fix(theme): persist preference before view transition

src/contexts/ThemeContext.tsx

@@ -1,22 +1,64 @@
 import {
+  useCallback,
   useState,
   type MouseEvent as ReactMouseEvent,
   type ReactNode,
 } from "react";
 import { ThemeContext } from "../hooks/useTheme";
 
+const THEME_STORAGE_KEY = "waveflow.theme.is_dark";
+
+// Read the persisted preference synchronously so the very first render already
+// matches the user's last choice. Survives crashes during the View Transitions
+// animation (issue #34): even if the webview dies mid-toggle, the new value
+// has already been written to localStorage before startViewTransition runs.
+const readStoredTheme = (): boolean => {
+  if (typeof window === "undefined") return false;
+  try {
+    return window.localStorage.getItem(THEME_STORAGE_KEY) === "true";
+  } catch {
+    return false;
+  }
+};
+
+const writeStoredTheme = (isDark: boolean) => {
+  if (typeof window === "undefined") return;
+  try {
+    window.localStorage.setItem(THEME_STORAGE_KEY, isDark ? "true" : "false");
+  } catch {
+    // localStorage unavailable (private mode, quota) — preference simply
+    // won't survive the next launch. Not worth surfacing to the user.
+  }
+};
+
 export function ThemeProvider({ children }: { children: ReactNode }) {
-  const [isDark, setIsDark] = useState(false);
+  const [isDark, setIsDark] = useState<boolean>(readStoredTheme);
 
-  const toggleTheme = (event?: ReactMouseEvent) => {
-    const flipTheme = () => setIsDark((prev) => !prev);
+  const toggleTheme = useCallback((event?: ReactMouseEvent) => {
+    let nextValue = false;
+    const flipTheme = () =>
+      setIsDark((prev) => {
+        nextValue = !prev;
+        return nextValue;
+      });
+
+    // Persist BEFORE triggering any animation. Some Linux WebKitGTK builds
+    // crash the webview during startViewTransition on certain GPU/Wayland
+    // stacks (issue #34) — writing first guarantees the next launch picks
+    // up the new theme even if this transition kills the process.
+    const persistNext = (value: boolean) => writeStoredTheme(value);
 
     // Fallback: no View Transitions API support → instant swap
     if (typeof document === "undefined" || !document.startViewTransition) {
       flipTheme();
+      persistNext(nextValue);
       return;
     }
 
+    // Compute & persist the future value before the animation starts so the
+    // write lands even if the compositor crashes mid-transition.
+    persistNext(!isDark);
+
     const transition = document.startViewTransition(flipTheme);
 
     // Radial reveal from the click point
@@ -48,7 +90,7 @@ export function ThemeProvider({ children }: { children: ReactNode }) {
           // Animation failed — the theme has still toggled via flipTheme()
         });
     }
-  };
+  }, [isDark]);
 
   return (
     <ThemeContext.Provider value={{ isDark, toggleTheme }}>