enhancement: add `elastic es text-structure` (find-structure, find-field-structure, test-grok-pattern)

[MattDevy]

Summary

The _text_structure API family (find_structure, find_field_structure, find_message_structure, test_grok_pattern) is not exposed anywhere under elastic es. This API infers mappings and ingest pipelines from a sample of unstructured data — it is the core of "smart ingest" workflows where the user has a file but no schema.

Current surface

No commands under elastic es or elastic es ingest match text-structure or find-structure. Verified via:

elastic es --help | grep -iE "text|struct|infer"  # no hits

Missing endpoints

CLI command	REST endpoint
elastic es text-structure find-structure	POST /_text_structure/find_structure
elastic es text-structure find-field-structure	GET /_text_structure/find_field_structure
elastic es text-structure find-message-structure	POST /_text_structure/find_message_structure
elastic es text-structure test-grok-pattern	POST /_text_structure/test_grok_pattern

Motivation / use case

The elasticsearch-file-ingest skill uses _text_structure/find_structure via node-es-transformer for the --infer-mappings workflow: agent receives a CSV/JSON/ND-JSON file, asks ES to propose mappings + an ingest pipeline, then ingests. This is a common enough workflow that it is the primary reason scripts/ingest.js is kept in the skill after the CLI migration (see PR #359).

Without CLI coverage, there is no elastic-native way to do schema inference — users must fall back to either curl -T data.csv "$ES/_text_structure/find_structure" or a Node helper.

find_structure takes a binary body (the sample) rather than JSON, which may need special handling in the codegen model — suggesting --input-file as the idiomatic way to pass it.

Codegen note

All four endpoints are in the ES OpenAPI spec under the text_structure namespace. If the codegen excludes them because of the non-JSON body, please flag that as a codegen limitation.

Environment

• CLI: 0.1.0-alpha.1
• Surfaced during: https://github.com/elastic/agent-skills-sandbox elasticsearch skills migration (PR #359)

[JoshMock]

Same as #178: as long as they don't break Serverless support, go for it.

[margaretjgu]

All text-structure commands were added to main as part of #269:

• elastic stack es text-structure find-structure
• elastic stack es text-structure find-field-structure
• elastic stack es text-structure find-message-structure
• elastic stack es text-structure test-grok-pattern