etcd(ticdc): update etcd cluster member correctly

[wk989898]

What problem does this PR solve?

Issue Number: close #12368

What is changed and how it works?

When updating etcd client URLs, remove the client that is not a member of the etcd cluster.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

tiup playground $VERSION --db 1 --kv 1 --pd 3 --ticdc 1 --tiflash 0 --without-monitor
tiup cdc:$VERSION cli changefeed create --sink-uri 'blackhole://'
tiup playground scale-out --pd 1
tiup playground display
tiup playground scale-in --pid 153389 # pick any one from the display

Print only once

[2026/05/21 10:03:39.588 +00:00] [INFO] [client.go:447] ["update endpoints"] [numChange=3->4] [lastEndpoints="[http://127.0.0.1:2382,http://127.0.0.1:2379,http://127.0.0.1:2384]"] [endpoints="[http://127.0.0.1:44765,http://127.0.0.1:2382,http://127.0.0.1:2384,http://127.0.0.1:2379]"]

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

Fixed the bug of using an incorrect etcd client when scaling PD nodes

[gemini-code-assist]

Code Review

This pull request updates the update method in pkg/etcd/client.go to synchronize the internal client cache with a provided list of endpoints, ensuring that stale clients are removed. The review feedback identifies a potential resource leak where clients are deleted without being closed and suggests a performance optimization by pre-allocating the map capacity.

[joechenrh]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: asddongmen, lidezhu

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Details

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• OWNERS [asddongmen,lidezhu]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-05-22 13:19:52.307440159 +0000 UTC m=+12662.277605224: ☑️ agreed by lidezhu.
• 2026-05-22 14:36:14.56699746 +0000 UTC m=+17244.537162517: ☑️ agreed by asddongmen.

[wk989898]

/retest

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #12649.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #12650.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #12651.