fix: validate top-level JSON arrays in JsonSchemaValidator

[Harbor404]

Related Issues

• Fixes JsonSchemaValidator rejects valid arrays and skips constraints on empty arrays #13032

Proposed Changes

JsonSchemaValidator treated every top-level JSON array as a list of OpenAI function-calling tool calls. As a result, [1, 2] was validated element-by-element against an array schema, while [] skipped validation entirely and could bypass minItems.

This change validates the whole payload once for regular schemas. Per-message validation now runs only for OpenAI function-calling schemas or non-empty function-calling message lists, preserving the existing tool-call behavior.

• Updated JsonSchemaValidator.run() to choose whole-payload or per-tool-call validation based on the schema and payload.
• Added a helper to detect function-calling message lists.
• Added regression tests for a valid integer array and an empty array that violates minItems.
• Added a release note.

How did you test it?

• hatch run test:unit test/components/validators/test_json_schema.py -q --no-cov --tb=short
  • 22 passed
• hatch run test:types haystack/components/validators/json_schema.py
  • Success: no issues found in 1 source file
• hatch run fmt-check haystack/components/validators/json_schema.py test/components/validators/test_json_schema.py
  • passed

Before the fix, the two new tests failed as expected: [1, 2] produced validation_error, and [] was accepted.

Notes for the reviewer

Function-calling payloads may use either a full OpenAI function-calling schema or a schema that describes one function-call object while the message contains a list. Both existing paths are preserved by detecting non-empty function-calling message lists instead of always iterating over arrays.

This PR is a draft because the repository currently allows only one non-draft PR per community contributor, and #13059 is already open. It can be marked ready for review once that PR is merged or closed.

This PR was fully generated with an AI assistant. I have reviewed the changes and run the relevant tests.

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have updated the related issue with new insights and changes.
• I have added unit tests and updated the docstrings.
• I used a conventional commit type for the PR title.
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run focused tests, formatting, and type checks.

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