Desktop Workspace Interaction Spec

The desktop workspace should apply the following selection and drag behaviours:

Click on a non-selected card: clear any existing selection, then select the clicked card only.
Click on a selected card: keep the selection and open the detail panel for that card (no selection change).
Drag on a non-selected card: clear the selection, select the dragged card, then drag that single card.
Drag on a selected card: drag the entire current selection without altering which cards are selected.
Cmd/Ctrl + click on a non-selected card: add that card to the existing selection.
Cmd/Ctrl + click on a selected card: expand the selection by adding the stack of cards beneath the clicked card.
Cmd/Ctrl + drag on a non-selected card: replace the current selection with the entire stack beneath the pointer, then drag that stack.
Cmd/Ctrl + drag on a selected card: replace the current selection with the stack beneath the pointer, then drag that stack.
Touch long-press: behaves like a stack-select gesture, expanding the selection to the stack under the pressed card without requiring modifier keys.

These rules ensure the selection model remains predictable while supporting stack-aware gestures unique to the desktop workspace.