docs: add lockfile conflict resolution to CONTRIBUTING.md

.github/workflows/ci.yml

@@ -20,9 +20,8 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: pnpm/action-setup@v4
-        with:
-          version: 10
+      - name: Install pnpm
+        run: corepack enable
 
       - uses: actions/setup-node@v4
         with:

CONTRIBUTING.md

@@ -83,6 +83,24 @@ git push origin <your-branch>
    - **Description:** What changed and why
    - **Related Issue:** Link to the issue (e.g., "Closes #42")
 
+## Resolving Merge Conflicts
+
+CI uses `pnpm install --frozen-lockfile`, which **fails if the lockfile is out of sync** with `package.json`. This prevents broken lockfiles (with conflict markers, duplicate keys, etc.) from being merged into `main`.
+
+If you encounter merge conflicts in `pnpm-lock.yaml` or `package.json`, follow these steps on your PR branch:
+
+```bash
+git checkout issue/<issue-number>-<short-description>
+git merge main
+# Resolve conflicts in package.json and pnpm-lock.yaml
+pnpm install
+git add .
+git commit -m "chore: resolve merge conflicts"
+git push origin issue/<issue-number>-<short-description>
+```
+
+**Do not** resolve lockfile conflicts on GitHub's web editor. Always resolve locally and run `pnpm install` to regenerate a clean lockfile before pushing.
+
 ## Pull Request Guidelines
 
 - One feature/fix per PR

package.json

@@ -3,6 +3,7 @@
   "version": "0.0.1",
   "private": true,
   "description": "An open-source platform for creating, building, and sharing games",
+  "packageManager": "pnpm@10.28.0",
   "scripts": {
     "dev:web": "pnpm --filter @gamesung/web dev",
     "dev:server": "pnpm --filter @gamesung/server dev",