design: Add active-active design docs

[flowbehappy]

What problem does this PR solve?

Add Active-Active design documents

Issue Number: ref #64281

Problem Summary:

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[tiprow]

Hi @flowbehappy. Thanks for your PR.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.8046%. Comparing base (669341d) to head (421c8f4).
⚠️ Report is 31 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #64294        +/-   ##
================================================
+ Coverage   72.7418%   73.8046%   +1.0628%     
================================================
  Files          1859       1865         +6     
  Lines        504114     513172      +9058     
================================================
+ Hits         366702     378745     +12043     
+ Misses       115137     112470      -2667     
+ Partials      22275      21957       -318     

Flag	Coverage Δ
integration	42.7483% <ø> (?)
unit	73.1534% <ø> (+0.8420%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.8700% <ø> (ø)
parser	∅ <ø> (∅)
br	45.5364% <ø> (-0.8141%)	⬇️

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[xhebox]

/ok-to-test

[lcwangchao]

/retest

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-11-11 03:50:06.504915816 +0000 UTC m=+760455.947945696: ☑️ agreed by lcwangchao.
• 2025-11-11 06:06:09.474863451 +0000 UTC m=+768618.917893340: ☑️ agreed by xhebox.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Connor1996, lcwangchao, xhebox

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