review 002: the protocol core reviewed — readiness-contract hardening + two convention fixes

The batch-1 gate review (tasks/implementation/review-protocol-core.md):
all eight criteria examined (seam contracts, wire fidelity, access
control, teardown/lifecycle, conventions, wasm, POC fidelity, docs
sync); the gate to batch 2 opens. Findings R-1/R-2 were corrected in
the review change; R-3..R-5 are doc residues fixed in the same change;
R-6 is accepted with rationale.

- R-1 (major): the datagram stage's Ok(None) re-park is unsafe against
  a zero-yield egress — a next_reply that is a pure instantly-ready
  Ok(None) with no await wins every select! poll and livelocks the
  stage on a current-thread runtime (empirically reproduced; the
  landed unit test's mutex masked the hazard at its lock's yield
  boundary; multi-thread survives). Fix: the Ok(None) handler yields
  before re-parking; a pinning unit test drives the strictest
  zero-yield violator.
- R-2: the two into_inner expect()s (consumer sessions) become typed
  Result<_, SpentSessionError> — convention 2's no-panic rule; spent-
  session unit tests pin the shape; test call sites updated.
- R-3/R-4/R-5: doc residues — stale task-time phrasings in
  egress.rs/producer.rs, producer.md's register() sketch reconciled
  to the landed signature, the establishment-bound test doc reworded
  to what the substrate-free probe actually pins.
- R-6 (accepted): the wasm gate rides a transitive getrandom/wasm_js
  feature unification (alkcall -> jsonschema/referencing -> ahash) —
  verified compiling clean today; noted for OQ-SK2-06.

Verified: cargo test 348 green; --all-features green; clippy
--all-targets -D warnings clean; fmt --check clean; both wasm checks
clean (from a clean wasm target dir); cargo doc --no-deps clean.
The bind-only-identity reconciliation from the integration session
was independently verified as correct (ADR-006 as landed; the suite
pins it). Batch boundary holds: no local/composed code exists.

docs/architecture/producer.md

@@ -140,7 +140,9 @@ let producer = Socks5Producer::builder()
     .egress(egress_factory)        // EgressFactory — required for ASSOCIATE
     .accept(bind_accept_factory)   // BindAcceptFactory — required for BIND
     .build();
-producer.register(&mut channel_core)?;   // register_openable_with_establisher
+// register(&core, &registry, auth, witness) — the establisher rides
+// the registration (the optional witness is the CF-006 test probe).
+producer.register(&core, &registry, auth, None)?;
 ```
 
 Missing callbacks = those commands refuse RFC-faithfully