fix(dbx-cli): 修复空存储下 context 回退

- 在 GUI runtime 不可用且 headless storage 无法打开时返回空上下文

- 增加空 app data 与不可打开 app data 的 dbx-cli 回归测试

crates/dbx-cli/src/commands.rs

@@ -257,10 +257,7 @@ async fn context(args: &[String]) -> CliEnvelope<serde_json::Value> {
     match crate::runtime_client::get_json("/context").await {
         Ok(data) => ok(CliSource::GuiRuntime, data),
         Err(_) => {
-            let configs = match load_headless_connections().await {
-                Ok(configs) => configs,
-                Err(err) => return err,
-            };
+            let configs = load_headless_connections().await.unwrap_or_default();
             ok(
                 CliSource::Headless,
                 serde_json::json!({
@@ -910,6 +907,37 @@ mod tests {
         std::env::remove_var("DBX_APP_DATA_DIR");
     }
 
+    #[tokio::test]
+    async fn context_returns_headless_minimal_context_for_empty_or_unopenable_app_data() {
+        let _guard = ENV_LOCK.lock().unwrap();
+        let dir = tempfile::tempdir().unwrap();
+        let empty_app_data = dir.path().join("empty-app-data");
+        let unopenable_app_data = dir.path().join("app-data-file");
+        std::fs::write(&unopenable_app_data, "not a directory").unwrap();
+
+        for app_data in [&empty_app_data, &unopenable_app_data] {
+            std::env::set_var("DBX_APP_DATA_DIR", app_data);
+
+            let data = success_data(dispatch(vec!["context".into(), "--format".into(), "json".into()]).await);
+
+            assert_eq!(data["runtime"], "headless");
+            assert!(data["activeConnection"].is_null());
+            assert_eq!(data["configSource"], "headless");
+        }
+
+        std::env::set_var("DBX_APP_DATA_DIR", &unopenable_app_data);
+        assert_failure_code(
+            dispatch(vec!["conn".into(), "list".into(), "--format".into(), "json".into()]).await,
+            CliErrorCode::InternalError,
+        );
+        assert_failure_code(
+            dispatch(vec!["conn".into(), "show".into(), "missing".into(), "--format".into(), "json".into()]).await,
+            CliErrorCode::InternalError,
+        );
+
+        std::env::remove_var("DBX_APP_DATA_DIR");
+    }
+
     #[tokio::test]
     async fn runtime_discovery_serves_context_selection_and_current_result_limit() {
         let _guard = ENV_LOCK.lock().unwrap();