*: cherry-pick TiFlash graceful shutdown related PRs to release-8.5

[gengliqi]

What problem does this PR solve?

Issue Number: ref #61826, #62421, #62414

Problem Summary:

What changed and how does it work?

Cherry-pick #62355, #62085 and #62386 to release-8.5

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

[gengliqi]

/cc @windtalker @guo-shaoge

[codecov]

Codecov Report

❌ Patch coverage is 74.04580% with 34 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-8.5@17d2b2e). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #63268   +/-   ##
================================================
  Coverage               ?   57.1578%           
================================================
  Files                  ?       1780           
  Lines                  ?     631506           
  Branches               ?          0           
================================================
  Hits                   ?     360955           
  Misses                 ?     246273           
  Partials               ?      24278           

Flag	Coverage Δ
integration	37.1332% <2.2900%> (?)
unit	72.7606% <74.0458%> (?)

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

Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	52.7667% <0.0000%> (?)

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[gengliqi]

/retest

[tiprow]

@gengliqi: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/retest

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[windtalker]

lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-09-01 04:13:35.712815048 +0000 UTC m=+759107.590646002: ☑️ agreed by windtalker.
• 2025-09-01 06:37:58.164754615 +0000 UTC m=+767770.042585570: ☑️ agreed by guo-shaoge.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: guo-shaoge, windtalker, yudongusa
Once this PR has been reviewed and has the lgtm label, please assign elsa0520 for approval. For more information see the Code Review Process.
Please ensure that each of them provides their approval before proceeding.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS [guo-shaoge,windtalker]
• pkg/planner/OWNERS
• pkg/sessionctx/variable/OWNERS [yudongusa]

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