chore: consume alkcall 0.5.0; OQ-TN-09 resolved by ADR-049

alkcall 0.5.0 landed the review 006 remediation (filed from this
crate's Phase 0 pass):
- E-01/N-1: channel-open establishment phase (ADR-049) —
  register_openable_with_establisher, bounded await, teardown-on-
  failure, typed channel:open_failed reply (reason in details);
  ChannelClient::open_channel returns ChannelOpenError
- E-02: OperationSpec.description disclosed via discovery
- E-03/E-04/N-2: teardown-race log, early-arrival bound docs,
  count accessor

alktunnels updates:
- Cargo.toml: alkcall 0.4.0 -> 0.5.0 (lockfile resolves 0.5.0)
- AGENTS.md convention 11: pin note updated; ADR-049 marked
  load-bearing (tunnel opens use register_openable_with_establisher)
- phase-0-findings OQ-TN-09: RESOLVED by ADR-049 — the in-band
  control-frame hunch is superseded (establishment is the open op's
  reply, not a stream frame); residual for Phase 1 narrowed to
  half-open semantics; v1 needs no mid-stream control frame
- phase-0-findings OQ-TN-08: per-op metadata residue resolved by
  E-02 (description field; OQ-40 enumerate half stays deferred)
- tun2proxy prior-art + alktty-pattern sections: frame-vocabulary
  notes updated to point at the ADR-049 supersession
- upstream posture paragraph updated: review 006 is the working
  proof of the ask-early rule

Verification: cargo test (0 tests, ok), clippy --all-targets
-D warnings, fmt --check, wasm32 check, doc --no-deps — all clean

AGENTS.md

@@ -161,10 +161,14 @@ just spawned implementation agents.
     `Identity`, `IdentityProvider`, `AccessControl`,
     `OwnershipProvider`, `HandlerError`, `StreamError` come from
     `alkcall::core`. Do not vendor copies into this crate. alkcall is
-    v0.4.x — breaking changes are expected at this major-zero stage;
+    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 = "0.4.0"` (lockfile
-    resolves 0.4.1) and bump deliberately.
+    rather than working around them. Pin `alkcall = "0.5.0"` and bump
+    deliberately. The 0.5.0 establishment phase (ADR-049) 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.
 
 12. **BAST document for the wire format** — when the tunnel wire format
     gains binary framing (if any beyond pass-through), it carries a