/**
 * Resolve the effective HEAD ref for evidence validation in a worktree context.
 *
 * When a task branch exists, returns `"task/<taskId>"`. Otherwise falls back to `"HEAD"`.
 * Used by validateCommit's `--is-ancestor` check so commits on a worktree's task
 * branch are correctly recognized as reachable.
 *
 * @task T-WT-1
 * @task T9600
 * @epic T9586
 */
export declare function getEffectiveHead(projectRoot: string, taskId?: string): Promise<string>;
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