[ML] Fix Transform upgrade test

[davidkyle]

The test failed comparing an int to a long

Closes #132892

[elasticsearchmachine]

Pinging @elastic/ml-core (Team:ML)

[davidkyle]

The upgrade test failed because the original check for a mixed cluster isMinTransportVersionSameAsCurrent depends on the order in which the nodes are upgraded. If the master node this code runs on has not been upgraded yet the test will pass.

[prwhelan]

Nice find

[davidkyle]

The upgrade tests from 8.19.5 are failing because the transform upgrade code is fighting it out with the automatic system index upgrader.

First the system index migrator moves .transform-internal-007 to .transform-internal-007-reindexed-for-10

[2025-10-03T10:31:34,304][INFO ][o.e.s.t.SystemIndexMigrator] [v8.19.5-0] preparing to migrate old index [.transform-internal-007] from feature [transform] to new index [.transform-internal-007-reindexed-for-10]
[2025-10-03T10:31:34,305][INFO ][o.e.s.t.SystemIndexMigrator] [v8.19.5-0] migrating index [.transform-internal-007] from feature [transform] to new index [.transform-internal-007-reindexed-for-10]
[2025-10-03T10:31:34,305][INFO ][o.e.s.t.SystemIndexMigrator] [v8.19.5-0] creating new system index [.transform-internal-007-reindexed-for-10] from feature [transform]
[2025-10-03T10:31:34,312][INFO ][o.e.c.m.MetadataCreateIndexService] [v8.19.5-0] creating index [.transform-internal-007-reindexed-for-10] in project [default], cause [migrate-system-index], templates [], shards [1]/[1]
[2025-10-03T10:31:34,386][INFO ][o.e.c.m.MetadataIndexStateService] [v8.19.5-0] adding [index.blocks.write] block to indices [[.transform-internal-007/_WTe27ThRGS_FRhiiZKK3A]]
[2025-10-03T10:31:34,450][INFO ][o.e.c.m.MetadataIndexStateService] [v8.19.5-0] completed adding [index.blocks.write] block to indices [.transform-internal-007]
[2025-10-03T10:31:34,540][INFO ][o.e.c.m.MetadataDeleteIndexService] [v8.19.5-0] [.transform-internal-007/_WTe27ThRGS_FRhiiZKK3A] deleting index
[2025-10-03T10:31:34,586][INFO ][o.e.s.t.SystemIndexMigrator] [v8.19.5-0] Successfully migrated old index [.transform-internal-007] to new index [.transform-internal-007-reindexed-for-10] from feature [transform]

Then POST /_transform/_upgrade is called the final act of which is to delete old indices and because it does not recognise .transform-internal-007-reindexed-for-10 that is deleted too.

[2025-10-03T10:31:40,876][INFO ][o.e.x.t.a.TransportUpgradeTransformsAction] [v8.19.5-0] [mixed-complex-transform] Updated transform [NONE]
[2025-10-03T10:31:40,878][INFO ][o.e.c.m.MetadataDeleteIndexService] [v8.19.5-0] [.transform-internal-007-reindexed-for-10/m6txlkEcTjCPy1jRR3Rk_A] deleting index
/* The new system index has just been deleted !! */
[2025-10-03T10:31:40,918][INFO ][o.e.x.t.a.TransportUpgradeTransformsAction] [v8.19.5-0] Successfully upgraded all transforms, (updated: [0], no action [7])

[davidkyle]

@prwhelan I've added 84329e4 to address the rolling upgrade failure described above. Please can you take another look

[prwhelan]

Nice find