feat: add schema version system with outdated save detection

Introduces a schema version field to GameState. Saves without the
current schema version are flagged on load (showing a modal prompting
reset or proceed), and cloud saves from outdated clients are rejected
server-side. Removes all backfill code now that outdated saves are
handled via the reset flow instead.

New POST /game/reset endpoint creates a fresh save for players who
choose to reset. Save version and current schema version are displayed
in the sidebar below the app version.

apps/web/src/api/client.ts

@@ -75,6 +75,9 @@ export const handleAuthCallback = async (code: string): Promise<AuthResponse> =>
 export const loadGame = async (): Promise<LoadResponse> =>
   request<LoadResponse>("/game/load");
 
+export const resetProgress = async (): Promise<LoadResponse> =>
+  request<LoadResponse>("/game/reset", { method: "POST" });
+
 export const saveGame = async (body: SaveRequest): Promise<SaveResponse> =>
   request<SaveResponse>("/game/save", {
     method: "POST",

apps/web/src/components/game/ClickArea.tsx

@@ -10,7 +10,7 @@ interface FloatText {
 }
 
 export const ClickArea = (): React.JSX.Element => {
-  const { state, handleClick, formatNumber } = useGame();
+  const { state, handleClick, formatNumber, saveSchemaVersion, currentSchemaVersion } = useGame();
   const [floats, setFloats] = useState<FloatText[]>([]);
   const nextIdRef = useRef(0);
 
@@ -41,6 +41,11 @@ export const ClickArea = (): React.JSX.Element => {
     <section className="click-area">
       <h1 className="game-title">Elysium</h1>
       <p className="game-version">v{__WEB_VERSION__}</p>
+      {currentSchemaVersion > 0 && (
+        <p className="game-schema-version">
+          Save: v{saveSchemaVersion} / Latest: v{currentSchemaVersion}
+        </p>
+      )}
       <h2>Guild Hall</h2>
       <div className="click-button-wrapper">
         <button

apps/web/src/components/game/GameLayout.tsx

@@ -13,6 +13,7 @@ import { CodexToast } from "./CodexToast.js";
 import { EditProfileModal } from "./EditProfileModal.js";
 import { EquipmentPanel } from "./EquipmentPanel.js";
 import { OfflineModal } from "./OfflineModal.js";
+import { OutdatedSchemaModal } from "./OutdatedSchemaModal.js";
 import { PrestigePanel } from "./PrestigePanel.js";
 import { ApotheosisPanel } from "./ApotheosisPanel.js";
 import { TranscendencePanel } from "./TranscendencePanel.js";
@@ -52,9 +53,10 @@ const BASE_TABS: { id: Tab; label: string }[] = [
 ];
 
 export const GameLayout = (): React.JSX.Element => {
-  const { state, isLoading, error, battleResult, dismissBattle, lastSavedAt, isSyncing, forceSync, newCodexEntryIds, newStoryChapterIds, loginBonus, dismissLoginBonus } = useGame();
+  const { state, isLoading, error, battleResult, dismissBattle, lastSavedAt, isSyncing, forceSync, newCodexEntryIds, newStoryChapterIds, loginBonus, dismissLoginBonus, schemaOutdated } = useGame();
   const [activeTab, setActiveTab] = useState<Tab>("adventurers");
   const [editingProfile, setEditingProfile] = useState(false);
+  const [dismissedOutdatedWarning, setDismissedOutdatedWarning] = useState(false);
 
   if (isLoading) {
     return (
@@ -91,6 +93,9 @@ export const GameLayout = (): React.JSX.Element => {
         onForceSync={forceSync}
       />
       <OfflineModal />
+      {schemaOutdated && !dismissedOutdatedWarning && (
+        <OutdatedSchemaModal onDismiss={() => { setDismissedOutdatedWarning(true); }} />
+      )}
       <AchievementToast />
       <CodexToast />
       <StoryToast />

apps/web/src/components/game/OutdatedSchemaModal.tsx

@@ -0,0 +1,49 @@
+import { useState } from "react";
+import { useGame } from "../../context/GameContext.js";
+
+interface OutdatedSchemaModalProps {
+  onDismiss: () => void;
+}
+
+export const OutdatedSchemaModal = ({ onDismiss }: OutdatedSchemaModalProps): React.JSX.Element => {
+  const { resetProgress } = useGame();
+  const [isResetting, setIsResetting] = useState(false);
+
+  const handleReset = async (): Promise<void> => {
+    setIsResetting(true);
+    await resetProgress();
+    setIsResetting(false);
+  };
+
+  return (
+    <div className="modal-overlay">
+      <div className="modal offline-modal">
+        <h2>⚠️ Outdated Save Data</h2>
+        <p>
+          Your save data is from an older version of Elysium and may cause bugs or unexpected
+          behaviour. Cloud saves are <strong>disabled</strong> until you reset your progress.
+        </p>
+        <p>
+          Resetting will start you fresh — all progress will be lost.
+        </p>
+        <div className="outdated-modal-actions">
+          <button
+            className="outdated-modal-reset-button"
+            onClick={() => { void handleReset(); }}
+            disabled={isResetting}
+            type="button"
+          >
+            {isResetting ? "Resetting…" : "Reset Progress"}
+          </button>
+          <button
+            className="modal-close-button"
+            onClick={onDismiss}
+            type="button"
+          >
+            Proceed with Bugs
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+};

apps/web/src/context/GameContext.tsx

@@ -113,6 +113,7 @@ import {
   craftRecipe as craftRecipeApi,
   loadGame,
   prestige as prestigeApi,
+  resetProgress as resetProgressApi,
   saveGame,
   startExploration as startExplorationApi,
   transcend as transcendApi,
@@ -217,6 +218,14 @@ interface GameContextValue {
   dismissStoryChapter: (id: string) => void;
   /** Record the player's choice for a story chapter */
   completeChapter: (chapterId: string, choiceId: string) => void;
+  /** True when the loaded save is from an older schema version */
+  schemaOutdated: boolean;
+  /** The save's schema version (0 if missing) */
+  saveSchemaVersion: number;
+  /** The server's current expected schema version */
+  currentSchemaVersion: number;
+  /** Reset all progress to a fresh save state (resolves schema outdated) */
+  resetProgress: () => Promise<void>;
 }
 
 const GameContext = createContext<GameContextValue | null>(null);
@@ -249,6 +258,9 @@ export const GameProvider = ({ children }: { children: React.ReactNode }): React
   const isAutoPrestigingRef = useRef(false);
   const isAutoBossingRef = useRef(false);
   const reloadRef = useRef<() => Promise<void>>(() => Promise.resolve());
+  const [schemaOutdated, setSchemaOutdated] = useState(false);
+  const [saveSchemaVersion, setSaveSchemaVersion] = useState(0);
+  const [currentSchemaVersion, setCurrentSchemaVersion] = useState(0);
   const [newCodexEntryIds, setNewCodexEntryIds] = useState<string[]>([]);
   const codexProcessedRef = useRef<Set<string>>(new Set());
   const [newStoryChapterIds, setNewStoryChapterIds] = useState<string[]>([]);
@@ -278,6 +290,9 @@ export const GameProvider = ({ children }: { children: React.ReactNode }): React
         setLoginBonus(data.loginBonus);
       }
       setLoginStreak(data.loginStreak ?? 1);
+      setSchemaOutdated(data.schemaOutdated);
+      setSaveSchemaVersion(data.state.schemaVersion ?? 0);
+      setCurrentSchemaVersion(data.currentSchemaVersion);
       // Fetch number format preference from profile (fire-and-forget, non-blocking)
       void fetch(`/api/profile/${data.state.player.discordId}`)
         .then(async (res) => {
@@ -1029,6 +1044,28 @@ export const GameProvider = ({ children }: { children: React.ReactNode }): React
     });
   }, []);
 
+  const resetProgress = useCallback(async () => {
+    setIsLoading(true);
+    setError(null);
+    try {
+      const data = await resetProgressApi();
+      setState(data.state);
+      setLastSavedAt(data.state.player.lastSavedAt);
+      setSchemaOutdated(false);
+      setOfflineGold(0);
+      setOfflineEssence(0);
+      setLoginBonus(null);
+      if (data.signature) {
+        signatureRef.current = data.signature;
+        localStorage.setItem("elysium_save_signature", data.signature);
+      }
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Failed to reset progress");
+    } finally {
+      setIsLoading(false);
+    }
+  }, []);
+
   const dismissLoginBonus = useCallback(() => {
     setLoginBonus(null);
   }, []);
@@ -1085,6 +1122,10 @@ export const GameProvider = ({ children }: { children: React.ReactNode }): React
         newStoryChapterIds,
         dismissStoryChapter,
         completeChapter,
+        schemaOutdated,
+        saveSchemaVersion,
+        currentSchemaVersion,
+        resetProgress,
       }}
     >
       {children}

apps/web/src/styles.css

@@ -180,6 +180,13 @@ body {
   font-size: 0.65rem;
   color: var(--colour-text-muted);
   opacity: 0.7;
+  margin-bottom: 0.25rem;
+}
+
+.game-schema-version {
+  font-size: 0.6rem;
+  color: var(--colour-text-muted);
+  opacity: 0.6;
   margin-bottom: 0.5rem;
 }
 
@@ -833,6 +840,35 @@ body {
   background: var(--colour-accent-light);
 }
 
+/* ===================== OUTDATED SCHEMA MODAL ===================== */
+.outdated-modal-actions {
+  display: flex;
+  flex-direction: column;
+  gap: 0.5rem;
+  margin-top: 1rem;
+}
+
+.outdated-modal-reset-button {
+  background: #c0392b;
+  border: none;
+  border-radius: var(--radius);
+  color: #fff;
+  cursor: pointer;
+  font-size: 1rem;
+  font-weight: 700;
+  padding: 0.6rem 2rem;
+  transition: background 0.15s;
+}
+
+.outdated-modal-reset-button:hover:not(:disabled) {
+  background: #e74c3c;
+}
+
+.outdated-modal-reset-button:disabled {
+  cursor: not-allowed;
+  opacity: 0.6;
+}
+
 /* ===================== BATTLE MODAL ===================== */
 .battle-modal {
   max-width: 520px;