feat(review 006 Unit 1): channel-open establishment phase + typed client error (E-01, N-1)

Implements ADR-049 Unit 1 — the open-op wrapper gains an awaited,
bounded establishment phase, and the client stops erasing the error.

- OpenEstablisher hook + Establishment/EstablishmentError types:
  register_openable_with_establisher awaits the establisher bounded
  (earlier of dispatch deadline and per-registration timeout, else
  ESTABLISHMENT_TIMEOUT = 10s) after allocation, before the reply and
  before the pump handler is spawned (ADR-049 §1/§2). Implementation
  note: the establisher takes (input, auth) only — the channel's
  yield-once BiStream belongs exclusively to the pump handler
  (amendment recorded in ADR-049).
- Establishment failure: teardown_channel + opener-ledger take +
  policy.on_close un-increment (allocation and teardown balance;
  the ledger take is the atomic gate, ADR-047 §7), reply
  channel:open_failed with details {reason, message} — reason ∈
  dial_failed / unknown_resource / resource_shortage / handler_error
  / timeout (ADR-049 §3). SSH contract consumer-visible: a failed
  open never returns a channel_id.
- register_openable unchanged (no establisher = always-OK; existing
  registrations compile and behave identically — compat gate test).
- ChannelClient::open_channel returns ChannelOpenError (breaking at
  0.5.0): CallFailed { error: CallError } carries the wire error
  verbatim (establishment_reason() branches on details.reason);
  MissingChannelId / AdoptFailed cover the local-only shapes
  (ADR-049 §4, review 006 N-1).
- Tests cover all four verification gates from the review: e2e
  establisher failure through a real channels connection (typed
  reason + no-channel + ledger un-increment), bounded timeout,
  no-establisher compat, establisher-success pump round-trip; plus
  reason-vocabulary mapping and bound arithmetic.
- Bump to 0.5.0 (open_channel error-type change is semver-relevant).

Verification: cargo test (608 passed), clippy --all-targets -D
warnings, fmt --check, doc --no-deps, wasm32 check — all clean.

docs/reviews/006-channel-open-establishment-gap-review.md

@@ -19,8 +19,16 @@ consumer visibility), **N-2** (dead counter), **N-3** (panic posture,
 pinned). **E-01 + N-1 are resolved by ADR-049**
 (`docs/architecture/decisions/049-channel-open-establishment-phase.md`
 — split-hook `OpenEstablisher`, bounded await, `channel:open_failed`
-typed error). The original remediation sketch below is superseded by
-the "Remediation plan (post-verification)" section; the original sketch
+typed error). **Unit 1 (E-01 + N-1) is implemented** in alkcall 0.5.0
+(`OpenEstablisher` + `register_openable_with_establisher`, wrapper
+establishment phase with bounded await, `channel:open_failed` typed
+error, `ChannelOpenError` typed client error — all four verification
+gates landed as tests; two implementation-shape notes recorded in
+ADR-049's amendment: the establisher does not receive the channel
+`Connection` (yield-once BiStream belongs to the pump handler), and
+the bound is the earlier of dispatch deadline and per-registration
+timeout). The original remediation sketch below is superseded by the
+"Remediation plan (post-verification)" section; the original sketch
 is retained for the record.
 
 Findings continue the review numbering with prefix `E` (001–005 used
@@ -383,7 +391,13 @@ returns a typed error carrying the `CallError`. Concurrency is safe:
 the dispatcher spawns Once invocations as independent tasks
 (`dispatch.rs` `spawn_once_dispatch`), so an awaited establisher does
 not head-of-line-block channel 0. Version 0.5.0 (the `open_channel`
-error-type change is semver-relevant).
+error-type change is semver-relevant). **Status: IMPLEMENTED
+(2026-09-06)** — with two implementation-shape notes recorded in
+ADR-049's amendment: the establisher takes `(input, auth)` only (the
+yield-once channel `BiStream` belongs exclusively to the pump
+handler), and the effective bound is `min(dispatch deadline,
+registration timeout | ESTABLISHMENT_TIMEOUT)`. All four verification
+gates below are tests in the crate.
 
 **Unit 2 — E-02 (ride the 0.5.0 release).** Additive
 `description: Option<String>` on `OperationSpec` — note this is four