Functional overview

"Solo cards" are artifacts that do NOT have any children. For example a User story without any "Task".

They are shown in their coresponding "cell", that is their own line (they are top-level cards) and their corresponding column according to their "status value".

We will display "skeletons" (like loading skeletons) for children of cards that DO have children, in order to visually distinguish them and to prepare story #13627 .

Technical overview

We will pass the cardwall column mappings information via the DOM and "data" attribute. At this stage, the mapping will only contain "top-level" cards such as "User stories".

The Front-end will be responsible for "resolving" in which columns goes a given card.

We need to pass a "has_children" (name subject to change) information in the taskboard/:id/cards REST route. This information is similar to the "has_children" of backlog items. It allows the front-end to distinguish which cards are "solo items".

Precisions on the mapping between a field and its cardwall column:
The field can be any select box field, with all bindings: custom values, bound to users, bound to user groups.
The field can even be a multi-select box.
One may also select multiple list values for a single column, for example when "status" is either "On going" or "Waiting", it goes in the "Ongoing" column. In this case, we will follow the existing behaviour and the cardwall will show cards that have either of those values in the column.