fix(event_handler): normalize Union and RootModel sequences in body validation

[danjhd]

Issue number: closes #8057

Summary

Changes

Fixed a bug in the OpenAPI validation middleware where body parameters with Union types containing sequences (e.g., Union[Model, List[Model]]) or RootModel[List[Model]] were incorrectly normalized. The middleware was extracting only the first element from list inputs instead of preserving the full list.

Key changes:

• Added _is_or_contains_sequence() helper function to detect sequences within Union types and RootModel wrappers
• Updated _normalize_field_value() to use the new helper, ensuring proper handling of complex type annotations
• Added comprehensive test coverage for Union and RootModel sequence handling

User experience

Before:

When defining an endpoint with a body parameter like Union[Item, List[Item]] and sending a JSON array with multiple items:

@app.post("/items")
def handler(items: Annotated[Union[Item, List[Item]], Body()]):
    return {"count": len(items) if isinstance(items, list) else 1}

Sending [{"name": "item1"}, {"name": "item2"}, {"name": "item3"}] would incorrectly pass only the first item to the handler, causing data loss.

After:

The handler now correctly receives the full list when a list is sent, or a single item when a single object is sent. Both Union[Model, List[Model]] and RootModel[List[Model]] patterns work as expected, allowing flexible API designs that accept either single items or collections.

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[boring-cyborg]

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[leandrodamascena]

Hey @danjhd thanks a lot for working on this. I fixed errors in mypy/ruff and asked Claude to add more tests.

Everything is fine to merge now.

APPROVED!

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.64%. Comparing base (2ab8f39) to head (8de34a2).
⚠️ Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
...ls/event_handler/middlewares/openapi_validation.py	94.11%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8067      +/-   ##
===========================================
- Coverage    96.65%   96.64%   -0.01%     
===========================================
  Files          282      282              
  Lines        13775    13790      +15     
  Branches      1096     1102       +6     
===========================================
+ Hits         13314    13328      +14     
  Misses         339      339              
- Partials       122      123       +1     

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[boring-cyborg]

Awesome work, congrats on your first merged pull request and thank you for helping improve everyone's experience!