OptionalColorAccent color for the tab's dot + active underline. Channel tabs carry a distinct color
(plugin-supplied or a deterministic hash of the name); the Activity tab uses its own
fixed accent in CSS, so its Color is left undefined.
OptionalDataKind-specific payload.
Font Awesome icon class for the tab strip (e.g. fa-solid fa-chalkboard).
Stable unique key (activity, or the channel's registered key).
What the tab renders.
Tab strip label (channel name, or "Activity").
One tab on the call overlay's tabbed surface panel (the right panel): a channel surface (left cluster) or the session-activity tab (right-aligned).