Let the session own its bind state, written by bound() alone

docs/decisions.md

@@ -715,6 +715,15 @@ rule and an index of the titles below.
   assembled that way. What goes there is traffic already answered, which is why each group reaches
   `sessionError` like every other one given up on.
 
+- **The bind state is the session's, `bound()` alone writes it, and it holds through a reconnect's
+  gap.** Maintainer's call, 2026-09-28. `client()` and `server()` call `bound()` as a hand-wired
+  session does, so one method is the one spelling, and `loggedIn` went as a second spelling of
+  `boundAs !== undefined`. Clearing the state at `teardown()` was rejected: `bindAllows()` and
+  `acceptsOptionalParams()` then answer yes to everything while the link is down, so a
+  receiver-bound client queues a `submit_sm` the peer refuses and a receipt built then carries TLVs a
+  pre-3.4 peer must not get — goal 4. Valid while the reconnect loop binds again with the same bind
+  type to the same peer.
+
 - **A message id base is merged at most once.** A receipt carries nothing but `<base>-<n>`, so a
   straggler for a message whose group is gone cannot be told from a receipt for a later message the
   peer handed the same ids — an SMSC whose id counter restarts with its process is the realistic