From d6a141873958d40b293bf1ad9dfb65d153b8beee Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Max=20G=C3=B6rner?=
 <5477952+MaxG87@users.noreply.github.com>
Date: Sat, 22 Aug 2026 23:13:31 +0200
Subject: [PATCH 1/8] feat: Improve reporting on unmount errors

Users do not want to see a stack trace in case the device could not be
unmounted. Instead, they'd prefer to get a useful error message without
scrolling. This new feature will provide that.
---
 .../butter-backup/src/butter_backup/cli.py    | 41 +++++++++++++------
 .../tests/cli/test_cli_commands.py            |  2 +-
 .../src/shell_interface/run_cmd.py            |  9 ++--
 .../src/storage_device_managers/__init__.py   |  6 +--
 .../tests/test_mount_unmount.py               | 15 ++++++-
 5 files changed, 53 insertions(+), 20 deletions(-)

diff --git a/projects/butter-backup/src/butter_backup/cli.py b/projects/butter-backup/src/butter_backup/cli.py
index 9511959..7067297 100644
--- a/projects/butter-backup/src/butter_backup/cli.py
+++ b/projects/butter-backup/src/butter_backup/cli.py
@@ -221,7 +221,14 @@ def close(
                 )
                 continue
             sh.refresh_sudo(parsed_config.SudoPassCmd)
-            sdm.unmount_device(map_name)
+            try:
+                sdm.unmount_device(map_name)
+            except sdm.UnmountError as e:
+                typer.echo(
+                    f"Speichermedium {cfg.Name} konnte nicht ausgehängt werden: {e}",
+                    err=True,
+                )
+                continue
             sdm.close_decrypted_device(map_name)
 
 
@@ -250,6 +257,7 @@ def backup(
     """
     setup_logging(verbose)
     parsed_config = _read_configuration(config)
+    had_unmount_error = False
     for cfg in parsed_config.DeviceConfigurations:
         if _skip_device(
             cfg,
@@ -265,17 +273,26 @@ def backup(
         sh.refresh_sudo(parsed_config.SudoPassCmd)
         open_dir = parsed_config.OpenDirectory
         dest = open_dir / cfg.Name if open_dir is not None else None
-        with (
-            sdm.decrypted_device(cfg.device(), cfg.DevicePassCmd) as decrypted,
-            sdm.mounted_device(
-                decrypted, dest, compression=cfg.compression()
-            ) as mount_dir,
-        ):
-            backend.do_backup(mount_dir, parsed_config.SudoPassCmd)
-            # A backup could take so long that the sudo session expires. In this
-            # case the user would have to enter the password again to unmount and
-            # close the device. To prevent this, the sudo session is refreshed.
-            sh.refresh_sudo(parsed_config.SudoPassCmd)
+        try:
+            with (
+                sdm.decrypted_device(cfg.device(), cfg.DevicePassCmd) as decrypted,
+                sdm.mounted_device(
+                    decrypted, dest, compression=cfg.compression()
+                ) as mount_dir,
+            ):
+                backend.do_backup(mount_dir, parsed_config.SudoPassCmd)
+                # A backup could take so long that the sudo session expires. In this
+                # case the user would have to enter the password again to unmount and
+                # close the device. To prevent this, the sudo session is refreshed.
+                sh.refresh_sudo(parsed_config.SudoPassCmd)
+        except sdm.UnmountError as e:
+            typer.echo(
+                f"Speichermedium {cfg.Name} konnte nicht ausgehängt werden: {e}",
+                err=True,
+            )
+            had_unmount_error = True
+    if had_unmount_error:
+        raise typer.Exit(1)
 
 
 @app.command()
diff --git a/projects/butter-backup/tests/cli/test_cli_commands.py b/projects/butter-backup/tests/cli/test_cli_commands.py
index 43724b2..5aa0345 100644
--- a/projects/butter-backup/tests/cli/test_cli_commands.py
+++ b/projects/butter-backup/tests/cli/test_cli_commands.py
@@ -477,7 +477,7 @@ def test_unmount_error_does_not_cause_content_deletion(
     # This test "successfully" provoked the buggy behaviour before the bug was fixed.
     mocker.patch(
         "storage_device_managers.unmount_device",
-        side_effect=sdm.UnmountError("Mocked unmount error"),
+        side_effect=sdm.UnmountError("Mocked unmount error", b"Mocked stderr"),
     )
 
     config = complement_configuration(encrypted_device, tmp_path)
diff --git a/projects/shell-interface/src/shell_interface/run_cmd.py b/projects/shell-interface/src/shell_interface/run_cmd.py
index e2cd956..52adbaa 100644
--- a/projects/shell-interface/src/shell_interface/run_cmd.py
+++ b/projects/shell-interface/src/shell_interface/run_cmd.py
@@ -1,6 +1,7 @@
 import os
 import subprocess
 from collections import abc
+from dataclasses import dataclass
 from pathlib import Path
 
 StrPathList = abc.Sequence[str | Path]
@@ -10,8 +11,10 @@ class PassCmdError(RuntimeError):
     pass
 
 
+@dataclass(frozen=True)
 class ShellInterfaceError(RuntimeError):
-    pass
+    errmsg: str
+    stderr: bytes | None
 
 
 def run_cmd(
@@ -58,7 +61,7 @@ def run_cmd(
         result = subprocess.run(cmd, capture_output=capture_output, check=True, env=env)
     except subprocess.CalledProcessError as e:
         errmsg = f"Shell-Befehl `{cmd}` ist fehlgeschlagen."
-        raise ShellInterfaceError(errmsg) from e
+        raise ShellInterfaceError(errmsg, e.stderr) from e
     return result
 
 
@@ -112,5 +115,5 @@ def pipe_pass_cmd_to_real_cmd(
         )
     except subprocess.CalledProcessError as e:
         errmsg = f"Shell-Befehl `{command}` ist fehlgeschlagen."
-        raise ShellInterfaceError(errmsg) from e
+        raise ShellInterfaceError(errmsg, e.stderr) from e
     return completed_process
diff --git a/projects/storage-device-managers/src/storage_device_managers/__init__.py b/projects/storage-device-managers/src/storage_device_managers/__init__.py
index 3ddf300..6f930dc 100644
--- a/projects/storage-device-managers/src/storage_device_managers/__init__.py
+++ b/projects/storage-device-managers/src/storage_device_managers/__init__.py
@@ -49,7 +49,7 @@ class InvalidDecryptedDevice(ValueError):
     pass
 
 
-class UnmountError(RuntimeError):
+class UnmountError(sh.ShellInterfaceError):
     pass
 
 
@@ -402,9 +402,9 @@ def unmount_device(device: Path) -> None:
     sync_device(device)
     cmd: sh.StrPathList = ["sudo", "umount", device]
     try:
-        sh.run_cmd(cmd=cmd)
+        sh.run_cmd(cmd=cmd, capture_output=True)
     except sh.ShellInterfaceError as e:
-        raise UnmountError from e
+        raise UnmountError(e.errmsg, e.stderr) from e
 
 
 def open_encrypted_device(device: Path, pass_cmd: str) -> Path:
diff --git a/projects/storage-device-managers/tests/test_mount_unmount.py b/projects/storage-device-managers/tests/test_mount_unmount.py
index 3c39955..884b151 100644
--- a/projects/storage-device-managers/tests/test_mount_unmount.py
+++ b/projects/storage-device-managers/tests/test_mount_unmount.py
@@ -143,13 +143,26 @@ def test_unmount_device_raises_unmounterror(tmp_path: Path) -> None:
         sdm.unmount_device(mountpoint)
 
 
+def test_unmount_device_preserves_shell_error_details(tmp_path: Path) -> None:
+    mountpoint = tmp_path
+    with pytest.raises(sdm.UnmountError) as exc_info:
+        sdm.unmount_device(mountpoint)
+
+    exc = exc_info.value
+    assert isinstance(exc, sh.ShellInterfaceError)
+    assert exc.errmsg.startswith("Shell-Befehl `['sudo', 'umount',")
+    assert str(mountpoint) in exc.errmsg
+    assert exc.stderr is not None
+    assert exc.stderr.strip()
+
+
 def test_mounted_device_does_not_delete_content_on_umount_error(
     device_with_fs, compression_kwargs: CompressionKwargsT, mocker
 ) -> None:
     device, _ = device_with_fs
     mocker.patch(
         "storage_device_managers.unmount_device",
-        side_effect=sdm.UnmountError("Mocked unmount error"),
+        side_effect=sdm.UnmountError("Mocked unmount error", b"Mocked stderr"),
     )
     user = sh.get_user()
     sentinel_text = "This file should not be deleted."

From 2cf7107808ea3a26fd6b72561d6b2318486d9533 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Max=20G=C3=B6rner?=
 <5477952+MaxG87@users.noreply.github.com>
Date: Sat, 22 Aug 2026 23:13:31 +0200
Subject: [PATCH 2/8] Add comment explaining why close_decrypted_device is
 skipped on unmount error

Co-authored-by: MaxG87 <5477952+MaxG87@users.noreply.github.com>
---
 projects/butter-backup/src/butter_backup/cli.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/projects/butter-backup/src/butter_backup/cli.py b/projects/butter-backup/src/butter_backup/cli.py
index 7067297..3091baa 100644
--- a/projects/butter-backup/src/butter_backup/cli.py
+++ b/projects/butter-backup/src/butter_backup/cli.py
@@ -228,6 +228,8 @@ def close(
                     f"Speichermedium {cfg.Name} konnte nicht ausgehängt werden: {e}",
                     err=True,
                 )
+                # The device is still mounted, so closing the decrypted device
+                # would fail. Leave it for the user to handle manually.
                 continue
             sdm.close_decrypted_device(map_name)
 

From 029caf98e579d0b9d051b2b0e460618b71109016 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Max=20G=C3=B6rner?=
 <5477952+MaxG87@users.noreply.github.com>
Date: Mon, 24 Aug 2026 21:53:26 +0200
Subject: [PATCH 3/8] refactor: Put failing command in exception directly

The receiver of the exception can decide on their own what to do about
this. There is no need to formulate the error message at the error site.
---
 .../shell-interface/src/shell_interface/run_cmd.py | 14 ++++++--------
 .../src/storage_device_managers/__init__.py        |  4 ++--
 .../tests/test_mount_unmount.py                    |  4 ++--
 3 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/projects/shell-interface/src/shell_interface/run_cmd.py b/projects/shell-interface/src/shell_interface/run_cmd.py
index 52adbaa..ff9624f 100644
--- a/projects/shell-interface/src/shell_interface/run_cmd.py
+++ b/projects/shell-interface/src/shell_interface/run_cmd.py
@@ -13,7 +13,7 @@ class PassCmdError(RuntimeError):
 
 @dataclass(frozen=True)
 class ShellInterfaceError(RuntimeError):
-    errmsg: str
+    command: StrPathList
     stderr: bytes | None
 
 
@@ -60,13 +60,12 @@ def run_cmd(
     try:
         result = subprocess.run(cmd, capture_output=capture_output, check=True, env=env)
     except subprocess.CalledProcessError as e:
-        errmsg = f"Shell-Befehl `{cmd}` ist fehlgeschlagen."
-        raise ShellInterfaceError(errmsg, e.stderr) from e
+        raise ShellInterfaceError(cmd, e.stderr) from e
     return result
 
 
 def pipe_pass_cmd_to_real_cmd(
-    pass_cmd: str, command: StrPathList, *, capture_output: bool = False
+    pass_cmd: str, cmd: StrPathList, *, capture_output: bool = False
 ) -> subprocess.CompletedProcess[bytes]:
     """
     Pipe result of first command to second command
@@ -83,7 +82,7 @@ def pipe_pass_cmd_to_real_cmd(
     -----------
     pass_cmd
         command to run in shell and whose output is piped to the second command
-    command
+    cmd
         command to run in shell and whose input is piped from the first command
     capture_output
         whether to capture the output of the real command; if `True`, the output is
@@ -111,9 +110,8 @@ def pipe_pass_cmd_to_real_cmd(
         raise PassCmdError(errmsg) from e
     try:
         completed_process = subprocess.run(
-            command, input=pwd_proc.stdout, check=True, capture_output=capture_output
+            cmd, input=pwd_proc.stdout, check=True, capture_output=capture_output
         )
     except subprocess.CalledProcessError as e:
-        errmsg = f"Shell-Befehl `{command}` ist fehlgeschlagen."
-        raise ShellInterfaceError(errmsg, e.stderr) from e
+        raise ShellInterfaceError(cmd, e.stderr) from e
     return completed_process
diff --git a/projects/storage-device-managers/src/storage_device_managers/__init__.py b/projects/storage-device-managers/src/storage_device_managers/__init__.py
index 6f930dc..eb56401 100644
--- a/projects/storage-device-managers/src/storage_device_managers/__init__.py
+++ b/projects/storage-device-managers/src/storage_device_managers/__init__.py
@@ -404,7 +404,7 @@ def unmount_device(device: Path) -> None:
     try:
         sh.run_cmd(cmd=cmd, capture_output=True)
     except sh.ShellInterfaceError as e:
-        raise UnmountError(e.errmsg, e.stderr) from e
+        raise UnmountError(e.command, e.stderr) from e
 
 
 def open_encrypted_device(device: Path, pass_cmd: str) -> Path:
@@ -510,7 +510,7 @@ def encrypt_device(device: Path, password_cmd: str) -> UUID:
         str(new_uuid),
         device,
     ]
-    sh.pipe_pass_cmd_to_real_cmd(pass_cmd=password_cmd, command=format_cmd)
+    sh.pipe_pass_cmd_to_real_cmd(pass_cmd=password_cmd, cmd=format_cmd)
     return new_uuid
 
 
diff --git a/projects/storage-device-managers/tests/test_mount_unmount.py b/projects/storage-device-managers/tests/test_mount_unmount.py
index 884b151..eb4c689 100644
--- a/projects/storage-device-managers/tests/test_mount_unmount.py
+++ b/projects/storage-device-managers/tests/test_mount_unmount.py
@@ -150,8 +150,8 @@ def test_unmount_device_preserves_shell_error_details(tmp_path: Path) -> None:
 
     exc = exc_info.value
     assert isinstance(exc, sh.ShellInterfaceError)
-    assert exc.errmsg.startswith("Shell-Befehl `['sudo', 'umount',")
-    assert str(mountpoint) in exc.errmsg
+    assert exc.command[:2] == ["sudo", "umount"]
+    assert mountpoint in exc.command
     assert exc.stderr is not None
     assert exc.stderr.strip()
 

From de9b75b9e6ff02763336812216afe3c44775d459 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Max=20G=C3=B6rner?=
 <5477952+MaxG87@users.noreply.github.com>
Date: Mon, 24 Aug 2026 22:02:06 +0200
Subject: [PATCH 4/8] feat: Improve style of error reporting

Instead of putting the complete exception to the string, only the STDERR
is given now. This reduces the error message to the necessary
information.
---
 projects/butter-backup/src/butter_backup/cli.py | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/projects/butter-backup/src/butter_backup/cli.py b/projects/butter-backup/src/butter_backup/cli.py
index 3091baa..64da253 100644
--- a/projects/butter-backup/src/butter_backup/cli.py
+++ b/projects/butter-backup/src/butter_backup/cli.py
@@ -153,6 +153,13 @@ def _open_device(
         typer.echo(f"Speichermedium {cfg.Name} wurde in {mount_dir} geöffnet.")
 
 
+def _unmount_errmsg(cfg: cp.DeviceConfiguration, e: sdm.UnmountError) -> str:
+    if e.stderr is None:
+        return f"Speichermedium {cfg.Name} konnte nicht ausgehängt werden. Es ist keine Fehlermeldung verfügbar."
+    stderr = e.stderr.decode("utf-8", errors="replace")
+    return f"Aushängen des Speichermediums {cfg.Name} ist fehlgeschlagen. Die Fehlermeldung ist: {stderr}"
+
+
 @app.command("open")
 def cli_open(
     config: t.Annotated[Path | None, CONFIG_OPTION] = None,
@@ -224,10 +231,7 @@ def close(
             try:
                 sdm.unmount_device(map_name)
             except sdm.UnmountError as e:
-                typer.echo(
-                    f"Speichermedium {cfg.Name} konnte nicht ausgehängt werden: {e}",
-                    err=True,
-                )
+                typer.echo(_unmount_errmsg(cfg, e), err=True)
                 # The device is still mounted, so closing the decrypted device
                 # would fail. Leave it for the user to handle manually.
                 continue
@@ -288,10 +292,7 @@ def backup(
                 # close the device. To prevent this, the sudo session is refreshed.
                 sh.refresh_sudo(parsed_config.SudoPassCmd)
         except sdm.UnmountError as e:
-            typer.echo(
-                f"Speichermedium {cfg.Name} konnte nicht ausgehängt werden: {e}",
-                err=True,
-            )
+            typer.echo(_unmount_errmsg(cfg, e), err=True)
             had_unmount_error = True
     if had_unmount_error:
         raise typer.Exit(1)

From 357cbb6e9b888a7cf74875f1866a59fdf41e7d05 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Max=20G=C3=B6rner?=
 <5477952+MaxG87@users.noreply.github.com>
Date: Mon, 24 Aug 2026 22:31:30 +0200
Subject: [PATCH 5/8] fix: Unfreeze ShellInterfaceError exception dataclass

If frozen, the traceback cannot be set, which causes the error handling
to crash itself.
---
 projects/shell-interface/src/shell_interface/run_cmd.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/projects/shell-interface/src/shell_interface/run_cmd.py b/projects/shell-interface/src/shell_interface/run_cmd.py
index ff9624f..fd0964c 100644
--- a/projects/shell-interface/src/shell_interface/run_cmd.py
+++ b/projects/shell-interface/src/shell_interface/run_cmd.py
@@ -11,8 +11,11 @@ class PassCmdError(RuntimeError):
     pass
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=False)
 class ShellInterfaceError(RuntimeError):
+    # Setting frozen=True would prevent updating `__traceback__` in the except blocks,
+    # causing error handling to crash itself. Therefore frozen=False is used, contrary
+    # to the usual practice of making dataclasses frozen.
     command: StrPathList
     stderr: bytes | None
 

From 04b1fed35a691198edc78a16b9ce0a6916ea4c5e Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 24 Aug 2026 20:35:51 +0000
Subject: [PATCH 6/8] Add traceback regression test for ShellInterfaceError

Co-authored-by: MaxG87 <5477952+MaxG87@users.noreply.github.com>
---
 projects/shell-interface/tests/test_run_cmd.py | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/projects/shell-interface/tests/test_run_cmd.py b/projects/shell-interface/tests/test_run_cmd.py
index 9aea0f9..b71b203 100644
--- a/projects/shell-interface/tests/test_run_cmd.py
+++ b/projects/shell-interface/tests/test_run_cmd.py
@@ -22,6 +22,19 @@ def test_run_cmd_fails() -> None:
         sh.run_cmd(cmd=["false"])
 
 
+def test_shellinterfaceerror_can_be_raised_and_reraised_with_traceback() -> None:
+    error = sh.ShellInterfaceError(["false"], b"stderr")
+
+    with pytest.raises(sh.ShellInterfaceError) as exc_info:
+        raise error
+    assert exc_info.value is error
+    assert exc_info.value.__traceback__ is not None
+
+    with pytest.raises(sh.ShellInterfaceError) as exc_info:
+        raise error
+    assert exc_info.value.__traceback__ is not None
+
+
 @given(environment=st.dictionaries(environment_variable_names, echoable_text))
 def test_run_cmd_forwards_env(environment: dict[str, str]) -> None:
     proc = sh.run_cmd(cmd=["env"], capture_output=True, env=environment)

From dc137ece0528057d80357798bd39ba228982a3b0 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 25 Aug 2026 06:32:12 +0000
Subject: [PATCH 7/8] Fix exception masking in decrypted cleanup and add
 regressions

Co-authored-by: MaxG87 <5477952+MaxG87@users.noreply.github.com>
---
 .../tests/cli/test_cli_commands.py            | 83 +++++++++++++++++++
 .../src/storage_device_managers/__init__.py   | 10 ++-
 .../tests/test_device_manager.py              | 36 ++++++++
 3 files changed, 128 insertions(+), 1 deletion(-)

diff --git a/projects/butter-backup/tests/cli/test_cli_commands.py b/projects/butter-backup/tests/cli/test_cli_commands.py
index 5aa0345..43ceb92 100644
--- a/projects/butter-backup/tests/cli/test_cli_commands.py
+++ b/projects/butter-backup/tests/cli/test_cli_commands.py
@@ -1,6 +1,8 @@
 import datetime as dt
+import types
 import re
 import time
+from contextlib import contextmanager
 from pathlib import Path
 from tempfile import NamedTemporaryFile
 from uuid import UUID
@@ -503,3 +505,84 @@ def test_unmount_error_does_not_cause_content_deletion(
     assert result.exit_code == 0
     assert mount_of_device.exists()  # Target directory should be kept after closing.
     assert sdm.is_mounted(mount_of_device) is False
+
+
+def test_close_prints_unmount_error_and_keeps_device_open(
+    runner: CliRunner, mocker
+) -> None:
+    map_name = Path("/dev/mapper/mock-device")
+    cfg = types.SimpleNamespace(
+        Name="mock-device",
+        device=lambda: Path("/tmp/mock-device"),
+        map_name=lambda: map_name,
+    )
+    parsed = types.SimpleNamespace(
+        DeviceConfigurations=[cfg], SudoPassCmd=None, OpenDirectory=None
+    )
+    mocker.patch.object(cli, "_read_configuration", return_value=parsed)
+    mocker.patch.object(Path, "exists", return_value=True)
+    mocker.patch.object(
+        cli.sdm,
+        "get_mounted_devices",
+        return_value={str(map_name): {Path("/mnt/mock"): frozenset()}},
+    )
+    mocker.patch.object(cli.sh, "refresh_sudo")
+    mocker.patch.object(
+        cli.sdm,
+        "unmount_device",
+        side_effect=sdm.UnmountError(["sudo", "umount", map_name], b"Mocked stderr\n"),
+    )
+    close_mock = mocker.patch.object(cli.sdm, "close_decrypted_device")
+
+    result = runner.invoke(app, ["close"])
+
+    assert result.exit_code == 0
+    assert (
+        "Aushängen des Speichermediums mock-device ist fehlgeschlagen." in result.stderr
+    )
+    assert "Mocked stderr" in result.stderr
+    close_mock.assert_not_called()
+
+
+def test_backup_keeps_unmount_error_as_primary_failure(
+    runner: CliRunner, mocker
+) -> None:
+    @contextmanager
+    def _failing_mounted_device(*_args, **_kwargs):
+        yield Path("/mnt/mock")
+        raise sdm.UnmountError(
+            ["sudo", "umount", Path("/dev/mapper/mock-device")], b"Mocked stderr\n"
+        )
+
+    cfg = types.SimpleNamespace(
+        Name="mock-device",
+        DevicePassCmd="echo pw",
+        device=lambda: Path("/dev/disk/by-uuid/mock-device"),
+        compression=lambda: None,
+    )
+    parsed = types.SimpleNamespace(
+        DeviceConfigurations=[cfg], SudoPassCmd=None, OpenDirectory=None
+    )
+    mocker.patch.object(cli, "_read_configuration", return_value=parsed)
+    mocker.patch.object(cli, "_skip_device", return_value=False)
+    backend = mocker.Mock()
+    mocker.patch.object(cli.bb.BackupBackend, "from_config", return_value=backend)
+    mocker.patch.object(cli.sh, "refresh_sudo")
+    mocker.patch.object(
+        cli.sdm, "open_encrypted_device", return_value=Path("/dev/mapper/mock-device")
+    )
+    close_cmd = ["sudo", "cryptsetup", "close", "mock-device"]
+    mocker.patch.object(
+        cli.sdm,
+        "close_decrypted_device",
+        side_effect=sh.ShellInterfaceError(close_cmd, None),
+    )
+    mocker.patch.object(cli.sdm, "mounted_device", _failing_mounted_device)
+
+    result = runner.invoke(app, ["backup"])
+
+    assert result.exit_code == 1
+    assert (
+        "Aushängen des Speichermediums mock-device ist fehlgeschlagen." in result.stderr
+    )
+    assert "Mocked stderr" in result.stderr
diff --git a/projects/storage-device-managers/src/storage_device_managers/__init__.py b/projects/storage-device-managers/src/storage_device_managers/__init__.py
index eb56401..944f6c7 100644
--- a/projects/storage-device-managers/src/storage_device_managers/__init__.py
+++ b/projects/storage-device-managers/src/storage_device_managers/__init__.py
@@ -146,7 +146,15 @@ def decrypted_device(device: Path, pass_cmd: str) -> Iterator[Path]:
     decrypted = open_encrypted_device(device, pass_cmd)
     try:
         yield decrypted
-    finally:
+    except Exception:
+        try:
+            close_decrypted_device(decrypted)
+        except sh.ShellInterfaceError:
+            # If cleanup follows another failure (e.g. an unmount error), keep the
+            # original exception as root cause.
+            pass
+        raise
+    else:
         close_decrypted_device(decrypted)
 
 
diff --git a/projects/storage-device-managers/tests/test_device_manager.py b/projects/storage-device-managers/tests/test_device_manager.py
index 12cb51a..eae7099 100644
--- a/projects/storage-device-managers/tests/test_device_manager.py
+++ b/projects/storage-device-managers/tests/test_device_manager.py
@@ -76,6 +76,42 @@ def test_decrypted_device_closes_in_case_of_exception(encrypted_device) -> None:
     assert not dd.exists()
 
 
+def test_decrypted_device_preserves_original_exception_when_close_fails(mocker) -> None:
+    encrypted = Path("/dev/sdz1")
+    decrypted = Path("/dev/mapper/mock-decrypted")
+    close_cmd = ["sudo", "cryptsetup", "close", decrypted.name]
+    mocker.patch(
+        "storage_device_managers.open_encrypted_device", return_value=decrypted
+    )
+    mocker.patch(
+        "storage_device_managers.close_decrypted_device",
+        side_effect=sh.ShellInterfaceError(close_cmd, None),
+    )
+    with (
+        pytest.raises(MyCustomTestException),
+        sdm.decrypted_device(encrypted, "echo pw"),
+    ):
+        raise MyCustomTestException
+
+
+def test_decrypted_device_raises_close_error_without_prior_exception(mocker) -> None:
+    encrypted = Path("/dev/sdz1")
+    decrypted = Path("/dev/mapper/mock-decrypted")
+    close_cmd = ["sudo", "cryptsetup", "close", decrypted.name]
+    mocker.patch(
+        "storage_device_managers.open_encrypted_device", return_value=decrypted
+    )
+    mocker.patch(
+        "storage_device_managers.close_decrypted_device",
+        side_effect=sh.ShellInterfaceError(close_cmd, None),
+    )
+    with (
+        pytest.raises(sh.ShellInterfaceError),
+        sdm.decrypted_device(encrypted, "echo pw"),
+    ):
+        pass
+
+
 def test_decrypted_device_can_use_home_for_passcmd(encrypted_device) -> None:
     # Regression Test
     # Test if `decrypted_device` can use a program that is located in PATH. For

From d74317ecc1cdc6d5b897f8c7a010bf5d9c5e2d8f Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 25 Aug 2026 06:34:40 +0000
Subject: [PATCH 8/8] Add regressions for unmount cleanup error masking

Co-authored-by: MaxG87 <5477952+MaxG87@users.noreply.github.com>
---
 projects/butter-backup/tests/cli/test_cli_commands.py  | 10 ++++++----
 .../src/storage_device_managers/__init__.py            |  2 +-
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/projects/butter-backup/tests/cli/test_cli_commands.py b/projects/butter-backup/tests/cli/test_cli_commands.py
index 43ceb92..5692bb5 100644
--- a/projects/butter-backup/tests/cli/test_cli_commands.py
+++ b/projects/butter-backup/tests/cli/test_cli_commands.py
@@ -549,10 +549,12 @@ def test_backup_keeps_unmount_error_as_primary_failure(
 ) -> None:
     @contextmanager
     def _failing_mounted_device(*_args, **_kwargs):
-        yield Path("/mnt/mock")
-        raise sdm.UnmountError(
-            ["sudo", "umount", Path("/dev/mapper/mock-device")], b"Mocked stderr\n"
-        )
+        try:
+            yield Path("/mnt/mock")
+        finally:
+            raise sdm.UnmountError(
+                ["sudo", "umount", Path("/dev/mapper/mock-device")], b"Mocked stderr\n"
+            )
 
     cfg = types.SimpleNamespace(
         Name="mock-device",
diff --git a/projects/storage-device-managers/src/storage_device_managers/__init__.py b/projects/storage-device-managers/src/storage_device_managers/__init__.py
index 944f6c7..aeb072d 100644
--- a/projects/storage-device-managers/src/storage_device_managers/__init__.py
+++ b/projects/storage-device-managers/src/storage_device_managers/__init__.py
@@ -149,7 +149,7 @@ def decrypted_device(device: Path, pass_cmd: str) -> Iterator[Path]:
     except Exception:
         try:
             close_decrypted_device(decrypted)
-        except sh.ShellInterfaceError:
+        except Exception:
             # If cleanup follows another failure (e.g. an unmount error), keep the
             # original exception as root cause.
             pass