Reject Python 3.12+ autocommit connections in the Database constructor

Connections created with sqlite3.connect(autocommit=True) make
commit() a documented no-op, and autocommit=False connections are
permanently inside a transaction - in both modes every write made
by this library appeared to work in-process but was silently
discarded when the connection closed. Database() now raises
TransactionError for these connections instead of losing data.

Tests are skipped on Python versions before 3.12, where the
autocommit parameter does not exist.

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

tests/test_constructor.py

@@ -1,6 +1,8 @@
 from sqlite_utils import Database
+from sqlite_utils.db import TransactionError
 from sqlite_utils.utils import sqlite3
 import pytest
+import sys
 
 
 def test_recursive_triggers():
@@ -54,3 +56,31 @@ def test_database_close(tmpdir, memory):
     db.close()
     with pytest.raises(sqlite3.ProgrammingError):
         db.execute("select 1 + 1")
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 12),
+    reason="sqlite3.connect(autocommit=) requires Python 3.12",
+)
+@pytest.mark.parametrize("autocommit", [True, False])
+def test_autocommit_connections_are_rejected(tmpdir, autocommit):
+    # These connection modes break commit()/rollback() in ways that
+    # silently lose data, so the constructor refuses them
+    conn = sqlite3.connect(str(tmpdir / "test.db"), autocommit=autocommit)
+    with pytest.raises(TransactionError):
+        Database(conn)
+    conn.close()
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 12),
+    reason="sqlite3.LEGACY_TRANSACTION_CONTROL requires Python 3.12",
+)
+def test_legacy_transaction_control_connection_is_accepted(tmpdir):
+    conn = sqlite3.connect(
+        str(tmpdir / "test.db"), autocommit=sqlite3.LEGACY_TRANSACTION_CONTROL
+    )
+    db = Database(conn)
+    db["t"].insert({"id": 1}, pk="id")
+    assert [r["id"] for r in db["t"].rows] == [1]
+    db.close()