chore: consolidate outputs to state string

[davidsbatista]

Related Issues

• partly fixes https://github.com/deepset-ai/haystack-private/issues/450

Proposed Changes:

• 4 functions in tools/tool.py had the same small loop copy-pasted: copy a config dict, and if it has a handler, convert it with serialize_callable/deserialize_callable.
• Pulled that loop out into two small shared helpers (_convert_handler, _convert_handler_in_configs), and had all 4 functions call them instead.
• The logic difference between the two config types stays where it was.

How did you test it?

• Added test_serialize_outputs_to_state/test_deserialize_outputs_to_state first (they had no dedicated unit tests before, only indirect coverage via Tool.to_dict/from_dict round-trips), confirmed they pass against the old implementation, then refactored.

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've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test: and added ! in case the PR includes breaking changes.
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run pre-commit hooks and fixed any issue.

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
haystack-docs	Ignored		Jul 7, 2026 2:41pm

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

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Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/tools
tool.py
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