kad: Fix local provider eviction and removal panics

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+
+- kad: Prevent local provider eviction, expiration, and removal panics; `max_provider_keys` now applies separately to remote provider keys and local registrations (up to 2× in total), and rejected registrations are reported ([#665](https://github.com/paritytech/litep2p/issues/665))
+
 ## [0.15.2] - 2026-09-04
 
 This is a security release.

src/protocol/libp2p/kademlia/config.rs

@@ -312,6 +312,9 @@ impl ConfigBuilder {
 
     /// Set maximum number of provider keys in the memory store.
     ///
+    /// The limit applies separately to the provider keys of remote peers and to the keys this
+    /// node provides itself, so up to twice this many keys can be held in total.
+    ///
     /// If unspecified, the default maximum number of provider keys is 1024.
     pub fn with_max_provider_keys(mut self, max_provider_keys: usize) -> Self {
         self.memory_store_config.max_provider_keys = max_provider_keys;

src/protocol/libp2p/kademlia/mod.rs

@@ -1287,17 +1287,22 @@ impl Kademlia {
                                 addresses,
                             };
 
-                            self.store.put_local_provider(key.clone(), quorum);
-
-                            self.engine.start_add_provider(
-                                query_id,
-                                key.clone(),
-                                provider,
-                                self.routing_table
-                                    .closest(&Key::new(key), self.replication_factor)
-                                    .into(),
-                                quorum,
-                            );
+                            if self.store.put_local_provider(key.clone(), quorum) {
+                                self.engine.start_add_provider(
+                                    query_id,
+                                    key.clone(),
+                                    provider,
+                                    self.routing_table
+                                        .closest(&Key::new(key), self.replication_factor)
+                                        .into(),
+                                    quorum,
+                                );
+                            } else {
+                                let _ = self
+                                    .event_tx
+                                    .send(KademliaEvent::QueryFailed { query_id })
+                                    .await;
+                            }
                         }
                         Some(KademliaCommand::StopProviding {
                             key,