Add sglang-cherrypick skill for batching bot-cherry-pick dispatches

.claude/skills/sglang-cherrypick/SKILL.md

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+---
+name: sglang-cherrypick
+description: Trigger the bot-cherry-pick workflow for a batch of merged PRs onto a release branch and monitor each run to completion. Use when an SGLang release manager asks to cherry-pick a list of PRs to a release branch.
+---
+
+# SGLang Cherry-Pick
+
+Trigger `.github/workflows/bot-cherry-pick.yml` for each PR in a list, then monitor the resulting workflow runs and report per-PR success/failure with links to the created cherry-pick PRs (or the failure reason).
+
+## Slash Command
+
+`/sglang-cherrypick <target_branch> <pr1> [pr2 pr3 ...]`
+
+Examples:
+- `/sglang-cherrypick release/v0.5.7 25956 25958 25987`
+- `/sglang-cherrypick release/v0.5.7 25956,25958,25987` (comma-separated also accepted)
+
+## Arguments
+
+- **`target_branch`** (required): Release branch in the form `release/vX.Y` or `release/vX.Y.Z`. Must already exist on `origin` (i.e., `sgl-project/sglang`).
+- **`pr_numbers`** (required, one or more): Merged PR numbers to cherry-pick. Each must be a positive integer.
+
+## Repository
+
+Always targets the upstream repo `sgl-project/sglang`. The workflow's job guard (`if: github.repository == 'sgl-project/sglang'`) means triggering it on a fork is a no-op.
+
+## Workflow
+
+### Step 1 — Validate arguments
+
+Fail fast before triggering anything.
+
+```bash
+# target branch shape (matches the workflow's own validator)
+[[ "$TARGET_BRANCH" =~ ^release/v[0-9]+\.[0-9]+(\.[0-9]+)?$ ]] || die "Invalid target_branch"
+
+# branch exists on upstream
+gh api "repos/sgl-project/sglang/branches/$TARGET_BRANCH" --jq '.name' >/dev/null || die "Branch not found"
+
+# each PR is numeric, exists, MERGED, and has a recorded merge commit
+declare -A PR_TO_SHA=()
+declare -A PR_TO_TITLE=()
+for PR in "${PRS[@]}"; do
+  [[ "$PR" =~ ^[0-9]+$ ]] || die "PR '$PR' is not a positive integer"
+  PR_JSON=$(gh pr view "$PR" --repo sgl-project/sglang --json state,mergeCommit,title) \
+    || die "PR #$PR not found"
+  STATE=$(jq -r .state <<<"$PR_JSON")
+  [[ "$STATE" == "MERGED" ]] || die "PR #$PR is not MERGED (state=$STATE)"
+  SHA=$(jq -r '.mergeCommit.oid // empty' <<<"$PR_JSON")
+  [[ -n "$SHA" ]] || die "PR #$PR has no merge commit recorded"
+  PR_TO_SHA[$PR]="$SHA"
+  PR_TO_TITLE[$PR]=$(jq -r .title <<<"$PR_JSON")
+done
+```
+
+Report any failures and **stop** — do not trigger partial batches.
+
+### Step 2 — Pre-flight: list changed files and detect conflicts locally
+
+Before dispatching any workflow, simulate each cherry-pick locally with `git merge-tree` to (a) show the user which files would change and (b) catch conflicts before paying for a CI run. `git merge-tree --write-tree` is a side-effect-free 3-way merge — it touches neither the working tree nor any ref.
+
+**2a. Locate the upstream remote (`sgl-project/sglang`).** Both the dual-remote (`upstream` + `origin` fork) and single-remote setups need to work.
+
+```bash
+UPSTREAM_REMOTE=$(git remote -v \
+  | awk '$2 ~ /[:\/]sgl-project\/sglang(\.git)?$/ && $3 == "(fetch)" {print $1; exit}')
+[[ -n "$UPSTREAM_REMOTE" ]] || die "No remote points to sgl-project/sglang"
+```
+
+**2b. Fetch the target branch and each PR's merge commit.** Fetch the commits by SHA (in case they're not on a ref the user has locally) and the target branch in one call.
+
+```bash
+git fetch "$UPSTREAM_REMOTE" "$TARGET_BRANCH" "${PR_TO_SHA[@]}" --quiet \
+  || die "Failed to fetch from $UPSTREAM_REMOTE"
+
+TARGET_REF="refs/remotes/$UPSTREAM_REMOTE/$TARGET_BRANCH"
+```
+
+**2c. Index existing cherry-pick PRs on the target branch.** One `gh pr list` call gets every cherry-pick PR ever filed against this branch (any state). For each input PR, we cross-reference by the title suffix `(#<PR>)` that the bot workflow always uses.
+
+```bash
+# Fetch all cherry-pick PRs against this branch (any state), then bucket by
+# source-PR number using the title pattern "(#<source_pr>)".
+EXISTING_CP_JSON=$(gh pr list --repo sgl-project/sglang \
+  --base "$TARGET_BRANCH" \
+  --label cherry-pick \
+  --state all \
+  --limit 200 \
+  --json number,title,url,state)
+
+declare -A PR_TO_EXISTING_CP=()   # source_pr -> JSON array of existing cherry-pick PRs
+for PR in "${PRS[@]}"; do
+  PR_TO_EXISTING_CP[$PR]=$(jq -c \
+    "[.[] | select(.title | contains(\"(#${PR})\"))]" <<<"$EXISTING_CP_JSON")
+done
+```
+
+For each input PR, classify the existing cherry-picks:
+
+- **`MERGED`** present → the cherry-pick already landed. **Skip** this PR in Step 3.
+- **`OPEN`** present (and no `MERGED`) → a previous dispatch is still in flight. **Warn**, ask the user whether to skip or re-dispatch, but default to **skip** (re-dispatching creates a duplicate).
+- Only `CLOSED` (no merged, no open) → previous attempts were abandoned; safe to re-dispatch.
+- Empty → no prior attempt; proceed normally.
+
+**2d. For each PR, run `git merge-tree` and diff the result.** The semantics of `cherry-pick` are: 3-way-merge with base = parent of source commit, ours = target tip, theirs = source commit. For merge commits the workflow uses `-m 1`, which means base = **first** parent — `${SHA}^` resolves to `${SHA}^1` for both regular and merge commits, so one form covers both.
+
+```bash
+declare -A PR_TO_CONFLICTS=()
+declare -A PR_TO_FILES=()
+
+for PR in "${PRS[@]}"; do
+  SHA="${PR_TO_SHA[$PR]}"
+
+  # --write-tree: print the resulting tree SHA on success
+  # Exit 0 = clean merge; exit 1 = conflicts
+  if MERGE_OUT=$(git merge-tree --write-tree \
+                   --merge-base="${SHA}^" \
+                   "$TARGET_REF" "$SHA" 2>&1); then
+    RESULT_TREE=$(head -1 <<<"$MERGE_OUT")
+    PR_TO_CONFLICTS[$PR]=""
+    # Show files that actually differ between target tip and the merged tree.
+    # This is more accurate than `git show --name-status $SHA` because it
+    # accounts for changes already present on the release branch. As a
+    # side-effect, an already-cherry-picked commit shows up here as "0 files".
+    PR_TO_FILES[$PR]=$(git diff --name-status "$TARGET_REF" "$RESULT_TREE")
+  else
+    # Conflict output format (git ≥2.40): first line is the (partial) tree,
+    # remaining lines list conflicted paths and informational messages.
+    # We just capture and surface it; user decides what to do.
+    PR_TO_CONFLICTS[$PR]="$MERGE_OUT"
+    PR_TO_FILES[$PR]=$(git show --name-status --format= "$SHA" 2>/dev/null)
+  fi
+done
+```
+
+**2e. Print a pre-flight report.** One table summarizing each PR, followed by per-PR file lists. The "Prior cherry-pick" column uses the classification from 2c.
+
+```markdown
+## Cherry-Pick Pre-Flight — `release/vX.Y.Z`
+
+| PR     | Title                    | Merge SHA | Prior cherry-pick    | Conflicts    | # files |
+|--------|--------------------------|-----------|----------------------|--------------|---------|
+| #25733 | [Bug] Fix V4-Pro NaN ... | 79ea30d1  | ✅ merged as #26063  | clean        | 0       |
+| #25562 | [bugfix] Fix wrong ...   | b19052c9  | none                 | **CONFLICT** | —       |
+| #25585 | [Bugfix] Fix missing ... | 86c6c77f  | none                 | clean        | 2       |
+
+### Files (PR #25585 — clean)
+M  python/sglang/srt/layers/communicator.py
+M  python/sglang/srt/models/deepseek_v4.py
+
+### Conflict detail (PR #25562)
+<merge-tree output: conflicted paths and reasons>
+```
+
+**2f. Gate before dispatching.** Stop and report if any PR is in either of these states:
+
+- `git merge-tree` reports a **conflict** — the workflow would just fail; let the user fix or remove that PR.
+- Already has a **MERGED** cherry-pick PR on the target branch — re-dispatching would create a redundant PR. Skip it (or, if the user really wants a re-run, they can pass an explicit override list).
+- Has an **OPEN** cherry-pick PR with no merged one — default to skipping with a warning; surface the open PR's URL so the user can review/merge/close it before re-dispatching.
+
+Only PRs that are **clean** AND have **no merged-or-open** prior cherry-pick should proceed to Step 3.
+
+As a sanity check, a clean pre-flight that shows **0 files changed** is the structural signature of "this commit is already on the branch" — if you see it without an existing merged cherry-pick PR being detected (rare, e.g. the original PR was force-merged onto the release branch directly), surface that too and skip the dispatch.
+
+### Step 3 — Dispatch each PR's workflow run
+
+`gh workflow run` (gh ≥2.45) prints the dispatched run's URL on stdout — parse it directly. Fall back to the snapshot/diff polling only if the URL isn't returned (older gh).
+
+```bash
+# Snapshot once up front in case we need the fallback path.
+mapfile -t SEEN < <(gh run list \
+  --workflow=bot-cherry-pick.yml \
+  --repo sgl-project/sglang \
+  --limit 50 \
+  --json databaseId --jq '.[].databaseId')
+
+declare -A PR_TO_RUN=()  # pr_number -> run_id
+
+for PR in "${PRS[@]}"; do
+  DISPATCH_OUT=$(gh workflow run bot-cherry-pick.yml \
+    --repo sgl-project/sglang \
+    -f pr_number="$PR" \
+    -f target_branch="$TARGET_BRANCH" 2>&1) || { echo "$DISPATCH_OUT"; die "dispatch failed for PR #$PR"; }
+
+  # Preferred path: gh prints the run URL like
+  #   https://github.com/sgl-project/sglang/actions/runs/26275460359
+  RUN_URL=$(grep -oE 'https://github.com/[^[:space:]]+/actions/runs/[0-9]+' \
+              <<<"$DISPATCH_OUT" | head -1)
+  RUN_ID="${RUN_URL##*/}"
+
+  # Fallback for older gh that doesn't print the URL: poll the runs list,
+  # filter to workflow_dispatch events we haven't seen yet.
+  if [[ -z "$RUN_ID" ]]; then
+    for _ in $(seq 1 30); do
+      sleep 2
+      CANDIDATE=$(gh run list \
+        --workflow=bot-cherry-pick.yml \
+        --repo sgl-project/sglang \
+        --limit 10 \
+        --json databaseId,event \
+        --jq '[.[] | select(.event=="workflow_dispatch") | .databaseId] | .[0]')
+      if [[ -n "$CANDIDATE" ]] \
+         && ! printf '%s\n' "${SEEN[@]}" | grep -qx "$CANDIDATE" \
+         && ! printf '%s\n' "${PR_TO_RUN[@]}" | grep -qx "$CANDIDATE"; then
+        RUN_ID="$CANDIDATE"
+        break
+      fi
+    done
+  fi
+
+  if [[ -z "$RUN_ID" ]]; then
+    echo "::warning::No new workflow run detected for PR #$PR within 60s"
+    PR_TO_RUN[$PR]="UNKNOWN"
+  else
+    PR_TO_RUN[$PR]="$RUN_ID"
+  fi
+done
+```
+
+**Notes:**
+- The workflow has `concurrency: cherry-pick-${{ target_branch }}` with `cancel-in-progress: false`. So multiple dispatches against the same target branch **queue serially**, not in parallel. That's fine — we batch the triggers and the GitHub side serializes execution.
+- `gh workflow run` is fire-and-forget; the dispatched run shows up in `gh run list` within a few seconds.
+
+### Step 4 — Monitor each run to completion
+
+Use `gh run watch` per run id, sequentially (since they execute serially anyway).
+
+```bash
+for PR in "${PRS[@]}"; do
+  RUN_ID="${PR_TO_RUN[$PR]}"
+  [[ "$RUN_ID" == "UNKNOWN" ]] && continue
+
+  gh run watch "$RUN_ID" \
+    --repo sgl-project/sglang \
+    --exit-status \
+    --interval 15 \
+    >/dev/null 2>&1 || true   # we read conclusion below; don't abort the loop on fail
+done
+```
+
+`gh run watch` blocks until the run completes. Use `--interval 15` to be polite on rate limits.
+
+### Step 5 — Collect outcomes per PR
+
+For each PR, fetch the run conclusion and (if successful) the URL of the created cherry-pick PR.
+
+```bash
+for PR in "${PRS[@]}"; do
+  RUN_ID="${PR_TO_RUN[$PR]}"
+
+  if [[ "$RUN_ID" == "UNKNOWN" ]]; then
+    echo "PR #$PR: UNKNOWN (no run found)"
+    continue
+  fi
+
+  CONCLUSION=$(gh run view "$RUN_ID" --repo sgl-project/sglang \
+    --json conclusion,status,url \
+    --jq '"\(.status) \(.conclusion) \(.url)"')
+
+  STATUS=$(awk '{print $1}' <<<"$CONCLUSION")
+  RESULT=$(awk '{print $2}' <<<"$CONCLUSION")
+  RUN_URL=$(awk '{print $3}' <<<"$CONCLUSION")
+
+  if [[ "$RESULT" == "success" ]]; then
+    # Find the cherry-pick PR created by this run. Title format from the workflow:
+    #   "[Cherry-pick to <BRANCH>] <ORIG TITLE> (#<PR>)"
+    CP_PR=$(gh pr list --repo sgl-project/sglang \
+      --base "$TARGET_BRANCH" \
+      --label cherry-pick \
+      --state all \
+      --limit 30 \
+      --json number,title,url,createdAt \
+      --jq "[.[] | select(.title | contains(\"(#${PR})\"))][0]")
+
+    CP_URL=$(jq -r '.url // "N/A"' <<<"$CP_PR")
+    CP_NUM=$(jq -r '.number // "?"' <<<"$CP_PR")
+    echo "PR #$PR  -> SUCCESS  cherry-pick PR #$CP_NUM ($CP_URL)  [run: $RUN_URL]"
+  else
+    # Failure: pull the cherry-pick step's last error line so the user sees why.
+    REASON=$(gh run view "$RUN_ID" --repo sgl-project/sglang --log-failed 2>/dev/null \
+      | grep -m1 -E "::error::" \
+      | sed -E 's/^[^:]*::error::?//' \
+      || echo "(see run logs)")
+    echo "PR #$PR  -> $RESULT  reason: $REASON  [run: $RUN_URL]"
+  fi
+done
+```
+
+### Step 6 — Final summary
+
+Print one table sorted by input order:
+
+```markdown
+## Cherry-Pick Batch Summary — `release/v0.5.7`
+
+| PR  | Status   | Cherry-pick PR | Run | Notes |
+|-----|----------|----------------|-----|-------|
+| #25956 | success | #26031 | run/12345 | — |
+| #25958 | failure | —      | run/12346 | Cherry-pick of <SHA> onto release/v0.5.7 failed due to conflicts |
+| #25987 | success | #26032 | run/12347 | — |
+
+**Totals:** N succeeded, M failed, K unknown.
+```
+
+For any **failure**, suggest the manual fallback from the workflow's own error message:
+
+> Resolve locally: `git checkout release/v0.5.7 && git cherry-pick <SHA>`, fix conflicts, push a branch, and open the PR by hand.
+
+## Common Failure Modes
+
+| Symptom | Cause | Action |
+|---------|-------|--------|
+| `PR #X is not merged (state=OPEN)` | PR not yet merged | Wait for merge or pass `--commit-sha` (not supported by this slash command) |
+| `Target branch '...' does not exist` | Typo or branch not cut yet | Confirm branch name; release manager may not have cut it |
+| `Cherry-pick of <SHA> onto <BRANCH> failed due to conflicts` | Code drift on release branch (should already have been caught in Step 2 pre-flight) | Do it manually as instructed above |
+| Pre-flight `git merge-tree` reports a conflict | Same as above, caught locally before any CI run | Remove that PR from the batch and resolve manually |
+| `No remote points to sgl-project/sglang` | Skill invoked from a checkout that only has a fork remote | Add the upstream remote: `git remote add upstream https://github.com/sgl-project/sglang.git` |
+| Pre-flight `git merge-tree` errors with `unknown option` | git < 2.38 | Upgrade git, or run the skill on a machine with a modern git |
+| Pre-flight reports `Prior cherry-pick: merged as #N` | The PR has already been cherry-picked and merged onto this release branch | Skip this PR — re-dispatching would create a duplicate PR. Verify #N is the right one before removing from the list. |
+| Pre-flight reports `Prior cherry-pick: OPEN as #N` | A previous dispatch is still in flight (PR not yet merged or closed) | Default: skip and ask the user to land or close #N first. Re-dispatching creates a parallel duplicate that needs to be cleaned up afterwards. |
+| Pre-flight is clean but `# files = 0` and no prior cherry-pick PR was found | Commit landed on the release branch by direct merge (not via the bot), or via a rebase that rewrote the SHA | Skip the dispatch — the change is already there. Surface this anomaly so the user knows the bot wasn't the source. |
+| Multiple runs but only one detected | Two dispatches landed in the same `gh run list` poll cycle | Re-run for the missing PR, or look up its run by hand: `gh run list --workflow=bot-cherry-pick.yml --event workflow_dispatch -L 20` |
+| `403` on `gh workflow run` | Missing `actions:write` on the token | Use a token that has workflow dispatch rights on `sgl-project/sglang` |
+
+## Notes
+
+- The skill **never modifies** the workflow file. It only dispatches it.
+- The skill operates on the upstream repo only (`sgl-project/sglang`); the user's fork is irrelevant here.
+- Per-branch concurrency means picking 20 PRs to the same release branch will take ~20× the runtime of one. There is no parallelism to be gained client-side. If the user batches across **different** target branches, those run concurrently.
+- Do not skip the merged-state precheck — the workflow will reject unmerged PRs, but we want a single batched validation report up front rather than N individual workflow failures.
+- The skill should be invoked with `gh auth status` already passing; if not, surface the auth error and stop.