ci: add auto cherry-pick workflow for backporting

[jac0626]

Add a GitHub Actions workflow to automatically cherry-pick merged PRs to target branches based on backport-to-* labels. Supports both automatic trigger on PR merge and manual trigger via workflow dispatch.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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##             master    #3106   +/-   ##
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  Coverage          ?   46.30%           
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  Files             ?       66           
  Lines             ?    13923           
  Branches          ?        0           
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  Hits              ?     6447           
  Misses            ?     7476           
  Partials          ?        0           

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[XuanYang-cn]

Review Summary

Thanks for working on this! The auto cherry-pick workflow is a great addition, but it needs several enhancements to meet our requirements.

Required Changes:

1. ❌ Add Manual Trigger Support

Currently the workflow only triggers automatically. We need a manual trigger for retry scenarios.

Required: Add workflow_dispatch trigger with inputs:

on:
  workflow_dispatch:
    inputs:
      pr_number:
        description: 'PR number to cherry-pick'
        required: true
        type: number
      target_branch:
        description: 'Target branch (e.g., 2.5, 2.6)'
        required: true
        type: string
  pull_request_target:
    types: [closed, labeled]

---

2. ❌ Skip PRs with proto_gen Changes

PRs that modify the proto_gen/ directory should be skipped automatically since they require special handling.

Required: Add file checking before cherry-pick:

FILES_CHANGED=$(gh pr view $PR_NUMBER --json files -q '.files[].path')
if echo "$FILES_CHANGED" | grep -q "proto_gen/"; then
  gh pr comment $PR_NUMBER --body "⚠️ **Auto Cherry-Pick Skipped**
  This PR modifies \`proto_gen/\` directory. If backporting is needed, please cherry-pick manually.
  
  Target branches: $TARGET_BRANCHES"
  exit 0
fi

---

3. ❌ Use Label-Based Approach Instead of Label Parsing

Current implementation uses labels like "... to N.x" which is fragile and only supports one target.

Required: Change to use explicit version labels:

• Use labels: backport/2.6, backport/2.5, etc.
• Support multiple target branches per PR
• Loop through all backport/* labels

Example logic:

TARGET_VERSIONS=$(gh pr view $PR_NUMBER --json labels -q '.labels[].name | select(startswith("backport/")) | sub("backport/"; "")')

for VERSION in $TARGET_VERSIONS; do
  # Find matching branch and cherry-pick
  # Create separate backport PR for each version
done

---

4. ❌ Add Success Tracking Label

Required: After successful cherry-pick, add backport/succeeded label to the original PR. Keep the backport/X.Y labels for reference (don't remove them).

---

5. ⚠️ Improve Author Notifications

Current implementation only comments on failure.

Required: Always notify the author with clear status:

• ✅ Success: List which branches were successfully backported
• ⚠️ Skipped: Proto changes detected, manual action may be needed
• ❌ Failed: Conflicts detected, manual cherry-pick required

Summary of Label Design:

• backport/2.6, backport/2.5 → Target release branches (can have multiple)
• backport/succeeded → Added after all cherry-picks complete successfully
• backport/manual → (Optional) Flag for PRs requiring manual handling

Please update the workflow to address these requirements. Let me know if you have questions!

[XuanYang-cn]

Thanks to warp's help on the review comments

[XuanYang-cn]

@jac0626 Please provide a design doc for this, because it reduces all contributors labor on cherry-pick simple PRs and requires a little bit more actions on a PR.

Please add the design in the lark doc first, and add the rules in CONTRIBUTING.md

[jac0626]

@jac0626 Please provide a design doc for this, because it reduces all contributors labor on cherry-pick simple PRs and requires a little bit more actions on a PR.

Please add the design in the lark doc first, and add the rules in CONTRIBUTING.md

ack

[jac0626]

proto_gen

directory pymilvus/grpc_gen ？ @XuanYang-cn

[XuanYang-cn]

/lgtm

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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