update

docs/concord-usage.md

@@ -312,13 +312,19 @@ as an inline row only when its author passes
 ## Membership
 
 ```rust
-let states = cord02::guestbook::coalesce(&rumors, now_ms, Some(&refounder_pk), |actor, target, citation| {
+let states = cord02::guestbook::coalesce(&rumors, now_ms, &refounders, |actor, target, citation| {
     citation_ok(&owner, &community_id, actor, citation, &control.roles.floors)
         && control.roles.can_act_on_member(actor, &owner, target, Permissions::KICK)
 });
 let members = cord02::guestbook::complete_memberlist(&states, &observed, &granted, &control.banned, &BTreeMap::new());
 ```
 
+- `refounders` is the set of npubs whose rotations minted an epoch this client
+  verified (`CommunityState.refounders`) — a snapshot chunk is honored only from
+  one of them, and an empty set honors none. A rotation that delivered this
+  client no key still names its minter, so the set is filled by any base rotation
+  whose continuity verifies against a root held (`rekey::walk`); a List entry's
+  `refounder`, read by `list::JoinMaterial::refounder`, is the other source.
 - `observed` is npub → ms for every author this client has seen publish anything
   usable, which is what makes a member visible before their Join arrives. Only
   count it forward.
@@ -553,6 +559,14 @@ fragment at every index below it. `merge` resolves a `frags` disagreement to the
 larger value. (`13302`, the single-event List, is retired by the spec — a
 replaceable kind cannot fragment.)
 
+A join material may also carry two hex extensions this crate does not write but
+does read, because they are the only place a device that never held a rotation can
+learn who minted an epoch: `refounder` names the npub whose Refounding minted the
+entry's `root_epoch`, and `held_roots` is the retained prior epochs
+(`[{epoch, key, refounder?, control_pk?, retired_at?}]`). `JoinMaterial::refounder()`
+and `JoinMaterial::held_roots()` decode both; unknown fields are round-tripped
+regardless, so a document that carries them keeps them.
+
 The payload's 32-byte values are **unpadded base64url at every depth**, which is
 section-scoped to §8: CORD-05 invites stay hex. The writer re-encodes them on
 every serialization, so its output is always the canonical 43-character spelling;