Pin trigger preamble paren and quote-styled identifier branches

_scan_for_trigger_begin has dedicated branches for paren tracking
(WHEN clauses), double-quoted / bracketed / backtick identifiers, and
line / block comments between TRIGGER and BEGIN. Existing tests
covered the negative cases (string-literal containing CREATE TRIGGER,
nested CREATE TRIGGER) but never fed a preamble where those constructs
appear legitimately, so a refactor that drops paren_depth tracking
or one of the quote handlers would silently regress.

Pin the positive cases: WHEN with paren-nested BEGIN-flag, double-
quoted/bracketed/backtick table names with doubled-character escapes,
and -- / /* */ comments between ON-clause and BEGIN.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: antoineleclair

tests/test_split_trigger_preamble_quotes_and_parens.py

@@ -0,0 +1,118 @@
+r"""Pin: ``_scan_for_trigger_begin`` correctly handles paren-depth and
+quote-styled identifiers inside the trigger preamble (between
+``TRIGGER`` and ``BEGIN``).
+
+The scanner has dedicated branches for ``(`` / ``)`` paren tracking,
+``"quoted"`` / ``[bracketed]`` / ``\`backtick\``` identifiers, and
+``--`` / ``/* */`` comments inside the preamble. Existing tests
+exercise:
+
+- TEMP / TEMPORARY trigger
+- INSTEAD OF trigger
+- string-literal-with-CREATE-TRIGGER negative case
+- nested CREATE TRIGGER
+
+But never feed a preamble containing those legitimately. Without
+paren tracking a ``WHEN (BEGIN_FLAG = 1)`` clause would FALSE-match
+the standalone ``BEGIN``; without quote-styled-identifier handling
+a column name like ``"BEGIN"`` (quoted reserved word) would do the
+same.
+"""
+
+from __future__ import annotations
+
+from dqliteclient.connection import _split_top_level_statements
+
+
+class TestPreambleParenTracking:
+    def test_when_clause_with_begin_token_in_paren_does_not_split(self) -> None:
+        # If paren_depth tracking were missing, the BEGIN token inside
+        # WHEN (...) would be matched as the trigger body opener and
+        # the body delimiters would be misaligned.
+        sql = (
+            "CREATE TRIGGER aud AFTER UPDATE ON x "
+            "FOR EACH ROW WHEN (NEW.a = 'BEGIN' OR OLD.b > 0) BEGIN\n"
+            "  UPDATE y SET v=1;\n"
+            "END;"
+        )
+        pieces = _split_top_level_statements(sql)
+        assert len(pieces) == 1, f"got {len(pieces)} pieces: {pieces!r}"
+
+    def test_nested_when_clauses(self) -> None:
+        sql = (
+            "CREATE TRIGGER aud AFTER UPDATE ON x "
+            "FOR EACH ROW WHEN ((NEW.a > 0) AND (NEW.b < 10)) BEGIN\n"
+            "  UPDATE y SET v=1;\n"
+            "END;"
+        )
+        pieces = _split_top_level_statements(sql)
+        assert len(pieces) == 1
+
+
+class TestPreambleQuotedIdentifiers:
+    def test_double_quoted_table_name_in_preamble(self) -> None:
+        sql = (
+            'CREATE TRIGGER aud AFTER INSERT ON "my table" BEGIN\n'
+            "  UPDATE y SET v=1;\n"
+            "END;"
+        )
+        pieces = _split_top_level_statements(sql)
+        assert len(pieces) == 1, f"got {len(pieces)} pieces: {pieces!r}"
+
+    def test_double_quoted_with_doubled_quote_escape(self) -> None:
+        # SQLite identifier quoting: "" inside "..." is a literal "
+        sql = (
+            'CREATE TRIGGER aud AFTER INSERT ON "weird""name" BEGIN\n'
+            "  UPDATE y SET v=1;\n"
+            "END;"
+        )
+        pieces = _split_top_level_statements(sql)
+        assert len(pieces) == 1
+
+    def test_bracketed_table_name_in_preamble(self) -> None:
+        sql = (
+            "CREATE TRIGGER aud AFTER INSERT ON [my table] BEGIN\n"
+            "  UPDATE y SET v=1;\n"
+            "END;"
+        )
+        pieces = _split_top_level_statements(sql)
+        assert len(pieces) == 1
+
+    def test_backtick_table_name_in_preamble(self) -> None:
+        sql = (
+            "CREATE TRIGGER aud AFTER INSERT ON `my table` BEGIN\n"
+            "  UPDATE y SET v=1;\n"
+            "END;"
+        )
+        pieces = _split_top_level_statements(sql)
+        assert len(pieces) == 1
+
+    def test_backtick_with_doubled_backtick_escape(self) -> None:
+        sql = (
+            "CREATE TRIGGER aud AFTER INSERT ON `weird``name` BEGIN\n"
+            "  UPDATE y SET v=1;\n"
+            "END;"
+        )
+        pieces = _split_top_level_statements(sql)
+        assert len(pieces) == 1
+
+
+class TestPreambleComments:
+    def test_line_comment_between_trigger_and_begin(self) -> None:
+        sql = (
+            "CREATE TRIGGER aud AFTER INSERT ON x -- migration v3\n"
+            "BEGIN\n"
+            "  UPDATE y SET v=1;\n"
+            "END;"
+        )
+        pieces = _split_top_level_statements(sql)
+        assert len(pieces) == 1
+
+    def test_block_comment_between_trigger_and_begin(self) -> None:
+        sql = (
+            "CREATE TRIGGER aud AFTER INSERT ON x /* notes */ BEGIN\n"
+            "  UPDATE y SET v=1;\n"
+            "END;"
+        )
+        pieces = _split_top_level_statements(sql)
+        assert len(pieces) == 1