langchain-migration-deep-dive

# LangChain Migration Deep Dive ## Current State !`npm list 2>/dev/null | grep -E "openai|langchain|llamaindex" | head -10` ## Overview Migrate from raw SDK calls (OpenAI, Anthropic) or other frameworks (LlamaIndex, custom agents) to LangChain. Covers codebase scanning, pattern-by-pattern migration, side-by-side validation, and feature-flagged rollout. ## Step 1: Assess Codebase ```typescript // Scan for migration targets import * as fs from "fs"; import * as path from "path"; interface MigrationItem { file: string; line: number; pattern: string; complexity: "low" | "medium" | "high"; } function scanForMigration(dir: string): MigrationItem[] { const items: MigrationItem[] = []; const patterns = [ { regex: /openai\.chat\.completions\.create/g, name: "OpenAI direct call", complexity: "low" as const }, { regex: /new OpenAI\(/g, name: "OpenAI SDK init", complexity: "low" as const }, { regex: /anthropic\.messages\.create/g, name: "Anthropic direct call", complexity: "low" as const }, { regex: /from llama_index/g, name: "LlamaIndex import", complexity: "medium" as const }, { regex: /VectorStoreIndex/g, name: "LlamaIndex vector store", complexity: "high" as const }, { regex: /function_call|tool_choice/g, name: "Manual tool calling", complexity: "high" as const }, ]; // Recursive file scan function scan(dir: string) { for (const entry of fs.readdirSync(dir, { withFileTypes: true })) { if (entry.isDirectory() && !entry.name....