[cDAC] Relax HRESULT validation to allow divergent failure codes

[max-charlamb]

Summary

The cDAC's DEBUG validation asserts compare HRESULTs between the cDAC and legacy DAC using exact equality (Debug.Assert(hrLocal == hr)). This causes the debugger process to crash when the cDAC and native DAC return different failure HRESULTs for the same invalid input.

For example, when GetMethodTableData is called with a garbage method table pointer, the cDAC may throw InvalidOperationException (0x80131C49) while the native DAC returns E_INVALIDARG (0x80070057). Both correctly reject the input, but the exact HRESULT comparison fires a fatal Debug.Assert that terminates the debugger mid-command — causing flaky CI failures like SOS.VarargPInvokeInteropMD in the cDAC_windows_x64_release job.

No consumer (ClrMD, SOS, managed debugger) branches on specific failure codes from these APIs — they only check success vs failure.

Changes

New file: DebugExtensions.cs — adds Debug.ValidateHResult() as a C# 14 static extension method on System.Diagnostics.Debug:

Debug.ValidateHResult(hr, hrLocal);

With two validation modes via HResultValidationMode:

• Exact — HRESULTs must match exactly (available for APIs where the specific code matters)
• AllowDivergentFailures (default) — success HRESULTs (S_OK, S_FALSE) must match exactly, but any two failing HRESULTs (negative values) are considered equivalent

Converted all 113 call sites across 5 files from:

Debug.Assert(hrLocal == hr, $"cDAC: {hr:x}, DAC: {hrLocal:x}");

to:

Debug.ValidateHResult(hr, hrLocal);

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[Copilot]

Pull request overview

This PR updates the cDAC Legacy layer’s DEBUG cross-validation to stop asserting on exact HRESULT equality when both the cDAC and legacy/native DAC correctly fail, but return different failure codes. This avoids debugger-process termination and associated test flakiness while still preserving strict validation for success results.

Changes:

• Introduces Debug.ValidateHResult() (with HResultValidationMode) to centralize HRESULT comparison rules.
• Replaces ~113 Debug.Assert(hrLocal == hr, ...) call sites with Debug.ValidateHResult(hr, hrLocal) across the Legacy implementation.
• Preserves strict matching for success HRESULTs while allowing divergent failure HRESULTs by default.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/SOSDacImpl.cs	Replaces legacy-vs-cDAC HRESULT equality asserts with Debug.ValidateHResult.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/SOSDacImpl.IXCLRDataProcess.cs	Same replacement for IXCLRDataProcess-related validation asserts.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ClrDataStackWalk.cs	Uses Debug.ValidateHResult when cross-validating stack-walk HRESULTs in DEBUG.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ClrDataMethodInstance.cs	Replaces per-site “allow any failing HRESULT” logic with the shared validator.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ClrDataFrame.cs	Updates frame HRESULT validation to use the shared validator.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/DebugExtensions.cs	Adds centralized HRESULT validation helper and mode enum.

[rcj1]

As long as none of these callers differentiate between failures, then looks good to me