db.execute() write statements now commit automatically

Raw write statements previously opened an implicit transaction that
stayed open until something committed it - the write was visible on
the same connection, making it look saved, but was silently rolled
back when the connection closed. execute() now commits any implicit
transaction it opens, so raw writes behave like every other write
in the library: committed as soon as they run, unless an explicit
transaction (db.begin() or db.atomic()) is open, in which case they
join it.

Row-returning writes such as INSERT ... RETURNING via db.query()
commit once their rows have been iterated. atomic(), commit() and
rollback() now issue literal COMMIT/ROLLBACK statements, which have
identical semantics in every sqlite3 connection mode. The CLI bulk
command uses db.atomic() instead of 'with db.conn:'.

This simplifies the transaction contract to: everything commits
immediately unless you explicitly opened a transaction. Docs
updated throughout; changelog and upgrading guide cover the
breaking change for code that relied on rolling back uncommitted
execute() writes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UnLnhsH25Nnv7LHhekUfPd

tests/test_constructor.py

@@ -35,14 +35,17 @@ def test_database_context_manager(tmpdir):
     path = str(tmpdir / "test.db")
     with Database(path) as db:
         db["t"].insert({"id": 1})
-        # A raw write left uncommitted on purpose:
+        # Raw writes commit automatically too
         db.execute("insert into t (id) values (2)")
+        # An explicitly opened transaction left uncommitted on purpose:
+        db.begin()
+        db.execute("insert into t (id) values (3)")
     # The connection is closed...
     with pytest.raises(sqlite3.ProgrammingError):
         db.execute("select 1")
-    # ... and the uncommitted change was rolled back, not committed
+    # ... and the open explicit transaction was rolled back, not committed
     db2 = Database(path)
-    assert [r["id"] for r in db2["t"].rows] == [1]
+    assert [r["id"] for r in db2["t"].rows] == [1, 2]
     db2.close()