Better handling skill depdenencies on ENV VAR. (#9017)

An experimental flow for env var skill dependencies. Skills can now
declare required env vars in SKILL.md; if missing, the CLI prompts the
user to get the value, and Core will store it in memory (eventually to a
local persistent store)
<img width="790" height="169" alt="image"
src="https://github.com/user-attachments/assets/cd928918-9403-43cb-a7e7-b8d59bcccd9a"
/>

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

@@ -1146,6 +1146,22 @@ impl StatefulWidgetRef for &TextArea {
 }
 
 impl TextArea {
+    pub(crate) fn render_ref_masked(
+        &self,
+        area: Rect,
+        buf: &mut Buffer,
+        state: &mut TextAreaState,
+        mask_char: char,
+    ) {
+        let lines = self.wrapped_lines(area.width);
+        let scroll = self.effective_scroll(area.height, &lines, state.scroll);
+        state.scroll = scroll;
+
+        let start = scroll as usize;
+        let end = (scroll + area.height).min(lines.len() as u16) as usize;
+        self.render_lines_masked(area, buf, &lines, start..end, mask_char);
+    }
+
     fn render_lines(
         &self,
         area: Rect,
@@ -1175,6 +1191,26 @@ impl TextArea {
             }
         }
     }
+
+    fn render_lines_masked(
+        &self,
+        area: Rect,
+        buf: &mut Buffer,
+        lines: &[Range<usize>],
+        range: std::ops::Range<usize>,
+        mask_char: char,
+    ) {
+        for (row, idx) in range.enumerate() {
+            let r = &lines[idx];
+            let y = area.y + row as u16;
+            let line_range = r.start..r.end - 1;
+            let masked = self.text[line_range.clone()]
+                .chars()
+                .map(|_| mask_char)
+                .collect::<String>();
+            buf.set_string(area.x, y, &masked, Style::default());
+        }
+    }
 }
 
 #[cfg(test)]