Structural observations and plotting depth

Structural dip/azimuth describe a plane: azimuth is dip direction, not hole azimuth. Source signs, angle units and north references require validation. Core alpha/beta remain distinct and require a validated survey and core reference convention before conversion to plane orientation.

The external darkmine-data-skills GSWA converter provides a --preserve-issues structural expansion (currently a development candidate). In that mode, one row represents one source observation. The flat table retains source from/to bounds and uses depth = from as its point plotting anchor. A missing end depth stays null; an absent end-depth source column need not be created. The plotting anchor does not replace interval extent. plot_tadpole_log and structural_to_tadpole use the supplied depth column without inferring a midpoint. Alternative anchors must be prepared explicitly.

Tadpole plots require complete dip/dip-direction measurements. They do not render descriptor-only or alpha/beta-only observations as fabricated planes. Orientation normalization and alpha/beta interpretation are separate from source-preserving conversion.

The legacy baselode.adaptors.raw_gswa.convert.convert_structures path remains separate: it collapses bounds and has no conflict-preserving attribute expansion. The preserving mode is implemented in the external converter, not that adaptor.