Switch empty-folder cleanup to bucket policy (#8292)

* Fix Spark _temporary cleanup and add issue #8285 regression test

* Generalize empty folder cleanup for Spark temp artifacts

* Revert synchronous folder pruning and add cleanup diagnostics

* Add actionable empty-folder cleanup diagnostics

* Fix Spark temp marker cleanup in async folder cleaner

* Fix Spark temp cleanup with implicit directory markers

* Keep explicit directory markers non-implicit

* logging

* more logs

* Switch empty-folder cleanup to bucket policy

* Seaweed-X-Amz-Allow-Empty-Folders

* less logs

* go vet

* less logs

* refactoring

weed/util/buckets_test.go

@@ -0,0 +1,63 @@
+package util
+
+import "testing"
+
+func TestExtractBucketPath(t *testing.T) {
+	for _, tt := range []struct {
+		name         string
+		base         string
+		target       string
+		requireChild bool
+		expected     string
+		ok           bool
+	}{
+		{
+			name:         "child paths return bucket",
+			base:         "/buckets",
+			target:       "/buckets/test/folder/file",
+			requireChild: true,
+			expected:     "/buckets/test",
+			ok:           true,
+		},
+		{
+			name:         "bucket root without child fails when required",
+			base:         "/buckets",
+			target:       "/buckets/test",
+			requireChild: true,
+			ok:           false,
+		},
+		{
+			name:         "bucket root allowed when not required",
+			base:         "/buckets",
+			target:       "/buckets/test",
+			requireChild: false,
+			expected:     "/buckets/test",
+			ok:           true,
+		},
+		{
+			name:         "path outside buckets fails",
+			base:         "/buckets",
+			target:       "/data/test/folder",
+			requireChild: true,
+			ok:           false,
+		},
+		{
+			name:         "trailing slash on base is normalized",
+			base:         "/buckets/",
+			target:       "/buckets/test/sub",
+			requireChild: true,
+			expected:     "/buckets/test",
+			ok:           true,
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			got, ok := ExtractBucketPath(tt.base, tt.target, tt.requireChild)
+			if ok != tt.ok {
+				t.Fatalf("expected ok=%v, got %v", tt.ok, ok)
+			}
+			if got != tt.expected {
+				t.Fatalf("expected path %q, got %q", tt.expected, got)
+			}
+		})
+	}
+}