[cDAC] Implement GetManagedStoppedContext for cDAC

[barosiak]

Summary

Implement GetManagedStoppedContext in the cDAC DBI layer, porting the logic from the native DAC. Add the InteropDebuggingHijacked field to the Thread data descriptor.

Changes

• Port GetManagedStoppedContext to managed cDAC with #if DEBUG legacy validation
• Add InteropDebuggingHijacked to Thread data descriptor (native, managed, docs)
• Add mock infrastructure for ResumableFrame and redirected thread frames
• Add tests covering all code paths

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[Copilot]

Pull request overview

Ports the DAC GetManagedStoppedContext implementation to the cDAC managed DBI layer, exposes the InteropDebuggingHijacked field on the Thread descriptor, and adds mock infrastructure plus tests covering each branch (hijacked, filter-context, redirected-thread, no-context).

Changes:

• Implement GetManagedStoppedContext in DacDbiImpl mirroring native logic (hijacked → null; else filter context; else RedirectedThreadFrame::TargetContextPtr), with #if DEBUG legacy parity validation.
• Add InteropDebuggingHijacked to the Thread data descriptor on both native (threads.h, datadescriptor.inc) and managed (Data/Thread.cs, MockDescriptors.Thread.cs) sides, plus docs.
• Add MockResumableFrame and AddRedirectedThreadFrame helpers; new [Theory] tests covering all four code paths.

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/threads.h	Expose m_fInteropDebuggingHijacked offset via cdac_data<Thread>.
src/coreclr/vm/datadescriptor/datadescriptor.inc	Register Thread.InteropDebuggingHijacked (T_UINT32).
src/native/managed/cdac/.../Data/Thread.cs	Add InteropDebuggingHijacked [Field].
src/native/managed/cdac/.../Dbi/DacDbiImpl.cs	Port GetManagedStoppedContext from native DAC with debug-time legacy validation.
src/native/managed/cdac/tests/MockDescriptors/MockDescriptors.Thread.cs	Add layout/property for InteropDebuggingHijacked; expose DebuggerFilterContext.
src/native/managed/cdac/tests/MockDescriptors/MockDescriptors.Frame.cs	Add MockResumableFrame, RedirectedThreadFrameIdentifierValue, AddRedirectedThreadFrame.
src/native/managed/cdac/tests/DacDbiImplTests.cs	Add four [Theory] tests covering the implementation's branches.
docs/design/datacontracts/Thread.md	Document new InteropDebuggingHijacked field.

[rcj1]

We should not be doing all these field reads outside of the contract APIs. The idea is that the contract encapsulate the important concepts about runtime structures, and that the consumers - the DacDbi and SOS APIs, for example - can put them together without looking at the offsets and other implementation details of the runtime. For example you could have a Thread API GetRedirectedContext to get the redirected context (or NULL if it doesn't exist), and an API IsInteropDebuggingHijacked

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

[Copilot]

Copilot's findings

• Files reviewed: 10/10 changed files
• Comments generated: 1

[noahfalk]

This looks good to me, either with the current API shape or if we merge more of it into ThreadData.

[Copilot]

Copilot's findings

• Files reviewed: 13/13 changed files
• Comments generated: 2

[Copilot]

Copilot's findings

• Files reviewed: 13/13 changed files
• Comments generated: 2

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

[rcj1]

lgtm