[CI] MultiClusterSpecMatchPhraseFunctionIT test {csv-spec:match-phrase-function.matchPhraseOnToStringOverIndexedTextFieldIsExact} failing

**Build Scans:**
- [elasticsearch-intake #48479 / 9.5.5_bwc-snapshots](https://gradle-enterprise.elastic.co/s/77jdko76utt6o)
- [elasticsearch-pull-request #182316 / 9.5.5_part_3_bwc-snapshots](https://gradle-enterprise.elastic.co/s/cikvrcvecuwfg)
- [elasticsearch-pull-request #182316 / 9.5.5_part_3_bwc-snapshots](https://gradle-enterprise.elastic.co/s/akuqve2b5pimc)
- [elasticsearch-intake #48478 / 9.5.5_bwc-snapshots](https://gradle-enterprise.elastic.co/s/awf5bznt44hii)
- [elasticsearch-intake #48477 / 9.5.5_bwc-snapshots](https://gradle-enterprise.elastic.co/s/phok2t5szodda)
- [elasticsearch-pull-request #182304 / 9.5.5_part_3_bwc-snapshots](https://gradle-enterprise.elastic.co/s/nagbixohglo2w)
- [elasticsearch-pull-request #182303 / 9.5.5_part_3_bwc-snapshots](https://gradle-enterprise.elastic.co/s/7j7xbnmzae4wi)
- [elasticsearch-pull-request #182304 / 9.5.5_part_3_bwc-snapshots](https://gradle-enterprise.elastic.co/s/4hwnu46gz4asg)
- [elasticsearch-pull-request #182301 / 9.5.5_part_3_bwc-snapshots](https://gradle-enterprise.elastic.co/s/zmuougcnutdvu)
- [elasticsearch-pull-request #182303 / 9.5.5_part_3_bwc-snapshots](https://gradle-enterprise.elastic.co/s/axeiaxqvu6oou)

**Reproduction Line:**
```
./gradlew ":x-pack:plugin:esql:qa:server:multi-clusters:v9.5.5#csvSpecTests#newToOld" -Dtests.class="org.elasticsearch.xpack.esql.ccq.MultiClusterSpecMatchPhraseFunctionIT" -Dtests.method="test {csv-spec:match-phrase-function.matchPhraseOnToTextOverIndexedKeywordField}" -Dtests.seed=D37C74811AAD74F1 -Dtests.bwc=true -Dtests.locale=kxv-Telu-IN -Dtests.timezone=America/North_Dakota/Center -Druntime.java=27
```

**Applicable branches:**
main

**Reproduces locally?:**
N/A

**Failure History:**
[See dashboard](https://es-delivery-stats.elastic.dev/app/dashboards#/view/dcec9e60-72ac-11ee-8f39-55975ded9e63?_g=(refreshInterval:(pause:!t,value:60000),time:(from:now-7d%2Fd,to:now))&_a=(controlGroupState:(initialChildControlState:('0c0c9cb8-ccd2-45c6-9b13-96bac4abc542':(dataViewId:fbbdc689-be23-4b3d-8057-aa402e9ed0c5,fieldName:task.keyword,order:0,selectedOptions:!(),title:'GradleTask',type:optionsListControl),'4e6ad9d6-6fdc-4fcc-bf1a-aa6ca79e0850':(dataViewId:fbbdc689-be23-4b3d-8057-aa402e9ed0c5,fieldName:className.keyword,order:1,selectedOptions:!(org.elasticsearch.xpack.esql.ccq.MultiClusterSpecMatchPhraseFunctionIT),title:'Suite',type:optionsListControl),'144933da-5c1b-4257-a969-7f43455a7901':(dataViewId:fbbdc689-be23-4b3d-8057-aa402e9ed0c5,fieldName:name.keyword,order:2,selectedOptions:!('test%20%7Bcsv-spec%3Amatch-phrase-function.matchPhraseOnToStringOverIndexedTextFieldIsExact%7D'),title:'Test',type:optionsListControl)))))

**Failure Message:**
```
org.elasticsearch.client.ResponseException: method [POST], host [http://[::1]:35429], URI [/_query?pretty=true&error_trace=true], status line [HTTP/1.1 400 Bad Request]
---
error:
root_cause:
- type: "verification_exception"
reason: "verification_exception: Found 1 problem\nline 2:22: [MatchPhrase] function\
\ cannot operate on [TO_TEXT(author.keyword)], which is not a field from an\
\ index mapping"
stack_trace: "org.elasticsearch.common.io.stream.NotSerializableExceptionWrapper:\
\ verification_exception: Found 1 problem\nline 2:22: [MatchPhrase] function\
\ cannot operate on [TO_TEXT(author.keyword)], which is not a field from an\
\ index mapping\n\tat org.elasticsearch.xpack.esql.optimizer.LocalLogicalPlanOptimizer.localOptimize(LocalLogicalPlanOptimizer.java:104)\n\
\tat org.elasticsearch.xpack.esql.planner.PlannerUtils.lambda$localPlan$14(PlannerUtils.java:444)\n\
\tat org.elasticsearch.xpack.esql.core.tree.Node.lambda$transfo
[truncated]
```

**Issue Reasons:**
- [main] 1 consecutive failures in test test {csv-spec:match-phrase-function.matchPhraseOnToStringOverIndexedTextFieldIsExact}
- [main] 5 consecutive failures in step 9.5.5_bwc-snapshots
- [main] 60 consecutive failures in step 9.5.5_part_3_bwc-snapshots
- [main] 1 consecutive failures in step 9.4.8_part_3_bwc-snapshots
- [main] 4 consecutive failures in step 8.19.22_part_3_bwc-snapshots
- [main] 1 consecutive failures in pipeline elasticsearch-intake
- [main] 1 consecutive failures in pipeline elasticsearch-pull-request
- [main] 74 failures in test test {csv-spec:match-phrase-function.matchPhraseOnToStringOverIndexedTextFieldIsExact} (12.4% fail rate in 598 executions)
- [main] 5 failures in step 9.5.5_bwc-snapshots (100.0% fail rate in 5 executions)
- [main] 60 failures in step 9.5.5_part_3_bwc-snapshots (100.0% fail rate in 60 executions)
- [main] 2 failures in step part-3 (0.7% fail rate in 273 executions)
- [main] 2 failures in step releasetestcheckesqlqa3_release-tests (1.3% fail rate in 149 executions)
- [main] 4 failures in step 8.19.22_part_3_bwc-snapshots (100.0% fail rate in 4 executions)
- [main] 5 failures in pipeline elasticsearch-intake (7.0% fail rate in 71 executions)
- [main] 32 failures in pipeline elasticsearch-pull-request (10.4% fail rate in 308 executions)

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

Start with the x-pack:plugin:esql:qa:server:multi-clusters:v9.5.5#csvSpecTests#newToOld Gradle task and MultiClusterSpecMatchPhraseFunctionIT, using the reported test method and seed. Read the match-phrase CSV spec and the failure's verification exception, then compare behavior across the BWC branches. Done means the test completes without partial cluster results in the affected snapshot runs.

Written by the indexing model from the issue text.