feat: server-authoritative save — wait for server before game starts

- Store starts in ready:false — no game actions until authority loaded
- useSaveSync signals serverLoaded (success, empty, or unreachable)
- GameSync orchestrates: logged in → wait server, guest → localStorage
- Home shows loading screen until ready
- localStorage = cache only, server = authority for logged-in users

Frontend/src/store/useGameStore.ts

@@ -1,4 +1,5 @@
 // useGameStore.ts — Zustand store, source unique de l'état game
+// Serveur = autorité. localStorage = fallback invité uniquement.
 // Lazy calculation pattern : gains passifs calculés au read depuis lastTick
 
 import { create } from "zustand";
@@ -17,7 +18,7 @@ import {
 
 const SAVE_KEY = "clickerz_state";
 
-function loadState(): GameState {
+function loadLocalState(): GameState {
   try {
     const raw = localStorage.getItem(SAVE_KEY);
     if (!raw) return { ...DEFAULT_STATE, lastTick: Date.now() };
@@ -28,7 +29,7 @@ function loadState(): GameState {
   }
 }
 
-function saveState(state: GameState): void {
+function saveLocal(state: GameState): void {
   localStorage.setItem(SAVE_KEY, JSON.stringify(state));
 }
 
@@ -36,6 +37,7 @@ interface GameStore {
   // State
   state: GameState;
   playSeconds: number;
+  ready: boolean; // true once the authoritative state is loaded
 
   // Derived (recalculated on tick)
   canPrestige: boolean;
@@ -49,19 +51,25 @@ interface GameStore {
   prestige: () => void;
   reset: () => void;
   loadFromServer: (serverState: GameState) => void;
+  initGuest: () => void; // fallback when no server save (guest mode)
   generatorCost: typeof genCost;
 }
 
+// Start with DEFAULT_STATE — game is NOT ready until loadFromServer or initGuest
+const initialState = { ...DEFAULT_STATE, lastTick: Date.now() };
+
 export const useGameStore = create<GameStore>((set, get) => ({
-  state: loadState(),
+  state: initialState,
   playSeconds: 0,
-  canPrestige: canPrestigeCheck(loadState()),
-  productionPerSecond: totalProductionPerSecond(loadState()),
+  ready: false,
+  canPrestige: false,
+  productionPerSecond: 0,
 
   tick: () => {
+    if (!get().ready) return;
     set((s) => {
       const updated = applyIdleGains(s.state, Date.now());
-      saveState(updated);
+      saveLocal(updated);
       return {
         state: updated,
         playSeconds: s.playSeconds + 1,
@@ -72,9 +80,10 @@ export const useGameStore = create<GameStore>((set, get) => ({
   },
 
   click: () => {
+    if (!get().ready) return;
     set((s) => {
       const updated = applyClick(applyIdleGains(s.state, Date.now()));
-      saveState(updated);
+      saveLocal(updated);
       return {
         state: updated,
         canPrestige: canPrestigeCheck(updated),
@@ -84,11 +93,12 @@ export const useGameStore = create<GameStore>((set, get) => ({
   },
 
   buy: (genId: string) => {
+    if (!get().ready) return;
     set((s) => {
       const withIdle = applyIdleGains(s.state, Date.now());
       const updated = buyGenerator(withIdle, genId);
       if (!updated) return s;
-      saveState(updated);
+      saveLocal(updated);
       return {
         state: updated,
         productionPerSecond: totalProductionPerSecond(updated),
@@ -97,10 +107,11 @@ export const useGameStore = create<GameStore>((set, get) => ({
   },
 
   buyNode: (nodeId: string) => {
+    if (!get().ready) return;
     set((s) => {
       const updated = buyEvolutionNode(s.state, nodeId);
       if (!updated) return s;
-      saveState(updated);
+      saveLocal(updated);
       return {
         state: updated,
         productionPerSecond: totalProductionPerSecond(updated),
@@ -109,10 +120,11 @@ export const useGameStore = create<GameStore>((set, get) => ({
   },
 
   prestige: () => {
+    if (!get().ready) return;
     set((s) => {
       if (!canPrestigeCheck(s.state)) return s;
       const updated = applyPrestige(s.state);
-      saveState(updated);
+      saveLocal(updated);
       return {
         state: updated,
         canPrestige: canPrestigeCheck(updated),
@@ -123,24 +135,38 @@ export const useGameStore = create<GameStore>((set, get) => ({
 
   reset: () => {
     const fresh = { ...DEFAULT_STATE, lastTick: Date.now() };
-    saveState(fresh);
+    saveLocal(fresh);
     set({
       state: fresh,
       playSeconds: 0,
+      ready: true,
       canPrestige: false,
       productionPerSecond: 0,
     });
   },
 
+  // Server save loaded — this IS the authority
   loadFromServer: (serverState: GameState) => {
     const hydrated = applyIdleGains(serverState, Date.now());
-    saveState(hydrated);
+    saveLocal(hydrated); // mirror to localStorage as cache
     set({
       state: hydrated,
+      ready: true,
       canPrestige: canPrestigeCheck(hydrated),
       productionPerSecond: totalProductionPerSecond(hydrated),
     });
   },
 
+  // Guest mode — no server save, use localStorage or fresh state
+  initGuest: () => {
+    const local = loadLocalState();
+    set({
+      state: local,
+      ready: true,
+      canPrestige: canPrestigeCheck(local),
+      productionPerSecond: totalProductionPerSecond(local),
+    });
+  },
+
   generatorCost: genCost,
 }));