Return the fail-closed measured way to join two Vlada substrate tables, including an explicit DIRECT_OK, DIRECT_DECLARED_KEY, NEEDS_GRAIN, ROUTE_THROUGH_DIM, ROUTE_MULTIHOP, or DO_NOT_SERVE directive. Direct joins come from (in order) the measured connection registry, the VALIDATED join graph (catalog.json join_edges: uniqueness >= 0.999 and match >= 0.80, measured live), or the semantic layer's declared shared surrogate key (DIRECT_DECLARED_KEY, labelled not-live-measured); a validated or declared direct join is always preferred over a route and never refused. Route coverage (min_coverage) is the weaker side of the weakest hop; a route under 50% is labelled low_coverage_route. Unproved composite, NEEDS_GRAIN, quarantined, impossible, or N:M direct evidence cannot be served. With only table_a, it lists every executable connection from that table.