fix: improve custom prompt documentation and actually use prompt descriptions (#5332)

Expand the custom prompts documentation and link it from other guides. Show saved prompt metadata in the slash-command popup, with tests covering description fallbacks.

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

@@ -164,10 +164,17 @@ impl CommandPopup {
                     CommandItem::Builtin(cmd) => {
                         (format!("/{}", cmd.command()), cmd.description().to_string())
                     }
-                    CommandItem::UserPrompt(i) => (
-                        format!("/{PROMPTS_CMD_PREFIX}:{}", self.prompts[i].name),
-                        "send saved prompt".to_string(),
-                    ),
+                    CommandItem::UserPrompt(i) => {
+                        let prompt = &self.prompts[i];
+                        let description = prompt
+                            .description
+                            .clone()
+                            .unwrap_or_else(|| "send saved prompt".to_string());
+                        (
+                            format!("/{PROMPTS_CMD_PREFIX}:{}", prompt.name),
+                            description,
+                        )
+                    }
                 };
                 GenericDisplayRow {
                     name,
@@ -221,6 +228,7 @@ impl WidgetRef for CommandPopup {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use pretty_assertions::assert_eq;
 
     #[test]
     fn filter_includes_init_when_typing_prefix() {
@@ -322,4 +330,35 @@ mod tests {
             "prompt with builtin name should be ignored"
         );
     }
+
+    #[test]
+    fn prompt_description_uses_frontmatter_metadata() {
+        let popup = CommandPopup::new(vec![CustomPrompt {
+            name: "draftpr".to_string(),
+            path: "/tmp/draftpr.md".to_string().into(),
+            content: "body".to_string(),
+            description: Some("Create feature branch, commit and open draft PR.".to_string()),
+            argument_hint: None,
+        }]);
+        let rows = popup.rows_from_matches(vec![(CommandItem::UserPrompt(0), None, 0)]);
+        let description = rows.first().and_then(|row| row.description.as_deref());
+        assert_eq!(
+            description,
+            Some("Create feature branch, commit and open draft PR.")
+        );
+    }
+
+    #[test]
+    fn prompt_description_falls_back_when_missing() {
+        let popup = CommandPopup::new(vec![CustomPrompt {
+            name: "foo".to_string(),
+            path: "/tmp/foo.md".to_string().into(),
+            content: "body".to_string(),
+            description: None,
+            argument_hint: None,
+        }]);
+        let rows = popup.rows_from_matches(vec![(CommandItem::UserPrompt(0), None, 0)]);
+        let description = rows.first().and_then(|row| row.description.as_deref());
+        assert_eq!(description, Some("send saved prompt"));
+    }
 }