-- What a change replaces (novox/hq ADR 0217, to-be 44).
--
-- Two records the mesh did not keep, and each time a change took effect unseen it was the one
-- missing. A settings layer is replaced whole, and the layer it replaced was nowhere: on 2026-10-05
-- one placement set for one module on one machine dropped that machine's whole layer for it, and
-- the old one was read back from a database backup (novox/hq issue 304). And of what a machine was sent the
-- mesh kept only a digest — enough to say *whether* it changed, never *what*.

-- Every layer that was replaced or cleared, with when it had been set and when it went. Not a
-- foreign key to settings: the row it was is the row being replaced.
create table settings_history (
    node        uuid        references node(id) on delete cascade,
    module      text        not null,
    values      jsonb       not null,
    set_at      timestamptz,
    replaced_at timestamptz not null default now(),
    -- set · clear
    replaced_by text        not null
);
create index settings_history_by_layer on settings_history (module, node, replaced_at desc);

-- What a machine was last sent, summarised: per resource its id, type, a digest of it and of each
-- field, and a container's mounts. Not the declaration: a file's content may carry a secret, and
-- this lands in the store's backups. Read only to compare a plan with what was sent; what a machine
-- *should* be is composed from the mesh's records every time, as before (migration 0014).
alter table node add column sent_summary jsonb;