feat: codex tool tips (#7440)

<img width="551" height="316" alt="Screenshot 2025-12-01 at 12 22 26"
src="https://github.com/user-attachments/assets/6ca3deff-8ef8-4f74-a8e1-e5ea13fd6740"
/>

codex-rs/tui/src/tooltips.rs

@@ -0,0 +1,49 @@
+use lazy_static::lazy_static;
+use rand::Rng;
+
+const RAW_TOOLTIPS: &str = include_str!("../tooltips.txt");
+
+lazy_static! {
+    static ref TOOLTIPS: Vec<&'static str> = RAW_TOOLTIPS
+        .lines()
+        .map(str::trim)
+        .filter(|line| !line.is_empty() && !line.starts_with('#'))
+        .collect();
+}
+
+pub(crate) fn random_tooltip() -> Option<&'static str> {
+    let mut rng = rand::rng();
+    pick_tooltip(&mut rng)
+}
+
+fn pick_tooltip<R: Rng + ?Sized>(rng: &mut R) -> Option<&'static str> {
+    if TOOLTIPS.is_empty() {
+        None
+    } else {
+        TOOLTIPS.get(rng.random_range(0..TOOLTIPS.len())).copied()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use rand::SeedableRng;
+    use rand::rngs::StdRng;
+
+    #[test]
+    fn random_tooltip_returns_some_tip_when_available() {
+        let mut rng = StdRng::seed_from_u64(42);
+        assert!(pick_tooltip(&mut rng).is_some());
+    }
+
+    #[test]
+    fn random_tooltip_is_reproducible_with_seed() {
+        let expected = {
+            let mut rng = StdRng::seed_from_u64(7);
+            pick_tooltip(&mut rng)
+        };
+
+        let mut rng = StdRng::seed_from_u64(7);
+        assert_eq!(expected, pick_tooltip(&mut rng));
+    }
+}