[illia1f]

Streaming without a dispatch cancellation token uses a smaller iterator, and parallel event publication with one handler avoids the task array. Exception construction moves into throw helpers while preserving exception types, parameter names, and synchronous failure behavior.

• Replace handwritten compiler polyfills with private PolySharp references and annotate successful map lookups.
• Cover cancellation, stream disposal, overlapping enumerations, event failures, and allocation behavior.

Validation:

• Release build: zero warnings and errors.
• Release tests: 3,563 passed across net8.0, net10.0, and net462; none skipped.
• All four packages passed API compatibility validation against published 1.0.0-preview.9; target frameworks and dependencies were checked.
• Sample HTTP checks passed for creation, queries, cancellation, cross-module event delivery, and validation rejection.
• Packing succeeded with one warning for the non-packable sample project.

Package versions remain at preview.9. Publishing requires a new version and matching changelog section.