add create-eth backmerge skill

skills/create-eth-backmerge/SKILL.md

@@ -0,0 +1,123 @@
+---
+name: create-eth-backmerge
+description: "Back-merge upstream (scaffold-eth-2) changes into the create-eth repository and publish to npm. Use this skill when: the user wants to do a backmerge, sync upstream, or pull SE-2 changes into create-eth. This is a recurring workflow (weekly/biweekly) that syncs the upstream-main branch, merges it into a backmerge branch, resolves conflicts, creates a changeset, and opens a PR."
+---
+
+# create-eth Backmerge
+
+Back-merge upstream scaffold-eth-2 changes into the create-eth repo and prepare for npm publish.
+
+**This skill must be run from inside a clone of the `scaffold-eth/create-eth` repository.**
+
+## Pre-flight Checks
+
+Before starting, verify:
+
+1. You're inside a `create-eth` repo (check for `templates/` dir and the repo remote pointing to `scaffold-eth/create-eth`)
+2. Working tree is clean (`git status` — warn if dirty)
+3. The `gh` CLI is available (used later for PR creation)
+
+## Step 1: Sync upstream-main from scaffold-eth-2
+
+Add the upstream remote if it doesn't exist, fetch latest from scaffold-eth-2, update the local `upstream-main` branch, and push it to origin so GitHub stays in sync:
+
+```bash
+# Add upstream remote if not already configured
+git remote add upstream https://github.com/scaffold-eth/scaffold-eth-2.git 2>/dev/null || true
+
+# Fetch latest from upstream scaffold-eth-2
+git fetch upstream
+
+# Update local upstream-main to match upstream's main
+git checkout upstream-main
+git reset --hard upstream/main
+
+# Push to origin so GitHub fork's upstream-main is synced
+git push origin upstream-main --force
+```
+
+## Step 2: Update local main and create backmerge branch
+
+```bash
+git checkout main
+git pull origin main
+git checkout -b backmerge-DD-MM-YY
+```
+
+Use today's date for the branch name (e.g. `backmerge-27-02-26`). If the branch already exists, ask the user whether to delete and recreate it.
+
+## Step 3: Merge upstream-main
+
+```bash
+git merge upstream-main
+```
+
+## Step 4: Resolve conflicts
+
+**Key concept — SE-2 root vs create-eth structure:** SE-2 is a monorepo with files at root level. In create-eth, those files live inside `templates/base/` (shared) or `templates/<solidity_framework>/` (Hardhat/Foundry-specific). SE-2 backmerges should almost never modify the root of create-eth — upstream changes need to land in the corresponding template directory instead.
+
+If merge conflicts occur:
+
+1. List all conflicted files with `git diff --name-only --diff-filter=U`
+2. Handle known conflicts automatically:
+   - **Root `yarn.lock`**: Reset to ours — `git checkout --ours yarn.lock` then run `yarn install` to regenerate it
+   - **Root `package.json`**: Reset to ours — `git checkout --ours package.json`. Then check if `upstream-main` added any new scripts (especially `next:serve` in the template base `package.json`) and manually add them
+   - **Root-level files that belong in templates** (e.g. `AGENTS.md`, `.agents/`): Reset to ours (`git checkout --ours` or `git rm`), then apply the upstream changes to the corresponding file inside `templates/base/` or `templates/<solidity_framework>/`
+3. For all other conflicts, show the conflicted files to the user and help resolve them interactively
+4. After resolving, stage all changes: `git add .`
+5. Complete the merge: `git commit --no-edit`
+
+## Step 5: Gather upstream changes and create changeset
+
+Before creating the changeset, collect the list of upstream SE-2 PRs included in this backmerge. Run `git log upstream-main --not main --oneline` (or inspect the merge) and extract the SE-2 PR references. Build a summary list like:
+
+```
+- description of change (https://github.com/scaffold-eth/scaffold-eth-2/pull/XXXX)
+- another change (https://github.com/scaffold-eth/scaffold-eth-2/pull/YYYY)
+```
+
+This list will be used in both the changeset and the PR body.
+
+Now create the changeset:
+
+```bash
+yarn changeset add
+```
+
+When prompted:
+
+- Select **patch** for the version bump
+- For the summary, use the list of upstream SE-2 PR descriptions with links. Example:
+
+```
+- up solidity version and scaffold-ui (https://github.com/scaffold-eth/scaffold-eth-2/pull/1218)
+```
+
+After changeset is created, commit it:
+
+```bash
+git add .
+git commit -m "chore: add changeset for backmerge"
+```
+
+## Step 6: Push and create PR
+
+```bash
+git push origin backmerge-DD-MM-YY
+```
+
+The PR title format is `backmerge DD-MM-YY` using today's date. The body lists the upstream SE-2 PRs being merged.
+
+Create the PR using `gh`:
+
+```bash
+gh pr create \
+  --title "backmerge DD-MM-YY" \
+  --body "- change description (https://github.com/scaffold-eth/scaffold-eth-2/pull/XXXX)
+- another change (https://github.com/scaffold-eth/scaffold-eth-2/pull/YYYY)" \
+  --base main
+```
+
+Replace the placeholder title date and body with the actual values.
+
+**Important**: Since create-eth is forked from SE-2, the GitHub UI may default the PR target to the upstream repo. Tell the user to double-check that the PR targets `scaffold-eth/create-eth` `main` branch, NOT the upstream SE-2 repo. If `gh` creates it against the wrong repo, instruct the user to close and recreate manually or adjust in the UI.