feat: Enable components to automatically accept multiple connections if their input type is list

[sjrl]

Related Issues

• fixes https://github.com/deepset-ai/haystack-private/issues/241

Proposed Changes:

Natively support connecting multiple outputs directly to another component without needing the user to define a Joiner component.

For example, a user may want to connect multiple output edges of the FileTypeRouter to all go to the same converter (e.g. ImageConverter). Before you would have to define a ListJoiner as an in-between component. The changes introduced in this PR would allow you to directly connect all outputs from the FileTypeRouter to the ImageConverter.

How did you test it?

• Need to add tests

Notes for the reviewer

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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Project	Deployment	Review	Updated (UTC)
haystack-docs	Ready	Preview, Comment	Jan 23, 2026 1:58pm

[coveralls]

Pull Request Test Coverage Report for Build 21288609240

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 62 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.03%) to 92.428%

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Files with Coverage Reduction	New Missed Lines	%
core/pipeline/async_pipeline.py	2	66.67%
core/component/types.py	3	92.68%
core/pipeline/pipeline.py	3	93.16%
core/pipeline/base.py	54	86.68%

Totals
Change from base Build 21284971239:	-0.03%
Covered Lines:	14783
Relevant Lines:	15994

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💛 - Coveralls