Left pane in topic view disappears after refresh or navigation from external site

When viewing a topic the left pane disappears after hitting refresh, navigating via back button after following a link to an external site, clicking on a direct link to the topic from an external site, etc.

Reproduce the issue in a topic view by refreshing, using the back button after visiting an external site, and opening a direct topic link from outside the application. No file or test is named, so first locate the topic-view navigation and state entry points; done means the left pane remains visible in each reported navigation path.

Written by the indexing model from the issue text.