feat: prepare pinned card workspace sources

tests/test_stemctl.py

@@ -298,6 +298,14 @@ class StemctlContractTests(unittest.TestCase):
         self.assertEqual(by_instance.selector, "rp2350-pointers-final")
         self.assertEqual(by_container.selector, "3aca2c1c4c7a")
 
+    def test_env_sources_selects_a_card_and_supports_read_only_check(self) -> None:
+        parser = rvctl.build_parser()
+        args = parser.parse_args(["env", "sources", "inf", "pointers", "--check"])
+        self.assertEqual(args.env_command, "sources")
+        self.assertEqual(args.series, "inf")
+        self.assertEqual(args.card, "pointers")
+        self.assertTrue(args.check)
+
     def test_mcp_select_switches_both_sockets_with_one_current_symlink(self) -> None:
         with tempfile.TemporaryDirectory() as temporary:
             root = Path(temporary)