refactor: code review improvements

- Add 30s timeout to Stockfish evaluation to prevent hanging promises
- Add FEN validation and depth cap (max 30) to Stockfish API route
- Create ErrorBoundary component with specialized fallbacks for chess game and tutor
- Extract useChessSounds hook for better audio management
- Add React.memo to EvaluationBar and CapturedPieces for performance
- Add useMemo to CapturedPieces for sorted pieces calculation
- Improve tacticDetection to return empty array instead of "none" type
- Add filterMeaningfulTactics and hasTactics helper functions
- Translate hardcoded UI strings (stockfishLevel, download, evalChange)
- Update translations for EN, DE, FR, IT, PL
- Add uuid to Jest transformIgnorePatterns for ESM compatibility
- Update tests to use new filterMeaningfulTactics function

src/app/analysis/__tests__/page.test.tsx

@@ -31,10 +31,15 @@ jest.mock("@/lib/stockfish", () => {
 jest.mock("@/lib/tacticDetection", () => {
     const detectMissedTactics = jest.fn();
     const uciToSan = jest.fn();
+    const filterMeaningfulTactics = jest.fn((tactics) => {
+        if (!tactics) return [];
+        return tactics.filter((t: { tactic_type: string }) => t.tactic_type !== "none");
+    });
     return {
         __esModule: true,
         detectMissedTactics,
         uciToSan,
+        filterMeaningfulTactics,
         __mock: { detectMissedTactics, uciToSan },
     };
 });

src/app/analysis/page.tsx

@@ -12,7 +12,7 @@ import { useTranslation } from "@/lib/i18n/useTranslation";
 import { Personality, PERSONALITIES } from "@/lib/personalities";
 import { Stockfish, StockfishEvaluation } from "@/lib/stockfish";
 import { detectChessFormat, ChessFormat } from "@/lib/chessFormatDetector";
-import { detectMissedTactics, DetectedTactic, uciToSan } from "@/lib/tacticDetection";
+import { detectMissedTactics, DetectedTactic, uciToSan, filterMeaningfulTactics } from "@/lib/tacticDetection";
 import { lookupPossibleOpenings, buildMoveSequenceFromSteps, OpeningMetadata } from "@/lib/openings";
 import { getGenAIModel } from "@/lib/gemini";
 import { ChatSession } from "@google/generative-ai";
@@ -326,8 +326,7 @@ IMPORTANT:
                 const evalBefore = details.evalBefore!.score / 100;
                 const evalAfter = details.evalAfter!.score / 100;
                 const mateInfo = details.evalAfter!.mate !== null ? `Mate in ${details.evalAfter!.mate}` : "No mate detected";
-                const tactics = (details.missedTactics || [])
-                    .filter(t => t.tactic_type !== "none")
+                const tactics = filterMeaningfulTactics(details.missedTactics)
                     .map(t => `${t.tactic_type}${t.material_delta ? ` (~${(t.material_delta / 100).toFixed(1)} pawns)` : ""}`)
                     .join("; ") || "None";
 
@@ -406,7 +405,7 @@ INSTRUCTIONS:
     };
 
     const currentDetails = currentIndex > 0 ? stepDetails[currentIndex] : undefined;
-    const tacticSummary = (currentDetails?.missedTactics || []).filter(t => t.tactic_type !== "none");
+    const tacticSummary = filterMeaningfulTactics(currentDetails?.missedTactics);
 
     return (
         <div className="flex flex-col min-h-screen bg-gray-100 dark:bg-gray-900">

src/app/api/v1/stockfish/route.ts

@@ -1,9 +1,22 @@
 import { NextRequest, NextResponse } from "next/server";
 import { evaluateStockfish } from "@/lib/server/stockfishEngine";
 import { StockfishEvaluation } from "@/lib/stockfish";
+import { Chess } from "chess.js";
 
 export const runtime = "nodejs";
 
+/**
+ * Validates a FEN string by attempting to create a Chess instance
+ */
+function isValidFEN(fen: string): boolean {
+  try {
+    new Chess(fen);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
 export async function POST(request: NextRequest) {
   try {
     const body = await request.json();
@@ -13,6 +26,11 @@ export async function POST(request: NextRequest) {
       return NextResponse.json({ error: "Missing or invalid FEN" }, { status: 400 });
     }
 
+    // Validate FEN string format and chess position validity
+    if (!isValidFEN(fen)) {
+      return NextResponse.json({ error: "Invalid FEN: position is not a valid chess position" }, { status: 400 });
+    }
+
     const parsedDepth = Number(depth);
     const parsedMultiPV = Number(multiPV);
 
@@ -20,11 +38,15 @@ export async function POST(request: NextRequest) {
       return NextResponse.json({ error: "Depth must be a positive number" }, { status: 400 });
     }
 
+    // Cap depth to prevent excessive computation
+    const maxDepth = 30;
+    const safeDepth = Math.min(parsedDepth, maxDepth);
+
     if (!Number.isFinite(parsedMultiPV) || parsedMultiPV <= 0) {
       return NextResponse.json({ error: "multiPV must be a positive number" }, { status: 400 });
     }
 
-    const evaluation: StockfishEvaluation = await evaluateStockfish(fen, parsedDepth, parsedMultiPV);
+    const evaluation: StockfishEvaluation = await evaluateStockfish(fen, safeDepth, parsedMultiPV);
     return NextResponse.json({ evaluation });
   } catch (error) {
     console.error("Stockfish API error", error);