Create BATS tests for limactl-mcp

[jandubois]

I had an idea how to test limactl-mcp with BATS, so I wrote this PoC. I think it works well, but must obviously be fleshed out some more.

This PR depends on #3744 and assumes it has been merged already.

[jandubois]

One thing I found while writing the test was that run_shell_command returns an object that has additional JSON embedded as a string:

$ echo '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"run_shell_command","arguments":{"command":["cat","os-release"],"directory":"/etc"}}}' >&"${MCP[1]}"

$ read -t 1 -r line <&"${MCP[0]}"; jq . <<<"$line"
{
  "jsonrpc": "2.0",
  "id": 3,
  "result": {
    "content": [
      {
        "type": "text",
        "text": "{\"stdout\":\"PRETTY_NAME=\\\"Ubuntu 25.04\\\"\\nNAME=\\\"Ubuntu\\\"\\nVERSION_ID=\\\"25.04\\\"\\nVERSION=\\\"25.04 (Plucky Puffin)\\\"\\nVERSION_CODENAME=plucky\\nID=ubuntu\\nID_LIKE=debian\\nHOME_URL=\\\"https://www.ubuntu.com/\\\"\\nSUPPORT_URL=\\\"https://help.ubuntu.com/\\\"\\nBUG_REPORT_URL=\\\"https://bugs.launchpad.net/ubuntu/\\\"\\nPRIVACY_POLICY_URL=\\\"https://www.ubuntu.com/legal/terms-and-policies/privacy-policy\\\"\\nUBUNTU_CODENAME=plucky\\nLOGO=ubuntu-logo\\n\",\"stderr\":\"\",\"exit_code\":0}"
      }
    ]
  }
}

So you need to extract .text, unmarshall the result into JSON and then extract .stdout, which is quite cumbersome. I don't know if this will bother an LLM, but doesn't this also increase the number of tokens used for the content by escaping all the quotes and backslashes?

Is there a reason this can't be a normal nested object?

[jandubois]

Beyond the encoded JSON thing, I don't understand the schema of the output: Why is content an array? I don't understand how there can be more than one set of results given that the tool only accepts a single command.

And what does type: text mean? Especially given that text is a json string. Could it also be object? Isn't this all too complex for a tool command?

So I would expect the output of run_shell_command to look more like this:

{
  "jsonrpc": "2.0",
  "id": 3,
  "result": {
    "stdout": "...",
    "stderr": "",
    "exit_code": 0
  }
}