[CI] CoreWithMultipleProjectsClientYamlTestSuiteIT test {yaml=cluster.stats/10_basic/Dense vector stats} failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #9065 / windows-2025_checkpart2_platform-support-windows
• elasticsearch-pull-request #78148 / part-2
• elasticsearch-pull-request #77684 / part-2

Reproduction Line:

gradlew ":x-pack:qa:multi-project:core-rest-tests-with-multiple-projects:yamlRestTest" --tests "org.elasticsearch.multiproject.test.CoreWithMultipleProjectsClientYamlTestSuiteIT" -Dtests.method="test {yaml=cluster.stats/10_basic/Dense vector stats}" -Dtests.seed=213FDFC01DBBA67 -Dtests.locale=dua -Dtests.timezone=Europe/Bratislava -Druntime.java=24

Applicable branches:
main

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: Failure at [cluster.stats/10_basic:351]: 
Expected: <5>
     but: was <8>

Issue Reasons:

• [main] 3 failures in test test {yaml=cluster.stats/10_basic/Dense vector stats} (0.6% fail rate in 486 executions)
• [main] 2 failures in step part-2 (1.4% fail rate in 141 executions)
• [main] 2 failures in pipeline elasticsearch-pull-request (1.4% fail rate in 144 executions)

Note:
This issue was created using new test triage automation. Please report issues or feedback to es-delivery.

[elasticsearchmachine]

This has been muted on branch main

Mute Reasons:

• [main] 3 failures in test test {yaml=cluster.stats/10_basic/Dense vector stats} (0.6% fail rate in 486 executions)
• [main] 2 failures in step part-2 (1.4% fail rate in 141 executions)
• [main] 2 failures in pipeline elasticsearch-pull-request (1.4% fail rate in 144 executions)

Build Scans:

• elasticsearch-periodic-platform-support #9065 / windows-2025_checkpart2_platform-support-windows
• elasticsearch-pull-request #78148 / part-2
• elasticsearch-pull-request #77684 / part-2

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[nielsbauman]

Similar to #130678 (comment), rerouting to the search team since the failure seems to be related to vectors/embeddings. Also note that the failure doesn't seem related to multi-project, as there are also failures for non-multi-project test suites, for example: https://gradle-enterprise.elastic.co/s/rittchi5fd6zg.

[elasticsearchmachine]

Pinging @elastic/es-search-relevance (Team:Search Relevance)

[nielsbauman]

Actually, ignore my previous comment. I discovered that it's caused by the ILM history data stream being created during the execution of this test. In the regular x-pack REST tests, we disable the ILM history store:

elasticsearch/x-pack/plugin/src/yamlRestTest/java/org/elasticsearch/xpack/test/rest/XPackRestIT.java

Lines 40 to 41 in f9d96dc

	// disable ILM history, since it disturbs tests using _all
	.setting("indices.lifecycle.history_index_enabled", "false")

So we just need to update the multi-project version to also disable the history store.