[gjwang]

将已实测、已公开的 LangChain 文档首读示例整理为可直接运行的 examples/langchain_docs.py，补齐英中 README 与 Agent 任务入口。读者通过 uv 直接运行，无需复制展示帖代码或准备模型、钱包、账户 key。

脚本只在原公开代码前增加 PEP 723 依赖声明，固定当前 langchain[mcp]1.4.9 / FastMCP4.1.6 / MCP2.3.0；保持普通 UA 默认、显式内部 QA 标记以及 beta 提示。README 命令关闭 LangSmith tracing。

验证：

• 新脚本与已公开版本完整 AST 相同，与原真实四次HTTP200观测的全部函数 AST 相同；新增元数据 TOML 可解析、Python 语法有效。
• 复用原 native0／两工具成功与公开 UA 分支检查；本次未重新安装依赖或发送产品请求，不冒新现场验收。
• 仅四文件，英中命令及范围一致，diff-check通过。

验收项: README 与 AGENTS 能直接定位运行文件；脚本依赖、beta及无模型首读边界清楚，不改现有示例与 TypeScript 路径。

Follow-up validation at 2026-11-07 16:19 UTC: downloaded the exact merged examples/langchain_docs.py from f6199662a459abebccba5c3451d80bf5e9a199e4 (SHA256 d0bc55c7698c166c8d859fc60c59bf5c264858d40b18cf49c4fc49e699baab18) into a fresh task directory and empty task-local uv cache. uv run --script --python 3.11 examples/langchain_docs.py completed with Python 3.11.14 and native exit 0: PEP 723 installed 86 packages, protocol 2026-07-28, exactly search_docs/read_doc, both successful, with the expected Quickstart result and non-empty document. The langchain.mcp beta warning remained visible. Total dependency setup plus execution was 5.76 seconds for this one run, not a performance benchmark.

The run used BLOCKVECTRA_INTERNAL_QA=1 and LANGSMITH_TRACING=false, no model, account, API key or chain RPC. It is internal first-use QA, not customer adoption. HTTP counts were not traced and are unknown; no four-request count is inferred from the earlier SDK run. Top-level dependency pins are not a complete transitive lock. The task environment was removed after retaining the resolved package list and raw output; no source or published file was changed.