Constant SUB_ISSUES 

pub const SUB_ISSUES: &str = "query($id:ID!,$first:Int!,$after:String,$nestedFirst:Int!,$boardItems:Int!,$duplicates:Boolean!){\n      node(id:$id){__typename\n        ... on Issue{subIssues(first:$first,after:$after){\n          pageInfo{hasNextPage endCursor}\n          nodes{__typename ...BoardIssue}\n        }}}\n    } fragment BoardIssue on Issue{__typename id title body url createdAt updatedAt state stateReason(enableDuplicate:$duplicates) repository{nameWithOwner} parent{id} subIssuesSummary{total}\n      labels(first:$nestedFirst){nodes{id name color}pageInfo{hasNextPage}}\n      projectItems(first:$boardItems){nodes{id project{number}\n        fieldValues(first:$nestedFirst){nodes{\n          ... on ProjectV2ItemFieldSingleSelectValue{name field{\n            ... on ProjectV2SingleSelectField{id name options{id name}}\n          }}\n          ... on ProjectV2ItemFieldTextValue{text field{... on ProjectV2Field{id name}}}\n          ... on ProjectV2ItemFieldLabelValue{labels(first:$nestedFirst){nodes{id name color}pageInfo{hasNextPage}}}\n        }pageInfo{hasNextPage}}}pageInfo{hasNextPage}}}";

One project’s tasks: the sub-issues of the issue that project is.

The work this costs is the project’s own size. Nothing about it grows as the board gains projects, or as those projects gain tasks.