Function getOrCreatePending

src/compute-engine/sequence.ts:505–514

(ce: ComputeEngine, name: string)

   * For multi-index: Map<string, Expression> with keys like '0,0', 'n,0'
   */
  base: Map<number | string, Expression>;
  /**
   * Recurrence definition.
   * For single-index: variable is a string (e.g., 'n')
   * For multi-index: variables is an array (e.g., ['n', 'k'])
   */
  recurrence?: {
    variable?: string;
    variables?: string[];
    latex: string;
  };
  /** Whether this appears to be a multi-index sequence */
  isMultiIndex: boolean;