Bound stale dedup order storage

bitchat/Services/MessageDeduplicationService.swift

@@ -43,6 +43,10 @@ final class LRUDeduplicationCache<Value> {
         map.count
     }
 
+    var orderStorageCountForTesting: Int {
+        order.count
+    }
+
     /// Checks if a key exists in the cache
     func contains(_ key: String) -> Bool {
         map[key] != nil
@@ -65,11 +69,13 @@ final class LRUDeduplicationCache<Value> {
         }
 
         trimIfNeeded()
+        compactIfNeeded()
     }
 
     /// Removes a specific key from the cache
     func remove(_ key: String) {
-        map.removeValue(forKey: key)
+        guard map.removeValue(forKey: key) != nil else { return }
+        compactIfNeeded()
     }
 
     /// Clears all entries from the cache
@@ -93,13 +99,6 @@ final class LRUDeduplicationCache<Value> {
             let candidate = order[head]
             head += 1
 
-            // Periodically compact the consumed prefix, matching the previous
-            // cache behavior without scanning unconsumed order nodes.
-            if head >= 32 && head * 2 >= order.count {
-                order.removeFirst(head)
-                head = 0
-            }
-
             guard let liveEntry = map[candidate.key],
                   liveEntry.generation == candidate.generation else {
                 continue
@@ -110,6 +109,24 @@ final class LRUDeduplicationCache<Value> {
         }
         return false
     }
+
+    private func compactIfNeeded() {
+        let unconsumedCount = order.count - head
+        let staleNodeCount = unconsumedCount - map.count
+        let shouldDropConsumedPrefix = head >= 32 && head * 2 >= order.count
+        let shouldRemoveStaleNodes = staleNodeCount >= 32 && staleNodeCount * 2 >= unconsumedCount
+
+        guard shouldDropConsumedPrefix || shouldRemoveStaleNodes else { return }
+
+        if shouldRemoveStaleNodes {
+            order = order[head...].filter { candidate in
+                map[candidate.key]?.generation == candidate.generation
+            }
+        } else {
+            order.removeFirst(head)
+        }
+        head = 0
+    }
 }
 
 // MARK: - Content Normalizer

bitchatTests/MessageDeduplicationServiceTests.swift

@@ -166,6 +166,29 @@ struct LRUDeduplicationCacheTests {
         #expect(cache.contains("c"))
     }
 
+    @Test func repeatedRemovalAndReinsertionCompactsStaleNodes() {
+        let cache = LRUDeduplicationCache<Int>(capacity: 3)
+        cache.record("a", value: 0)
+
+        for value in 1...1_001 {
+            cache.remove("a")
+            cache.record("a", value: value)
+        }
+
+        #expect(cache.count == 1)
+        #expect(cache.value(for: "a") == 1_001)
+        #expect(cache.orderStorageCountForTesting <= 32)
+
+        cache.record("b", value: 1)
+        cache.record("c", value: 2)
+        cache.record("d", value: 3)
+
+        #expect(!cache.contains("a"))
+        #expect(cache.contains("b"))
+        #expect(cache.contains("c"))
+        #expect(cache.contains("d"))
+    }
+
     // MARK: - Edge Cases
 
     @Test func emptyKey_works() {