[app-server] expose environment info RPC

[maxj-oai]

Why

App-server clients that configure named execution environments need to discover an environment's shell and working directory before selecting it for a thread or turn. Because the environment can run on a different operating system than app-server, its working directory is represented as a canonical file: URI rather than a host-local path string. The probe also needs a bounded response time: an exec-server that completes initialization but never answers environment/info must not hold the environment serialization queue indefinitely.

What changed

• Add an experimental environment/info app-server RPC for named environments.
• Route the probe through the managed environment connection and return target-native shell metadata plus the default working directory as a PathUri.
• Return connection and protocol failures as JSON-RPC errors.
• Bound the exec-server probe response to 30 seconds and remove timed-out calls from the pending-request table so later environment mutations can proceed.
• Cover successful responses, omitted working directories, unknown environments, connection failures, and pending-call cleanup.

Protocol examples

Request:

{
  "id": 42,
  "method": "environment/info",
  "params": {
    "environmentId": "remote-a"
  }
}

Successful response:

{
  "id": 42,
  "result": {
    "shell": {
      "name": "zsh",
      "path": "/bin/zsh"
    },
    "cwd": "file:///workspace"
  }
}

If the exec-server initializes but does not answer the probe within 30 seconds:

{
  "id": 42,
  "error": {
    "code": -32603,
    "message": "failed to get info for environment `remote-a`: exec-server protocol error: timed out waiting for exec-server `environment/info` response after 30s"
  }
}

Testing

• App-server integration coverage for successful info (including omitted cwd), unknown environments, and connection failures.
• Exec-server RPC coverage verifying a timed-out call is removed from the pending-request table.