How should contributions from outside GitHub be submitted? (fork pull requests are refused)

[jiku0730]

CONTRIBUTING.md describes the usual flow — fork, branch, test, "Push to your fork and submit a pull request" — but creating the pull request is refused for my account:

$ gh pr create -R github/gh-stack --base main --head jiku0730:fix/detect-external-branch-rename
pull request create failed: GraphQL: jiku0730 does not have the correct permissions
to execute `CreatePullRequest` (createPullRequest)

$ gh api -X POST repos/github/gh-stack/pulls -f head='jiku0730:...' -f base=main
{"message": "Not Found", "status": "404"}

The fork and the branch are fine (repos/github/gh-stack/compare/main...jiku0730:fix/detect-external-branch-rename reports ahead_by: 1, 7 files), so this looks like a repository or org setting rather than something on my end. Of the 110 pull requests this repository has, the 100 I can list (from #12 in April through #402) all have github/gh-stack itself as the head repository — I could not find a single one from a fork, which suggests this is how the project is set up rather than a temporary restriction.

So: are contributions from outside GitHub accepted, and if so, how should a patch be submitted?

I ask because I have one ready. Issue #423 describes it: renaming a stacked branch with git branch -m leaves .git/gh-stack pointing at the old name, after which every command that resolves the current branch reports "is not part of a stack" — and a stack that has not been submitted has no stack number, so unstack <n> --local cannot clear it either.

The patch detects this in loadStack by walking the branch's reflog, and offers to point the stack at the new name after confirming with the user. It adds tests, and go vet ./... and go test -race -count=1 ./... pass:

main...jiku0730:gh-stack:fix/detect-external-branch-rename

Happy to reshape it however suits the project — or to leave it as a description in the issue if patches from outside are not something you take. It would just be good to know which, so I can point future reports in the right direction too.