add the release notes for v8.5.8 (#21892)

[ti-chi-bot]

This is an automated cherry-pick of #21892

What is changed, added or deleted? (Required)

As in the title

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)

What is the related PR or file link(s)?

• This PR is translated from: add the release notes for v8.5.8 docs#23522
• Other reference link(s):

AI agent involvement

• The changes in this PR were primarily made by an AI agent on behalf of the PR author.

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

Summary by CodeRabbit

• 新功能

  • 新增 TiDB 8.5.8 版本发布说明，涵盖性能优化与多组件问题修复。
  • 更新版本目录及发布时间线，标注 8.5.8 发布日期为 2026-08-27。

• 文档

  • 更新试用入口说明，移除 TiDB 8.5.7 的离线包下载链接。

[ti-chi-bot]

@qiancai This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[ti-chi-bot]

@ti-chi-bot: ## If you want to know how to resolve it, please read the guide in TiDB Dev Guide.

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[coderabbitai]

📝 Walkthrough

Walkthrough

新增 TiDB 8.5.8 发布说明，包含版本信息、改进提升和错误修复。版本索引与发布时间线新增 8.5.8 条目。8.5.7 试用链接移除离线包下载链接。

Changes

TiDB 8.5.8 发布

Layer / File(s)	Summary
发布说明内容 releases/release-8.5.8.md, releases/release-8.5.7.md	新增 8.5.8 的版本信息、改进提升、错误修复和代码变更链接。8.5.7 仅保留快速体验和生产部署链接。
版本索引与时间线 TOC-pingkai.md, TOC-tidb-releases.md, releases/_index.md, releases/release-timeline.md	多个版本入口和时间线新增 TiDB 8.5.8，并记录发布日期 2026-08-27。

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to d22ef

This documentation-only change is merge-ready after normal review, with one minor wording clarification and confirmation that the offline-package link remains available; no actionable merge-blocking risk remains.

Suggested reviewers: qiancai

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	描述包含变更概述、关联 PR、AI agent 勾选项和其他模板章节，但未勾选适用版本。变更说明“As in the title”也未提供足够的具体信息。	请在版本列表中勾选实际适用的版本，至少确认 master，必要时勾选 v8.5。请具体说明新增 v8.5.8 发布说明、更新版本索引和时间线，以及相关链接调整。

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	标题“add the release notes for v8.5.8 (#21892)”准确概括了新增 TiDB v8.5.8 发布说明这一主要变更。
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (6 skipped: 6 unsupported.)

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: e96d47dc-1bf9-4ea7-a1b3-5c72e578eb56

📥 Commits

Reviewing files that changed from the base of the PR and between d189954 and d22ef65.

📒 Files selected for processing (6)

• TOC-pingkai.md
• TOC-tidb-releases.md
• releases/_index.md
• releases/release-8.5.7.md
• releases/release-8.5.8.md
• releases/release-timeline.md

Included review availability: Your plan provides up to 4 included reviews per hour; 3 remain after this review.

[qiancai]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

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• OWNERS [qiancai]

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