/**
 * BubbleState — internal physics + render state for a single bubble.
 * State split enforced: ILayoutEngine writes physics fields, ITweenSystem writes render fields.
 * Renderer reads ONLY renderX, renderY, renderRadius, renderScale.
 */
export interface BubbleState {
    id: string;
    label: string;
    value: number;
    color: string;
    /** Resolved fill opacity (0–1). 1 = fully opaque. */
    opacity: number;
    icon?: string;
    x: number;
    y: number;
    radius: number;
    vx: number;
    vy: number;
    renderX: number;
    renderY: number;
    renderRadius: number;
    renderScale: number;
    targetScale: number;
    tweenProgress: number;
    tweenFrom?: Readonly<{
        x: number;
        y: number;
        radius: number;
    }>;
    shadowCache?: OffscreenCanvas | HTMLCanvasElement;
    shadowDirty: boolean;
}