fix: restore auto-variadic socket state in remove_component

[rautaditya2606]

Related Issues

• Fixes PipelineBase.remove_component does not reset auto-variadic socket state when reusing components #12205

Proposed Changes

• Updated PipelineBase.remove_component in haystack/core/pipeline/base.py to call socket.__post_init__() and set socket.wrap_input_in_list = True when resetting input sockets of a removed component or when a receiver's remaining senders count drops to $\le 1$.
• Added unit test test_remove_component_resets_auto_variadic_socket_mutation in test/core/pipeline/test_pipeline_base.py.
• Added a release note file in releasenotes/notes/.

How did you test it?

hatch run test:unit test/core/pipeline/test_pipeline_base.py
hatch run test:types
hatch run fmt

All 149 pipeline base tests pass cleanly, formatting is verified, and mypy reports zero issues.

Notes for the reviewer

• Connecting multiple senders to a list[T] socket promotes it to auto-variadic (is_lazy_variadic=True, wrap_input_in_list=False).
• Previously, remove_component only set socket.senders = [], leaving is_lazy_variadic=True and wrap_input_in_list=False intact. Reusing the component in a single-sender pipeline caused silent input processing bugs (unwanted flattening).
• Re-invoking socket.__post_init__() safely re-derives variadic status from the socket's declared type annotation, restoring default socket behavior.

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.
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run the pre-commit hooks and fixed any issues.

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Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/core/pipeline
base.py
Project Total

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

[anakin87]

@sjrl could you please take a look when you have some time?

My impression is that the current fix is problematic and corrupts Variadic components during removal.

But you know this part better than me...

[rautaditya2606]

@sjrl could you please take a look when you have some time?

My impression is that the current fix is problematic and corrupts Variadic components during removal.

But you know this part better than me...

Thanks for the feedback. I've updated the implementation so only the removed component's socket state is restored. Receiver sockets in the active pipeline are no longer modified.