(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/views.py

@@ -25,6 +25,7 @@ from .forms import (
     CreateHostConfigForm,
     GlobalConfigForm,
     HostConfigForm,
+    IncompleteCleanupForm,
     ManualBackupForm,
     RetentionApplyForm,
     SshCredentialGenerateForm,
@@ -34,7 +35,7 @@ from .forms import (
 from .host_ops import ensure_host_directories
 from .models import BackupRun, GlobalConfig, HostConfig, ScheduleConfig, SnapshotRecord, SshCredential
 from .preflight import collect_backup_gate, effective_host_config_preview, run_remote_preflight
-from .retention import run_sql_retention_apply, run_sql_retention_plan
+from .retention import run_incomplete_cleanup, run_sql_retention_apply, run_sql_retention_plan
 from .self_check import collect_self_checks, summarize_self_checks
 from .scheduler import next_due_after
 from .snapshot_discovery import discover_snapshots, inspect_snapshot_discovery
@@ -569,6 +570,7 @@ def host_retention_plan(request, host: str):
     schedule = _schedule_for_host(host_config)
     scheduled_prune_limit = schedule.prune_max_delete if schedule and schedule.prune else None
     delete_count = len(plan["delete"])
+    incomplete_count = len(plan["incomplete"])
     context = {
         "host": host_config,
         "kind": kind,
@@ -587,6 +589,14 @@ def host_retention_plan(request, host: str):
                 "confirm_delete_count": delete_count,
             },
         ),
+        "incomplete_cleanup_form": IncompleteCleanupForm(
+            host_name=host_config.host,
+            expected_delete_count=incomplete_count,
+            initial={
+                "max_delete": incomplete_count,
+                "confirm_delete_count": incomplete_count,
+            },
+        ),
     }
     return render(request, "pobsync_backend/retention_plan.html", context)
 
@@ -643,6 +653,40 @@ def apply_host_retention(request, host: str):
     return target
 
 
+@staff_member_required
+@require_POST
+def cleanup_host_incomplete_snapshots(request, host: str):
+    host_config = get_object_or_404(HostConfig, host=host)
+    try:
+        plan = run_sql_retention_plan(host=host_config.host, kind="all", protect_bases=True)
+    except PobsyncError as exc:
+        messages.error(request, str(exc))
+        return redirect("host_retention_plan", host=host_config.host)
+
+    incomplete_count = len(plan.get("incomplete") or [])
+    form = IncompleteCleanupForm(
+        request.POST,
+        host_name=host_config.host,
+        expected_delete_count=incomplete_count,
+    )
+    if not form.is_valid():
+        messages.error(request, "Incomplete cleanup confirmation is invalid.")
+        return redirect("host_retention_plan", host=host_config.host)
+
+    try:
+        result = run_incomplete_cleanup(
+            prefix=Path(settings.POBSYNC_HOME),
+            host=host_config.host,
+            yes=True,
+            max_delete=form.cleaned_data["max_delete"],
+        )
+    except PobsyncError as exc:
+        messages.error(request, str(exc))
+    else:
+        messages.success(request, f"Deleted {len(result['deleted'])} incomplete snapshot(s) for {host_config.host}.")
+    return redirect("host_retention_plan", host=host_config.host)
+
+
 @staff_member_required
 def edit_host_config(request, host: str):
     host_config = get_object_or_404(HostConfig, host=host)