test: add boundary tests for uint32 vs uint64 db_id across message types

ExecSqlRequest uses uint64 db_id (accepting values > 2^32-1) while
ExecRequest uses uint32 db_id (rejecting them). Added tests verifying
this protocol invariant to prevent accidental swaps of the validators.

Closes #134

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: antoineleclair

tests/test_messages_requests.py

@@ -521,6 +521,18 @@ def test_valid_values_accepted(self) -> None:
         HeartbeatRequest(timestamp=0)
         OpenRequest(name="test.db", flags=0, vfs="")
 
+    def test_exec_sql_accepts_large_db_id(self) -> None:
+        """134: ExecSqlRequest uses uint64 db_id, accepting values > uint32 max."""
+        msg = ExecSqlRequest(db_id=2**32, sql="SELECT 1")
+        assert msg.db_id == 2**32
+
+    def test_exec_rejects_large_db_id(self) -> None:
+        """134: ExecRequest uses uint32 db_id, rejecting values > uint32 max."""
+        import pytest
+
+        with pytest.raises(ValueError, match="db_id"):
+            ExecRequest(db_id=2**32, stmt_id=0)
+
     def test_bool_rejected_for_uint32_db_id(self) -> None:
         """Bool must not be silently accepted as a uint32 field."""
         import pytest