Enhancement: Save a copy of office documents to another format (Collabora)
Office documents opened in Collabora Online could be renamed but not saved as a
copy or exported to another format back into oCIS storage: "Save As" silently
did nothing. Collabora exposes "Save As" as a host-delegated operation - it
posts a UI_SaveAs message and waits for the integration to reply with the
target filename via Action_SaveAs - but the app-provider integration never
opened that postMessage channel.
The app-provider now announces itself to the editor with Host_PostmessageReady
once the iframe has loaded, requests the grouped Save-As control via
ui_defaults (SaveAsMode=group), and on UI_SaveAs prompts for the copy's
name and replies with Action_SaveAs. The collaboration service already
implements WOPI PutRelativeFile, so the copy is written into the same space,
respecting the user's permissions. The chosen file extension selects the export
format (e.g. docx to pdf/odt, xlsx to ods, pptx to pdf).