/**
 * Generic "count items by a derived key" reducer. Four independent
 * reimplementations of this existed before the extraction: the audit
 * synthesis summary breakdowns (severity/lens/grounding-status/runtime-status
 * — src/audit/reporting/synthesis.ts, 4 call sites sharing one local
 * `countBy`), the shared audit-deliverable renderer's severity/lens
 * breakdowns (src/shared/reporting/auditDeliverable.ts), remediate's
 * outcomes-report close-out (src/remediate/phases/close.ts), and remediate's
 * findings digest (src/remediate/intake.ts). Single-sourced here so a future
 * fifth breakdown doesn't reimplement it a fifth time.
 *
 * A `selectKey` returning `undefined` or `""` skips the item — it is never
 * counted under an empty-string bucket. This matches the original
 * synthesis.ts behavior (its `if (!key) continue;` guard), which some
 * consumers rely on (e.g. the grounding-status breakdown, where most findings
 * have no grounding verdict at all).
 */
export declare function countBy<T>(items: Iterable<T>, selectKey: (item: T) => string | undefined): Record<string, number>;
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