fix: improve username validation in sendMessage

[Rajkaran-122]

Summary

This PR removes an unsafe type assertion in the message sending flow and improves username validation with safer type handling.

What Changed

• Removed an unsafe type assertion
• Added proper username validation
• Improved type safety without changing existing behavior

Why

This makes the code easier to maintain and reduces the risk of invalid values reaching the message handling logic.

Testing

• Existing tests pass
• Added validation tests where applicable

Checklist

• Follows the project's coding conventions
• No breaking changes
• Type safety improved

[dionisio-bot]

Looks like this PR is not ready to merge, because of the following issues:

• This PR is missing the 'stat: QA assured' label
• This PR is missing the required milestone or project

Please fix the issues and try again

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Latest commit: 94ef784

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[coderabbitai]

Walkthrough

Changes

Message validation

Layer / File(s)	Summary
Validate message user apps/meteor/server/lib/messages/sendMessage.ts	prepareMessageObject rejects users without a username using error-invalid-user and assigns the validated username directly to message.u.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Suggested labels: type: bug

Suggested reviewers: sampaiodiego

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: tighter username validation in sendMessage.

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[cubic-dev-ai]

No issues found across 1 file

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