#604 makes `~/` links clickable and passes them through unchanged, since only
the server knows the session host's home. The html-view mint read `~/x.html`
as workspace-relative and answered 404, so the preview fell back to the
source view. It now expands `~/` against this host's home, as the attachment
route does, and refuses it in a Docker case (that `~` is the container's)
with the same message as the attachment and folder routes.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>