feat: crate-init — module skeleton (params, wire, producer, consumer, error)

- src/{params,wire,producer,consumer,error}.rs skeletons with module
  docs per overview.md §Module Map; lib.rs crate docs + re-exports
- constants in params.rs (OP_TUNNEL_OPEN, TUNNEL_ALPN,
  TUNNEL_OPEN_SCOPE) + establishment_reason helper (delegates to
  alkcall 0.7.0's ChannelOpenError::establishment_reason)
- MAX_DATAGRAM_LEN (65535) in wire.rs (ADR-003's frame-time bound)
- async-trait dropped: skeleton confirms no trait (ADR-004)

Verified: cargo check, clippy --all-targets -D warnings (native +
wasm32), fmt --check, test, wasm32 check — all clean

tasks/tunnels/crate-init.md

@@ -1,7 +1,7 @@
 ---
 id: tunnels/crate-init
 name: Initialize the alktunnels module skeleton (params, wire, producer, consumer, error)
-status: pending
+status: completed
 depends_on: [architecture/oq-promotion-sync]
 scope: narrow
 risk: low
@@ -67,14 +67,14 @@ pub mod consumer;
 
 ## Acceptance Criteria
 
-- [ ] `src/lib.rs` declares `error`, `params`, `wire`, `producer`,
+- [x] `src/lib.rs` declares `error`, `params`, `wire`, `producer`,
       `consumer` with doc comments; public API re-exports listed (empty
       bodies fine)
-- [ ] Every skeleton module compiles (`cargo check` clean)
-- [ ] `cargo clippy --all-targets -- -D warnings` clean
-- [ ] `cargo fmt --check` clean
-- [ ] `cargo check --target wasm32-unknown-unknown` passes
-- [ ] No comments in code beyond doc comments (convention 1)
+- [x] Every skeleton module compiles (`cargo check` clean)
+- [x] `cargo clippy --all-targets -- -D warnings` clean
+- [x] `cargo fmt --check` clean
+- [x] `cargo check --target wasm32-unknown-unknown` passes
+- [x] No comments in code beyond doc comments (convention 1)
 
 ## References
 
@@ -84,8 +84,29 @@ pub mod consumer;
 
 ## Notes
 
-> Agent fills during implementation.
+- All five skeleton modules created per the task's shapes, with module
+  docs pointing at the spec docs + ADRs and `tunnels/*` tasks that fill
+  them in.
+- Constants placed early (`OP_TUNNEL_OPEN`, `TUNNEL_ALPN`,
+  `TUNNEL_OPEN_SCOPE` in params.rs — they are part of the wire surface,
+  not producer-only, so they live in the shared module per the module
+  map's "params.rs … + open-op input schema").
+- `establishment_reason` is a thin delegation to
+  `ChannelOpenError::establishment_reason` (alkcall 0.7.0 has the
+  method upstream); the crate-level helper keeps the POC's free-fn
+  shape for consumers and re-exports the typed error.
+- `MAX_DATAGRAM_LEN` (65535) placed in wire.rs — the one codec constant
+  ADR-003 pins regardless of the codec functions landing later.
+- **`async-trait` dropped** per the task's IF: the skeleton confirms no
+  trait is needed (ADR-004 — halves functions, not traits);
+  `cargo check` passes without it.
 
 ## Summary
 
-> Agent fills this on completion.
+Module skeleton landed (error/params/wire/producer/consumer + lib.rs
+docs + re-exports); Cargo.toml unchanged except `async-trait` dropped
+(ADR-004 confirmation). Verified: `cargo check`, `cargo clippy
+--all-targets -- -D warnings`, `cargo fmt --check`, `cargo test`,
+`cargo check --target wasm32-unknown-unknown`,
+`cargo clippy --target wasm32-unknown-unknown -- -D warnings` — all
+clean.