UPSERT under a BEFORE UPDATE trigger corrupts the index, so DELETE leaves a row

CREATE TABLE t(a INTEGER PRIMARY KEY, c INTEGER);
CREATE TABLE u(a INTEGER PRIMARY KEY, c INTEGER);
CREATE INDEX i ON t(c);
CREATE INDEX j ON u(c);
INSERT INTO t VALUES(1,1);
INSERT INTO u VALUES(1,1);
CREATE TRIGGER tg BEFORE UPDATE ON t BEGIN UPDATE t SET c=c+1 WHERE a=NEW.a; END;
CREATE TRIGGER ug BEFORE UPDATE ON u BEGIN UPDATE u SET c=c+1 WHERE a=NEW.a; END;

INSERT INTO t VALUES(1,9) ON CONFLICT(a) DO UPDATE SET c=c+5;
SELECT count(*), group_concat(c) FROM (SELECT c FROM t WHERE c>0 ORDER BY c);
-- Turso:  2|2,6
-- SQLite: 1|6
-- one row is read twice, at the value the trigger wrote and at the value the row holds

DELETE FROM t WHERE a=1;
SELECT count(*) FROM t WHERE c>0;
-- Turso:  1
-- SQLite: 0
-- the table is empty and the stale entry outlives the row it pointed at

PRAGMA integrity_check;
-- Turso:  wrong # of entries in index i
-- SQLite: ok
-- against a file rather than :memory:, sqlite3 opening it reports the same line

UPDATE u SET c=c+5 WHERE a=1;
SELECT count(*) FROM u WHERE c>0;
-- both 1, so the same trigger under a plain UPDATE keeps the index right