Add cached Langfuse PromptService

src/core/langfuse/PromptGateway.ts

@@ -0,0 +1,10 @@
+export interface RawPrompt {
+  name: string;
+  version: number;
+  config: Record<string, unknown>;
+  compile(variables: Record<string, unknown>): { role: 'system' | 'user' | 'assistant'; content: string }[];
+}
+
+export interface PromptFetcher {
+  fetch(promptName: string): Promise<RawPrompt>;
+}

src/core/langfuse/PromptService.ts

@@ -0,0 +1,46 @@
+import type { PromptFetcher, RawPrompt } from './PromptGateway';
+import type { CompiledPrompt } from './types';
+
+interface CacheEntry {
+  raw: RawPrompt;
+  fetchedAt: number;
+}
+
+export class PromptService {
+  private readonly cache = new Map<string, CacheEntry>();
+
+  constructor(
+    private readonly fetcher: PromptFetcher,
+    private readonly cacheEnabled: boolean
+  ) {}
+
+  async getCompiled(promptName: string, variables: Record<string, unknown>): Promise<CompiledPrompt> {
+    const raw = await this.getRaw(promptName);
+    return {
+      name: raw.name,
+      version: raw.version,
+      config: raw.config,
+      messages: raw.compile(variables),
+    };
+  }
+
+  invalidate(promptName?: string): void {
+    if (promptName) {
+      this.cache.delete(promptName);
+    } else {
+      this.cache.clear();
+    }
+  }
+
+  private async getRaw(promptName: string): Promise<RawPrompt> {
+    if (this.cacheEnabled) {
+      const cached = this.cache.get(promptName);
+      if (cached) return cached.raw;
+    }
+    const raw = await this.fetcher.fetch(promptName);
+    if (this.cacheEnabled) {
+      this.cache.set(promptName, { raw, fetchedAt: Date.now() });
+    }
+    return raw;
+  }
+}

src/core/langfuse/types.ts

@@ -0,0 +1,6 @@
+export interface CompiledPrompt {
+  name: string;
+  version: number;
+  config: Record<string, unknown>;
+  messages: { role: 'system' | 'user' | 'assistant'; content: string }[];
+}