fix: pick deterministic conversion strategy for union receivers

[Diwak4r]

Related Issues

• fixes Pipeline connection type conversion is non-deterministic across processes #12282

Proposed Changes:

_get_conversion_strategy resolves the strategy for a Union receiver by collecting the strategies of every member into a set and, when neither WRAP nor UNWRAP is among them, falling back to strategies.pop(). Because enum members hash by identity, set.pop() is non-deterministic across processes (ASLR): the same sender/receiver pair could resolve to different conversion strategies on different runs.

Example: converting a ChatMessage to str | list[str] could resolve to either CHAT_MESSAGE_TO_STR or WRAP_CHAT_MESSAGE_TO_STR depending on the process.

This PR replaces the set.pop() with a deterministic scan of the receiver's union members in declaration order, returning the strategy of the first member that yields one. The chosen strategy now honors the order in which the user declared the union members.

How did you test it?

Added regression assertions to test_types_are_compatible_with_conversion:

• ChatMessage -> str | list[str] resolves to CHAT_MESSAGE_TO_STR
• ChatMessage -> list[str] | str resolves to WRAP_CHAT_MESSAGE_TO_STR

Under the previous code, the first assertion would flip between the two strategies at random across processes; both now always pass.

Ran the full test_type_utils.py and test_recursive_splitter.py suites: 1122 tests pass.

Notes for the reviewer

The existing WRAP/UNWRAP preference loop is unchanged; only the fallback selection is now deterministic.

Checklist

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• I have updated the related issue with new insights and changes.
• I have added unit tests and updated the docstrings.
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• 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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