hex-grid-morphological-close-hull

Compute a unified outer hull around a group of hex tiles that includes multiple disconnected sub-clusters separated by 1-tile gaps. Use when: (1) rendering nested hierarchy hulls (e.g. "package" hull wrapping multiple "sub-region" hex islands), (2) the naive boundary trace outlines each island separately instead of as one bag, (3) flood-fill from outside walks THROUGH the 1-hex gaps and marks them exterior, (4)…