fix(recovery): use modern no-log-replay mount option and report stderr

hydra/system_recovery.py

@@ -150,8 +150,12 @@ def sync_tree(root):
 
 class Btrfs:
     def run(self, argv):
+        try:
             return subprocess.run(argv, check=True, text=True, stdout=subprocess.PIPE,
                                   stderr=subprocess.PIPE, env=dict(os.environ, LC_ALL='C')).stdout
+        except subprocess.CalledProcessError as exc:
+            detail = (exc.stderr or '').strip()[:2000]
+            raise RecoveryError(f'{argv[0]} failed ({exc.returncode}): {detail}') from exc
     def info(self, path):
         output = self.run(['btrfs', 'subvolume', 'show', str(path)])
         fields = dict(line.strip().split(':', 1) for line in output.splitlines() if ':' in line)
@@ -476,7 +480,7 @@ def mounted(backend, device, filesystem, writable=False):
         options = ['rw' if writable else 'ro', 'nosuid', 'nodev', 'noexec']
         if filesystem == 'btrfs':
             options.append('subvolid=5')
-            if not writable: options.append('nologreplay')
+            if not writable: options.append('rescue=nologreplay')
         backend.run(['mount', '-t', filesystem, '-o', ','.join(options), device, str(directory)])
         did_mount = True
         if filesystem == 'btrfs':

tests/test_system_recovery.py

@@ -252,6 +252,14 @@ s.restore(sys.argv[3])
                 self.assertEqual((self.top / '@root/kernel').read_text(), 'old kernel')
 
 class NativeBoundaryTests(unittest.TestCase):
+    def test_failed_native_command_includes_bounded_stderr(self):
+        backend = r.Btrfs()
+        error = subprocess.CalledProcessError(32, ['mount'], stderr='specific mount failure\n' + 'x' * 5000)
+        with patch.object(r.subprocess, 'run', side_effect=error):
+            with self.assertRaisesRegex(r.RecoveryError, 'specific mount failure') as caught:
+                backend.run(['mount', '-t', 'btrfs', '/dev/example', '/run/example'])
+        self.assertLess(len(str(caught.exception)), 2300)
+
     def test_btrfs_show_parser_and_readonly_property(self):
         backend = r.Btrfs()
         sample = '''@snapshots/example/root
@@ -292,7 +300,7 @@ class NativeBoundaryTests(unittest.TestCase):
                 with self.assertRaises(r.RecoveryError):
                     with r.mounted(backend, '/dev/fake', 'btrfs'): pass
             self.assertEqual([argv[0] for argv in calls], ['mount', 'btrfs', 'umount'])
-            self.assertIn('ro,nosuid,nodev,noexec,subvolid=5,nologreplay', calls[0])
+            self.assertIn('ro,nosuid,nodev,noexec,subvolid=5,rescue=nologreplay', calls[0])
     def test_cli_requires_matching_confirmation_before_probe(self):
         with patch.object(r, 'DeviceProbe') as probe, patch.object(sys, 'stderr', new_callable=io.StringIO):
             self.assertEqual(r.main(['restore', '--root-uuid', ROOT_UUID, '--checkpoint', ROOT_PART, '--execute']), 1)