fix(postgres): coerce LIMIT before SQL interpolation

core/wren/src/wren/connector/postgres.py

@@ -220,6 +220,20 @@ def _coerce_decimal(value: PyDecimal | None, target_type: pa.DataType):
     return pa.array(values, type=arrow_type, from_pandas=True)
 
 
+def _coerce_limit(limit: int | None) -> int | None:
+    """Validate and coerce a user-supplied ``limit`` to a non-negative ``int``.
+
+    ``int(limit)`` rejects strings like ``"5 OR 1=1"`` so the value can be
+    safely interpolated into SQL. Negative limits are also rejected.
+    """
+    if limit is None:
+        return None
+    coerced = int(limit)
+    if coerced < 0:
+        raise ValueError(f"limit must be non-negative, got {coerced}")
+    return coerced
+
+
 class PostgresConnector(ConnectorABC):
     """Native psycopg3 implementation of the Wren postgres connector."""
 
@@ -251,6 +265,7 @@ def __init__(self, connection_info):
     def query(self, sql: str, limit: int | None = None) -> pa.Table:
         # Strip terminating ``;`` even when no LIMIT wrapper is applied so
         # client-pasted statements match dry_run / limited composition rules.
+        limit = _coerce_limit(limit)
         sql = strip_trailing_semicolon(sql)
         if limit is not None:
             sql = f"SELECT * FROM ({sql}) AS _sub LIMIT {limit}"

core/wren/tests/unit/test_postgres_coerce_limit.py

@@ -0,0 +1,61 @@
+"""Postgres query must coerce LIMIT before SQL interpolation.
+
+``postgres`` imports ``psycopg`` at module load. Unit CI does not install the
+``postgres`` extra, so stub ``psycopg`` in ``sys.modules`` before importing the
+connector module (same pattern as ``test_postgres_semicolon_unlimited``).
+"""
+
+from __future__ import annotations
+
+import sys
+import types
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+
+def _ensure_psycopg_stub() -> None:
+    if "psycopg" in sys.modules:
+        return
+    mod = types.ModuleType("psycopg")
+    errors = types.ModuleType("psycopg.errors")
+    sys.modules["psycopg"] = mod
+    sys.modules["psycopg.errors"] = errors
+
+
+_ensure_psycopg_stub()
+
+from wren.connector import postgres as pg_mod  # noqa: E402
+
+
+def _connector():
+    c = object.__new__(pg_mod.PostgresConnector)
+    c.connection = MagicMock()
+    c._closed = False
+    return c
+
+
+def test_reject_negative_limit():
+    c = _connector()
+    with pytest.raises(ValueError, match="non-negative"):
+        c.query("SELECT 1", limit=-1)
+
+
+def test_reject_injection_string():
+    c = _connector()
+    with pytest.raises(ValueError):
+        c.query("SELECT 1", limit="1; DROP TABLE t")
+
+
+def test_numeric_string_limit_interpolated():
+    c = _connector()
+    cursor = MagicMock()
+    cursor.__enter__ = MagicMock(return_value=cursor)
+    cursor.__exit__ = MagicMock(return_value=False)
+    c.connection.cursor.return_value = cursor
+    with patch.object(pg_mod, "_build_pg_arrow_table", return_value="tbl"):
+        out = c.query("SELECT 1", limit="3")
+    assert out == "tbl"
+    executed = cursor.execute.call_args[0][0]
+    assert "LIMIT 3" in executed
+    assert "DROP" not in executed