diff --git a/desktop/src/stores/chatStore.test.ts b/desktop/src/stores/chatStore.test.ts
index 75058a32..2474343a 100644
--- a/desktop/src/stores/chatStore.test.ts
+++ b/desktop/src/stores/chatStore.test.ts
@@ -695,6 +695,117 @@ describe('chatStore history mapping', () => {
     })
   })
 
+  it('does not duplicate a hydrated assistant reply when live output replays after reconnect', () => {
+    useChatStore.setState({
+      sessions: {
+        [TEST_SESSION_ID]: makeSession({
+          messages: [
+            {
+              id: 'live-user',
+              type: 'user_text',
+              content: 'live prompt',
+              transcriptMessageId: 'transcript-user-1',
+              timestamp: 1,
+            },
+            {
+              id: 'live-assistant',
+              type: 'assistant_text',
+              content: 'live answer',
+              transcriptMessageId: 'transcript-assistant-1',
+              timestamp: 2,
+            },
+          ],
+          streamingText: 'live answer',
+          chatState: 'streaming',
+        }),
+      },
+    })
+
+    useChatStore.getState().handleServerMessage(TEST_SESSION_ID, {
+      type: 'message_complete',
+      usage: { input_tokens: 1, output_tokens: 2 },
+    })
+
+    expect(useChatStore.getState().sessions[TEST_SESSION_ID]?.messages).toMatchObject([
+      {
+        id: 'live-user',
+        type: 'user_text',
+        transcriptMessageId: 'transcript-user-1',
+      },
+      {
+        id: 'live-assistant',
+        type: 'assistant_text',
+        content: 'live answer',
+        transcriptMessageId: 'transcript-assistant-1',
+      },
+    ])
+    expect(notifyDesktopMock).not.toHaveBeenCalled()
+  })
+
+  it('collapses duplicate assistant replies after transcript id hydration', async () => {
+    vi.mocked(sessionsApi.getMessages).mockResolvedValueOnce({
+      messages: [
+        {
+          id: 'transcript-user-1',
+          type: 'user',
+          timestamp: '2026-04-06T00:00:00.000Z',
+          content: 'live prompt',
+        },
+        {
+          id: 'transcript-assistant-1',
+          type: 'assistant',
+          timestamp: '2026-04-06T00:00:01.000Z',
+          content: 'live answer',
+        },
+      ],
+    })
+
+    useChatStore.setState({
+      sessions: {
+        [TEST_SESSION_ID]: makeSession({
+          messages: [
+            {
+              id: 'live-user',
+              type: 'user_text',
+              content: 'live prompt',
+              transcriptMessageId: 'transcript-user-1',
+              timestamp: 1,
+            },
+            {
+              id: 'live-assistant',
+              type: 'assistant_text',
+              content: 'live answer',
+              transcriptMessageId: 'transcript-assistant-1',
+              timestamp: 2,
+            },
+            {
+              id: 'replayed-assistant',
+              type: 'assistant_text',
+              content: 'live answer',
+              timestamp: 3,
+            },
+          ],
+        }),
+      },
+    })
+
+    await useChatStore.getState().loadHistory(TEST_SESSION_ID)
+
+    expect(useChatStore.getState().sessions[TEST_SESSION_ID]?.messages).toMatchObject([
+      {
+        id: 'live-user',
+        type: 'user_text',
+        transcriptMessageId: 'transcript-user-1',
+      },
+      {
+        id: 'live-assistant',
+        type: 'assistant_text',
+        content: 'live answer',
+        transcriptMessageId: 'transcript-assistant-1',
+      },
+    ])
+  })
+
   it('retries transcript id hydration after the assistant message is persisted', async () => {
     vi.useFakeTimers()
     vi.mocked(sessionsApi.getMessages)
diff --git a/desktop/src/stores/chatStore.ts b/desktop/src/stores/chatStore.ts
index 4ac7bcb7..7a384c82 100644
--- a/desktop/src/stores/chatStore.ts
+++ b/desktop/src/stores/chatStore.ts
@@ -352,9 +352,21 @@ function appendAssistantTextMessage(
   model?: string,
   transcriptMessageId?: string,
 ): UIMessage[] {
-  if (!content.trim()) return messages
+  const trimmedContent = content.trim()
+  if (!trimmedContent) return messages
 
   const last = messages[messages.length - 1]
+  // Wake/reconnect replay can resend persisted assistant text without a
+  // transcript id. Ignore chunks that are already present in the hydrated tail.
+  if (
+    last?.type === 'assistant_text' &&
+    last.transcriptMessageId &&
+    !transcriptMessageId &&
+    last.content.trim().includes(trimmedContent)
+  ) {
+    return messages
+  }
+
   const canMergeIntoLast =
     last?.type === 'assistant_text' &&
     (
@@ -581,12 +593,38 @@ function mergeRestoredTranscriptMessageIds(
   return changed ? merged : messages
 }
 
+function dropDuplicateTranscriptTextMessages(messages: UIMessage[]): UIMessage[] {
+  const seen = new Set<string>()
+  const deduped: UIMessage[] = []
+  let changed = false
+
+  for (const message of messages) {
+    if (
+      (message.type === 'user_text' || message.type === 'assistant_text') &&
+      message.transcriptMessageId
+    ) {
+      const key = `${message.type}:${message.transcriptMessageId}:${message.content.trim()}`
+      if (seen.has(key)) {
+        changed = true
+        continue
+      }
+      seen.add(key)
+    }
+
+    deduped.push(message)
+  }
+
+  return changed ? deduped : messages
+}
+
 function mergeRestoredHistoryIntoLiveMessages(
   messages: UIMessage[],
   restoredMessages: UIMessage[],
 ): UIMessage[] {
   return mergeRestoredTerminalGoalEvents(
-    mergeRestoredTranscriptMessageIds(messages, restoredMessages),
+    dropDuplicateTranscriptTextMessages(
+      mergeRestoredTranscriptMessageIds(messages, restoredMessages),
+    ),
     restoredMessages,
   )
 }
@@ -1493,7 +1531,8 @@ export const useChatStore = create<ChatStore>((set, get) => ({
           apiRetry: null,
         }))
         useTabStore.getState().updateTabStatus(sessionId, 'idle')
-        const notification = wasAgentRunning
+        const appendedCompletionMessage = completionMessages !== session.messages
+        const notification = wasAgentRunning && appendedCompletionMessage
           ? buildAgentCompletionNotification(sessionId, completionMessages, text)
           : null
         if (notification) {