tui: skip identical consecutive entries in local composer history (#2352)

This PR avoids inserting duplicate consecutive messages into the Chat
Composer's local history.

Author: nornagon-openai

codex-rs/tui/src/bottom_pane/chat_composer_history.rs

@@ -55,11 +55,18 @@ impl ChatComposerHistory {
     /// Record a message submitted by the user in the current session so it can
     /// be recalled later.
     pub fn record_local_submission(&mut self, text: &str) {
-        if !text.is_empty() {
-            self.local_history.push(text.to_string());
-            self.history_cursor = None;
-            self.last_history_text = None;
+        if text.is_empty() {
+            return;
+        }
+
+        // Avoid inserting a duplicate if identical to the previous entry.
+        if self.local_history.last().is_some_and(|prev| prev == text) {
+            return;
         }
+
+        self.local_history.push(text.to_string());
+        self.history_cursor = None;
+        self.last_history_text = None;
     }
 
     /// Should Up/Down key presses be interpreted as history navigation given
@@ -187,6 +194,29 @@ mod tests {
     use codex_core::protocol::Op;
     use std::sync::mpsc::channel;
 
+    #[test]
+    fn duplicate_submissions_are_not_recorded() {
+        let mut history = ChatComposerHistory::new();
+
+        // Empty submissions are ignored.
+        history.record_local_submission("");
+        assert_eq!(history.local_history.len(), 0);
+
+        // First entry is recorded.
+        history.record_local_submission("hello");
+        assert_eq!(history.local_history.len(), 1);
+        assert_eq!(history.local_history.last().unwrap(), "hello");
+
+        // Identical consecutive entry is skipped.
+        history.record_local_submission("hello");
+        assert_eq!(history.local_history.len(), 1);
+
+        // Different entry is recorded.
+        history.record_local_submission("world");
+        assert_eq!(history.local_history.len(), 2);
+        assert_eq!(history.local_history.last().unwrap(), "world");
+    }
+
     #[test]
     fn navigation_with_async_fetch() {
         let (tx, rx) = channel::<AppEvent>();