/**
 * .gitattributes installer for AIDLC NDJSON merge hygiene (AC-19).
 *
 * merge=union lets parallel branches append to the same session/cost/
 * transition logs and merge without conflict. Duplicated lines from
 * same-position appends are handled at read time by whole-line dedup
 * (AC-20, design F7).
 *
 * Idempotent: exact-line match before append, never duplicates entries.
 */
export declare const MERGE_UNION_LINES: string[];
/**
 * merge=union lines missing from the repo-root .gitattributes. Read-only
 * half of installGitattributes, shared with `aidlc doctor`
 * (update-spring-clean AC-13).
 */
export declare function missingGitattributesLines(projectRoot: string): string[];
/**
 * Ensure the merge=union entries exist in the repo-root .gitattributes.
 * Returns the lines actually added (empty when already installed).
 */
export declare function installGitattributes(projectRoot: string): string[];
/**
 * Whole-line NDJSON dedup (AC-20): merge=union duplicates are
 * byte-identical, while distinct same-second events differ somewhere in
 * the line — so line identity never false-dedups (design F7).
 */
export declare function dedupLines(lines: string[]): string[];
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