space_visits: one row per visit (check-in/out, is_host, in/out notes);
partial UNIQUE (space_id,member_id) WHERE checked_out_at IS NULL = one
open visit per member. RLS additive/default-deny: SELECT = any space
member (presence is social), NO client write policy (validated
self-resolved service-client actions only; immutable history). No new
permission code; org-wide attendance is all-members by product decision.
spaces.host_requires_card (bool, default true) gates host check-in.
Mirrored in schema.sql, types, DATABASE_SCHEMA, DB_SCHEMA_MAP.
