunk stream with the same
    backpressure; datagram-boundary preservation, if required, is a
    wire-format decision for an ADR, not an accident.

11. **Vendored core types come from alkcall** — `Connection`,
    `ProtocolHandler`, `BiStream`, `BidiStreamSource`, `AuthContext`,
    `Identity`, `IdentityProvider`, `AccessControl`,
    `OwnershipProvider`, `HandlerError`, `StreamError` come from
    `alkcall::core`. Do not vendor copies into this crate. alkcall is
    v0.5.x — breaking changes are expected at this major-zero stage;
    this is an early consumer, so we find and fix issues upstream
    rather than working around them. Pin `alkcall = "0.7.0"` and bump
    deliberately. The 0.6.0 establishment surface (ADR-049 + amendment
    2) is load-bearing for this crate: tunnel opens use
    `register_openable_with_establisher` so a refused target dial is
    a typed `channel:open_failed` call error, never a phantom channel,
    and the establisher returns the dialed handle via
    `Establishment::new(plan)` (typed-opaque `ChannelPlan` — its
    `Send + Sync` bound constrains plan payloads; socket handles carry
    `+ Sync`) — no side-channel handoff. The 0.7.0 identity surface
    (ledger CF-005/CF-006) is load-bearing for the serving side: a
    connect-side serving op resolves the caller identity in
    precedence order — payload `auth_token` >
    `ServingConfig.identity` > transport identity (set via
    `Connection::set_identity` before dialing) — and the establisher/
    pump handler receive the per-call opener identity, not the
    install-time context.

12. **BAST document for the wire format** — when the tunnel wire format
    gains binary framing (if any beyond pass-through), it carries a
    BAST (Binary Abstract Syntax Tree) document as its machine-readable
    spec under `docs/architecture/`, conforming to the BAST meta-schema
    at `https://alk.dev/bast/v1/schema`. BAST is plain JSON — no
    dependency required to author or consume it. alktunnels does not
    depend on alktype; hand-rolled codecs are fine for trivial formats,
    with the BAST doc as the contract. Do not roll your own offset map
    or validator for complex formats — use alktype (as an optional dep)
    when that surfaces.

13. **Access control** — the producer's openable channels get
    authorization for free via `ChannelCore::register_openable`, which
    wires `AccessControl` into the operation spec (the registry runs
    the ACL before the open handler). Scope-gate tunnel opens (e.g.
    `TUNNEL_OPEN_SCOPE`, shape following alktty's `TTY_OPEN_SCOPE`) and
    optionally consult `OwnershipProvider` for resource ownership
    (`provider.owns(id_ref, kind, &id, "tunnel")` — the 4-arg shape;
    `OwnershipStore::record` is the 3-arg shape). Tunnels reach local
    networks — treat the open gate as the security boundary. See
    alknet ADR-024 (registry layering, alkcall ADR-019), alknet
    ADR-050 (ownership, alkcall ADR-011).

14. **Feature flags** — substrate backends may be feature-gated if the
    need arises. The base crate should compile lean (no socket/platform
    deps unless the feature is on). Verify both `cargo test` (default)
    and `cargo test --all-features` pass if features are added.

15. **Naming** — Rust standard: `snake_case` for functions/variables/
    modules, `PascalCase` for types/traits, `SCREAMING_SNAKE_CASE` for
    constants.

16. **Module structure** — one module per file under `src/`, re-exported
    from `src/lib.rs`. Public API surface is `lib.rs` re-exports. The
    expected shape (to be finalized in the architecture docs): a
    producer half (adapter / open-handler for `alk/tunnel`-family
    ALPNs), a consumer half (a typed session/client that opens tunnel
    channels), and shared wire/target-addressing modules. Backend
    modules are feature-gated and never imported from the
    shared/producer/consumer modules.

17. **ALPN naming** — this crate owns the `alk/tunnel`-family ALPN(s).
    One ALPN per protocol per alkcall ADR-004; keep the `alk/` prefix
    convention. If multiple tunnel flavors need distinct ALPNs (e.g.
    stream vs datagram), decide via ADR before the first consumer —
    ALPN strings are wire-stable once published.

## Verification Commands

Run these before committing. All must pass.

```bash
cargo test                                    # full suite
cargo clippy --all-targets -- -D warnings
cargo fmt --check
cargo doc --no-deps                           # if docs changed
cargo test --all-features                     # if features are added
cargo check --target wasm32-unknown-unknown   # default crate stays wasm-clean
cargo clippy --target wasm32-unknown-unknown -- -D warnings
cargo publish --dry-run --allow-dirty         # before a release
```

The wasm check is the structural guard for the "default crate is
wasm-clean" invariant (same as alktty) — run it whenever a
non-backend module changes.

## Architecture Context

- `docs/architecture/` — will hold the authoritative spec (Phase 1 of
  the SDD process). It does not exist yet; Phase 0 research lives in
  `docs/research/`. Read it before non-trivial changes once it exists.
- The prior art for this crate:
  - **alknet-channels POC** —
    `/workspace/@alkdev/alknet/docs/research/alknet-channels/poc-summary.md`
    (§POC Target 3: tunnel handler). Validates the demux→Connection→
    handler→mux path and the two-pump tunnel shape over a stand-in
    transport. POC code at `/workspace/alknet-channels-poc/`.
  - **alkcall** — `/workspace/@alkdev/alkcall` (v0.4.x, crates.io).
    The substrate: call protocol + channels multiplexing. The tunnel
    crate consumes `alkcall::core` types and the channels
    `ChannelCore`/`ChannelClient`/`register_openable` surface.
  - **alktty** — `/workspace/@alkdev/alktty` (v0.1, crates.io). The
    sibling pattern to follow: a producer/consumer protocol crate on
    alkcall channels, with the backend inversion point, wasm-clean
    default crate, and feature-gated local backend.
- Key upstream ADRs that inform this crate's design (alknet numbers;
  alkcall's ports live in `/workspace/@alkdev/alkcall/docs/architecture/
  decisions/`):
  - alknet ADR-093 / alkcall ADR-035 — channels pure channel
    multiplexing (8-byte header, no `stream_type`); the tunnel payload
    is raw bytes inside the `BiStream`
  - alknet ADR-078 / alkcall ADR-050 — two-pump shutdown-on-completion
    (the tunnel handler pattern); the helper is pinned upstream as
    `alkcall::channels::pump_bidi` — use it, do not hand-roll
  - alkcall ADR-049 (amendment 2) — the establishment phase; the
    establisher returns the dialed handle via `Establishment::new`
    (typed-opaque `ChannelPlan`), replacing the POC's side-channel
    handoff
  - alknet ADR-074 / alkcall ADR-038 — `ChannelConnection` as a
    `BidiStreamSource`; every handler (TTY, tunnel, call) receives a
    `Connection`
  - alknet ADR-075 / alkcall ADR-039 — `ChannelsAdapter` /
    `ChannelManager` (substrate-agnostic demux; `params` is
    ALPN-specific — for tunnels, the target resource)
  - alknet ADR-071 / alkcall ADR-034 — channels wire format (one-way
    door)
  - alkcall ADR-037 — channel lifecycle operations (`channel/open` on
    channel 0; `params` carries the tunnel target)
  - alkcall ADR-042 — hub relay (byte-for-byte data-channel forwarding
    with ID rewrite — tunnels traverse relays transparently)
  - alkcall ledger CF-005/CF-006 (0.7.0) — the connect-side serving
    identity seam: caller identity precedence (token >
    `ServingConfig.identity` > transport), per-call opener identity
    on the open-op hooks (the reverse-flow POC's W1, resolved)
  - alknet ADR-085 — workspace scope: `alknet/tunnel` was flagged
    "POC-validated, minimal spec needed, not yet specced"; this crate
    is that spec
- What the POCs settled (Phase 0 complete — 2026-09-07): both POCs
  ran clean (forward UDP POC + reverse-flow POC; see
  `docs/research/poc-summary.md` and `reverse-poc-summary.md`). The
  remaining Phase 1 work is the spec: OQ promotion, params JSON ADR,
  ALPN ADR, codec ADR (UDP framing mandatory per F-2), and the
  producer/consumer API surface (the consumer session type owns
  teardown — reverse POC W3).
- If a TODO references a design direction that an ADR has since decided
  against, the TODO is stale — remove it and align with the ADR. Do not
  implement the rejected design.