/**
 * Returns a predicate: is the source at `sourceIndex` one already deployed in
 * the pipeline (read-only in the add-source flow)? Always `false` outside
 * add-source mode. Reads the positions from context, captured once at seed.
 *
 * Keyed by position, not by `details.name` — the name is user-editable, so a
 * name-keyed check flipped a freshly added source to "deployed" the moment the
 * user typed a name that already existed.
 */
export declare const useIsExistingSource: () => ((sourceIndex: number) => boolean);