Validate BND mate and event identity
Source:R/structural_identity.R
rduckvep_prepare_breakend_pairs.RdThe input relation has `event_index`, `chrom`, `pos`, `id`, `ref`, `alt` and `info`. The native builder returns one row per physical source record and never merges a record with its mate. `status` is `reciprocal`, `unproven`, `conflict`, `invalid` or `not_applicable`; `reason` is a stable identifier. ALT syntax alone never proves a fusion, phase or inserted-only sequence: `fusion_status` is always `not_asserted` and `phase_status` `not_evaluated`.