Legal holds, step 2: who a hold covers

A hold reaches an account by name, through any of its addresses'
domains, its groups or its tenant, as they are now, so an account added
to a held domain later is held too. An account that leaves a held
domain, group or tenant stays held: the registry write hook adds it to
the hold by name on every account change, whoever makes it (LH-2).
Server::holds_on answers for the deletion paths, from the store each
time so a hold binds every node at once.

crates/common/src/lib.rs

@@ -68,6 +68,7 @@ use utils::{
 pub mod auth;
 pub mod cache;
 pub mod audit; // inbuxa: the audit log (audit-hold-lock spec, AU)
+pub mod hold; // inbuxa: legal holds (audit-hold-lock spec, LH)
 pub mod config;
 pub mod expr;
 pub mod i18n;