-- Local SQLite (Room). No network, no accounts.
CREATE TABLE history (
  id          INTEGER PRIMARY KEY AUTOINCREMENT,
  expression  TEXT    NOT NULL CHECK (length(expression) > 0),
  result      TEXT    NOT NULL,
  created_at  INTEGER NOT NULL            -- epoch ms UTC; grouped by local day in the UI
);
CREATE INDEX history_created ON history(created_at);
-- Memory value, angle unit, theme and the current (unfinished) expression live in DataStore.