feat(frontend): client-side result caching (5min TTL)

frontend/src/api.ts

@@ -3,6 +3,8 @@
 const API_URL = import.meta.env.VITE_API_URL || "";
 
 const TIMEOUT_MS = 120_000;
+const CACHE_TTL_MS = 5 * 60 * 1000;
+const cache = new Map<string, { data: AnalysisResult; timestamp: number }>();
 
 export interface Violation {
   rule: string;
@@ -36,7 +38,29 @@ export interface AnalysisResult {
   metrics: Metrics;
 }
 
+function cacheKey(repoUrl: string, branch: string): string {
+  return `${repoUrl.trim().toLowerCase()}@${branch.trim()}`
+}
+
+function getCached(repoUrl: string, branch: string): AnalysisResult | null {
+  const key = cacheKey(repoUrl, branch)
+  const entry = cache.get(key)
+  if (entry && Date.now() - entry.timestamp < CACHE_TTL_MS) {
+    return entry.data
+  }
+  cache.delete(key)
+  return null
+}
+
+function setCache(repoUrl: string, branch: string, data: AnalysisResult): void {
+  const key = cacheKey(repoUrl, branch)
+  cache.set(key, { data, timestamp: Date.now() })
+}
+
 export async function analyze(repoUrl: string, branch: string): Promise<AnalysisResult> {
+  const cached = getCached(repoUrl, branch)
+  if (cached) return cached
+
   const controller = new AbortController();
   const timeout = setTimeout(() => controller.abort(), TIMEOUT_MS);
 
@@ -51,7 +75,9 @@ export async function analyze(repoUrl: string, branch: string): Promise<Analysis
       const error = await resp.json().catch(() => ({ detail: resp.statusText }));
       throw new Error(error.detail || `HTTP ${resp.status}`);
     }
-    return resp.json();
+    const data: AnalysisResult = await resp.json()
+    setCache(repoUrl, branch, data)
+    return data
   } catch (err) {
     if (err instanceof DOMException && err.name === "AbortError") {
       throw new Error(`Request timed out after ${TIMEOUT_MS / 1000}s — the repository may be too large or unreachable`);