fix(ui): force resize-event size during post-resize draw (macOS Terminal.app, ConHost) (#993)

Some terminal emulators (macOS Terminal.app, Windows ConHost) briefly report stale dimensions via `crossterm::terminal::size()` after a resize. ratatui's `draw()` calls `autoresize()` internally, queries the backend, and shrinks the viewport back to the stale dimension — leaving the newly-expanded area filled with stale content from the previous frame (the duplicate-panel symptom users have reported).

The fix adds `force_size` / `clear_forced_size` to `ColorCompatBackend` and forces the resize-event size for the post-resize draw, then clears the forcing for subsequent frames. Same class of fix as #582 but covers an additional emulator family.

Thanks to @ArronAI007 for tracking down the autoresize→stale-size→short-buffer interaction.

crates/tui/src/tui/color_compat.rs

@@ -21,6 +21,11 @@ pub(crate) struct ColorCompatBackend<W: Write> {
     inner: CrosstermBackend<W>,
     depth: ColorDepth,
     palette_mode: PaletteMode,
+    /// During a resize event the terminal emulator may report stale dimensions
+    /// for a brief window (observed on macOS Terminal.app and Windows ConHost).
+    /// Forcing the expected size prevents ratatui's internal `autoresize` from
+    /// shrinking the viewport back to the stale dimension inside `draw()`.
+    forced_size: Option<Size>,
 }
 
 impl<W: Write> ColorCompatBackend<W> {
@@ -29,8 +34,17 @@ impl<W: Write> ColorCompatBackend<W> {
             inner: CrosstermBackend::new(writer),
             depth,
             palette_mode,
+            forced_size: None,
         }
     }
+
+    pub(crate) fn force_size(&mut self, size: Size) {
+        self.forced_size = Some(size);
+    }
+
+    pub(crate) fn clear_forced_size(&mut self) {
+        self.forced_size = None;
+    }
 }
 
 impl<W: Write> Write for ColorCompatBackend<W> {
@@ -88,7 +102,10 @@ impl<W: Write> Backend for ColorCompatBackend<W> {
     }
 
     fn size(&self) -> io::Result<Size> {
-        self.inner.size()
+        match self.forced_size {
+            Some(size) => Ok(size),
+            None => self.inner.size(),
+        }
     }
 
     fn window_size(&mut self) -> io::Result<WindowSize> {

crates/tui/src/tui/ui.rs

@@ -18,7 +18,7 @@ use crossterm::{
 };
 use ratatui::{
     Frame, Terminal,
-    layout::{Constraint, Direction, Layout, Rect},
+    layout::{Constraint, Direction, Layout, Rect, Size},
     prelude::Widget,
     style::Style,
     text::Span,
@@ -1643,11 +1643,29 @@ async fn run_event_loop(
 
                 terminal.clear()?;
                 app.handle_resize(final_w, final_h);
+                // #macos-resize: some terminals (macOS Terminal.app, Windows
+                // ConHost) briefly report stale dimensions via
+                // `terminal::size()` after a resize. ratatui's `draw()` calls
+                // `autoresize()` internally, which queries the backend size;
+                // if it sees the old dimension it shrinks the viewport back,
+                // leaving the newly-expanded area filled with stale content
+                // from the previous frame (duplicate UI panels).
+                //
+                // We force the backend to report the resize-event size for
+                // this single draw so the buffer matches the real viewport.
+                {
+                    let backend = terminal.backend_mut();
+                    backend.force_size(Size::new(final_w, final_h));
+                }
                 // Draw immediately so the cleared screen gets repainted before
                 // any other events can interleave. Without this, the next
                 // iteration's draw can race against fast follow-up input and
                 // leave the user staring at a blank/partial frame.
                 terminal.draw(|f| render(f, app))?;
+                {
+                    let backend = terminal.backend_mut();
+                    backend.clear_forced_size();
+                }
                 app.needs_redraw = false;
                 continue;
             }