docs(sasch40): document cache busting, easter egg invisibility, and localStorage persistence

projects/sasch40/AGENTS.md

@@ -108,6 +108,32 @@ This document records the foundational design decisions, their rationale ("Why")
 
 ---
 
+### 8. Unhashed Asset Cache Invalidation (`nginx.conf`)
+*   **The Decision**: Unhashed static files (`/assets/scenes/*.jpg`, `/assets/characters/*/*.jpg`) MUST be served with `Cache-Control: "no-cache, no-store, must-revalidate"` and `Expires: -1`.
+*   **Why**: In mobile browsers (Safari iOS, Chrome Mobile), default caching headers (`expires 30d`) cause updated character portraits and scene backgrounds to remain stale for weeks on user devices.
+*   **The Rule**: In `nginx.conf`, static media matches `\.(png|jpg|jpeg|gif|ico|svg|webp|mp3|wav|ogg)$` with `no-cache, no-store, must-revalidate`. Bundled JS/CSS matches `\.(js|css)$` with `public, immutable` for 1 year.
+
+---
+
+### 9. Easter Egg Invisibility Pattern (`TavernView.vue`)
+*   **The Decision**: Secret hotspots (e.g. `secret-tap-hotspot` in the Schankraum) must be 100% invisible initially.
+*   **Why**: An Easter egg marked with a glowing button or text badge is not a secret; it invites immediate trivial clicking.
+*   **The Rule**:
+    *   The button must render with transparent background, no border, no outline, no box shadow, no hover change, and no tooltip (`:title="undefined"`).
+    *   Only upon the user's first click does it reveal the gold key icon, play a celebratory fanfare, unlock the Easter egg in the game store (+500 points), and transition to the secret room.
+
+---
+
+### 10. LocalStorage Persistence & Clean Game Reset (`gameStore.ts`)
+*   **The Decision**: Game state automatically synchronizes to `localStorage` (`sasch40_game_save_v1`) on every mutation and is cleanly wiped when clicking *„🔄 NOCHMAL SPIELEN“*.
+*   **Why**: Mobile users frequently refresh or switch apps to snap photos. Without persistence, a browser reload resets their progress back to Act I.
+*   **The Rule**:
+    *   `useGameStore` automatically initializes from `localStorage` if valid data exists.
+    *   `store.$subscribe` writes the state to `localStorage` whenever any value changes.
+    *   `resetGame()` clears `localStorage.removeItem(...)`, sets all stats to zero, and returns to the Prequel Intro.
+
+---
+
 ## 🛠️ Build, Test & Deployment Workflow
 
 ### Fast Docker Packaging (Local ARM64 Compile)