server: keep unsynced region stats leader-only

[okJiang]

What problem does this PR solve?

Issue Number: ref #10719

Follower handling allowed several Region statistics APIs to execute against the follower-local Region cache.

RegionSyncer does not synchronize query statistics, approximate size and key counts, or CPU usage. A follower could therefore return stale, missing, or zero statistics for these APIs.

What is changed and how does it work?

Keep Region query, size, key, CPU, and histogram statistics APIs on the leader.

Continue allowing follower-local handling for Region metadata and flow APIs whose required fields are synchronized.

Add an integration test that verifies direct follower handling is rejected while normal forwarding to the leader succeeds.

Check List

Tests

• Integration test
• Manual test

Manual test:

• Verified direct follower handling is rejected for all seven affected statistics APIs.
• Verified the same requests succeed after forwarding to the leader.
• Verified safe Region metadata and flow APIs continue to execute on followers.

Code changes

• Has HTTP APIs changed

Release note

Keep Region query, size, key, CPU, and histogram statistics APIs on the PD leader when follower handling is enabled.

Summary by CodeRabbit

• Bug Fixes
  • Updated access handling for region query, sizing, key, CPU, and histogram endpoints.
  • Requests to leader-only region APIs from follower nodes now return a clear error when the cluster is not bootstrapped.
• Tests
  • Added coverage for follower behavior across additional region-related endpoints.

[ti-chi-bot]

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 6dc2e1dd-87f9-4970-a07f-2ab82d116c6c

📥 Commits

Reviewing files that changed from the base of the PR and between fad3ff9 and aafd682.

📒 Files selected for processing (2)

• server/api/router.go
• tests/server/api/api_test.go

---

📝 Walkthrough

Walkthrough

Region ranking and histogram APIs are reassigned from region read routing to cluster routing. Follower API coverage now verifies leader-only region endpoints return cluster-not-bootstrapped errors without forwarding.

Changes

Region API routing

Layer / File(s)	Summary
Cluster middleware routing and follower validation server/api/router.go, tests/server/api/api_test.go	Region ranking and histogram endpoints move to clusterRouter, while readflow, confver, and version remain on regionReadRouter. Follower requests to leader-only paths are expected to return HTTP 500 with the cluster-not-bootstrapped message.

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

Possibly related PRs

• tikv/pd#10682: Updates related region endpoint routing and follower no-forward behavior.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title matches the main change: keeping affected region statistics APIs leader-only.
Description check	✅ Passed	The description follows the template and includes the issue, change summary, tests, code changes, and release note.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[ti-chi-bot]

@okJiang: 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
pull-unit-test-next-gen-3	aafd682	link	true	/test pull-unit-test-next-gen-3

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.36%. Comparing base (070828c) to head (aafd682).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11065      +/-   ##
==========================================
+ Coverage   79.23%   79.36%   +0.12%     
==========================================
  Files         540      541       +1     
  Lines       76010    76354     +344     
==========================================
+ Hits        60226    60597     +371     
+ Misses      11533    11497      -36     
- Partials     4251     4260       +9     

Flag	Coverage Δ
unittests	79.36% <100.00%> (+0.12%)	⬆️

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