fix: Don't trigger keybindings view on input burst (#7980)

Human TL;DR - in some situations, pasting/rapidly inputting text will
currently cause `?` characters to be stripped from the input message
content, and display the key bindings helper. For instance, writing
"Where is X defined? Can we do Y?" results in "Where is X defined Can we
do Y" being added to the message draft area. This is mildly annoying.

The fix was a simple one line addition. Added a test, ran linters, and
all looks good to me. I didn't create an issue to link to in this PR - I
had submitted this bug as a report a while ago but can't seem to find it
now. Let me know if it's an absolute must for the PR to be accepted.

I have read the CLA Document and I hereby sign the CLA

Below is Codex's summary.

---

# `?` characters toggling shortcuts / being dropped

## Symptom

On Termux (and potentially other terminal environments), composing text
in the native input field and sending it to the TTY can cause:

- The shortcuts overlay to appear (as if `?` was pressed on an empty
prompt), and
- All of the literal `?` characters in the text to be **missing** from
the composer input,
  even when `?` is not the first character.

This typically happens when the composer was previously empty and the
terminal delivers the text as a rapid sequence of key events rather than
a single bracketed paste event.

## Root cause

The TUI has two relevant behaviors:

1. **Shortcut toggle on `?` when empty**
- `ChatComposer::handle_shortcut_overlay_key` treats a plain `?` press
as a toggle between the shortcut summary and the full shortcut overlay,
but only when the composer is empty.
- When it toggles, it consumes the key event (so `?` is *not* inserted
into the text input).

2. **“Paste burst” buffering for fast key streams**
- The TUI uses a heuristic to detect “paste-like” input bursts even when
the terminal doesn’t send an explicit paste event.
- During that burst detection, characters can be buffered (and the text
area can remain empty temporarily) while the system decides whether to
treat the stream as paste-like input.

In Termux’s “send composed text all at once” mode, the input often
arrives as a very fast stream of `KeyCode::Char(...)` events. While that
stream is being buffered as a burst, the visible textarea can still be
empty. If a `?` arrives during this window, it matches “empty composer”
and is interpreted as “toggle shortcuts” instead of “insert literal
`?`”, so the `?` is dropped.

## Fix

Make the `?` toggle conditional on not being in any paste-burst
transient state.

Implementation:

- `ChatComposer::handle_shortcut_overlay_key` now checks
`!self.is_in_paste_burst()` in addition to `self.is_empty()` before
toggling.
- This ensures that when input is arriving as a fast burst (including
the “pending first char” case), `?` is treated as normal text input
rather than a UI toggle.

## Test coverage

Added a test that simulates a Termux-like fast stream:

- Sends `h i ? t h e r e` as immediate successive `KeyEvent::Char`
events (no delays).
- Asserts that a paste burst is active and the textarea is still empty
while buffering.
- Flushes the burst and verifies:
  - The final text contains the literal `?` (`"hi?there"`), and
  - The footer mode is not `ShortcutOverlay`.

## Notes

This fix intentionally keeps the existing UX:

- `?` still toggles shortcuts when the composer is genuinely empty and
the user is not in the middle of entering text.
- `?` typed while composing content (including IME/native-input fast
streams) remains literal.

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

@@ -1511,7 +1511,8 @@ impl ChatComposer {
 
         let toggles = matches!(key_event.code, KeyCode::Char('?'))
             && !has_ctrl_or_alt(key_event.modifiers)
-            && self.is_empty();
+            && self.is_empty()
+            && !self.is_in_paste_burst();
 
         if !toggles {
             return false;
@@ -2171,6 +2172,35 @@ mod tests {
         assert_eq!(composer.footer_mode(), FooterMode::ContextOnly);
     }
 
+    #[test]
+    fn question_mark_does_not_toggle_during_paste_burst() {
+        use crossterm::event::KeyCode;
+        use crossterm::event::KeyEvent;
+        use crossterm::event::KeyModifiers;
+
+        let (tx, _rx) = unbounded_channel::<AppEvent>();
+        let sender = AppEventSender::new(tx);
+        let mut composer = ChatComposer::new(
+            true,
+            sender,
+            false,
+            "Ask Codex to do anything".to_string(),
+            false,
+        );
+
+        for ch in ['h', 'i', '?', 't', 'h', 'e', 'r', 'e'] {
+            let _ = composer.handle_key_event(KeyEvent::new(KeyCode::Char(ch), KeyModifiers::NONE));
+        }
+        assert!(composer.is_in_paste_burst());
+        assert_eq!(composer.textarea.text(), "");
+
+        std::thread::sleep(ChatComposer::recommended_paste_flush_delay());
+        let _ = composer.flush_paste_burst_if_due();
+
+        assert_eq!(composer.textarea.text(), "hi?there");
+        assert_ne!(composer.footer_mode, FooterMode::ShortcutOverlay);
+    }
+
     #[test]
     fn shortcut_overlay_persists_while_task_running() {
         use crossterm::event::KeyCode;