Add HttpContent.CopyToAsync polyfills with CancellationToken

[Copilot]

HttpContent.CopyToAsync gained two CancellationToken-accepting overloads in .NET 5. The existing HttpContent polyfills covered ReadAsStreamAsync/ReadAsByteArrayAsync/ReadAsStringAsync but not CopyToAsync, leaving no way to pass a cancellation token on older target frameworks.

Polyfills added (PolyShim/Net50/HttpContent.cs)

• Task CopyToAsync(Stream, CancellationToken)
• Task CopyToAsync(Stream, TransportContext?, CancellationToken)

Both follow the established pattern for this file: check cancellationToken.ThrowIfCancellationRequested() up front, then delegate to the native non-cancellable overload.

await content.CopyToAsync(stream, cancellationToken);
await content.CopyToAsync(stream, transportContext, cancellationToken);

The other two overloads documented on the CopyToAsync API page — CopyToAsync(Stream) and CopyToAsync(Stream, TransportContext?) — already exist on every supported target framework via the abstract HttpContent base class, so they don't require a polyfill.

Other changes

• Added tests in PolyShim.Tests/Net50/HttpClientTests.cs covering both new overloads, including cancellation behavior.
• Regenerated Signatures.md to reflect the new polyfills.

[Tyrrrz]

@copilot

[Tyrrrz]

@copilot resolve merge conflicts by merging latest prime and regenerating signatures

[Copilot]

Copilot review overview

🟡 Changes recommended

The success tests call existing instance overloads rather than the new polyfills.

Review effort: Balanced
Findings: 1

Open (1)

• Pass a cancellation token to invoke the new overload · New

What changed in this PR

Adds .NET 5 HttpContent.CopyToAsync cancellation-token polyfills for older targets.

Changes:

• Adds both cancellation-aware overloads.
• Adds success and cancellation tests.
• Regenerates API signatures.

File	Description
Signatures.md	Documents the new overloads.
PolyShim/​Net50/​HttpContent.cs	Implements both polyfills.
PolyShim.Tests/​Net50/​HttpClientTests.cs	Adds copy and cancellation tests.

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[Copilot]

@copilot resolve merge conflicts by merging latest prime and regenerating signatures

Merged the latest prime branch and regenerated Signatures.md. Merge commit: 39bdf3d.

[codecov]

Codecov Report

❌ Patch coverage is 94.73684% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.18%. Comparing base (9930c2b) to head (8b0e3e5).

Files with missing lines	Patch %	Lines
PolyShim/Net50/HttpContent.cs	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            prime     #149      +/-   ##
==========================================
+ Coverage   88.12%   88.18%   +0.05%     
==========================================
  Files         347      347              
  Lines        7773     7811      +38     
  Branches      557      557              
==========================================
+ Hits         6850     6888      +38     
  Misses        754      754              
  Partials      169      169              

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