[AsyncV2] Runtime support for breakpoints and stepping

[max-charlamb]

Summary

This PR enables debugger support for stepping into and setting breakpoints in Runtime Async methods. Runtime Async methods generate two MethodDesc variants with the same metadata token: an async "thunk" (Task-returning adapter) and the actual async method implementation. Without this change, the debugger incorrectly interacts with async thunks, causing step-in failures and breakpoint binding issues.

Problem

When stepping into or setting breakpoints on async methods:

1. Step-in operations would fail to trace through async thunks to the real implementation
2. Breakpoints could bind to async thunks, which lack proper debug metadata

Solution

New AsyncThunkStubManager (stubmgr.cpp, stubmgr.h)

Added a new stub manager to recognize and handle async thunk methods during debugger stepping for async v2 methods

Conditionally Skip Async Thunks in Breakpoint Binding (controller.cpp)

Don't bind breakpoints to async thunk using module/token id. Only bind if specified exactly by MethodDesc to allow PrecodeStubManager to work properly.

Handle Async Thunks in Step Patch Triggering (controller.cpp)

Added stub detection in DebuggerStepper::TriggerPatch:

• When a step patch lands on a stub (e.g., async thunk), traces through it to find the real target
• Calls TraceManager for TRACE_MGR_PUSH traces to resolve the async variant
• Patches the real target and continues execution instead of stopping in the thunk

Hide Async Thunks from Debugger Stack Walks (frameinfo.cpp, dacdbiimplstackwalk.cpp)

Extended the frame 'NoMetadata' logic to use IsDiagnosticsHidden():

• Covers async thunks, IL stubs, and wrapper stubs
• These methods lack meaningful metadata

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[Copilot]

Pull request overview

This PR adds dedicated runtime and debugger support for async thunk methods so that breakpoints and stack walking operate on the underlying async methods rather than the thunk wrappers, and hides internal/diagnostics-only frames from the debugger.

Changes:

• Introduces AsyncThunkStubManager and wires it into the stub manager initialization and DAC type system so async thunk code can be recognized and traced correctly.
• Adjusts debugger stack walking, breakpoint binding, and IL patching logic to skip async thunk methods (and generally IsDiagnosticsHidden methods), routing behavior instead to the corresponding async method variants.
• Extends debugger frame metadata (fNoMetadata) and stack walking filters so methods marked IsDiagnosticsHidden are not exposed in the debugger, while preserving existing special handling for IL stubs like multicast and tailcall call-target stubs.

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/stubmgr.h	Declares the new AsyncThunkStubManager (including DAC hooks) to recognize and manage async thunk methods as stubs.
src/coreclr/vm/stubmgr.cpp	Implements AsyncThunkStubManager (init, stub detection, tracing, DAC memory enumeration) and adds logic in PrecodeStubManager::DoTraceStub to redirect unjitted async thunk calls to the underlying async method.
src/coreclr/vm/appdomain.cpp	Registers AsyncThunkStubManager::Init() during SystemDomain::Attach, ensuring the new stub manager is active at runtime startup.
src/coreclr/inc/vptr_list.h	Adds AsyncThunkStubManager to the DAC vtable list so DAC can recognize and instantiate it for debugging.
src/coreclr/debug/ee/frameinfo.cpp	Updates stack-walk filtering to hide frameless methods marked IsDiagnosticsHidden, while still surfacing certain IL stubs (multicast and tailcall call target) as before.
src/coreclr/debug/ee/debugger.cpp	Changes MapAndBindFunctionPatches to early-return for async thunk methods, avoiding binding breakpoints directly to them.
src/coreclr/debug/ee/controller.cpp	Ensures AddILPatch skips DebuggerJitInfo instances for async thunk methods so IL breakpoints bind to the underlying async method instead.
src/coreclr/debug/daccess/dacdbiimplstackwalk.cpp	Marks frames for IsDiagnosticsHidden methods as fNoMetadata, aligning DAC-side frame metadata with the new hidden-from-diagnostics behavior.

[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

[Copilot]

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[Copilot]

Pull request overview

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