diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/DesktopArrivalDetectorTests.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/DesktopArrivalDetectorTests.cs
index 1722b3aa..02d4f1e7 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/DesktopArrivalDetectorTests.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/DesktopArrivalDetectorTests.cs
@@ -178,6 +178,94 @@ namespace AutopilotMonitor.Agent.V2.Core.Tests.Monitoring
             detector.ResetForRealUserSwitch();
         }
 
+        // ============================================================================
+        // Owner resolution: WTS primary, WMI fallback (session 4d5a0b78 fix, 2026-06-11)
+        // ============================================================================
+        // Session 4d5a0b78: WMI Win32_Process.GetOwner failed on EVERY poll on a device
+        // (wmiErrorCount == pollCount), the owner was never resolved and desktop_arrived
+        // never fired — the Desktop half of the completion AND-gate starved. WTS session
+        // queries are now the primary path; WMI is only consulted when WTS yields no user.
+
+        private static DesktopArrivalDetector BuildDetector(TempDirectory tmp) =>
+            new DesktopArrivalDetector(new AgentLogger(tmp.Path, AgentLogLevel.Info));
+
+        [Fact]
+        public void ResolveOwner_uses_WTS_result_without_consulting_WMI()
+        {
+            using var tmp = new TempDirectory();
+            using var detector = BuildDetector(tmp);
+            var wmiCalled = false;
+            detector.SessionOwnerResolver = sessionId => "CONTOSO\\alice";
+            detector.ProcessOwnerResolver = pid => { wmiCalled = true; return "CONTOSO\\bob"; };
+
+            var owner = detector.ResolveOwner(processId: 1234, sessionId: 2);
+
+            Assert.Equal("CONTOSO\\alice", owner);
+            Assert.False(wmiCalled);
+        }
+
+        [Fact]
+        public void ResolveOwner_falls_back_to_WMI_when_WTS_returns_null()
+        {
+            using var tmp = new TempDirectory();
+            using var detector = BuildDetector(tmp);
+            detector.SessionOwnerResolver = sessionId => null;
+            detector.ProcessOwnerResolver = pid => "CONTOSO\\alice";
+
+            Assert.Equal("CONTOSO\\alice", detector.ResolveOwner(1234, 2));
+        }
+
+        [Fact]
+        public void ResolveOwner_falls_back_to_WMI_when_WTS_returns_empty()
+        {
+            // WTSQuerySessionInformation can succeed with an empty user name (no user
+            // associated with the session) — must be treated like a miss, not a real owner.
+            using var tmp = new TempDirectory();
+            using var detector = BuildDetector(tmp);
+            detector.SessionOwnerResolver = sessionId => "";
+            detector.ProcessOwnerResolver = pid => "CONTOSO\\alice";
+
+            Assert.Equal("CONTOSO\\alice", detector.ResolveOwner(1234, 2));
+        }
+
+        [Fact]
+        public void ResolveOwner_falls_back_to_WMI_when_WTS_throws()
+        {
+            using var tmp = new TempDirectory();
+            using var detector = BuildDetector(tmp);
+            detector.SessionOwnerResolver = sessionId => throw new System.ComponentModel.Win32Exception(5);
+            detector.ProcessOwnerResolver = pid => "CONTOSO\\alice";
+
+            Assert.Equal("CONTOSO\\alice", detector.ResolveOwner(1234, 2));
+        }
+
+        [Fact]
+        public void ResolveOwner_returns_null_when_both_paths_fail()
+        {
+            using var tmp = new TempDirectory();
+            using var detector = BuildDetector(tmp);
+            detector.SessionOwnerResolver = sessionId => null;
+            detector.ProcessOwnerResolver = pid => null;
+
+            Assert.Null(detector.ResolveOwner(1234, 2));
+        }
+
+        [Fact]
+        public void ResolveOwner_passes_session_id_to_WTS_and_pid_to_WMI()
+        {
+            using var tmp = new TempDirectory();
+            using var detector = BuildDetector(tmp);
+            int? seenSessionId = null;
+            int? seenPid = null;
+            detector.SessionOwnerResolver = sessionId => { seenSessionId = sessionId; return null; };
+            detector.ProcessOwnerResolver = pid => { seenPid = pid; return null; };
+
+            detector.ResolveOwner(processId: 4711, sessionId: 3);
+
+            Assert.Equal(3, seenSessionId);
+            Assert.Equal(4711, seenPid);
+        }
+
         // ============================================================================
         // DAD-liveness telemetry (2026-05-15) — Started / FirstPoll / NoCandidate
         // ============================================================================
diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/SystemSignals/DesktopArrivalDetector.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/SystemSignals/DesktopArrivalDetector.cs
index db92dd1b..90dbfeb9 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/SystemSignals/DesktopArrivalDetector.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/SystemSignals/DesktopArrivalDetector.cs
@@ -4,6 +4,7 @@ using System.Diagnostics;
 using System.Management;
 using System.Threading;
 using AutopilotMonitor.Agent.V2.Core.Logging;
+using AutopilotMonitor.Agent.V2.Core.Monitoring.Interop;
 using SharedEventTypes = AutopilotMonitor.Shared.Constants.EventTypes;
 
 namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals
@@ -14,6 +15,13 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals
     /// Used for enrollment completion in no-ESP scenarios (WDP v2, ESP disabled) and
     /// as a backup signal for AccountSetup phase correction.
     /// <para>
+    /// Owner resolution (session 4d5a0b78 fix, 2026-06-11): primary path is a WTS session
+    /// query (<c>WTSQuerySessionInformation</c> with WTSUserName/WTSDomainName) — fast and
+    /// independent of the WinMgmt service; WMI <c>Win32_Process.GetOwner</c> is the fallback.
+    /// On the affected device class GetOwner failed on every poll, so the owner was never
+    /// resolved and the Desktop half of the completion AND-gate starved.
+    /// </para>
+    /// <para>
     /// <b>Liveness telemetry</b> (state-change-only, max 3 events per detector lifetime, NOT periodic):
     /// </para>
     /// <list type="bullet">
@@ -44,9 +52,16 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals
         private bool _explorerEverSeen;            // any explorer.exe observed at all (session 0 OR not)
         private bool _anyNonZeroSessionEverSeen;   // explorer.exe in a non-SYSTEM session observed
         private int _wmiErrorCountSinceStart;
+        private int _wtsErrorCountSinceStart;
         private bool _noCandidateFired;
         private readonly int _noCandidateTimeoutMinutes;
 
+        // Test seams (session 4d5a0b78 fix): owner resolution is injectable so unit tests can
+        // drive the WTS-primary / WMI-fallback order without a live session manager or WinMgmt.
+        // Null = production defaults (GetSessionOwnerViaWts / GetProcessOwnerViaWmi).
+        internal Func<int, string> SessionOwnerResolver { get; set; }
+        internal Func<int, string> ProcessOwnerResolver { get; set; }
+
         /// <summary>
         /// System/service account names that should NOT be considered real users.
         /// </summary>
@@ -132,6 +147,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals
             _explorerEverSeen = false;
             _anyNonZeroSessionEverSeen = false;
             _wmiErrorCountSinceStart = 0;
+            _wtsErrorCountSinceStart = 0;
             _noCandidateFired = false;
 
             ArmTimer(startReason: "real-user-switch-reset");
@@ -188,8 +204,8 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals
 
                         _anyNonZeroSessionEverSeen = true;
 
-                        var owner = GetProcessOwner(proc.Id);
-                        if (owner == null)
+                        var owner = ResolveOwner(proc.Id, proc.SessionId);
+                        if (string.IsNullOrEmpty(owner))
                             continue;
 
                         // Check against exclusion list
@@ -302,6 +318,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals
                         { "explorerProcessCount", explorerProcessCount },
                         { "anyNonZeroSessionObserved", _anyNonZeroSessionEverSeen },
                         { "wmiErrorCount", _wmiErrorCountSinceStart },
+                        { "wtsErrorCount", _wtsErrorCountSinceStart },
                     });
             }
             catch (Exception ex) { _logger.Verbose($"DesktopArrivalDetector: first-poll emit failed: {ex.Message}"); }
@@ -337,6 +354,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals
                         { "explorerEverSeen", _explorerEverSeen },
                         { "anyNonZeroSessionEverSeen", _anyNonZeroSessionEverSeen },
                         { "wmiErrorCount", _wmiErrorCountSinceStart },
+                        { "wtsErrorCount", _wtsErrorCountSinceStart },
                     });
             }
             catch (Exception ex) { _logger.Verbose($"DesktopArrivalDetector: no-candidate emit failed: {ex.Message}"); }
@@ -365,7 +383,65 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals
         }
 
         /// <summary>
-        /// Gets the owner of a process using WMI (Win32_Process.GetOwner).
+        /// Resolves the owning user of an explorer.exe candidate. Session 4d5a0b78 fix
+        /// (2026-06-11): the WMI <c>Win32_Process.GetOwner</c> call failed on every poll on
+        /// some devices (wmiErrorCount == pollCount) while the agent ran for over an hour —
+        /// the owner was never resolved, <c>desktop_arrived</c> never fired, and the Desktop
+        /// half of the completion AND-gate starved. WTS is now the primary path: a single
+        /// kernel round-trip against the session manager (no WinMgmt dependency, much
+        /// cheaper than a WMI query), keyed by the process's session id — explorer.exe runs
+        /// as the session's logged-on user. WMI remains the fallback when WTS returns no
+        /// user for the session.
+        /// <para>
+        /// Returns "DOMAIN\User" or "User", or null when both paths fail. Each path's
+        /// failures are counted separately (<see cref="_wtsErrorCountSinceStart"/> /
+        /// <see cref="_wmiErrorCountSinceStart"/>) and surfaced via the first_poll /
+        /// no_candidate liveness payloads.
+        /// </para>
+        /// </summary>
+        internal string ResolveOwner(int processId, int sessionId)
+        {
+            string owner = null;
+            try
+            {
+                owner = (SessionOwnerResolver ?? GetSessionOwnerViaWts)(sessionId);
+            }
+            catch (Exception ex)
+            {
+                _logger.Debug($"DesktopArrivalDetector: WTS owner resolution threw for session {sessionId}: {ex.Message}");
+            }
+            if (!string.IsNullOrEmpty(owner))
+                return owner;
+
+            _wtsErrorCountSinceStart++;
+            return (ProcessOwnerResolver ?? GetProcessOwnerViaWmi)(processId);
+        }
+
+        /// <summary>
+        /// Primary owner resolution: WTSQuerySessionInformation(WTSUserName/WTSDomainName)
+        /// for the process's session. Returns null when the API fails or the session has no
+        /// associated user (caller counts it and falls back to WMI).
+        /// </summary>
+        private string GetSessionOwnerViaWts(int sessionId)
+        {
+            try
+            {
+                var user = WtsNativeMethods.QuerySessionString(sessionId, WtsNativeMethods.WTSUserName);
+                if (string.IsNullOrEmpty(user))
+                    return null;
+
+                var domain = WtsNativeMethods.QuerySessionString(sessionId, WtsNativeMethods.WTSDomainName);
+                return string.IsNullOrEmpty(domain) ? user : $"{domain}\\{user}";
+            }
+            catch (Exception ex)
+            {
+                _logger.Debug($"DesktopArrivalDetector: WTS session query failed for session {sessionId}: {ex.Message}");
+                return null;
+            }
+        }
+
+        /// <summary>
+        /// Fallback owner resolution: WMI (Win32_Process.GetOwner).
         /// Returns "DOMAIN\User" or "User" string, or null on failure.
         /// <para>
         /// P3 fix (2026-05-15): WMI exceptions are caught here AND bumped onto
@@ -375,7 +451,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals
         /// leaving GetOwner-specific failures invisible.
         /// </para>
         /// </summary>
-        private string GetProcessOwner(int processId)
+        private string GetProcessOwnerViaWmi(int processId)
         {
             try
             {
diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Interop/WtsNativeMethods.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Interop/WtsNativeMethods.cs
new file mode 100644
index 00000000..61f02946
--- /dev/null
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Interop/WtsNativeMethods.cs
@@ -0,0 +1,61 @@
+using System;
+using System.Runtime.InteropServices;
+
+namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Interop
+{
+    /// <summary>
+    /// Win32 P/Invoke declarations for WTS (Remote Desktop Services) session queries.
+    /// Used by <c>DesktopArrivalDetector</c> to resolve the logged-on user of an
+    /// interactive session directly from the session manager — a single fast kernel
+    /// round-trip, unlike the WMI <c>Win32_Process.GetOwner</c> path which depends on
+    /// the WinMgmt service and fails persistently on some devices (session 4d5a0b78:
+    /// GetOwner failed on every poll while WTS-level session data stayed available).
+    /// </summary>
+    internal static class WtsNativeMethods
+    {
+        /// <summary>WTS_INFO_CLASS.WTSUserName — user name associated with the session.</summary>
+        public const int WTSUserName = 5;
+
+        /// <summary>WTS_INFO_CLASS.WTSDomainName — domain of the user associated with the session.</summary>
+        public const int WTSDomainName = 7;
+
+        /// <summary>WTS_CURRENT_SERVER_HANDLE — query the local machine.</summary>
+        public static readonly IntPtr WTS_CURRENT_SERVER_HANDLE = IntPtr.Zero;
+
+        [DllImport("wtsapi32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
+        public static extern bool WTSQuerySessionInformation(
+            IntPtr hServer,
+            int sessionId,
+            int wtsInfoClass,
+            out IntPtr ppBuffer,
+            out int pBytesReturned);
+
+        [DllImport("wtsapi32.dll")]
+        public static extern void WTSFreeMemory(IntPtr pMemory);
+
+        /// <summary>
+        /// Queries a string-typed WTS session property (<see cref="WTSUserName"/> /
+        /// <see cref="WTSDomainName"/>) for <paramref name="sessionId"/> on the local
+        /// machine. Returns <c>null</c> when the API call fails; an empty string is a
+        /// successful query with no value (e.g. no user associated with the session).
+        /// Always frees the WTS buffer.
+        /// </summary>
+        public static string QuerySessionString(int sessionId, int wtsInfoClass)
+        {
+            var buffer = IntPtr.Zero;
+            try
+            {
+                if (!WTSQuerySessionInformation(WTS_CURRENT_SERVER_HANDLE, sessionId, wtsInfoClass, out buffer, out var bytesReturned))
+                    return null;
+
+                // bytesReturned includes the trailing null terminator (2 bytes Unicode);
+                // <= 2 means "no characters".
+                return bytesReturned > 2 ? Marshal.PtrToStringUni(buffer) : string.Empty;
+            }
+            finally
+            {
+                if (buffer != IntPtr.Zero) WTSFreeMemory(buffer);
+            }
+        }
+    }
+}