The document preview declares two child slots handing the previewed file
and its Host path to other plugins: the header actions after its own
controls, and the empty state of a file it cannot render, where Retry stood.
Empty-state read failures now name their recourse: not-text and too-large
offer the handoff, not-found and non-regular paths offer nothing, and the
rest keep Retry. The unsupported-suffix empty state offers the same seat.
ui-open-in-app fills both seats with an "Open" split button (default
application, or the file manager reveal from its menu) and an empty-state
"Open in default app" button. Both call the Session Remote the Host already
publishes: canOpenWorkspacePath once per page decides whether they render,
openWorkspacePath runs each gesture. Only the pressed control disables while
its gesture settles; a failure announces once through a transient toast.
The delivery cards keep their own opener this iteration. The design, slot
pair, failure classification, and toast rule come from Yifffan's PR #4120.
zhc