Be cleaner about message cache dedupe after trimming inactive convos

frontend/src/test/integration.test.ts

@@ -167,17 +167,15 @@ describe('Integration: Duplicate Message Handling', () => {
   });
 });
 
-describe('Integration: No phantom unreads from mesh echoes (hitlist #8 regression)', () => {
-  it('does not increment unread when a mesh echo arrives after many unique messages', () => {
+describe('Integration: Trimmed cache entries can reappear (hitlist #7 regression)', () => {
+  it('increments unread when an evicted inactive-conversation message arrives again', () => {
     const state = createMockState();
     const convKey = 'channel_busy';
 
-    // Deliver 1001 unique messages — exceeding the old global
-    // seenMessageContentRef prune threshold (1000→500). Under the old
-    // dual-set design the global set would drop msg-0's key during pruning,
-    // so a later mesh echo of msg-0 would pass the global check and
-    // phantom-increment unread. With the fix, messageCache's per-conversation
-    // Cached messages remain the source of truth for inactive-conversation dedup.
+    // Deliver enough unique messages to evict msg-0 from the inactive
+    // conversation cache. Once it falls out of that window, a later arrival
+    // with the same content should be allowed back in instead of being
+    // suppressed forever by a stale content key.
     const MESSAGE_COUNT = 1001;
     for (let i = 0; i < MESSAGE_COUNT; i++) {
       const msg: Message = {
@@ -219,9 +217,8 @@ describe('Integration: No phantom unreads from mesh echoes (hitlist #8 regressio
     };
     const result = handleMessageEvent(state, echo, 'other_active_conv');
 
-    // Must NOT increment unread — the echo is a duplicate
-    expect(result.unreadIncremented).toBe(false);
-    expect(state.unreadCounts[stateKey]).toBe(MESSAGE_COUNT);
+    expect(result.unreadIncremented).toBe(true);
+    expect(state.unreadCounts[stateKey]).toBe(MESSAGE_COUNT + 1);
   });
 });
 

frontend/src/test/messageCache.test.ts

@@ -214,6 +214,76 @@ describe('messageCache', () => {
       expect(entry!.messages.some((m) => m.id === 0)).toBe(false);
     });
 
+    it('allows a trimmed-out message to be re-added after set() trimming', () => {
+      const messages = Array.from({ length: MAX_MESSAGES_PER_ENTRY + 1 }, (_, i) =>
+        createMessage({
+          id: i,
+          text: `message-${i}`,
+          received_at: 1700000000 + i,
+          sender_timestamp: 1700000000 + i,
+        })
+      );
+
+      messageCache.set('conv1', createEntry(messages));
+
+      const trimmedOut = createMessage({
+        id: 10_000,
+        text: 'message-0',
+        received_at: 1800000000,
+        sender_timestamp: 1700000000,
+      });
+
+      expect(messageCache.addMessage('conv1', trimmedOut)).toBe(true);
+      const entry = messageCache.get('conv1');
+      expect(entry!.messages.some((m) => m.id === 10_000)).toBe(true);
+    });
+
+    it('allows a trimmed-out message to be re-added after addMessage() trimming', () => {
+      const messages = Array.from({ length: MAX_MESSAGES_PER_ENTRY - 1 }, (_, i) =>
+        createMessage({
+          id: i,
+          text: `message-${i}`,
+          received_at: 1700000000 + i,
+          sender_timestamp: 1700000000 + i,
+        })
+      );
+      messageCache.set('conv1', createEntry(messages));
+
+      expect(
+        messageCache.addMessage(
+          'conv1',
+          createMessage({
+            id: MAX_MESSAGES_PER_ENTRY,
+            text: 'newest-a',
+            received_at: 1800000000,
+            sender_timestamp: 1800000000,
+          })
+        )
+      ).toBe(true);
+      expect(
+        messageCache.addMessage(
+          'conv1',
+          createMessage({
+            id: MAX_MESSAGES_PER_ENTRY + 1,
+            text: 'newest-b',
+            received_at: 1800000001,
+            sender_timestamp: 1800000001,
+          })
+        )
+      ).toBe(true);
+
+      const readdedTrimmedMessage = createMessage({
+        id: 10_001,
+        text: 'message-0',
+        received_at: 1900000000,
+        sender_timestamp: 1700000000,
+      });
+
+      expect(messageCache.addMessage('conv1', readdedTrimmedMessage)).toBe(true);
+      const entry = messageCache.get('conv1');
+      expect(entry!.messages.some((m) => m.id === 10_001)).toBe(true);
+    });
+
     it('auto-creates a minimal entry for never-visited conversations and returns true', () => {
       const msg = createMessage({ id: 10, text: 'First contact' });
       const result = messageCache.addMessage('new_conv', msg);