-- A reading says the path it was measured at (novox/hq issue 368).
--
-- A shrink is read against the largest reading of the last seven days. Readings were kept by machine,
-- module and item only, so when an item's path moved — on 2026-10-10 an agent's home moved from the
-- operator's own home to the agent account's (ADR 0266) — the new, fresh directory was read against
-- the old one's size, and `data-shrank` was raised for data that was never lost. A reading now keeps
-- its path, and the peak is read only from readings at the item's path now: a moved item starts its
-- size history again, and moving back to a path reads it against what that path held.
--
-- **Every reading kept so far is taken to be at its item's path now.** Where it was really measured
-- is not on record; taking the path now keeps every item's history, so a shrink that is real stays
-- raised. An item whose path moved before this migration stays compared with its old directory until
-- those readings leave the seven-day window. Readings of an item no longer kept keep no path, and are
-- read for nothing.
--
-- Numbered 0092, past 0091, the highest on main or any open branch when this was written.
alter table data_reading add column path text;

update data_reading r set path = d.path
  from data_item d
 where d.machine = r.machine and d.module = r.module and d.item = r.item;