I was thinking of a structure like this:

• top level and requirements:
  • search term
  • group searched
• top level or requirements
  • visibility: public or internal visibility and repository: enabled
  • visibility: public or internal and repository: enabled or private, groups/projects that user has guest role OR another role with read_code permissions
  • visibility: private and repository: enabled or private, groups/projects that user has repository role OR another role with read_code permissions

{
  "version": 2,
  "timeout": "30s",
  "num_context_lines": 20,
  "max_file_match_window": 1000,
  "max_file_match_results": 5,
  "max_line_match_window": 500,
  "max_line_match_results": 10,
  "max_line_match_results_per_file": 3,
  "forward_to": [
    {
      "endpoint": "http://localhost:6090/api/search",
      "query": {
        "and": {
          "children": [
            {
              "query_string": {
                "query": "test"
              }
            },
            {
              "meta": {
                "key": "traversal_ids",
                "value": "^9970-"
              }
            }
          ]
        },
        "or": {
          "children": [
            {
              "and": {
                "children": [
                  {
                    "meta": {
                      "key": "repository_access_level",
                      "value": 20
                    }
                  },
                  {
                    "or": {
                      "children": [
                        {
                          "meta": {
                            "key": "visibility_level",
                            "value": 10
                          }
                        },
                        {
                          "meta": {
                            "key": "visibility_level",
                            "value": 20
                          }
                        }
                      ]
                    }
                  }
                ]
              }
            },
            {
              "and": {
                "children": [
                  {
                    "or": {
                      "children": [
                        {
                          "meta": {
                            "key": "visibility_level",
                            "value": 10
                          }
                        },
                        {
                          "meta": {
                            "key": "visibility_level",
                            "value": 20
                          }
                        }
                      ]
                    }
                  },
                  {
                    "or": {
                      "children": [
                        {
                          "meta": {
                            "key": "repository_access_level",
                            "value": 10
                          }
                        },
                        {
                          "meta": {
                            "key": "repository_access_level",
                            "value": 20
                          }
                        }
                      ]
                    }
                  },
                  {
                    "or": {
                      "children": [
                        {
                          "meta": {
                            "key": "traversal_ids",
                            "value": "9970-457-"
                          }
                        },
                        {
                          "meta": {
                            "key": "traversal_ids",
                            "value": "9970-123-"
                          }
                        }
                      ]
                    }
                  }
                ]
              }
            },
            {
              "and": {
                "children": [
                  {
                    "meta": {
                      "key": "visibility_level",
                      "value": 0
                    }
                  },
                  {
                    "or": {
                      "children": [
                        {
                          "meta": {
                            "key": "repository_access_level",
                            "value": 10
                          }
                        },
                        {
                          "meta": {
                            "key": "repository_access_level",
                            "value": 20
                          }
                        }
                      ]
                    }
                  },
                  {
                    "or": {
                      "children": [
                        {
                          "meta": {
                            "key": "traversal_ids",
                            "value": "9970-234-789-"
                          }
                        },
                        {
                          "meta": {
                            "key": "repo_ids",
                            "value": [1, 56, 99]
                          }
                        }
                      ]
                    }
                  }
                ]
              }
            }
          ]
        }
      }
    }
  ]
}

This is tremendously helpful, thank you @terrichu! I'll give this a go. 🤝