update: add agent to do upstream sync

Signed-off-by: Wen Zhou <wenzhou@redhat.com>

Author: zdtsw

.claude/agents/sync-upstream.md

@@ -0,0 +1,115 @@
+# Sync Upstream
+
+Sync code from the upstream llm-d org to a user's fork and open a PR to opendatahub-io.
+
+## Input
+
+Ask the user: **"Sync to upstream/main HEAD or a specific commit SHA?"**
+
+- If the user provides a **commit SHA**, use that as the target commit
+- If no SHA is given, default to `upstream/main` HEAD
+
+## Workflow
+
+1. **Pre-flight checks**: Verify `origin` remote points to the user's fork (not upstream or opendatahub)
+2. **Fetch remotes**: Add/update `upstream` and `opendatahub` remotes, fetch `upstream/main` and `opendatahub/main`
+3. **Resolve target commit**: Use the user-provided SHA, or default to `upstream/main` HEAD. Verify it exists on `upstream/main`
+4. **Check for duplicates**: If a sync branch or PR for this SHA already exists, inform the user and stop
+5. **Create sync branch**: Create `sync/upstream-<short_sha>` based on `opendatahub/main`
+6. **Merge upstream**: Merge the target upstream commit into the sync branch. Resolve conflicts if needed
+7. **Push branch**: Push to `origin`
+8. **Confirm PR creation**: Ask the user whether to open a PR or stop with the branch pushed only
+9. **Open PR** (if confirmed): Open a PR to `opendatahub-io/workload-variant-autoscaler` targeting `main`
+
+## Commands
+
+```bash
+# 0. Save current branch to restore later
+ORIGINAL_BRANCH=$(git rev-parse --abbrev-ref HEAD)
+
+# 1. Pre-flight: verify origin is the user's fork
+ORIGIN_URL=$(git remote get-url origin)
+if echo "${ORIGIN_URL}" | grep -qE '(llm-d/llm-d-workload-variant-autoscaler|opendatahub-io/workload-variant-autoscaler)'; then
+  echo "Error: origin remote points to upstream or opendatahub, not your fork"
+  exit 1
+fi
+
+# 2. Set up remotes and fetch
+git remote add upstream https://github.com/llm-d/llm-d-workload-variant-autoscaler.git 2>/dev/null || true
+git remote set-url upstream https://github.com/llm-d/llm-d-workload-variant-autoscaler.git
+git remote add opendatahub https://github.com/opendatahub-io/workload-variant-autoscaler.git 2>/dev/null || true
+git remote set-url opendatahub https://github.com/opendatahub-io/workload-variant-autoscaler.git
+git fetch upstream main
+git fetch opendatahub main
+
+# 3. Resolve target commit
+TARGET_COMMIT="${USER_SHA:-upstream/main}"
+FULL_SHA=$(git rev-parse "${TARGET_COMMIT}")
+SHORT_SHA=$(git rev-parse --short "${TARGET_COMMIT}")
+git merge-base --is-ancestor "${FULL_SHA}" upstream/main || { echo "Error: commit not on upstream/main"; exit 1; }
+
+# 4. Check for duplicates
+BRANCH="sync/upstream-${SHORT_SHA}"
+if git show-ref --verify --quiet "refs/heads/${BRANCH}" || git show-ref --verify --quiet "refs/remotes/origin/${BRANCH}"; then
+  echo "Warning: branch ${BRANCH} already exists"
+  # Ask user whether to force-update or skip
+fi
+
+# 5. Create branch from opendatahub/main
+git checkout -b "${BRANCH}" opendatahub/main
+
+# 6. Merge upstream commit into the sync branch
+git merge --no-ff "${FULL_SHA}" --no-edit -m "Sync upstream llm-d/llm-d-workload-variant-autoscaler ${SHORT_SHA}"
+```
+
+## Conflict Resolution
+
+If step 6 produces merge conflicts:
+
+1. List conflicted files with `git diff --name-only --diff-filter=U`
+2. Show the conflicts to the user
+3. Attempt to resolve trivial conflicts automatically (whitespace, import order)
+4. For non-trivial conflicts, show the diff and ask the user how to resolve each file
+5. After all conflicts are resolved:
+   ```bash
+   git add -u
+   git commit --no-edit
+   ```
+
+## Push and Open PR
+
+```bash
+# 7. Push to origin (user's fork)
+git push -u origin "${BRANCH}"
+```
+
+**Before creating the PR, ask the user whether they want to open a PR to opendatahub-io or stop here (branch pushed only).**
+
+If the user chooses to open the PR:
+
+```bash
+# 8. Open PR to opendatahub-io
+FORK_OWNER=$(git remote get-url origin | sed -E 's|.*[:/]([^/]+)/[^/]+(.git)?$|\1|')
+
+gh pr create \
+  --repo opendatahub-io/workload-variant-autoscaler \
+  --base main \
+  --head "${FORK_OWNER}:${BRANCH}" \
+  --title "[sync] upstream llm-d main branch ${SHORT_SHA} [$(date -u +%Y-%m-%d)]" \
+  --body "Syncs llm-d/llm-d-workload-variant-autoscaler main branch into ODH main branch.
+
+Upstream commit: https://github.com/llm-d/llm-d-workload-variant-autoscaler/commit/${FULL_SHA}"
+
+# 9. Return to the original branch
+git checkout "${ORIGINAL_BRANCH}"
+```
+
+If `gh pr create` fails, inform the user that the branch has been pushed to `origin/${BRANCH}` and ask them to create the PR manually at `https://github.com/opendatahub-io/workload-variant-autoscaler/compare/main...${FORK_OWNER}:${BRANCH}`.
+
+## Error Handling
+
+- If the user-provided SHA does not exist on `upstream/main`, report the error and ask for a valid SHA
+- If conflicts cannot be resolved, abort the merge (`git merge --abort`), clean up (`git checkout "${ORIGINAL_BRANCH}" && git branch -D "${BRANCH}"`), and inform the user
+- If the branch already exists, ask the user whether to force-update or skip
+- On any failure after branch creation, clean up with `git checkout "${ORIGINAL_BRANCH}" && git branch -D "${BRANCH}"`
+- Always return the PR URL on success