langfuse-local-dev-loop

# Langfuse Local Dev Loop ## Overview Fast local development workflow with Langfuse tracing, immediate trace visibility, debug logging, and optional self-hosted local instance via Docker. ## Prerequisites - Completed `langfuse-install-auth` setup - Node.js 18+ with `tsx` for hot reload (`npm install -D tsx`) - Docker (optional, for self-hosted local instance) ## Instructions ### Step 1: Development Environment File ```bash # .env.local (git-ignored) LANGFUSE_PUBLIC_KEY=pk-lf-dev-... LANGFUSE_SECRET_KEY=sk-lf-dev-... LANGFUSE_BASE_URL=https://cloud.langfuse.com # Dev-specific settings NODE_ENV=development OPENAI_API_KEY=sk-... ``` ### Step 2: Dev-Optimized Langfuse Setup (v4+) ```typescript // src/lib/langfuse-dev.ts import { LangfuseSpanProcessor } from "@langfuse/otel"; import { NodeSDK } from "@opentelemetry/sdk-node"; import { LangfuseClient } from "@langfuse/client"; const isDev = process.env.NODE_ENV !== "production"; // Configure span processor with dev-friendly settings const processor = new LangfuseSpanProcessor({ // In dev: flush immediately for instant visibility ...(isDev && { exportIntervalMillis: 1000, maxExportBatchSize: 1 }), }); const sdk = new NodeSDK({ spanProcessors: [processor] }); sdk.start(); export const langfuse = new LangfuseClient(); // Print trace URLs in development export function logTrace(traceId: string) { if (isDev) { const host = process.env.LANGFUSE_BASE_URL || "https://cloud.langfuse.com"; console.log(`\n Trace: $...