fix: resolve postponed dataclass fields in ComponentTool

[pei711]

Related Issues

No existing issue found for dataclass field annotations. This complements #12739, which resolves postponed function parameter annotations. Reproduced on main at 87dba65.

Proposed Changes

ComponentTool cannot generate a schema for a dataclass whose string field annotations mention a nested dataclass or Annotated. This includes dataclasses in modules using from __future__ import annotations; construction raises SchemaGenerationError before the Agent can call the tool.

Resolve dataclass field hints in the defining class's namespace with include_extras=True, then apply the existing schema conversion. Keep recursive references as ForwardRef back-edges so previously supported recursive dataclasses still work. Public tool signatures and serialization formats are unchanged.

How did you test it?

• The two postponed-annotation regressions fail on the original implementation and pass with the fix. They cover nested schema descriptions, an Annotated constraint, serialization round trips, and sync/async public tool invocation.
• A recursive dataclass regression checks schema generation and public invocation.
• hatch run test:unit test/tools test/core/test_type_utils.py test/core/component test/components/agents -q --no-cov: 1750 passed, 18 deselected.
• hatch run test:types haystack/tools/parameters_schema_utils.py test/tools/test_component_tool.py: no issues found.
• Changed-file Ruff and all applicable pre-commit hooks pass; git diff --check passes.
• An independent module using real future annotations fails at tool construction on the original helper. With the fix, a real Haystack Agent executes the component tool through both run() and run_async(). Only the chat generator is scripted with MockChatGenerator; no provider API is called.

Checks ran on Windows with Python 3.13 through Hatch. The broader suite reports two existing warnings about _delegate_default not being JSON serializable. Cross-version CI is pending.

Checklist

• Read the contributor guidelines and code of conduct.
• Added regression tests and updated private helper docstrings.
• Used a conventional commit title.
• Added a release note.
• Ran applicable pre-commit hooks.

This PR was fully generated with OpenAI Codex, including the implementation, tests, and description. Codex reviewed the changes and ran the checks listed above; no human review is claimed.

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