feat(03-04): wire complete game flow with reward screen and review triggers

- Lesson completion now shows reward screen instead of going directly to forest
- Pre-generation starts at lesson begin (fire-and-forget)
- Stats accumulated (correct/errors/errorKeys) in progress after each lesson
- Review mode triggers every 3rd session
- Encouragement shown after 2x same level (repetition protection)
- Progress migration for older saved data without new fields

src/app.ts

@@ -1,7 +1,8 @@
 import type { ScreenName } from "./types";
 import { openDB, getProgress, saveProgress } from "./storage/db";
 import { initWelcomeScreen, initLessonScreen } from "./ui/screens";
-import { initForestScreen } from "./forest/scene";
+import { initForestScreen, renderForestScene } from "./forest/scene";
+import { startPreGeneration, initRewardScreen } from "./forest/reward";
 import { getGreeting } from "./companion/companion";
 import { companions } from "./companion/characters";
 import { showParentCodePrompt, initParentScreen } from "./ui/parent";
@@ -25,10 +26,44 @@ export function getDB(): IDBDatabase {
 
 const MAX_LEVEL = 6;
 
-async function handleLessonComplete(completedLevel: number): Promise<void> {
+/**
+ * Ensure progress object has all fields (migration for older saved data).
+ */
+function migrateProgress(
+	progress: NonNullable<Awaited<ReturnType<typeof getProgress>>>,
+): void {
+	if (!progress.errorKeyCounts) progress.errorKeyCounts = {};
+	if (!progress.lastPlayedLevels) progress.lastPlayedLevels = [];
+	if (progress.totalCorrect === undefined) progress.totalCorrect = 0;
+	if (progress.totalErrors === undefined) progress.totalErrors = 0;
+}
+
+async function handleLessonComplete(
+	completedLevel: number,
+	stats: {
+		totalCorrect: number;
+		totalErrors: number;
+		errorKeys: Record<string, number>;
+	},
+): Promise<void> {
 	// Update progress after lesson completion
 	const progress = await getProgress(db);
 	if (!progress) return;
+	migrateProgress(progress);
+
+	// Accumulate exercise stats (D-15, D-16)
+	progress.totalCorrect += stats.totalCorrect;
+	progress.totalErrors += stats.totalErrors;
+	for (const [key, count] of Object.entries(stats.errorKeys)) {
+		progress.errorKeyCounts[key] =
+			(progress.errorKeyCounts[key] ?? 0) + count;
+	}
+
+	// Track last played levels (keep last 3) for repetition detection
+	progress.lastPlayedLevels.push(completedLevel);
+	if (progress.lastPlayedLevels.length > 3) {
+		progress.lastPlayedLevels = progress.lastPlayedLevels.slice(-3);
+	}
 
 	// Add level to completedLevels if not already there
 	if (!progress.completedLevels.includes(completedLevel)) {
@@ -36,8 +71,11 @@ async function handleLessonComplete(completedLevel: number): Promise<void> {
 	}
 
 	// Advance to next level if this was the current level (LEVL-02, LEVL-03)
-	// Cap at MAX_LEVEL + 1 so we don't go beyond defined levels
-	if (completedLevel === progress.currentLevel && completedLevel < MAX_LEVEL) {
+	// Cap at MAX_LEVEL so we don't go beyond defined levels
+	if (
+		completedLevel === progress.currentLevel &&
+		completedLevel < MAX_LEVEL
+	) {
 		progress.currentLevel = completedLevel + 1;
 	}
 
@@ -52,9 +90,38 @@ async function handleLessonComplete(completedLevel: number): Promise<void> {
 
 	await saveProgress(db, progress);
 
-	// Re-init forest screen with updated progress, then navigate
-	await initForestScreen(db, startLessonFromForest);
-	showScreen("forest");
+	// Show REWARD screen instead of going directly to forest
+	showScreen("reward");
+
+	// Set companion avatar on reward screen
+	const companion = companions.find(
+		(c) => c.type === progress.selectedCharacter,
+	);
+	if (companion) {
+		const avatar = document.getElementById(
+			"reward-companion-avatar",
+		) as HTMLImageElement;
+		avatar.src = companion.avatarUrl;
+		avatar.alt = companion.name;
+	}
+
+	const elementId = await initRewardScreen(
+		db,
+		completedLevel,
+		progress.selectedCharacter,
+		() => {
+			// "Weiter ueben" -- start next lesson
+			startLessonFromForest(
+				Math.min(progress.currentLevel, MAX_LEVEL),
+			);
+		},
+		async () => {
+			// "Zurueck zum Wald" -- show forest with new element animated
+			await initForestScreen(db, startLessonFromForest);
+			await renderForestScene(db, elementId);
+			showScreen("forest");
+		},
+	);
 }
 
 async function handleLessonCancel(): Promise<void> {
@@ -69,9 +136,27 @@ function startLessonFromForest(level: number): void {
 		lessonCleanup = null;
 	}
 
-	// Get layout from progress (already loaded)
+	// Get layout and determine review/encouragement from progress
 	getProgress(db).then((progress) => {
-		const layout = progress?.selectedLayout ?? "de";
+		if (!progress) return;
+		migrateProgress(progress);
+
+		const layout = progress.selectedLayout ?? "de";
+
+		// Review every 3rd session (D-05)
+		const isReview =
+			progress.totalSessions > 0 &&
+			progress.totalSessions % 3 === 0;
+
+		// Encouragement if last 2 played levels are the same as current (D-06)
+		const last2 = progress.lastPlayedLevels.slice(-2);
+		const showEncouragement =
+			last2.length === 2 &&
+			last2[0] === level &&
+			last2[1] === level;
+
+		// Start image pre-generation (D-11) -- fire and forget
+		startPreGeneration(db);
 
 		showScreen("lesson");
 
@@ -81,6 +166,8 @@ function startLessonFromForest(level: number): void {
 			layout,
 			handleLessonComplete,
 			handleLessonCancel,
+			isReview,
+			showEncouragement,
 		);
 	});
 }
@@ -104,6 +191,8 @@ export async function initApp(): Promise<void> {
 
 	const progress = await getProgress(db);
 	if (progress && progress.selectedCharacter) {
+		migrateProgress(progress);
+
 		// Returning user -- init forest and go there
 		await initForestScreen(db, startLessonFromForest);
 		showScreen("forest");