feat(navigation): persist view params customisation

apps/client/src/common/stores/savedViewParams.ts

@@ -0,0 +1,62 @@
+import { create } from 'zustand';
+
+// params that are auth/preset markers, not user view customisation (see common/utils/urlPresets.ts)
+export const reservedParams = new Set(['token', 'n', 'alias']);
+
+interface SavedViewParamsStore {
+  params: Record<string, string>; // view key (e.g. "timer") -> search string without leading "?"
+  save: (view: string, search: string) => void;
+  clear: (view: string) => void;
+  clearAll: () => void;
+}
+
+/**
+ * Remembers the last view parameters used for each view so they can be
+ * restored when the user navigates back to that view through the menu.
+ * In-memory only: persists across SPA navigation, resets on a full page reload.
+ */
+export const useSavedViewParams = create<SavedViewParamsStore>((set) => ({
+  params: {},
+  save: (view, search) =>
+    set((state) => {
+      // ignore empty view keys and do not store empty entries, so the
+      // "saved changes" indicator only reflects genuine customisation
+      if (!view) return state;
+      const params = { ...state.params };
+      if (search) {
+        params[view] = search;
+      } else {
+        delete params[view];
+      }
+      return { params };
+    }),
+  clear: (view) =>
+    set((state) => {
+      if (!state.params[view]) return state;
+      const params = { ...state.params };
+      delete params[view];
+      return { params };
+    }),
+  clearAll: () => set({ params: {} }),
+}));
+
+/**
+ * Removes reserved (auth/preset) params from a search string, keeping only
+ * genuine view customisation.
+ */
+export function stripReservedParams(search: string): string {
+  const sp = new URLSearchParams(search);
+  reservedParams.forEach((key) => sp.delete(key));
+  return sp.toString();
+}
+
+/**
+ * Whether the search params contain any genuine view customisation,
+ * ignoring reserved params.
+ */
+export function hasCustomParams(searchParams: URLSearchParams): boolean {
+  for (const key of searchParams.keys()) {
+    if (!reservedParams.has(key)) return true;
+  }
+  return false;
+}