examples: langchain-mainstreet-trust-gate — refuse payments below reputation threshold

typescript/examples/langchain-mainstreet-trust-gate/.env-local

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+CDP_API_KEY_ID=
+CDP_API_KEY_SECRET=
+OPENAI_API_KEY=
+MAINSTREET_MIN_SCORE=30

typescript/examples/langchain-mainstreet-trust-gate/README.md

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+# MainStreet Trust-Gate Chatbot
+
+This example demonstrates a buyer agent that **refuses to pay any wallet scoring below a configurable MainStreet reputation threshold**.
+
+## What it does
+
+```
+user → "send 1 USDC to 0xAbc..."
+       ↓
+tool: mainstreet_trust_check
+       ├── fetch /api/agent/attestation/0xAbc
+       ├── verify EIP-712 signature against MainStreet operator (0xAC3c...)
+       ├── check freshness (<24h)
+       └── check score >= MIN_SCORE (default 30)
+       ↓ (only if ok)
+tool: CDP erc20 transfer
+```
+
+If the wallet's MainStreet score is below threshold (or no attestation exists, or signature invalid), the agent refuses and explains why.
+
+## Why this matters
+
+CDP Bazaar lists 800+ AI agents on Base. Some are legitimate businesses settling thousands of USDC; some are throwaway wallets that drained LPs and disappeared. **Today AgentKit users can pay any of them.** A trust gate prevents users from paying low-rep wallets they wouldn't pay if they could see the score.
+
+MainStreet is an EIP-712 reputation oracle on Base. Free attestation fetch, free off-chain verify, onchain verifier contract live at [`0x7397adb9713934c36d22aa54b4dbbcd70263592b`](https://basescan.org/address/0x7397adb9713934c36d22aa54b4dbbcd70263592b).
+
+## Configuration
+
+```env
+CDP_API_KEY_ID=...
+CDP_API_KEY_SECRET=...
+OPENAI_API_KEY=...
+MAINSTREET_MIN_SCORE=30   # default 30/100; raise for stricter gate
+```
+
+## Run
+
+```bash
+npm install
+npm start
+```
+
+Try:
+
+```
+you: what's the MainStreet score for 0xAC3ca7c5d3cDD7702fd08F9C4C28dAA22296aDa9?
+you: send 0.01 USDC to 0xAC3ca7c5d3cDD7702fd08F9C4C28dAA22296aDa9
+you: send 0.01 USDC to 0x0000000000000000000000000000000000000001
+```
+
+The first known address will pass the gate; the second (no attestation) will be refused with `reason: "no attestation found"`.
+
+## How verification works
+
+MainStreet attestations follow EIP-712 with this schema:
+
+```
+Attestation(
+  string version,         // "mainstreet-v1"
+  string subjectType,     // "agent-onchain"
+  bytes32 subject,        // sha256(toLowerCase(address))
+  uint8 score,            // 0-100
+  uint64 timestamp,       // ≤24h old
+  address operator,       // 0xAC3ca7c5d3cDD7702fd08F9C4C28dAA22296aDa9
+  uint64 nonce
+)
+```
+
+Domain: `{ name: "MainStreet", version: "1", chainId: 8453 }`.
+
+For on-chain verification (smart contract gate), call the deployed `MainStreetVerifier.requireMinScore()` instead — see [avisradar.app/integrations.html](https://avisradar.app/integrations.html).
+
+## Resources
+
+- MainStreet oracle landing: <https://avisradar.app/oracle.html>
+- Catalog of paid endpoints: <https://avisradar.app/api/agent/catalog>
+- Integration recipes for 10+ Base ecosystem platforms: <https://avisradar.app/api/agent/integrate>
+- npm package: [`@raskhaaa/mainstreet-oracle`](https://www.npmjs.com/package/@raskhaaa/mainstreet-oracle) (includes `/verifier` helpers)
+- Open-source repo: <https://github.com/philpof102-svg/mainstreet>

typescript/examples/langchain-mainstreet-trust-gate/chatbot.ts

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+/**
+ * MainStreet Trust-Gate Chatbot — AgentKit example.
+ *
+ * Demonstrates a buyer agent that REFUSES to pay any wallet scoring below
+ * a configurable MainStreet threshold. The reputation lookup is free; the
+ * payment only happens when score >= MIN_SCORE.
+ *
+ * Pattern:
+ *   user → "send 1 USDC to 0xAbc..."
+ *   ↓
+ *   tool: mainstreet_score_check → fetch + verify EIP-712 attestation
+ *   ↓ (score >= MIN_SCORE)
+ *   tool: native CDP transfer
+ *
+ * MainStreet docs: https://avisradar.app/oracle.html
+ * Deployed verifier on Base: 0x7397adb9713934c36d22aa54b4dbbcd70263592b
+ */
+import * as dotenv from "dotenv";
+import { ChatOpenAI } from "@langchain/openai";
+import { HumanMessage } from "@langchain/core/messages";
+import { MemorySaver } from "@langchain/langgraph";
+import { createReactAgent } from "@langchain/langgraph/prebuilt";
+import { AgentKit, walletActionProvider, erc20ActionProvider, CdpEvmWalletProvider } from "@coinbase/agentkit";
+import { getLangChainTools } from "@coinbase/agentkit-langchain";
+import { recoverTypedDataAddress } from "viem";
+import { tool } from "@langchain/core/tools";
+import { z } from "zod";
+
+dotenv.config();
+
+const MIN_SCORE = parseInt(process.env.MAINSTREET_MIN_SCORE || "30", 10);
+const MS_SIGNER = "0xAC3ca7c5d3cDD7702fd08F9C4C28dAA22296aDa9";
+
+const mainstreetTrustCheck = tool(
+  async ({ address }: { address: string }) => {
+    const att = await fetch(`https://avisradar.app/api/agent/attestation/${address}`).then((r) => r.json());
+    if (!att.payload) return JSON.stringify({ ok: false, reason: "no attestation found" });
+    const recovered = await recoverTypedDataAddress({
+      domain: att.eip712.domain,
+      types: att.eip712.types,
+      primaryType: "Attestation",
+      message: att.payload,
+      signature: att.signature,
+    });
+    if (recovered.toLowerCase() !== MS_SIGNER.toLowerCase()) return JSON.stringify({ ok: false, reason: "signature invalid" });
+    const ageSec = Math.floor(Date.now() / 1000) - Number(att.payload.timestamp);
+    if (ageSec > 86400) return JSON.stringify({ ok: false, reason: "attestation stale (>24h)" });
+    if (att.payload.score < MIN_SCORE)
+      return JSON.stringify({ ok: false, reason: `score ${att.payload.score} < ${MIN_SCORE}` });
+    return JSON.stringify({ ok: true, score: att.payload.score, tier: att.payload.score >= 60 ? "high" : "medium" });
+  },
+  {
+    name: "mainstreet_trust_check",
+    description: `Check MainStreet reputation BEFORE paying any wallet. Verifies an EIP-712 signed attestation. Returns {ok, score, tier} or {ok: false, reason}. Use this BEFORE every transfer/swap. Free.`,
+    schema: z.object({ address: z.string().describe("0x-prefixed wallet to check") }),
+  }
+);
+
+async function main() {
+  const walletProvider = await CdpEvmWalletProvider.configureWithWallet({
+    apiKeyId: process.env.CDP_API_KEY_ID!,
+    apiKeySecret: process.env.CDP_API_KEY_SECRET!,
+    networkId: "base-mainnet",
+  });
+  const agentkit = await AgentKit.from({
+    walletProvider,
+    actionProviders: [walletActionProvider(), erc20ActionProvider()],
+  });
+  const tools = [...(await getLangChainTools(agentkit)), mainstreetTrustCheck];
+  const agent = createReactAgent({
+    llm: new ChatOpenAI({ model: "gpt-4o-mini", temperature: 0 }),
+    tools,
+    checkpointer: new MemorySaver(),
+    messageModifier: `You are a careful onchain payment agent. NEVER send funds to an address without first calling mainstreet_trust_check. If the check returns ok:false, refuse the transfer and explain why.`,
+  });
+  const config = { configurable: { thread_id: "mainstreet-trust-gate" } };
+  console.log(`MainStreet Trust-Gate active. MIN_SCORE=${MIN_SCORE}. Type a request or "exit".`);
+  const readline = await import("node:readline/promises");
+  const rl = readline.createInterface({ input: process.stdin, output: process.stdout });
+  for (;;) {
+    const userInput = await rl.question("\nyou: ");
+    if (!userInput || userInput.trim().toLowerCase() === "exit") break;
+    const stream = await agent.stream({ messages: [new HumanMessage(userInput)] }, config);
+    for await (const chunk of stream) {
+      if ("agent" in chunk) console.log("\nagent:", chunk.agent.messages[chunk.agent.messages.length - 1].content);
+      else if ("tools" in chunk) console.log("\ntool:", chunk.tools.messages[0].content);
+    }
+  }
+  rl.close();
+}
+
+main().catch((e) => { console.error(e); process.exit(1); });

typescript/examples/langchain-mainstreet-trust-gate/package.json

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+{
+  "name": "@coinbase/agentkit-langchain-mainstreet-trust-gate-example",
+  "description": "AgentKit example — gate x402 payments by MainStreet reputation score before sending USDC",
+  "version": "1.0.0",
+  "private": true,
+  "author": "Coinbase Inc.",
+  "license": "Apache-2.0",
+  "scripts": {
+    "start": "NODE_OPTIONS='--no-warnings' tsx ./chatbot.ts",
+    "dev": "nodemon ./chatbot.ts"
+  },
+  "dependencies": {
+    "@coinbase/agentkit": "workspace:*",
+    "@coinbase/agentkit-langchain": "workspace:*",
+    "@langchain/core": "^1.1.0",
+    "@langchain/langgraph": "^1.2.0",
+    "@langchain/openai": "^1.2.0",
+    "dotenv": "^16.4.5",
+    "langchain": "^1.1.0",
+    "viem": "^2.0.0",
+    "zod": "^4.0.0"
+  },
+  "devDependencies": {
+    "nodemon": "^3.1.0",
+    "tsx": "^4.7.1"
+  }
+}

typescript/examples/langchain-mainstreet-trust-gate/tsconfig.json

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+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "preserveSymlinks": true,
+    "outDir": "./dist",
+    "rootDir": "."
+  },
+  "include": ["*.ts"]
+}