/**
 * Shared relation-property merge for the graph upsert (wave C), consumed by
 * BOTH backends — the entity-properties precedent: byte-identical merges in
 * two stores diverge eventually, so the rule lives once.
 *
 * Last-wins per key, EXCEPT origin precedence: a machine-derived write never
 * downgrades an agent-declared edge ("derived" cannot overwrite "declared" —
 * routine populator re-upserts would silently corrupt provenance), while
 * "declared" upgrading "derived" is an agent confirming a machine guess.
 */
export declare function mergeRelationProperties(existing: Record<string, string>, incoming: Record<string, string> | undefined): Record<string, string>;
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