e9da9c29d2
Make SubscriptionRegistry.TryResolveItemHandle confirm a live subscription genuinely binds fullRef->handle (via the reverse index) rather than trusting the forward-map hint + a bare liveness check. Fixes the cross-ref-same-handle hazard (wrong-tag borrow) while preserving the legitimate multiple-subscriptions-per-tag borrow. Adds cross-ref + same-ref-multi-sub tests; drops a duplicate SubscriptionEntry <summary>; documents the writer's supervisory-advise reconnect lifecycle.