The editor now tells you why no model is coming, instead of showing "building the model" until its fallback clears.
Before, a publish error was reported once per identical message. When the same failure repeated — you press "run all" again, an agent edits a cell, the notebook file changes on disk — the editor stayed silent: no model arrived, no error was shown, and the page waited out its three-minute fallback. Now every run someone asks for reports its outcome afresh, and the veil lifts with the reason (for example, a notebook whose top-level Part does not carry the notebook id; the message ends with the Parts and Assemblies that were found instead). Reports during a slider drag are still collapsed to one per identical state.
A page that opens or refreshes after the failure learns the reason at once, from the end of the connection handshake.
The header's button that opened the raw marimo editor is gone.
See the changelog for the complete list.