Fix SELECT on tables with bytea columns hanging in process worker

sqlit/domains/connections/providers/adapters/base.py

@@ -450,6 +450,22 @@ def execute_non_query(self, conn: Any, query: str) -> int:
         pass
 
 
+def _sanitize_cell(value: Any) -> Any:
+    """Convert non-picklable types to picklable equivalents.
+
+    psycopg2 returns memoryview for bytea columns which cannot be pickled
+    through multiprocessing.Pipe, causing the process worker to hang.
+    """
+    if isinstance(value, memoryview):
+        return bytes(value)
+    return value
+
+
+def _sanitize_row(row: Any) -> tuple:
+    """Sanitize a database row so it can be pickled safely."""
+    return tuple(_sanitize_cell(v) for v in row)
+
+
 class CursorBasedAdapter(DatabaseAdapter):
     """Base class for adapters using cursor-based execution (most SQL databases).
 
@@ -471,7 +487,7 @@ def execute_query(self, conn: Any, query: str, max_rows: int | None = None) -> t
             else:
                 rows = cursor.fetchall()
                 truncated = False
-            return columns, [tuple(row) for row in rows], truncated
+            return columns, [_sanitize_row(row) for row in rows], truncated
         return [], [], False
 
     def execute_non_query(self, conn: Any, query: str) -> int:

tests/unit/test_sanitize_row.py

@@ -0,0 +1,32 @@
+"""Unit tests for row sanitization in CursorBasedAdapter."""
+
+from __future__ import annotations
+
+from sqlit.domains.connections.providers.adapters.base import _sanitize_cell, _sanitize_row
+
+
+def test_sanitize_cell_converts_memoryview_to_bytes() -> None:
+    mv = memoryview(b"\xde\xad\xbe\xef")
+    result = _sanitize_cell(mv)
+    assert result == b"\xde\xad\xbe\xef"
+    assert isinstance(result, bytes)
+
+
+def test_sanitize_cell_passes_through_other_types() -> None:
+    assert _sanitize_cell(42) == 42
+    assert _sanitize_cell("hello") == "hello"
+    assert _sanitize_cell(None) is None
+    assert _sanitize_cell(3.14) == 3.14
+
+
+def test_sanitize_row_converts_memoryview_in_tuple() -> None:
+    row = (1, "row1", memoryview(b"\xca\xfe\xba\xbe"))
+    result = _sanitize_row(row)
+    assert result == (1, "row1", b"\xca\xfe\xba\xbe")
+    assert isinstance(result[2], bytes)
+
+
+def test_sanitize_row_without_memoryview_unchanged() -> None:
+    row = (1, "text", None, 3.14)
+    result = _sanitize_row(row)
+    assert result == (1, "text", None, 3.14)