Saving a draft

CmsSaveDraft writes the working copy, valid or not. The client names something new (Cms.newEntryId()), and the first save of an id nobody has makes the entry.

• A save names what it was made from (basedOn, the draft's updatedAt). A newer one on the server means someone else saved in between, and the save is refused with Cms.refusal.conflict instead of undoing their work. It is one statement, compare and set, so two saves cannot both win.
• A draft is bounded: maxDraftSize characters of JSON, values and Model together, one million by default. More is refused, and nothing is written.
• Two saves in the same instant still get different updatedAts, so the next save can tell them apart.
• It answers with the entry and the draft as patches, so the client holds both with no refetch. Every operation patches the entry with its state and its revision, so what is on screen follows what was done.
• Refused: a type the server does not know, an entry that is not there or is of another type, an archived entry, and, as Forbidden, a principal that is not an author and an author your transitions or allow refuse.

CmsDiscardDraft removes the working copy. A published entry is left as it was published. An entry that was never published has nothing left, so it is removed too, and the client is told both are gone.