fix(profiling): Add platform to envelope item header

[s1gr1d]

Adds the missing platform in the envelope item header.

Related: getsentry/sentry-docs#16135

Closes https://linear.app/getsentry/issue/JS-1540/ui-profiling-add-platform-to-profile-chunk-item-header (internal Linear)

[linear]

JS-1540 UI Profiling: Add `platform` to `profile_chunk` item header

[cursor]

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[Lms24]

really sorry for the nitpicking here but I'm curious on your thoughts: I don't particularly like the pattern of these "validator" functions. Here's why:

• I have to jump when debugging tests to get to the actual assertions
• the stack traces when the test fails point to this validator instead of the failed test. Not ideal when the validator is used in a lot of places

Also specifically for this case: We only check that the header includes some properties but we don't assert on its entire content.

I get that the larger validateProfile helper, encapsulates a lot more assertions. Making it more justified. But for this case, with only two assertions, I'd personally avoid DRY and directly add the assertions; or even change it to just one expect(header).toEqual(...) for extra robustness.

Feel free to ignore/overrule me here :D I might be missing a reason for this.

[s1gr1d]

I used this validator function here to make sure that when testing the headers, this set of assertions is used - so not a crazy reason that would overrule your concerns :D

Yes, it would make sense to just change it to this one-line assertion. The function only makes sense for the very large chunk-testing part.

Changed it to: expect(itemHeader).toEqual({ type: 'profile_chunk', platform: 'javascript' });

[Lms24]

Thanks for addressing my review!