[shuaiyafei]

Related Issues

Found through source inspection and reproduced locally. No existing issue is claimed.

Proposed Changes

Honor the documented priority of a runtime streaming callback before checking execution-context compatibility.

Currently, an unused async initialization callback makes a synchronous run fail even when a valid synchronous runtime callback replaces it. Conversely, an unused sync initialization callback produces an event-loop-blocking warning when the selected runtime callback is async.

Validate the initialization callback only when it will be used. Select a provided runtime callback by checking for None, so an empty callable collector is not silently replaced by the initialization callback.

The existing rejection of a selected async callback in a synchronous context and the warning for a selected sync callback in an async context remain covered.

How did you test it?

• The three affected cases fail before the fix: the sync runtime override, the misleading warning for an unused initialization callback, and an empty callable collection that never receives its chunks.
• hatch run test:unit test/dataclasses/test_streaming_chunk.py test/components/generators/chat/test_openai.py -q: 97 passed, 12 deselected. Integration tests are excluded by the unit-test command.
• hatch run test:types on both changed Python files: passed.
• hatch run fmt on both changed Python files and changed-file pre-commit checks: passed.
• Normal commit hook: passed.

Tested with Python 3.12.15 on macOS arm64. No live provider request or full-suite run was performed.

Notes for the reviewer

This restores the existing callback-priority contract without adding an API or dependency. The function docstring and a Reno bug-fix note describe the behavior.

This PR was fully generated with Codex. The changed paths were reviewed locally and verified with the tests and checks above.

Checklist

• Read the contributor guidelines and code of conduct.
• Added regression coverage and updated the affected docstring.
• Used a conventional commit title.
• Added a release note through the repository's Reno command.
• Ran formatting, typing, and pre-commit checks.

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[HaystackBot]

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[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/dataclasses
streaming_chunk.py
Project Total

This report was generated by python-coverage-comment-action

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