### Goal

Extract Begin of the deletion the generic BorderBox list shell from `OpenProject::Common::WorkPackageCardListComponent` intoEnd of the deletion a reusable Begin of the insertionBorderBox-backed list primitive intoEnd of the insertion `OpPrimer::BorderBoxListComponent`, Begin of the insertionmoveEnd of the insertion Begin of the deletion then make `WorkPackageCardListComponent` render through the newEnd of the deletion generic Begin of the insertionheader/action/menu chrome into that primitive, and keep OpenProject domain-specific item support outside `OpPrimer`.End of the insertion Begin of the deletion component.End of the deletion

This implementation is a static component extraction. Begin of the insertionGeneric header actions, header menus, and item menus are in scope as reusable list chrome.End of the insertion Sorting, reordering, drag-and-drop Begin of the insertionordering APIs,End of the insertion Begin of the deletion ordering, row action menus, header action menus,End of the deletion and Begin of the insertionaction-menu abstractions beyond these explicit slotsEnd of the insertion Begin of the deletion meetings adoptionEnd of the deletion are out of scope for this work package.

### Component API

`OpPrimer::BorderBoxListComponent` should provide these Begin of the insertiongenericEnd of the insertion slots:

- `header`
- `with_item`
- `with_empty_item`
- Begin of the deletion `with_work_package_item`
-End of the deletion `footer`

Begin of the insertionThe public collection slot should be called `items`, to distinguish the wrapper API from the underlying `Primer::Beta::BorderBox` row implementation.End of the insertion Callers are responsible for Begin of the deletion iterating collections andEnd of the deletion calling item slot methods in the order they want Begin of the insertionitemsEnd of the insertion Begin of the deletion rowsEnd of the deletion rendered. The component should render through Begin of the insertionPrimerEnd of the insertion Begin of the deletion Primer'sEnd of the deletion BorderBox under the hood and forward relevant system arguments such as ids, list ids, padding, classes, data attributes, and ARIA attributes.

Begin of the insertionThe generic header should support title, optional count, description, action buttons, and a menu slot. The generic item should renderEnd of the insertion Begin of the deletion `with_item` rendersEnd of the deletion arbitrary Begin of the insertioncontent and expose an optional menu slot. The footer should continue to render as a BorderBoxEnd of the insertion row Begin of the insertionrather than a BorderBox footer, preserving the existing list-body DOM contract.

`OpPrimer::BorderBoxListComponent` must not expose work-package-specific slots or classes.

### OpenProject list specialization

Add `OpenProject::Common::BorderBoxListComponent` as the manual OpenProject-specialized layer around `OpPrimer::BorderBoxListComponent`.

It should composeEnd of the insertion Begin of the deletion content. `with_empty_item` rendersEnd of the deletion an Begin of the insertion`OpPrimer::BorderBoxListComponent` instance, delegate the generic slot methods to it, and provide the generic list slots plus:

-End of the insertion Begin of the deletion explicit empty row.End of the deletion `with_work_package_item` Begin of the insertion

`with_work_package_item`End of the insertion provides a work-package Begin of the insertionitemEnd of the insertion Begin of the deletion rowEnd of the deletion bridge through a configurable item/card Begin of the deletion component, without hard-coding backlog-specific behavior into the genericEnd of the deletion component. Begin of the insertionThis keeps work-package support in `OpenProject::Common`, while still allowing manual callers to interleave work-package items with custom items. This component must not accept `work_packages:` and must not perform automatic collection iteration.End of the insertion

Begin of the insertionThe work-package item component class should be configurable once on the list through a constructor-level `work_package_item_component:` default, with per-item `component_klass:` override support.

This component is also the future home for other explicit OpenProject-specialized item slots, such as meeting items, if those become useful.

End of the insertion ### Work package wrapper

`OpenProject::Common::WorkPackageCardListComponent` should Begin of the insertionremain the automatic collection-oriented wrapper.End of the insertion Begin of the deletion become a convenience wrapper around `OpPrimer::BorderBoxListComponent`.End of the deletion

It should continue to support:

- `project:`
- `container:`
- `work_packages:`
- `drag_and_drop:`
- `item_component_klass:`
- `params:`
- `current_user:`
- delegated `header`
- delegated `footer`
- `empty_state`

When `work_packages:` are passed, `WorkPackageCardListComponent` should iterate the collection itself and add work-package Begin of the insertionitems through `OpenProject::Common::BorderBoxListComponent`.End of the insertion Begin of the deletion rows to the underlying `BorderBoxListComponent`.End of the deletion When no work packages are rendered, it should render `empty_state` through the underlying empty item slot.

Begin of the insertion`WorkPackageCardListComponent` should not expose manual item composition. Manual interleaving belongs to `OpenProject::Common::BorderBoxListComponent`.

End of the insertion ### Begin of the insertionBacklogs adoption

`Backlogs::InboxComponent` should use `OpenProject::Common::BorderBoxListComponent` directly, because it interleaves a custom show-more item between work-package items.

`Backlogs::SprintComponent` and `Backlogs::BucketComponent` should stay on `OpenProject::Common::WorkPackageCardListComponent`, because they render automatic work-package collections.

###End of the insertion Compatibility expectations

Existing backlogs rendering should keep the relevant DOM contract:

- container id from `dom_target(container)`
- list id from `dom_target(container, :list)`
- header id and collapsible linkage
- work package Begin of the insertionitemEnd of the insertion Begin of the deletion rowEnd of the deletion ids, classes, data attributes, and card rendering
- empty Begin of the insertionitemEnd of the insertion Begin of the deletion rowEnd of the deletion marker
- footer Begin of the insertionitemEnd of the insertion Begin of the deletion rowEnd of the deletion styling
- drag-and-drop data on the box

### Tests

Add Begin of the insertionor updateEnd of the insertion focused component specs for `OpPrimer::BorderBoxListComponent` covering:

- header, Begin of the insertiongenericEnd of the insertion item, empty item, Begin of the insertionitem menu,End of the insertion Begin of the deletion work-package item,End of the deletion and footer rendering
- forwarding of system arguments to the underlying BorderBox
- Begin of the insertionheader description, actions, menu, and count behavior
- empty item data merging
- noEnd of the insertion work-package Begin of the insertionreferences under `OpPrimer`

Add focused component specs for `OpenProject::Common::BorderBoxListComponent` covering:

- genericEnd of the insertion item Begin of the insertionpass-through through delegated slots
- constructor-level `work_package_item_component:` default
- per-item `component_klass:` override
- work-package item rendering through a supplied component class
- work-package item customization blocks
- no automatic collection iterationEnd of the insertion Begin of the deletion bridge behaviorEnd of the deletion

Update/keep `WorkPackageCardListComponent` specs covering:

- automatic `work_packages:` iteration
- delegated header and footer rendering
- `empty_state` rendering through the empty item slot
- container/list/header ids
- existing backlogs Begin of the insertionitemEnd of the insertion Begin of the deletion rowEnd of the deletion data/classes and drag-and-drop data Begin of the insertion

Update backlogs component specs to ensure the inbox show-more item remains interleaved and sprint/bucket DOM contracts remain stable.End of the insertion