Summary

This PR introduces a new index-level setting:

PUT /my_index
{
  "settings": {
    "index.mapping.source.auto_exclude_types": ["dense_vector", "binary" ... ] 
  }
}

Key innovations

1. ✨ Type-Driven Automation
   Automatically excludes all fields of specified types from _source at index time
2. ⚡️ Zero-Overhead Integration
   • Dynamically injects exclusions during mapping parsing
   • Requires no manual field declarations

Synergy with Related Work

Provides foundational infrastructure for #133337's hybrid source reconstruction:

auto_exclude_types → Pruned _source → Adaptive Hybrid Reconstruction

Why This Approach?

As discussed by @benwtrent:

@mayya-sharipova the idea is that you have one parameter to exclude all vector fields, by their type, instead of providing each unique vector field name.

I also suppose this unlocks future consideration of having an index level default for _source inclusion at query time type of setting that is applied by default for all queries.

But, your comment @mayya-sharipova makes me wonder if we should do something like:

{
  "_source": {
    "mapping_type_excludes": [ "dense_vector", "sparse_vector" ]
  }...
}

Instead of having something called include_vectors.

@jimczi would we add some index level setting that applies this default source filtering at query time? Is that the ultimate goal here?

Originally posted in #128735 (comment)

By implementing this through index.mapping.source.auto_exclude_types, we maintain backward compatibility with existing _source.includes/excludes. I believe this approach delivers immediate value while paving the way for more advanced source optimization techniques.