cloud: status, diff, apply (#7614)

Adds cli commands for getting the status of cloud tasks, and for
getting/applying the diffs from same.

codex-rs/cloud-tasks-client/src/mock.rs

@@ -1,6 +1,7 @@
 use crate::ApplyOutcome;
 use crate::AttemptStatus;
 use crate::CloudBackend;
+use crate::CloudTaskError;
 use crate::DiffSummary;
 use crate::Result;
 use crate::TaskId;
@@ -60,6 +61,14 @@ impl CloudBackend for MockClient {
         Ok(out)
     }
 
+    async fn get_task_summary(&self, id: TaskId) -> Result<TaskSummary> {
+        let tasks = self.list_tasks(None).await?;
+        tasks
+            .into_iter()
+            .find(|t| t.id == id)
+            .ok_or_else(|| CloudTaskError::Msg(format!("Task {} not found (mock)", id.0)))
+    }
+
     async fn get_task_diff(&self, id: TaskId) -> Result<Option<String>> {
         Ok(Some(mock_diff_for(&id)))
     }