docs: align remaining alloc-failure references with ADR-010 §2A (prepublish review for v0.3.0)

- README.md ADR index: ADR-010 status notes the §2A amendment
- ADR-009: amendment note records the §2A supersession (in-band path
  shrinks to nothing from registered producers)
- ADR-010 Consequences: dial_failed replaces the stale in-band
  allocate_failed retry-policy bullet
- AllocFailed doc comment + tty-backend.md: describe both failure
  surfaces (direct-path frame / channels-path dial_failed)

docs/architecture/decisions/009-channels-open-op-is-the-negotiation.md

@@ -21,6 +21,13 @@ cannot carry the allocated handle across — see ADR-010 §2). The R4
 tests that asserted the in-band frames for those classes now assert
 the call-error shape.
 
+Amended 2026-09-07 (ADR-010 §2A, alkcall 0.6.0 — review 007 R-01):
+`Establishment` gained its plan payload, so `allocate` also moved
+into the establisher — the in-band error-frame path on this channel
+shrinks to nothing from a registered producer (the frames remain the
+defense-in-depth fallback for no-establisher registrations and the
+direct path). See ADR-010 §2A.
+
 ## Context
 
 Before this ADR, the channels path carried the negotiation twice. The