[app-server] expose environment info RPC (#30291)

## 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:

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

Successful response:

```json
{
  "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:

```json
{
  "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.

---------

Co-authored-by: Michael Bolin <mbolin@openai.com>

codex-rs/app-server/src/message_processor.rs

@@ -1037,6 +1037,9 @@ impl MessageProcessor {
             ClientRequest::EnvironmentAdd { params, .. } => {
                 self.environment_processor.environment_add(params).await
             }
+            ClientRequest::EnvironmentInfo { params, .. } => {
+                self.environment_processor.environment_info(params).await
+            }
             ClientRequest::FsReadFile { params, .. } => self
                 .fs_processor
                 .read_file(params)

codex-rs/app-server/src/request_processors.rs

@@ -62,6 +62,9 @@ use codex_app_server_protocol::DynamicToolNamespaceTool;
 use codex_app_server_protocol::DynamicToolSpec;
 use codex_app_server_protocol::EnvironmentAddParams;
 use codex_app_server_protocol::EnvironmentAddResponse;
+use codex_app_server_protocol::EnvironmentInfoParams;
+use codex_app_server_protocol::EnvironmentInfoResponse;
+use codex_app_server_protocol::EnvironmentShellInfo;
 use codex_app_server_protocol::ExperimentalFeature as ApiExperimentalFeature;
 use codex_app_server_protocol::ExperimentalFeatureListParams;
 use codex_app_server_protocol::ExperimentalFeatureListResponse;

codex-rs/app-server/src/request_processors/environment_processor.rs

@@ -26,4 +26,30 @@ impl EnvironmentRequestProcessor {
             .map_err(|err| invalid_request(err.to_string()))?;
         Ok(Some(EnvironmentAddResponse {}.into()))
     }
+
+    pub(crate) async fn environment_info(
+        &self,
+        params: EnvironmentInfoParams,
+    ) -> Result<Option<ClientResponsePayload>, JSONRPCErrorError> {
+        let environment_id = params.environment_id;
+        let environment = self
+            .environment_manager
+            .get_environment(&environment_id)
+            .ok_or_else(|| invalid_request(format!("unknown environment id `{environment_id}`")))?;
+        let info = environment.info().await.map_err(|err| {
+            internal_error(format!(
+                "failed to get info for environment `{environment_id}`: {err}"
+            ))
+        })?;
+        Ok(Some(
+            EnvironmentInfoResponse {
+                shell: EnvironmentShellInfo {
+                    name: info.shell.name,
+                    path: info.shell.path,
+                },
+                cwd: info.cwd,
+            }
+            .into(),
+        ))
+    }
 }