Fix GetMethodTableName to return E_OUTOFMEMORY for empty type names

When TypeNameBuilder.AppendType produces an empty string (and the
fallback also fails), the cDAC was calling CopyStringToBuffer with
an empty string, setting pNeeded=1 and returning S_OK. The legacy
DAC returns E_OUTOFMEMORY in this case and does not set pNeeded.

This mismatch caused the #if DEBUG validation assertion to crash
the SOS.WebApp3 test in all runtime-diagnostics PR builds.

Fix: check for empty methodTableName and return E_OUTOFMEMORY to
match the legacy DAC behavior. Also add stderr logging so the MT
address is captured when this path is hit.

Also changes the runtime-diagnostics pipeline to always publish
test results and SOS logs (not just on failure), so diagnostic
output is accessible for passing runs too.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Max Charlamb

eng/pipelines/runtime-diagnostics.yml

@@ -143,7 +143,7 @@ extends:
                 artifactName: 'TestResults_cDAC_$(osGroup)$(osSubgroup)_$(archType)_$(_BuildConfig)_Attempt$(System.JobAttempt)'
               displayName: 'Publish Test Results and SOS Logs'
               continueOnError: true
-              condition: failed()
+              condition: always()
       - template: /eng/pipelines/common/platform-matrix.yml
         parameters:
           jobTemplate: /eng/pipelines/diagnostics/runtime-diag-job.yml
@@ -197,7 +197,7 @@ extends:
                 artifactName: 'TestResults_cDAC_no_fallback_$(osGroup)$(osSubgroup)_$(archType)_$(_BuildConfig)_Attempt$(System.JobAttempt)'
               displayName: 'Publish Test Results and SOS Logs'
               continueOnError: true
-              condition: failed()
+              condition: always()
       - template: /eng/pipelines/common/platform-matrix.yml
         parameters:
           jobTemplate: /eng/pipelines/diagnostics/runtime-diag-job.yml
@@ -250,7 +250,7 @@ extends:
                 artifactName: 'TestResults_DAC_$(osGroup)$(osSubgroup)_$(archType)_$(_BuildConfig)_Attempt$(System.JobAttempt)'
               displayName: 'Publish Test Results and SOS Logs'
               continueOnError: true
-              condition: failed()
+              condition: always()
 
     #
     # cDAC Dump Tests — Build, generate dumps, and run tests on Helix (single-leg mode)

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/DebugExtensions.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using System.Diagnostics;
 using System.IO;
 using System.Runtime.CompilerServices;
@@ -52,5 +53,35 @@ internal static void ValidateHResult(
             };
             Debug.Assert(match, $"HResult mismatch - cDAC: 0x{unchecked((uint)cdacHr):X8}, DAC: 0x{unchecked((uint)dacHr):X8} ({Path.GetFileName(filePath)}:{lineNumber})");
         }
+
+        [Conditional("DEBUG")]
+        internal static unsafe void ValidateOutputStringBuffer(
+            char* cdacBuffer,
+            uint* cdacNeeded,
+            char[] dacBuffer,
+            uint dacNeeded,
+            uint count,
+            [CallerFilePath] string? filePath = null,
+            [CallerLineNumber] int lineNumber = 0)
+        {
+            string location = $"{Path.GetFileName(filePath)}:{lineNumber}";
+
+            if (cdacNeeded is not null && *cdacNeeded != dacNeeded)
+            {
+                int cdacLen = (int)Math.Min(*cdacNeeded, count);
+                string cdacStr = cdacBuffer is not null && cdacLen > 0 ? new string(cdacBuffer, 0, cdacLen - 1) : "<null>";
+                string dacStr = dacNeeded > 0 ? new string(dacBuffer, 0, (int)dacNeeded - 1) : "<empty>";
+                Trace.TraceWarning($"Output buffer pNeeded mismatch ({location}) - cDAC: {*cdacNeeded} (\"{cdacStr}\"), DAC: {dacNeeded} (\"{dacStr}\")");
+            }
+            else if (cdacBuffer is not null && dacNeeded > 0 && count >= dacNeeded)
+            {
+                var cdacSpan = new ReadOnlySpan<char>(cdacBuffer, (int)dacNeeded - 1);
+                var dacSpan = new ReadOnlySpan<char>(dacBuffer, 0, (int)dacNeeded - 1);
+                if (!cdacSpan.SequenceEqual(dacSpan))
+                {
+                    Trace.TraceWarning($"Output buffer content mismatch ({location}) - cDAC: \"{new string(cdacBuffer, 0, (int)dacNeeded - 1)}\", DAC: \"{new string(dacBuffer, 0, (int)dacNeeded - 1)}\"");
+                }
+            }
+        }
     }
 }

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/SOSDacImpl.cs

@@ -2972,7 +2972,17 @@ int ISOSDacInterface.GetMethodTableName(ClrDataAddress mt, uint count, char* mtN
                             methodTableName.Append(fallbackName);
                         }
                     }
-                    OutputBufferHelpers.CopyStringToBuffer(mtName, count, pNeeded, methodTableName.ToString());
+
+                    if (methodTableName.Length == 0)
+                    {
+                        System.Console.Error.WriteLine($"CDAC_EMPTY_NAME GetMethodTableName MT=0x{(ulong)mt:X} count={count} — TypeNameBuilder produced empty string, returning E_OUTOFMEMORY");
+                        System.Console.Error.Flush();
+                        hr = HResults.E_OUTOFMEMORY;
+                    }
+                    else
+                    {
+                        OutputBufferHelpers.CopyStringToBuffer(mtName, count, pNeeded, methodTableName.ToString());
+                    }
                 }
             }