# Synthetic MCP fixture

`server.mjs` is a dependency-free stdio MCP server containing only synthetic
data. It advertises `echo` and `slugify`. With `FIXTURE_V2=1`, it removes
`slugify` and makes `echo.prefix` required, providing a stable breaking-change
probe for CI.

Build the CLI, then use any MCP client to drive the record command:

```bash
npm run build
node dist/cli.js record -o .dsh-echo/example.cassette.jsonl -- \
  node examples/fixture/server.mjs
```

Replay does not start the fixture server:

```bash
node dist/cli.js replay .dsh-echo/example.cassette.jsonl
```

Contract example:

```bash
node dist/cli.js snapshot --stdio "node examples/fixture/server.mjs" \
  -f /tmp/example.snapshot.json
node dist/cli.js snapshot --check --fail-on breaking \
  --stdio "env FIXTURE_V2=1 node examples/fixture/server.mjs" \
  -f /tmp/example.snapshot.json
```

The second command must exit with status 1 and report both a removed tool and a
new required property.