Rename runtime-async contract types and methods to follow framework guidelines

[Copilot]

Description

Runtime-async contract types and methods become immutable once baked into ReadyToRun images. The original names were implementation-focused and unclear for a public-facing contract.

Changes

Renamed three core runtime-async contract elements across C#, C++, and IL generation code:

• ExecutionAndSyncBlockStore → AsyncContextsSnapshot

  • Clarifies purpose: captures execution/synchronization context state at suspension points
  • Removes misleading "SyncBlock" term (distinct CLR concept)
  • Uses plural "Contexts" to reflect capturing multiple context types (ExecutionContext and SynchronizationContext)

• FinalizeTaskReturningThunk[<T>] → CreateAsyncMethodTask[<T>]

  • FinalizeValueTaskReturningThunk[<T>] → CreateAsyncMethodValueTask[<T>]
  • Describes action: creates Task wrapper for suspended async method
  • "Create" semantics match framework patterns (cf. Task.FromResult)

• CompletedTask(Result) → ValidateCompletedTask / GetCompletedTaskResult<T>

  • Distinguishes validation from retrieval operations
  • Aligns with awaiter GetResult() pattern

Updated references in:

• AsyncHelpers.CoreCLR.cs (managed implementations)
• corelib.h (VM type/method definitions)
• asyncthunks.cpp (thunk generation)
• AsyncThunks.cs (NativeAOT IL stubs)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Names of types and methods that are part of the runtime-async contract should be updated according to framework guidelines.</issue_title>
<issue_description>These types and methods are basically set in stone once they become part of ReadyToRun images. We should update the names to be more clear and descriptive as if they are public framework APIs.

Most of these are in AsyncHelpers. For example, ExecutionAndSyncBlockStore, FinalizeTaskReturningThunk, and AsyncHelpers.CompletedTask aren't great names or don't make sense.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Names of types and methods that are part of the runtime-async contract should be updated according to framework guidelines. #122512

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[jakobbotsch]

@copilot Rename ExecutionContextSnapshot to AsyncContextsSnapshot

[Copilot]

@copilot Rename ExecutionContextSnapshot to AsyncContextsSnapshot

Done in 0ba297b