feat: add goldrush skill for blockchain data across 100+ chains

skills/goldrush/SKILL.md

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+---
+name: goldrush
+description: |
+  Query blockchain data across 100+ chains using the GoldRush API by Covalent. Use this skill when you need wallet token balances, transaction history, NFT holdings, token prices, DEX pair data, real-time OHLCV price feeds, or any on-chain data. Supports REST API, real-time WebSocket streams, CLI, and x402 pay-per-request access without signup.
+---
+
+# GoldRush Blockchain Data
+
+## Overview
+GoldRush by Covalent provides blockchain data across 100+ chains through a unified REST API, real-time WebSocket streams, a CLI, and an x402 pay-per-request proxy. Use this skill to query on-chain data including wallet balances, token prices, transaction history, NFT holdings, and DEX pairs.
+
+## When to Use This Skill
+- Querying wallet token balances or portfolio value across chains
+- Fetching transaction history for an address
+- Getting current or historical token prices
+- Monitoring DEX pairs and liquidity data
+- Streaming real-time OHLCV price feeds via WebSocket
+- Building blockchain explorers, portfolio dashboards, or DeFi analytics tools
+- Accessing on-chain data with pay-per-request (no signup required via x402)
+
+## How It Works
+
+### Step 1: Get an API key
+Sign up at https://goldrush.dev for a free API key, or use x402 pay-per-request for no-signup access.
+
+### Step 2: Choose your access method
+- **REST API** — `https://api.covalenthq.com/v1/` — HTTP requests with `Authorization: Bearer YOUR_API_KEY`
+- **WebSocket** — Real-time streams for OHLCV price feeds and DEX pair monitoring
+- **CLI** — `npx @covalenthq/goldrush-cli` for terminal queries
+- **x402** — Pay-per-request proxy, agent-native, no API key required
+
+### Step 3: Make a query
+
+```bash
+# Get token balances for a wallet on Ethereum
+curl -H "Authorization: Bearer $GOLDRUSH_API_KEY"   "https://api.covalenthq.com/v1/eth-mainnet/address/0xYOUR_ADDRESS/balances_v2/"
+```
+
+```javascript
+// Using the GoldRush SDK
+import GoldRushClient from "@covalenthq/client-sdk";
+
+const client = new GoldRushClient(process.env.GOLDRUSH_API_KEY);
+const resp = await client.BalanceService.getTokenBalancesForWalletAddress(
+  "eth-mainnet",
+  "0xYOUR_ADDRESS"
+);
+```
+
+## Examples
+
+### Example 1: Wallet Token Balances
+```bash
+curl -H "Authorization: Bearer $GOLDRUSH_API_KEY"   "https://api.covalenthq.com/v1/eth-mainnet/address/0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045/balances_v2/"
+```
+
+### Example 2: Token Price History
+```bash
+curl -H "Authorization: Bearer $GOLDRUSH_API_KEY"   "https://api.covalenthq.com/v1/pricing/historical_by_addresses_v2/eth-mainnet/USD/0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48/"
+```
+
+### Example 3: Real-time DEX Pairs via CLI
+```bash
+npx @covalenthq/goldrush-cli stream dex-pairs --chain eth-mainnet
+```
+
+### Example 4: x402 Pay-per-request (no API key needed)
+```bash
+# Agent-native access — pay with USDC on Base
+npx @covalenthq/goldrush-cli --x402
+```
+
+## Best Practices
+- Use chain slugs like `eth-mainnet`, `matic-mainnet`, `base-mainnet` — full list at https://goldrush.dev/docs/networks
+- Cache responses where possible — balance data updates every block (~12s on Ethereum)
+- Use WebSocket streams for real-time data instead of polling REST
+- Store your API key in `GOLDRUSH_API_KEY` environment variable, never hardcode it
+- Use SDK cursor pagination rather than manual offset pagination
+
+## Common Pitfalls
+
+**Problem:** 401 Unauthorized  
+**Solution:** Ensure the API key is in the `Authorization: Bearer` header
+
+**Problem:** Unknown chain name  
+**Solution:** Use the chain slug format (e.g., `eth-mainnet`) — see https://goldrush.dev/docs/networks
+
+## Additional Resources
+- Docs: https://goldrush.dev/docs
+- npm MCP server: https://www.npmjs.com/package/@covalenthq/goldrush-mcp-server
+- Agent Skills: https://github.com/covalenthq/goldrush-agent-skills
+- Smithery: https://smithery.ai/server/covalenthq/goldrush-foundational-api