[cDAC] Add continuation support to RuntimeTypeSystem

[max-charlamb]

Summary

Add IsContinuation to the cDAC RuntimeTypeSystem contract, enabling the cDAC to identify and validate continuation MethodTables created by the async continuation feature.

Continuations are dynamically-created MethodTables (similar to arrays) whose parent is the base Continuation class stored in g_pContinuationClassIfSubTypeCreated. Without this change, the cDAC's MT→EEClass→MT validation roundtrip would reject valid continuation MTs.

Related discussion: #124780 (comment)

Changes

• datadescriptor.inc — Expose g_pContinuationClassIfSubTypeCreated as ContinuationMethodTable global pointer
• IRuntimeTypeSystem.cs — Add IsContinuation(TypeHandle) to the contract interface
• RuntimeTypeSystem_1.cs — Implement IsContinuation by checking ParentMethodTable == continuationMethodTablePointer
• RuntimeTypeSystemFactory.cs — Read the continuation MT global (gracefully handles missing global via TryReadGlobalPointer)
• TypeValidation.cs — Fix MT→EEClass→MT validation to allow continuations (like arrays/generics)
• Constants.cs — Add ContinuationMethodTable constant name
• Tests — 4 test methods (8 cases across architectures): true positive, true negative, null global, and CanonMT validation

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[Copilot]

Pull request overview

This PR adds continuation MethodTable identification to the cDAC RuntimeTypeSystem contract, enabling proper validation of dynamically-created continuation types used by the async continuation feature. Continuations are similar to arrays in that they are dynamically created and share EEClasses, requiring special handling in the MT→EEClass→MT validation roundtrip.

Changes:

• Exposes the g_pContinuationClassIfSubTypeCreated global pointer to cDAC for continuation identification
• Adds IsContinuation(TypeHandle) API to detect continuation types by checking parent MethodTable
• Fixes TypeValidation to handle continuation MTs alongside arrays and generic instantiations

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/coreclr/vm/datadescriptor/datadescriptor.inc	Exposes g_pContinuationClassIfSubTypeCreated as ContinuationMethodTable global pointer
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IRuntimeTypeSystem.cs	Adds IsContinuation method to contract interface with documentation
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Constants.cs	Adds ContinuationMethodTable constant name
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/RuntimeTypeSystemFactory.cs	Reads continuation MT global using TryReadGlobalPointer (handles missing global gracefully)
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/RuntimeTypeSystem_1.cs	Implements IsContinuation by comparing parent MT to continuation global pointer
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/RuntimeTypeSystemHelpers/TypeValidation.cs	Adds continuation check to MT→EEClass→MT validation logic alongside arrays/generics
src/native/managed/cdac/tests/MockDescriptors/MockDescriptors.RuntimeTypeSystem.cs	Adds test infrastructure for continuation MT global pointer
src/native/managed/cdac/tests/MethodTableTests.cs	Adds 4 comprehensive test methods covering true positive, true negative, null global, and CanonMT validation scenarios

[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.