(release) Add explicit incomplete snapshot cleanup

Add a dedicated cleanup path for incomplete snapshots instead of letting
retention prune them implicitly. The retention plan now exposes a guarded
form that requires host and delete-count confirmation before removing
.incomplete snapshot directories and their SQL records.

Keep scheduled/manual retention behavior unchanged, add path safety checks,
and cover cleanup success, confirmation failures, max-delete limits, and
unexpected paths in tests.

Refs #10

src/pobsync_backend/tests/test_views.py

@@ -1620,6 +1620,68 @@ class ViewTests(TestCase):
         self.assertContains(response, "Incomplete Snapshots")
         self.assertContains(response, "20260519-031500Z__BROKEN01")
         self.assertContains(response, "excluded from retention cleanup")
+        self.assertContains(response, "Delete incomplete snapshots")
+        self.assertContains(response, "Type 1 to confirm the current number of incomplete snapshots.")
+
+    def test_incomplete_cleanup_deletes_incomplete_snapshot_after_confirmation(self) -> None:
+        self.client.force_login(self.staff_user)
+        with TemporaryDirectory() as tmp:
+            home = Path(tmp) / "home"
+            host = HostConfig.objects.create(host="web-01", address="web-01.example.test")
+            incomplete_dir = Path(tmp) / "backups" / host.host / ".incomplete" / "20260519-031500Z__BROKEN01"
+            incomplete_dir.mkdir(parents=True)
+            incomplete_dir.joinpath("partial-file").write_text("interrupted\n")
+            record = SnapshotRecord.objects.create(
+                host=host,
+                kind=SnapshotRecord.Kind.INCOMPLETE,
+                dirname=incomplete_dir.name,
+                path=str(incomplete_dir),
+                status="failed",
+                started_at=datetime(2026, 5, 19, 3, 15, tzinfo=timezone.utc),
+            )
+
+            with override_settings(POBSYNC_HOME=str(home)):
+                response = self.client.post(
+                    reverse("cleanup_host_incomplete_snapshots", args=[host.host]),
+                    {
+                        "max_delete": "1",
+                        "confirm_host": host.host,
+                        "confirm_delete_count": "1",
+                    },
+                    follow=True,
+                )
+
+            self.assertFalse(incomplete_dir.exists())
+
+        self.assertRedirects(response, reverse("host_retention_plan", args=[host.host]))
+        self.assertContains(response, "Deleted 1 incomplete snapshot(s) for web-01.")
+        self.assertFalse(SnapshotRecord.objects.filter(pk=record.pk).exists())
+
+    def test_incomplete_cleanup_rejects_bad_confirmation(self) -> None:
+        self.client.force_login(self.staff_user)
+        host = HostConfig.objects.create(host="web-01", address="web-01.example.test")
+        SnapshotRecord.objects.create(
+            host=host,
+            kind=SnapshotRecord.Kind.INCOMPLETE,
+            dirname="20260519-031500Z__BROKEN01",
+            path=f"/backups/{host.host}/.incomplete/20260519-031500Z__BROKEN01",
+            status="failed",
+            started_at=datetime(2026, 5, 19, 3, 15, tzinfo=timezone.utc),
+        )
+
+        response = self.client.post(
+            reverse("cleanup_host_incomplete_snapshots", args=[host.host]),
+            {
+                "max_delete": "1",
+                "confirm_host": "wrong",
+                "confirm_delete_count": "1",
+            },
+            follow=True,
+        )
+
+        self.assertRedirects(response, reverse("host_retention_plan", args=[host.host]))
+        self.assertContains(response, "Incomplete cleanup confirmation is invalid.")
+        self.assertEqual(SnapshotRecord.objects.filter(kind=SnapshotRecord.Kind.INCOMPLETE).count(), 1)
 
     def test_host_detail_surfaces_retention_warnings(self) -> None:
         self.client.force_login(self.staff_user)