sessiontxn/staleread: don't overwrite StaleTSOProvider for single statement (#65110)

[ti-chi-bot]

This is an automated cherry-pick of #65110

What problem does this PR solve?

Issue Number: close #65090

Problem Summary:

What changed and how does it work?

CalculateAsOfTsExpr may be called multi times when there are multi select-as-of-timestamp statements in one SQL, multi TSO providers can break the consistent requirement.

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.

I reran the tests described in the issue and the unexpected error never appears with this PR.

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (release-8.5@fe0bc99). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #65128   +/-   ##
================================================
  Coverage               ?   72.6323%           
================================================
  Files                  ?       1676           
  Lines                  ?     468779           
  Branches               ?          0           
================================================
  Hits                   ?     340485           
  Misses                 ?     105632           
  Partials               ?      22662           

Flag	Coverage Δ
integration	49.7846% <100.0000%> (?)
unit	64.9264% <100.0000%> (?)

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	54.9586% <0.0000%> (?)

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: MyonKeminta, XuHuaiyu

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Details

Needs approval from an approver in each of these files:

• OWNERS [MyonKeminta,XuHuaiyu]
• pkg/expression/OWNERS [XuHuaiyu]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-12-19 01:45:00.208956633 +0000 UTC m=+1783045.022734195: ☑️ agreed by MyonKeminta.
• 2025-12-19 02:13:35.396954573 +0000 UTC m=+1784760.210732145: ☑️ agreed by XuHuaiyu.

[you06]

/retest

[ti-chi-bot]

@ti-chi-bot: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/unit-test	98fe823	link	true	/test unit-test

Full PR test history. Your PR dashboard.

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