feat(create-pr): add reuse_branch to keep one self-updating pull request

[marc0olo]

Closes #77.

create-pr appends a random suffix to branch_name on every run, so each run that finds a diff opens a new branch and a new pull request. While an earlier one is unmerged, every subsequent run legitimately still sees a diff against the base and opens another for the same content. They accumulate, and once a release lands they all go permanently conflicting, because the release commit folds those entries into a version section.

dfinity/icp-js-core accumulated 8 changelog pull requests representing 2 distinct changelog states: 3 with byte-identical diffs, and 5 that went conflicting after v6.0.0 and were closed unresolved. dfinity/pic-js currently has 6 open, 3 conflicting. This repo produced #82 the same way.

This is not about no-op runs — create-pr already skips when there is nothing to commit. The defect is purely branch reuse.

Change

New reuse_branch input on actions/create-pr. When enabled:

• branch_name is used as-is, with no random suffix.
• The branch is reset to the current commit (git checkout -B) and force pushed.
• An already-open pull request for that head and base is updated rather than duplicated — pulls.create would return 422 for a duplicate head.
• When there is nothing left to propose, that pull request is closed rather than left to go stale. This is what actually removes the permanent-conflict symptom.

New pull_request_updated output distinguishes an update from a creation; pull_request_created stays honest and reports false in the update case.

Defaults differ deliberately: false on the action, so existing callers such as create-release-pr are unchanged (release branches are already unique per version); true on the generate-changelog reusable workflow, where the accumulation happens. Flagging that explicitly, since it is a behaviour change for the five consuming repos on merge — happy to make it opt-in if you would rather roll it out per repo.

--force rather than --force-with-lease: the branch is reset from the base branch on every run, so the local ref never matches the remote one and a lease check would reject every push. The branch is bot-owned and fully regenerated each run, so there is no human work to clobber.

Verification

tsc and pnpm build clean, prettier --check . clean, both changed YAML files parse and the input threads through to the action step. Compiled output confirmed to contain the new behaviour: git checkout -B, git push --force, the reuse branch, and the find/close paths.

Not exercised against a live run — that needs a real push to main in a consuming repo.

Rebased onto main after #79. The bundle conflict I had expected did not materialise: git auto-merged the disjoint regions, and I verified the result matches a fresh pnpm build byte-for-byte, so no rebuild commit was needed.

🤖 Generated with Claude Code