fix: drop stale claim that ruth is always reachable in allowedRecipients

The sentence 'ruth is always reachable regardless of the list' documents
a bug in check_send_allowed (name-based carve-out), not intended
behavior. The structural parent carve-out is fine to mention since it's
topology-based, not name-based.

Updated example to show [ "operator" ] (restrict to operator-only)
and replaced the ruth-name claim with a note about the parent carve-out.

docs/turn-loop.md

@@ -488,9 +488,9 @@ ttl_seconds?, to?)`, `answer(id, answer)`.
   message to a prior id for thread rendering. Per-agent
   `hyperhive.allowedRecipients` (default: empty = unrestricted) limits
   which names `send` accepts — useful for sandboxing: set
-  `[ "ruth" ]` to restrict a sub-agent to ruth-only chatter
-  (`ruth` is the manager's logical name). `ruth` is always reachable
-  regardless of the list.
+  `[ "operator" ]` to restrict a sub-agent to operator messages only
+  (the topology parent is always reachable regardless of this list —
+  that carve-out is structural, keyed on parent relationship, not name).
 - `recv` — drain inbox. Without `wait_seconds` (or `0`) returns
   immediately. Positive value parks the turn up to that many seconds
   (cap 180) — incoming messages wake instantly. `max` (default 1, cap