AI-281: add @temporalio/langsmith samples

Four scenarios demonstrating the @temporalio/langsmith plugin:
activity-tracing, workflow-tracing, agent-pipeline, and message-handlers.
Each includes a worker, client, workflows, a mocha test, and a README.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: xumaple

.github/workflows/ci.yml

@@ -61,6 +61,7 @@ jobs:
             early-return
             empty
             hello-world
+            langsmith
             mutex
             nestjs-exchange-rates
             sleep-for-days

.scripts/list-of-samples.json

@@ -25,6 +25,7 @@
     "hello-world-mtls",
     "interceptors-opentelemetry",
     "lambda-worker",
+    "langsmith",
     "monorepo-folders",
     "mutex",
     "nestjs-exchange-rates",

README.md

@@ -155,6 +155,7 @@ and you'll be given the list of sample options.
   - [**OpenTelemetry**](./interceptors-opentelemetry): Use the Interceptors feature to add OpenTelemetry metrics reporting to your workflows.
   - [**Query Subscriptions**](./query-subscriptions): Use Redis Streams, Immer, and SDK Interceptors to subscribe to Workflow state.
 - [**gRPC calls**](./grpc-calls): Make raw gRPC calls for advanced queries not covered by the WorkflowClient API.
+- [**LangSmith**](./langsmith): Trace Workflows and Activities to [LangSmith](https://www.langchain.com/langsmith) using the `@temporalio/langsmith` plugin.
 
 #### Test APIs
 

langsmith/.eslintignore

@@ -0,0 +1,3 @@
+node_modules
+lib
+.eslintrc.js

langsmith/.eslintrc.js

@@ -0,0 +1,48 @@
+const { builtinModules } = require('module');
+
+const ALLOWED_NODE_BUILTINS = new Set(['assert']);
+
+module.exports = {
+  root: true,
+  parser: '@typescript-eslint/parser',
+  parserOptions: {
+    project: './tsconfig.json',
+    tsconfigRootDir: __dirname,
+  },
+  plugins: ['@typescript-eslint', 'deprecation'],
+  extends: [
+    'eslint:recommended',
+    'plugin:@typescript-eslint/eslint-recommended',
+    'plugin:@typescript-eslint/recommended',
+    'prettier',
+  ],
+  rules: {
+    // recommended for safety
+    '@typescript-eslint/no-floating-promises': 'error', // forgetting to await Activities and Workflow APIs is bad
+    'deprecation/deprecation': 'warn',
+
+    // code style preference
+    'object-shorthand': ['error', 'always'],
+
+    // relaxed rules, for convenience
+    '@typescript-eslint/no-unused-vars': [
+      'warn',
+      {
+        argsIgnorePattern: '^_',
+        varsIgnorePattern: '^_',
+      },
+    ],
+    '@typescript-eslint/no-explicit-any': 'off',
+  },
+  overrides: [
+    {
+      files: ['src/workflows.ts', 'src/workflows-*.ts', 'src/workflows/*.ts'],
+      rules: {
+        'no-restricted-imports': [
+          'error',
+          ...builtinModules.filter((m) => !ALLOWED_NODE_BUILTINS.has(m)).flatMap((m) => [m, `node:${m}`]),
+        ],
+      },
+    },
+  ],
+};

langsmith/.gitignore

@@ -0,0 +1,2 @@
+lib
+node_modules

langsmith/.npmrc

@@ -0,0 +1 @@
+package-lock=false

langsmith/.nvmrc

@@ -0,0 +1 @@
+22

langsmith/.post-create

@@ -0,0 +1,20 @@
+To begin development, install the Temporal CLI:
+
+Mac: {cyan brew install temporal}
+Other: Download and extract the latest release from https://github.com/temporalio/cli/releases/latest
+
+Start Temporal Server:
+
+{cyan temporal server start-dev}
+
+Use Node version 18+ (v22.x is recommended):
+
+Mac: {cyan brew install node@22}
+Other: https://nodejs.org/en/download/
+
+To see live traces in LangSmith, enable tracing:
+
+{cyan export LANGSMITH_TRACING=true}
+{cyan export LANGSMITH_API_KEY=...}
+
+Then run a scenario by path (see each scenario's README).

langsmith/.prettierignore

@@ -0,0 +1 @@
+lib