fix(01): add lesson cancel button and handle level 6 completion

- Back button in lesson screen to return to forest without completing
- "Alle Stufen geschafft!" message when all 6 levels are done
- Cap currentLevel at MAX_LEVEL to prevent out-of-bounds progression

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

index.html

@@ -38,6 +38,7 @@
 		</section>
 		<section id="screen-lesson" class="screen">
 			<div class="lesson">
+				<button class="lesson__back-btn" id="lesson-back-btn">&#x2190; Zurueck</button>
 				<div class="lesson__letter-area" id="letter-area">
 					<!-- Current letter appears here -->
 				</div>

src/app.ts

@@ -20,6 +20,8 @@ export function getDB(): IDBDatabase {
 	return db;
 }
 
+const MAX_LEVEL = 6;
+
 async function handleLessonComplete(completedLevel: number): Promise<void> {
 	// Update progress after lesson completion
 	const progress = await getProgress(db);
@@ -31,7 +33,8 @@ async function handleLessonComplete(completedLevel: number): Promise<void> {
 	}
 
 	// Advance to next level if this was the current level (LEVL-02, LEVL-03)
-	if (completedLevel === progress.currentLevel) {
+	// Cap at MAX_LEVEL + 1 so we don't go beyond defined levels
+	if (completedLevel === progress.currentLevel && completedLevel < MAX_LEVEL) {
 		progress.currentLevel = completedLevel + 1;
 	}
 
@@ -51,6 +54,11 @@ async function handleLessonComplete(completedLevel: number): Promise<void> {
 	showScreen("forest");
 }
 
+async function handleLessonCancel(): Promise<void> {
+	await initForestScreen(db, startLessonFromForest);
+	showScreen("forest");
+}
+
 function startLessonFromForest(level: number): void {
 	// Clean up previous lesson if any
 	if (lessonCleanup) {
@@ -69,6 +77,7 @@ function startLessonFromForest(level: number): void {
 			level,
 			layout,
 			handleLessonComplete,
+			handleLessonCancel,
 		);
 	});
 }

src/forest/scene.ts

@@ -48,6 +48,8 @@ export function renderLevelMap(
 	});
 }
 
+const MAX_LEVEL = 6;
+
 export async function initForestScreen(
 	db: IDBDatabase,
 	onStartLesson: (level: number) => void,
@@ -61,6 +63,19 @@ export async function initForestScreen(
 
 	renderLevelMap(mapContainer, progress, onStartLesson);
 
-	// Continue button starts the current level
-	continueBtn.onclick = () => onStartLesson(progress.currentLevel);
+	const allComplete = levels.every((l) =>
+		progress.completedLevels.includes(l.level),
+	);
+
+	if (allComplete) {
+		continueBtn.textContent = "Alle Stufen geschafft!";
+		continueBtn.disabled = true;
+		continueBtn.classList.add("forest__continue-btn--done");
+	} else {
+		continueBtn.textContent = "Weiter ueben";
+		continueBtn.disabled = false;
+		continueBtn.classList.remove("forest__continue-btn--done");
+		continueBtn.onclick = () =>
+			onStartLesson(Math.min(progress.currentLevel, MAX_LEVEL));
+	}
 }

src/styles/main.css

@@ -259,6 +259,15 @@ h3 {
 	transform: scale(1.05);
 }
 
+.forest__continue-btn--done {
+	background: var(--accent-gold);
+	cursor: default;
+}
+
+.forest__continue-btn--done:hover {
+	transform: none;
+}
+
 /* Lesson screen */
 .lesson {
 	display: flex;
@@ -269,6 +278,29 @@ h3 {
 	padding: 2rem;
 	min-height: 100vh;
 	background: var(--bg-cream);
+	position: relative;
+}
+
+.lesson__back-btn {
+	position: absolute;
+	top: 1rem;
+	left: 1rem;
+	font-family: "Quicksand", sans-serif;
+	font-size: 1rem;
+	font-weight: 600;
+	color: var(--text-warm);
+	background: var(--bg-forest);
+	border: 2px solid var(--accent-green);
+	border-radius: 12px;
+	padding: 0.5rem 1rem;
+	cursor: pointer;
+	transition: background 0.2s ease, transform 0.1s ease;
+}
+
+.lesson__back-btn:hover {
+	background: var(--accent-green);
+	color: white;
+	transform: scale(1.05);
 }
 
 .lesson__letter-area {

src/ui/screens.ts

@@ -79,9 +79,11 @@ export function initLessonScreen(
 	level: number,
 	layout: KeyboardLayout,
 	onComplete: (level: number) => void,
+	onCancel?: () => void,
 ): () => void {
 	const letterArea = document.getElementById("letter-area")!;
 	const keyboardContainer = document.getElementById("lesson-keyboard")!;
+	const backBtn = document.getElementById("lesson-back-btn") as HTMLButtonElement;
 	const state = createExerciseState(level);
 
 	// Render keyboard
@@ -131,6 +133,13 @@ export function initLessonScreen(
 
 	document.addEventListener("keydown", onKeyDown);
 
+	// Back button to cancel lesson
+	backBtn.onclick = () => {
+		document.removeEventListener("keydown", onKeyDown);
+		letterArea.innerHTML = "";
+		if (onCancel) onCancel();
+	};
+
 	// Return cleanup function
 	return () => {
 		document.removeEventListener("keydown", onKeyDown);