Depurar JSON-RPC con cast

# Ethereum RPC + Cast debugging

Version: `2.0.44-alpha.1`

## Boundary

Use only `http://127.0.0.1:8545` with an ephemeral Anvil instance. Never paste a personal private key or public RPC credential.

## Start

```powershell
node tools/labs/ethereum-rpc-cast-debugging/preflight.mjs
anvil --host 127.0.0.1 --port 8545 --chain-id 31337
```

In a second terminal:

```powershell
$env:RPC_URL="http://127.0.0.1:8545"
cast chain-id --rpc-url $env:RPC_URL
cast block-number --rpc-url $env:RPC_URL
cast rpc eth_getBlockByNumber latest false --rpc-url $env:RPC_URL
```

Bash equivalent:

```bash
export RPC_URL="http://127.0.0.1:8545"
cast chain-id --rpc-url $RPC_URL
cast block-number --rpc-url $RPC_URL
cast rpc eth_getBlockByNumber latest false --rpc-url $RPC_URL
```

Then provoke one failure per layer:

```bash
cast block-number --rpc-url http://127.0.0.1:8546            # transport: Connection refused
cast rpc eth_foo --rpc-url $RPC_URL                           # JSON-RPC: -32601 Method not found
cast rpc eth_call '{"data":"0x60006000fd"}' latest --rpc-url $RPC_URL   # EVM: code 3 execution reverted
```

Record endpoint, method, parameters, result or error, and the layer responsible: transport, JSON-RPC, or EVM.

## Cleanup

Stop Anvil with `Ctrl+C` and remove `RPC_URL` from the environment (`unset RPC_URL` in Bash).

import { spawnSync } from 'node:child_process';
import net from 'node:net';

const commands = ['anvil', 'cast'];
const versions = Object.fromEntries(
  commands.map((command) => {
    const result = spawnSync(command, ['--version'], { encoding: 'utf8' });
    return [command, { available: result.status === 0, version: (result.stdout || result.stderr || result.error?.message || '').trim().split('\n')[0] }];
  })
);

const rpcUrl = process.env.RPC_URL ?? '';
const rpcSafe = !rpcUrl || /^https?:\/\/(127\.0\.0\.1|localhost)(:\d+)?\/?$/i.test(rpcUrl);
const portFree = await new Promise((resolve) => {
  const server = net.createServer();
  server.once('error', () => resolve(false));
  server.listen(8545, '127.0.0.1', () => server.close(() => resolve(true)));
});

const report = { versions, rpcUrl: rpcUrl || '(unset)', rpcSafe, port8545Free: portFree };
console.log(JSON.stringify(report, null, 2));

if (commands.some((command) => !versions[command].available) || !rpcSafe) process.exit(1);

unset RPC_URL