fix(plugins): a Combobox shows a failed refresh instead of the old results

The query keeps its cached data when a reopened list fails to refresh, so the old items stayed
selectable and the error never showed. A failed search now clears the list so its error shows.
The migration guide maps addNewWorkspaceItem, which its registration-coverage test requires, and
the superseded-search test waits on a later search instead of sleeping.

public-docs/plugins/migration.md

@@ -81,6 +81,7 @@ Use this table as the complete registration checklist.
 | `plugin.addClientSide(fn)` in the old root entry                                              | Delete the wrapper and move the body of `fn` into the default client entry function                                         |
 | `client.addComposerPill(pill)` inside the old client callback                                 | `client.addComposerPill(pill)` inside `index.client.tsx` or an imported `client/` function                                  |
 | New composer item contribution                                                                | `client.addComposerItem(item)` in `index.client.tsx`; see [composer items](reference#composer-items)                        |
+| New New workspace item contribution                                                           | `client.addNewWorkspaceItem(item)` in `index.client.tsx`; see [New workspace items](reference#new-workspace-items)          |
 | New header contribution                                                                       | `client.addHeaderButton({ id, workspaceId, button })`                                                                       |
 | `plugin.addAttachmentSource(source)` in the old root entry                                    | `client.addAttachmentSource(source)` in `index.client.tsx`                                                                  |
 | New settings screen contribution                                                              | `client.addSettingsScreen(screen)` in `index.client.tsx`; see [settings screens](reference#settings-screens)                |

public-docs/plugins/migration.zh-CN.md

@@ -74,6 +74,7 @@ my-plugin/
 | 旧根入口中的 `plugin.addClientSide(fn)`                                                       | 删除这层包装，把 `fn` 的函数体移入默认的客户端入口函数                                                                 |
 | 旧客户端回调中的 `client.addComposerPill(pill)`                                               | `index.client.tsx` 或被导入的 `client/` 函数中的 `client.addComposerPill(pill)`                                        |
 | 新的编辑器项贡献                                                                              | `index.client.tsx` 中的 `client.addComposerItem(item)`;见[编辑器项](reference#composer-items)                          |
+| 新的“新建工作区”项贡献                                                                        | `index.client.tsx` 中的 `client.addNewWorkspaceItem(item)`;见[新建工作区项](reference#new-workspace-items)             |
 | 新的标题栏贡献                                                                                | `client.addHeaderButton({ id, workspaceId, button })`                                                                  |
 | 旧根入口中的 `plugin.addAttachmentSource(source)`                                             | `index.client.tsx` 中的 `client.addAttachmentSource(source)`                                                           |
 | 新的设置界面贡献                                                                              | `index.client.tsx` 中的 `client.addSettingsScreen(screen)`；见[设置界面](reference#settings-screens)                   |