failed results look failed on the canvas

A canvas card now shows when a job's result came back empty or unusable, and answers that contain SMILES strings or tables arrive whole.

canvas#

• A card for a job that returned an empty, placeholder or implausible result shows the failure message and a failed state, instead of a green status and a metric chip. You can tell at a glance which results to trust.
• The small preview a card shows when it first appears uses the same failed state.

chat#

• Lists of SMILES strings and markdown tables arrive intact. Short answers full of bond and ring notation are no longer replaced by a cut-off notice.
• An answer that is cut short gives the right reason for it.
• Long turns that chain several tools keep running when a background job reports back partway through.
• The end-of-turn summary counts the analysis that ran, and says when a turn was interrupted.