[Instrumentation.Hangfire] Fix 'FailedToInjectActivityContext' when no ActivityContext exists

[gao-artur]

Fixes #
Design discussion issue #

Changes

The HangfireInstrumentationJobFilterAttribute was trying to inject a default ActivityContext when there was no activity. This is not supported by the TraceContextPropagator and was leading to EventSource message

Failed to inject activity context in format: 'TraceContextPropagator', context: 'Invalid context'.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.70%. Comparing base (e5ebf34) to head (99a8dff).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...ation/HangfireInstrumentationJobFilterAttribute.cs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2990      +/-   ##
==========================================
- Coverage   69.79%   69.70%   -0.09%     
==========================================
  Files         386      388       +2     
  Lines       15917    15850      -67     
==========================================
- Hits        11109    11048      -61     
+ Misses       4808     4802       -6     

Flag	Coverage Δ
unittests-Instrumentation.Hangfire	84.61% <75.00%> (-8.98%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ation/HangfireInstrumentationJobFilterAttribute.cs	77.77% <75.00%> (-12.97%)	⬇️

... and 13 files with indirect coverage changes

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[gao-artur]

For some reason, this test started to fail intermittently when I added a new test. I guess it's related to the static configuration in the HangfireFixture. Adding AlwaysOnSampler seems to fix/workaround it.

[Kielek]

@fred2u, FYI