style!: adopt the core lint bar and migrate to it

The package carried no ruff configuration at all, so it ran on the defaults (E4+E7+E9+F) while infinito-nexus-core, its only consumer, holds itself to a far wider selection. Measured against that selection this tree had 224 findings. It now has none.

The selector list is core's verbatim so both repositories answer to one bar. target-version stays py39 rather than core's py311, because requires-python still declares >=3.9 and pyupgrade would otherwise propose syntax the declared minimum cannot run. Every ignore carries its reason: S603/S607 in particular, since running docker and dump binaries from PATH in list form is this tool's whole job and is already injection-safe.

Two conversions are judgement rather than mechanics. os.path.join(dir, '') was the rsync idiom for a trailing separator, which Path drops, so it becomes an explicit os.sep. os.path.abspath stays where Path.resolve() would follow symlinks and let a symlinked volume test as inside the snapshot subject.

BREAKING CHANGE: VersionMismatch is renamed VersionMismatchError.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/unit/backup/test_snapshot_faithfulness.py

@@ -10,6 +10,7 @@ from __future__ import annotations
 import os
 import tempfile
 import unittest
+from pathlib import Path
 from unittest import mock
 
 from baudolo.backup.snapshot import SnapshotError, snapshot_source, unsnapshotted
@@ -19,8 +20,8 @@ from baudolo.backup.volume import Backing
 class TestUnsnapshotted(unittest.TestCase):
     def setUp(self) -> None:
         self.subject = tempfile.mkdtemp()
-        self.mountpoint = os.path.join(self.subject, "volumes", "app", "_data")
-        os.makedirs(self.mountpoint)
+        self.mountpoint = str(Path(self.subject) / "volumes" / "app" / "_data")
+        Path(self.mountpoint).mkdir(parents=True)
 
     def backing(self, **kwargs) -> Backing:
         return Backing(kwargs.pop("mountpoint", self.mountpoint), **kwargs)
@@ -71,7 +72,7 @@ class TestUnsnapshotted(unittest.TestCase):
 
     def test_an_unreadable_mountpoint_is_not(self) -> None:
         reason = unsnapshotted(
-            self.backing(mountpoint=os.path.join(self.subject, "gone")), self.subject
+            self.backing(mountpoint=str(Path(self.subject) / "gone")), self.subject
         )
         self.assertIn("could not be read", reason)
 
@@ -79,12 +80,12 @@ class TestUnsnapshotted(unittest.TestCase):
 class TestSnapshotSource(unittest.TestCase):
     def setUp(self) -> None:
         self.subject = tempfile.mkdtemp()
-        self.mountpoint = os.path.join(self.subject, "volumes", "app", "_data")
-        os.makedirs(self.mountpoint)
-        self.snapshot = os.path.join(
-            self.subject, ".baudolo-tag", "volumes", "app", "_data"
+        self.mountpoint = str(Path(self.subject) / "volumes" / "app" / "_data")
+        Path(self.mountpoint).mkdir(parents=True)
+        self.snapshot = str(
+            Path(self.subject) / ".baudolo-tag" / "volumes" / "app" / "_data"
         )
-        os.makedirs(self.snapshot)
+        Path(self.snapshot).mkdir(parents=True)
         self.backing = Backing(self.mountpoint)
 
     def test_a_captured_volume_reads_from_the_snapshot(self) -> None:
@@ -114,7 +115,7 @@ class TestSnapshotSource(unittest.TestCase):
 
     def test_a_volume_created_after_the_snapshot_degrades(self) -> None:
         source, reason = snapshot_source(
-            lambda path: os.path.join(self.subject, "absent") + "/",
+            lambda path: str(Path(self.subject) / "absent") + "/",
             self.backing,
             self.subject,
         )