fix(tools): report deeply nested progress snapshots as usage errors

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

tools/progress.py

@@ -585,7 +585,7 @@ def main(argv=None):
             for path in args.compare:
                 try:
                     snapshots.append(json.loads(path.read_text(encoding="utf-8-sig")))
-                except (OSError, ValueError) as error:
+                except (OSError, ValueError, RecursionError) as error:
                     parser.error(f"{path}: {error}")
             for path, snapshot in zip(args.compare, snapshots):
                 try:

tools/tests/test_progress.py

@@ -59,6 +59,22 @@ class ProgressSnapshotTests(unittest.TestCase):
                 self.assertIn(message, stderr.getvalue())
                 self.assertNotIn("Traceback", stderr.getvalue())
 
+    def test_deeply_nested_snapshots_are_usage_errors(self):
+        for position in (0, 1):
+            with self.subTest(position=position), tempfile.TemporaryDirectory() as directory:
+                paths = [Path(directory) / "base snapshot.json", Path(directory) / "head snapshot.json"]
+                for path in paths:
+                    path.write_text(json.dumps(self.snapshot()), encoding="utf-8")
+                paths[position].write_text("[" * 100000 + "]" * 100000, encoding="utf-8")
+                stdout, stderr = io.StringIO(), io.StringIO()
+                with patch("sys.stdout", stdout), patch("sys.stderr", stderr):
+                    with self.assertRaises(SystemExit) as raised:
+                        progress.main(["--compare", *map(str, paths)])
+                self.assertEqual(raised.exception.code, 2)
+                self.assertEqual(stdout.getvalue(), "")
+                self.assertIn(str(paths[position]), stderr.getvalue())
+                self.assertIn("recursion", stderr.getvalue())
+
     def test_non_object_snapshots_are_usage_errors(self):
         for snapshot in (None, [], "progress", 7, True):
             with self.subTest(snapshot=snapshot):