Setup errors

Say what is missing and the command that fixes it, in a field a machine can read too.

Two shapes every CLI ends up needing, both saying what is missing and the command that fixes it:

// app/publish/data.tsx
import { authRequired, missingTool, type CmdProps } from 'decopin-cli';

export default function Data({ env }: CmdProps<'publish'>) {
  if (env.DECOPIN_TOKEN === undefined) {
    authRequired({ service: 'the registry', fix: 'export DECOPIN_TOKEN=…' });
  }
  if (Bun.which('cosign') === null) {
    missingTool({
      tool: 'cosign',
      reason: 'to sign the package',
      install: 'brew install cosign',
    });
  }
  return { published: true };
}

$ ./dist/index.js publish
Setup needed: Not authenticated to the registry
  export DECOPIN_TOKEN=…

These are ordinary errors, so they travel the error.tsx path and can be branched on with error.kind ('auth' / 'missing-tool'). The fix lines live on error.hints, and they reach --json as well:

{
  "error": {
    "code": "auth",
    "message": "Not authenticated to the registry",
    "exitCode": 1,
    "hints": ["export DECOPIN_TOKEN=…"]
  }
}

That last part is the point. A person reading gh auth login knows what to do next; an agent needs the same thing in a field it can read, which is why hints are not only formatting.