feat(02-03): create model caching utility

Add in-memory cache for provider model lists with 10-minute TTL.
Includes get/set/invalidate functions and cache key generation.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/lib/providers/cache.ts

@@ -0,0 +1,116 @@
+/**
+ * Model Caching Utility
+ *
+ * Simple in-memory cache for model lists from providers.
+ * Reduces API calls to external providers by caching results with TTL.
+ *
+ * Features:
+ * - 10-minute default TTL
+ * - Per-provider cache keys
+ * - Optional search query in cache key
+ * - Manual invalidation support
+ *
+ * Note: Cache is cleared on server restart (no persistence).
+ */
+
+import { ProviderModel } from "./types";
+import { ProviderType } from "@/types";
+
+/**
+ * Cache entry with data and timestamp
+ */
+interface CacheEntry<T> {
+  data: T;
+  timestamp: number;
+}
+
+/**
+ * Default cache TTL: 10 minutes
+ */
+const DEFAULT_TTL = 10 * 60 * 1000;
+
+/**
+ * In-memory cache storage
+ */
+const cache: Map<string, CacheEntry<ProviderModel[]>> = new Map();
+
+/**
+ * Get cached models for a key if not expired
+ *
+ * @param key - Cache key (use getCacheKey to generate)
+ * @param ttl - Optional custom TTL in milliseconds
+ * @returns Cached models or null if not in cache or expired
+ */
+export function getCachedModels(
+  key: string,
+  ttl: number = DEFAULT_TTL
+): ProviderModel[] | null {
+  const entry = cache.get(key);
+
+  if (!entry) {
+    return null;
+  }
+
+  const now = Date.now();
+  if (now - entry.timestamp > ttl) {
+    // Cache expired, remove entry
+    cache.delete(key);
+    return null;
+  }
+
+  return entry.data;
+}
+
+/**
+ * Store models in cache with current timestamp
+ *
+ * @param key - Cache key (use getCacheKey to generate)
+ * @param models - Models to cache
+ */
+export function setCachedModels(key: string, models: ProviderModel[]): void {
+  cache.set(key, {
+    data: models,
+    timestamp: Date.now(),
+  });
+}
+
+/**
+ * Invalidate cache entries
+ *
+ * @param key - Optional specific key to invalidate. If not provided, clears entire cache.
+ */
+export function invalidateCache(key?: string): void {
+  if (key) {
+    cache.delete(key);
+  } else {
+    cache.clear();
+  }
+}
+
+/**
+ * Generate a cache key for provider models
+ *
+ * @param provider - Provider type
+ * @param search - Optional search query
+ * @returns Cache key string
+ *
+ * @example
+ * getCacheKey("replicate")           // "replicate:models"
+ * getCacheKey("fal", "flux")         // "fal:search:flux"
+ */
+export function getCacheKey(provider: ProviderType, search?: string): string {
+  if (search) {
+    return `${provider}:search:${search}`;
+  }
+  return `${provider}:models`;
+}
+
+/**
+ * Get cache statistics (for debugging)
+ */
+export function getCacheStats(): { size: number; keys: string[] } {
+  return {
+    size: cache.size,
+    keys: Array.from(cache.keys()),
+  };
+}