diff --git a/packages/cli/src/ui/AppContainer.test.tsx b/packages/cli/src/ui/AppContainer.test.tsx
index 53da7cc32..031a9b61e 100644
--- a/packages/cli/src/ui/AppContainer.test.tsx
+++ b/packages/cli/src/ui/AppContainer.test.tsx
@@ -14,7 +14,7 @@ import {
   type Mock,
 } from 'vitest';
 import { render, cleanup } from 'ink-testing-library';
-import { AppContainer } from './AppContainer.js';
+import { AppContainer, dedupeNewestFirst } from './AppContainer.js';
 import {
   type Config,
   makeFakeConfig,
@@ -1405,3 +1405,28 @@ describe('AppContainer State Management', () => {
     });
   });
 });
+
+describe('dedupeNewestFirst', () => {
+  it('returns empty array for empty input', () => {
+    expect(dedupeNewestFirst([])).toEqual([]);
+  });
+
+  it('preserves order when there are no duplicates', () => {
+    expect(dedupeNewestFirst(['a', 'b', 'c'])).toEqual(['a', 'b', 'c']);
+  });
+
+  it('removes consecutive duplicates', () => {
+    expect(dedupeNewestFirst(['a', 'a', 'b'])).toEqual(['a', 'b']);
+  });
+
+  it('removes non-consecutive duplicates keeping the first (newest) occurrence', () => {
+    expect(
+      dedupeNewestFirst([
+        'first prompt',
+        'third prompt',
+        'second prompt',
+        'first prompt',
+      ]),
+    ).toEqual(['first prompt', 'third prompt', 'second prompt']);
+  });
+});
diff --git a/packages/cli/src/ui/AppContainer.tsx b/packages/cli/src/ui/AppContainer.tsx
index 89bb17bef..a0786b5ff 100644
--- a/packages/cli/src/ui/AppContainer.tsx
+++ b/packages/cli/src/ui/AppContainer.tsx
@@ -154,6 +154,20 @@ function isToolExecuting(pendingHistoryItems: HistoryItemWithoutId[]) {
   });
 }
 
+// Exported for tests. Given a newest-first list of messages, return a list
+// with duplicates removed, keeping the first (newest) occurrence of each.
+export function dedupeNewestFirst(messages: readonly string[]): string[] {
+  const seen = new Set<string>();
+  const result: string[] = [];
+  for (const msg of messages) {
+    if (!seen.has(msg)) {
+      seen.add(msg);
+      result.push(msg);
+    }
+  }
+  return result;
+}
+
 interface AppContainerProps {
   config: Config;
   settings: LoadedSettings;
@@ -451,20 +465,15 @@ export const AppContainer = (props: AppContainerProps) => {
         )
         .map((item) => item.text)
         .reverse();
+      // Current-session messages are already newest-first; combining with past
+      // messages gives a newest-first list. dedupeNewestFirst keeps the first
+      // (newest) occurrence so resubmitting an old prompt promotes it to
+      // "most recent" rather than leaving a stale copy at an older position.
       const combinedMessages = [
         ...currentSessionUserMessages,
         ...pastMessagesRaw,
       ];
-      const deduplicatedMessages: string[] = [];
-      if (combinedMessages.length > 0) {
-        deduplicatedMessages.push(combinedMessages[0]);
-        for (let i = 1; i < combinedMessages.length; i++) {
-          if (combinedMessages[i] !== combinedMessages[i - 1]) {
-            deduplicatedMessages.push(combinedMessages[i]);
-          }
-        }
-      }
-      setUserMessages(deduplicatedMessages.reverse());
+      setUserMessages(dedupeNewestFirst(combinedMessages).reverse());
     };
     fetchUserMessages();
   }, [historyManager.history, logger]);
diff --git a/packages/cli/src/ui/components/InputPrompt.test.tsx b/packages/cli/src/ui/components/InputPrompt.test.tsx
index 1691c0099..f8dded5a3 100644
--- a/packages/cli/src/ui/components/InputPrompt.test.tsx
+++ b/packages/cli/src/ui/components/InputPrompt.test.tsx
@@ -169,6 +169,7 @@ describe('InputPrompt', () => {
       navigateUp: vi.fn(),
       navigateDown: vi.fn(),
       handleSubmit: vi.fn(),
+      resetHistoryNav: vi.fn(),
     };
     mockedUseInputHistory.mockReturnValue(mockInputHistory);
 
@@ -741,6 +742,25 @@ describe('InputPrompt', () => {
     unmount();
   });
 
+  it('should reset history navigation after submitting on Enter', async () => {
+    mockedUseCommandCompletion.mockReturnValue({
+      ...mockCommandCompletion,
+      showSuggestions: false,
+      isPerfectMatch: false,
+    });
+    props.buffer.setText('a prompt from history');
+
+    const { stdin, unmount } = renderWithProviders(<InputPrompt {...props} />);
+    await wait();
+
+    stdin.write('\r');
+    await wait();
+
+    expect(props.onSubmit).toHaveBeenCalledWith('a prompt from history');
+    expect(mockInputHistory.resetHistoryNav).toHaveBeenCalled();
+    unmount();
+  });
+
   it('should submit directly on Enter when a complete leaf command is typed', async () => {
     mockedUseCommandCompletion.mockReturnValue({
       ...mockCommandCompletion,
diff --git a/packages/cli/src/ui/components/InputPrompt.tsx b/packages/cli/src/ui/components/InputPrompt.tsx
index 018c7d4b5..bbdf36f5c 100644
--- a/packages/cli/src/ui/components/InputPrompt.tsx
+++ b/packages/cli/src/ui/components/InputPrompt.tsx
@@ -280,6 +280,11 @@ export const InputPrompt: React.FC<InputPromptProps> = ({
     [],
   );
 
+  // Ref to inputHistory.resetHistoryNav, populated after useInputHistory runs.
+  // Needed because handleSubmitAndClear is passed into useInputHistory as
+  // onSubmit, so we can't reference inputHistory directly here without a cycle.
+  const resetHistoryNavRef = useRef<() => void>(() => {});
+
   const handleSubmitAndClear = useCallback(
     (submittedValue: string) => {
       // Expand any large paste placeholders to their full content before submitting
@@ -317,6 +322,10 @@ export const InputPrompt: React.FC<InputPromptProps> = ({
       buffer.setText('');
       onSubmit(finalValue);
 
+      // Reset history navigation so the next Up-arrow starts from the newest
+      // entry rather than advancing from whatever index the user picked.
+      resetHistoryNavRef.current();
+
       // Dismiss follow-up suggestion after submit
       followup.dismiss();
 
@@ -360,6 +369,8 @@ export const InputPrompt: React.FC<InputPromptProps> = ({
     onChange: customSetTextAndResetCompletionSignal,
   });
 
+  resetHistoryNavRef.current = inputHistory.resetHistoryNav;
+
   // When an arena session starts (agents appear), reset history position so
   // that pressing down-arrow immediately focuses the agent tab bar instead
   // of cycling through input history.