s3api: fix ListObjectsV2 NextContinuationToken duplication for nested prefix (#8294)

* s3api: fix duplicate ListObjectsV2 continuation token for nested prefix

* s3api: include prefix in common-prefix continuation token

weed/s3api/s3api_object_handlers_list_test.go

@@ -148,6 +148,26 @@ func Test_normalizePrefixMarker(t *testing.T) {
 	}
 }
 
+func TestBuildTruncatedNextMarker(t *testing.T) {
+	t.Run("does not duplicate prefix segment in next continuation token", func(t *testing.T) {
+		prefix := "export_2026-02-10_17-00-23"
+		nextMarker := "export_2026-02-10_17-00-23/4156000e.jpg"
+
+		actual := buildTruncatedNextMarker("xemu", prefix, nextMarker, false, "")
+		assert.Equal(t, "xemu/export_2026-02-10_17-00-23/4156000e.jpg", actual)
+	})
+
+	t.Run("keeps common prefix marker trailing slash", func(t *testing.T) {
+		actual := buildTruncatedNextMarker("xemu", "export_2026-02-10_17-00-23", "", true, "nested")
+		assert.Equal(t, "xemu/export_2026-02-10_17-00-23/nested/", actual)
+	})
+
+	t.Run("includes prefix for common prefix marker when request dir is empty", func(t *testing.T) {
+		actual := buildTruncatedNextMarker("", "foo", "", true, "bar")
+		assert.Equal(t, "foo/bar/", actual)
+	})
+}
+
 func TestAllowUnorderedParameterValidation(t *testing.T) {
 	// Test getListObjectsV1Args with allow-unordered parameter
 	t.Run("getListObjectsV1Args with allow-unordered", func(t *testing.T) {