fix(peer): bound aggregate remote library state

Per-peer library limits still allowed 64 authenticated identities to retain a
large aggregate map and repeatedly clone it for UI publication.

Cap retained remote availability at 16,384 rows. A peer whose new projection
would exceed the budget stays authenticated with an empty library slice, and
its accepted revision is retained so liveness does not repeatedly pull the same
over-budget snapshot.

Test Plan:
- `just test` -- passed outside the sandbox; 496 peer tests and all workspace
  targets passed.
- `just fmt` -- Rust formatting completed; the recipe then hit the pre-existing
  generated security-report Markdown-lint failures.
- `git diff --cached --check` -- passed.

crates/lanspread-peer/src/peer_db.rs

@@ -20,6 +20,7 @@ use lanspread_proto::{
 use tokio::time::Instant;
 
 pub const MAX_AUTHENTICATED_PEERS: usize = 64;
+const MAX_TOTAL_REMOTE_LIBRARY_GAMES: usize = 16_384;
 
 /// Monotonic identity for one successfully authenticated endpoint observation.
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
@@ -380,9 +381,23 @@ impl PeerGameDB {
                     })
             });
 
-        let incoming_library = library
-            .as_ref()
-            .map(|snapshot| (snapshot.revision, library_map(snapshot)));
+        let incoming_library = library.as_ref().map(|snapshot| {
+            let games = library_map(snapshot);
+            let current_count = self
+                .peers
+                .values()
+                .map(|peer| peer.games.len())
+                .sum::<usize>();
+            let replaced_count = self
+                .peers
+                .get(&endpoint.peer_id)
+                .map_or(0, |peer| peer.games.len());
+            let projected_count = current_count
+                .saturating_sub(replaced_count)
+                .saturating_add(games.len());
+            let admitted = (projected_count <= MAX_TOTAL_REMOTE_LIBRARY_GAMES).then_some(games);
+            (snapshot.revision, admitted)
+        });
         if let Some(peer) = self.peers.get_mut(&peer_id) {
             let previous_endpoint =
                 (peer.addr != addr).then(|| PeerEndpoint::new(peer.peer_id, peer.addr));
@@ -401,6 +416,7 @@ impl PeerGameDB {
                             .library_revision
                             .is_none_or(|current| revision > current) =>
                 {
+                    let games = games.unwrap_or_default();
                     let changed = peer.library_revision != Some(revision) || peer.games != games;
                     peer.library_revision = Some(revision);
                     peer.games = games;
@@ -446,7 +462,9 @@ impl PeerGameDB {
                 runtime_session_id,
                 library_revision: incoming_library.as_ref().map(|(revision, _)| *revision),
                 call_to_play_revision: None,
-                games: incoming_library.map_or_else(HashMap::new, |(_, games)| games),
+                games: incoming_library
+                    .and_then(|(_, games)| games)
+                    .unwrap_or_default(),
             },
         );
         self.addr_index.insert(addr, peer_id);
@@ -745,6 +763,18 @@ mod tests {
         }
     }
 
+    fn large_library(revision: u64, seed: u8) -> LibrarySnapshot {
+        LibrarySnapshot {
+            revision,
+            games: (0..lanspread_proto::MAX_LIBRARY_GAMES)
+                .map(|index| GameAvailability {
+                    game_id: format!("game-{seed}-{index:04}"),
+                    content_id: ContentId::from_bytes([seed; 32]),
+                })
+                .collect(),
+        }
+    }
+
     fn commit(
         db: &mut PeerGameDB,
         endpoint: PeerEndpoint,
@@ -785,6 +815,51 @@ mod tests {
         assert_eq!(db.peer_endpoint(&endpoint.peer_id), Some(endpoint));
     }
 
+    #[test]
+    fn aggregate_remote_library_budget_drops_only_the_oversized_projection() {
+        let mut db = PeerGameDB::new();
+        for seed in 1..=4 {
+            commit(
+                &mut db,
+                endpoint(seed, 12_000 + u16::from(seed)),
+                session(seed),
+                large_library(u64::from(seed), seed),
+                Some(0),
+            );
+        }
+        let fifth = endpoint(5, 12_005);
+        let ticket = db
+            .begin_candidate_negotiation(fifth)
+            .expect("fifth candidate should reserve");
+        let upsert = db
+            .commit_authenticated_snapshot(fifth, ticket, session(5), Some(large_library(5, 5)))
+            .expect("fifth snapshot should still authenticate")
+            .expect("fifth ticket should remain current");
+
+        assert!(upsert.library_changed);
+        assert_eq!(
+            db.peer_snapshots()
+                .iter()
+                .find(|peer| peer.peer_id == fifth.peer_id)
+                .expect("fifth peer should be retained")
+                .game_count,
+            0
+        );
+        assert_eq!(
+            db.revision_snapshot(&fifth.peer_id)
+                .expect("fifth peer should have a revision watermark")
+                .library_revision,
+            Some(5),
+        );
+        assert_eq!(
+            db.peer_snapshots()
+                .iter()
+                .map(|peer| peer.game_count)
+                .sum::<usize>(),
+            MAX_TOTAL_REMOTE_LIBRARY_GAMES
+        );
+    }
+
     #[test]
     fn clear_remote_peers_returns_peer_id_sorted_retirements() {
         let mut db = PeerGameDB::new();