Mapping type changes not properly validated with subobjects: false

[flash1293]

Elasticsearch Version

main

Installed Plugins

No response

Java Version

bundled

OS Version

MacOS 15.2

Problem Description

When using subobjects: false, the usual validation when changing field types is not triggered. Elasticsearch does change the type but will fail ingesting additional documents.

Steps to Reproduce

// step 1: create index
PUT my-index
{
  "mappings": {
    "subobjects": false,
    "properties": {
      "user.id": {
        "type": "long"
      }
    }
  }
}

// step 2: add some data
POST my-index/_doc
{
  "user.id": 123
}

// step 3: change mapping (succeeds by shouldn't)
PUT my-index/_mapping
{
    "properties": {
      "user.id": {
        "type": "keyword"
      }
    }
}

// step 4:trying to add more data fails
POST my-index/_doc
{
  "user.id": 123
}

This fails in step 4 with cannot change field "user.id" from index options=NONE to inconsistent index options=DOCS

Executing the same series of commands but omitting "subobjects": false in step 1 fails as expected in step 3 with mapper [user.id] cannot be changed from type [long] to [keyword] - this is what should happen with subobjects: false as well.

Logs (if relevant)

No response

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)