fix(terminal): rebuild the WebGL glyph atlas when the page comes back

A browser can drop the atlas's GPU memory without a context-loss event
(sleep/resume, a long-backgrounded tab, display/zoom change on macOS),
leaving every cell painted with a clipped or foreign glyph.

client/src/components/run/TerminalView.tsx

@@ -468,7 +468,8 @@ export const TerminalView = memo(function TerminalView({
       // A terminal mounted on a hidden tab sits in a 0×0 box (`display:none`):
       // fitting it there shrinks xterm to its 12×6 minimum, and that size would
       // reach tmux with the attach. It stays unfitted until it is shown.
-      const hasBox = () => !!containerRef.current?.clientWidth && !!containerRef.current.clientHeight;
+      const hasBox = () =>
+        !!containerRef.current?.clientWidth && !!containerRef.current.clientHeight;
       if (hasBox()) fit.fit();
       // Take the keyboard as soon as the pane is on screen: the terminal IS the
       // page here, and having to click it first meant the first thing typed went
@@ -761,6 +762,16 @@ export const TerminalView = memo(function TerminalView({
         refit();
       };
       document.fonts?.addEventListener("loadingdone", onFontLoaded);
+      // The browser may drop or reuse the WebGL glyph atlas's GPU memory without
+      // a context-loss event (sleep/resume, a long-backgrounded tab, a display or
+      // zoom change on macOS): xterm keeps slicing the old coordinates and every
+      // cell shows a clipped or foreign glyph while the buffer stays correct.
+      // Rebuilding the atlas when the page comes back is cheap and redraws clean.
+      const onPageShown = () => {
+        if (document.visibilityState === "visible") term.clearTextureAtlas();
+      };
+      document.addEventListener("visibilitychange", onPageShown);
+      window.addEventListener("focus", onPageShown);
       // Settings → Appearance changed the terminal's font or size: an open
       // pane takes it now, re-measured and re-fitted like a font landing.
       const onFontPref = () => {
@@ -779,6 +790,8 @@ export const TerminalView = memo(function TerminalView({
         searchRef.current = null;
         resizeObserver.disconnect();
         document.fonts?.removeEventListener("loadingdone", onFontLoaded);
+        document.removeEventListener("visibilitychange", onPageShown);
+        window.removeEventListener("focus", onPageShown);
         window.removeEventListener(FONT_SIZE_EVENT, onFontPref);
         term.textarea?.removeEventListener("focus", reassert);
         detachIme();