[API] Add propagation fuzz tests and fix findings

[martincostello]

Changes

Add fuzz tests for the propagator classes.

I thought it would be a good idea to add these after working on #7059 and #7060 due to the amount of string parsing they do.

In the process of adding the new fuzz tests, some bugs were found in the processing that have now been fixed.

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 99.09091% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.51%. Comparing base (888d1bf) to head (652be5f).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...enTelemetry.Extensions.Propagators/B3Propagator.cs	98.07%	1 Missing ⚠️
...lemetry.Extensions.Propagators/JaegerPropagator.cs	97.95%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7061      +/-   ##
==========================================
+ Coverage   88.29%   88.51%   +0.22%     
==========================================
  Files         270      270              
  Lines       12759    12884     +125     
==========================================
+ Hits        11265    11404     +139     
+ Misses       1494     1480      -14     

Flag	Coverage Δ
unittests-Project-Experimental	88.46% <99.09%> (+0.39%)	⬆️
unittests-Project-Stable	88.13% <99.09%> (-0.04%)	⬇️
unittests-Solution	88.46% <99.09%> (+0.25%)	⬆️

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

Files with missing lines	Coverage Δ
...nTelemetry.Api/Context/Propagation/B3Propagator.cs	89.07% <100.00%> (+2.75%)	⬆️
...metry.Api/Context/Propagation/BaggagePropagator.cs	88.23% <100.00%> (+2.08%)	⬆️
....Api/Context/Propagation/TraceContextPropagator.cs	93.37% <100.00%> (+2.97%)	⬆️
...lemetry.Api/Context/Propagation/TraceStateUtils.cs	91.07% <100.00%> (+6.37%)	⬆️
...enTelemetry.Extensions.Propagators/B3Propagator.cs	88.98% <98.07%> (+3.87%)	⬆️
...lemetry.Extensions.Propagators/JaegerPropagator.cs	95.28% <97.95%> (+1.25%)	⬆️

... and 8 files with indirect coverage changes

[Copilot]

Pull request overview

Adds a new OpenTelemetry.Api.FuzzTests test project to exercise propagation-related APIs with FsCheck-based property tests, aiming to harden string parsing and ensure stable behavior across a wide range of generated inputs.

Changes:

• Introduce a new fuzz test project (OpenTelemetry.Api.FuzzTests) targeting the repo’s test TFMs and using FsCheck.Xunit.
• Add property-based fuzz tests for TraceContextPropagator, BaggagePropagator, and B3Propagator, plus shared generators/helpers.
• Include the new fuzz test project in OpenTelemetry.slnx.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/OpenTelemetry.Api.FuzzTests/OpenTelemetry.Api.FuzzTests.csproj	New fuzz test project definition with FsCheck and OpenTelemetry.Api reference.
test/OpenTelemetry.Api.FuzzTests/Context/Propagation/TraceContextPropagatorFuzzTests.cs	Adds property tests for trace context inject/extract round-trips and determinism.
test/OpenTelemetry.Api.FuzzTests/Context/Propagation/BaggagePropagatorFuzzTests.cs	Adds property tests for baggage round-trips, size limits, and determinism.
test/OpenTelemetry.Api.FuzzTests/Context/Propagation/B3PropagatorFuzzTests.cs	Adds property tests for obsolete B3 propagator (single/multi header) round-trips and determinism.
test/OpenTelemetry.Api.FuzzTests/Context/Propagation/Generators.cs	Provides FsCheck generators for contexts and arbitrary header carriers.
test/OpenTelemetry.Api.FuzzTests/Context/Propagation/FuzzTestHelpers.cs	Shared getter/setter delegates, carrier cloning/comparison, and allowed-exception filter.
OpenTelemetry.slnx	Adds the new fuzz test project to the solution.

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