Implement CaptureState keyword merging fix

Query existing provider keywords and merge with requested keywords before CaptureState.
Enables provider with merged keywords if necessary to ensure CaptureState works
even when using keywords that haven't been previously enabled.

Co-authored-by: brianrob <[email protected]>

Author: Copilot

src/TraceEvent/TraceEventSession.cs

@@ -1116,6 +1116,22 @@ public void CaptureState(Guid providerGuid, ulong matchAnyKeywords = ulong.MaxVa
                     asArray[6] = (byte)(longVal >> 48);
                     asArray[7] = (byte)(longVal >> 56);
                 }
+                // Query existing keywords and merge them with requested keywords before capture state
+                ulong mergedKeywords = matchAnyKeywords;
+                Guid* providerPtr = stackalloc Guid[1];
+                *providerPtr = providerGuid;
+                long? existingKeywords = GetEnabledKeywordsForProviderAndSession(providerPtr, (ulong)m_SessionId);
+                if (existingKeywords.HasValue)
+                {
+                    mergedKeywords = matchAnyKeywords | (ulong)existingKeywords.Value;
+                    
+                    // Enable the provider with merged keywords first
+                    int enableHr = TraceEventNativeMethods.EnableTraceEx2(
+                        m_SessionHandle, providerGuid, TraceEventNativeMethods.EVENT_CONTROL_CODE_ENABLE_PROVIDER,
+                        TraceEventLevel.Verbose, mergedKeywords, 0, EnableProviderTimeoutMSec, parameters);
+                    Marshal.ThrowExceptionForHR(TraceEventNativeMethods.GetHRFromWin32(enableHr));
+                }
+
                 fixed (byte* filterDataPtr = asArray)
                 {
                     if (asArray != null)
@@ -1125,9 +1141,10 @@ public void CaptureState(Guid providerGuid, ulong matchAnyKeywords = ulong.MaxVa
                         filter.Size = asArray.Length;
                         filter.Ptr = filterDataPtr;
                     }
+
                     int hr = TraceEventNativeMethods.EnableTraceEx2(
                         m_SessionHandle, providerGuid, TraceEventNativeMethods.EVENT_CONTROL_CODE_CAPTURE_STATE,
-                        TraceEventLevel.Verbose, matchAnyKeywords, 0, EnableProviderTimeoutMSec, parameters);
+                        TraceEventLevel.Verbose, mergedKeywords, 0, EnableProviderTimeoutMSec, parameters);
                     Marshal.ThrowExceptionForHR(TraceEventNativeMethods.GetHRFromWin32(hr));
                 }
             }