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fix: use GITHUB_TOKEN for dependabot rebase workflow #126

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don-petry wants to merge 2 commits into from
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fix: use GITHUB_TOKEN for dependabot rebase workflow #126

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b711717
feat: add dependabot-rebase workflow for auto-merge serialization
Apr 6, 2026
9bee887
fix: use GITHUB_TOKEN for dependabot rebase comments
Apr 6, 2026
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62 changes: 62 additions & 0 deletions .github/workflows/dependabot-rebase.yml
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Original file line number Diff line number Diff line change
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# Dependabot rebase workflow
# Copy to .github/workflows/dependabot-rebase.yml

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The header comment Copy to .github/workflows/dependabot-rebase.yml is misleading now that this file already lives at that path. Consider removing or rewording it to describe the workflow’s purpose instead of implying it’s a template to be copied.

Suggested change
# Copy to .github/workflows/dependabot-rebase.yml
# Rebases open Dependabot PRs that have fallen behind main after pushes.

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#
# Problem: when branch protection requires branches to be up-to-date
# (strict status checks), merging one Dependabot PR makes the others fall
# behind. Dependabot does not auto-rebase PRs that are merely behind — it
# only rebases on its next scheduled run or when there are merge conflicts.
# This leaves auto-merge stalled until the next weekly Dependabot run.
#
# Solution: after every push to main (typically a merged PR), this workflow
# finds open Dependabot PRs that are behind and asks Dependabot to rebase
# them via the @dependabot rebase command. Dependabot performs the rebase
# with its own commit signature, preserving the automerge workflow's ability
# to verify the PR author.
#
# Important: never use the GitHub API update-branch endpoint to rebase
# Dependabot PRs — it replaces Dependabot's commit signature with GitHub's,
# which breaks dependabot/fetch-metadata verification and causes Dependabot
# to refuse future rebases on that PR.
name: Dependabot rebase behind PRs

on:
push:
branches:
- main

permissions: {}

jobs:
rebase:
runs-on: ubuntu-latest
permissions:
contents: read
pull-requests: write
steps:
- name: Rebase behind Dependabot PRs
env:
GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
REPO: ${{ github.repository }}
run: |
# Find open Dependabot PRs
PRS=$(gh pr list --repo "$REPO" --author "app/dependabot" \
--json number,headRefName \
--jq '.[] | "\(.number) \(.headRefName)"')

if [[ -z "$PRS" ]]; then
echo "No open Dependabot PRs"
exit 0
fi

while IFS=' ' read -r PR_NUMBER HEAD_REF; do
BEHIND=$(gh api "repos/$REPO/compare/main...$HEAD_REF" \

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HEAD_REF from Dependabot PRs typically contains slashes (e.g. dependabot/npm_and_yarn/...). Using it unescaped inside the REST path compare/main...$HEAD_REF will produce an invalid URL (extra path segments), causing gh api to 404 and the step to fail under the default bash -e runner shell. URL-encode the ref before calling the compare endpoint (or fetch the behind count via a PR/GraphQL field that doesn't require embedding the ref in the URL path).

Suggested change
BEHIND=$(gh api "repos/$REPO/compare/main...$HEAD_REF" \
ENCODED_HEAD_REF=$(python3 -c 'import sys, urllib.parse; print(urllib.parse.quote(sys.argv[1], safe=""))' "$HEAD_REF")
BEHIND=$(gh api "repos/$REPO/compare/main...$ENCODED_HEAD_REF" \

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--jq '.behind_by')

if [[ "$BEHIND" -gt 0 ]]; then
echo "PR #$PR_NUMBER ($HEAD_REF) is $BEHIND commit(s) behind — requesting rebase"
gh pr comment "$PR_NUMBER" --repo "$REPO" \
--body "@dependabot rebase"
else
echo "PR #$PR_NUMBER ($HEAD_REF) is up to date"
fi
done <<< "$PRS"