Would you welcome Ctrl/Cmd selection for sidebar action sweeps?

[NikitaMGrimm]

Would you welcome a follow-up PR to #14768 that lets Ctrl/Cmd build a pending selection across several sidebar action sweeps and individual icon clicks?

modifier-sweep-demo-trails.mp4

The current sweep applies Settle, Un-settle, or Wake when the mouse is released. For several separate ranges or individual threads, I'd like to build the whole selection first, using the same Ctrl/Cmd intuition as the sidebar's existing multi-selection.

Proposed behavior:

• Hold Ctrl (Cmd on macOS) and click an action icon or sweep across rows to add or remove pending targets. Separate gestures accumulate into one selection for the same action and section.
• Each gesture takes the inverse of its first row's pending selection as its target state, then paints that state across the range. For example, with A and B selected and C unselected, sweeping B → C removes B and leaves C unselected; A stays selected.
• The modifier can also be pressed after a click or drag has already started.
• Apply only when both the modifier and the primary mouse button are released, in either order. Releasing Ctrl while still dragging does not apply; releasing the mouse while holding Ctrl keeps the selection pending.
• Keep ordinary clicks/sweeps and existing Escape/blur cancellation. Escape also clears a pending selection between gestures.

The cursor trail, button/key indicators, and captions are recording aids. “D” is a demo thread's name, not a Ctrl+D shortcut.

I have a local prototype for the shared web/desktop sidebar, using the existing actions and environment capability checks. Native mobile touch behavior stays unchanged: I did not find either the linked action sweep or the corresponding Ctrl/Cmd selection there.

Validation: 189 focused sidebar tests passed, web typecheck passed, and scoped lint had no errors. The demo uses scripted pointer input through the actual UI and isolated server; native macOS and desktop execution were not separately verified.

Would you approve this direction and scope for a follow-up PR?