diff --git a/Motely.Tests/MotelySearchReliabilityTests.cs b/Motely.Tests/MotelySearchReliabilityTests.cs
new file mode 100644
index 00000000..92e384a0
--- /dev/null
+++ b/Motely.Tests/MotelySearchReliabilityTests.cs
@@ -0,0 +1,121 @@
+using Motely.Filters;
+using Xunit;
+
+namespace Motely.Tests;
+
+/// <summary>
+/// Reliability regressions for <see cref="MotelySearch{TBaseFilter}"/>.
+/// Both tests covered HIGH-severity items in ISSUES.md:
+///   1. Single-thread <see cref="MotelySearch{TBaseFilter}.RunSearchAsync"/> used to run the
+///      worker body synchronously on the caller, so awaiting it on the same context deadlocked.
+///   2. Multi-thread workers used to swallow exceptions silently — the completion source
+///      stayed unset and callers hung forever.
+/// </summary>
+public sealed class MotelySearchReliabilityTests
+{
+    /// <summary>Always-pass base filter so the worker actually runs for the seed list.</summary>
+    private readonly struct PassFilterDesc : IMotelySeedFilterDesc<PassFilterDesc.PassFilter>
+    {
+        public PassFilter CreateFilter(ref MotelyFilterCreationContext ctx) => new();
+
+        public readonly struct PassFilter : IMotelySeedFilter
+        {
+            public readonly VectorMask Filter(ref MotelyVectorSearchContext _) =>
+                VectorMask.AllBitsSet;
+        }
+    }
+
+    /// <summary>Base filter that throws inside the SIMD loop.</summary>
+    private readonly struct ThrowingFilterDesc : IMotelySeedFilterDesc<ThrowingFilterDesc.ThrowingFilter>
+    {
+        public ThrowingFilter CreateFilter(ref MotelyFilterCreationContext ctx) => new();
+
+        public readonly struct ThrowingFilter : IMotelySeedFilter
+        {
+            public readonly VectorMask Filter(ref MotelyVectorSearchContext _) =>
+                throw new InvalidOperationException("boom from worker");
+        }
+    }
+
+    [Fact]
+    public async Task RunSearchAsync_SingleThread_DoesNotDeadlockAwaitOnSameContext()
+    {
+        var settings = new MotelySearchSettings<PassFilterDesc.PassFilter>(new PassFilterDesc())
+            .WithListSearch(["AAAAAAAA"], 1)
+            .WithThreadCount(1)
+            .WithQuietMode(true);
+
+        using var search = settings.CreateSearch();
+
+        // The bug under fix: when totalWorkers == 1 the worker body used to run
+        // synchronously inside Start(), meaning RunSearchAsync()'s returned Task
+        // only completed after the search had already drained on the caller's
+        // thread — fatal for `await search.RunSearchAsync()` on a sync ctx.
+        // A bounded wait proves the Task yields and completes off-thread.
+        var run = search.RunSearchAsync();
+        var winner = await Task.WhenAny(run, Task.Delay(TimeSpan.FromSeconds(5)));
+        Assert.Same(run, winner);
+        await run; // no exception → completed cleanly
+        Assert.True(search.IsCompleted);
+    }
+
+    [Fact]
+    public async Task RunSearchAsync_SingleThread_SurfacesWorkerException()
+    {
+        var settings = new MotelySearchSettings<ThrowingFilterDesc.ThrowingFilter>(new ThrowingFilterDesc())
+            .WithListSearch(["AAAAAAAA"], 1)
+            .WithThreadCount(1)
+            .WithQuietMode(true);
+
+        using var search = settings.CreateSearch();
+        var ex = await Assert.ThrowsAnyAsync<Exception>(() => search.RunSearchAsync());
+        Assert.Contains("boom from worker", FlattenMessages(ex));
+    }
+
+    [Fact]
+    public async Task RunSearchAsync_MultiThread_SurfacesWorkerException()
+    {
+        // Many lanes / multiple workers so the throw lands on a worker thread,
+        // not the caller. Previously this would set _completionSource to nothing
+        // and the await would hang forever.
+        var seeds = Enumerable.Range(0, 1024).Select(i => $"S{i:D7}").ToArray();
+        var settings = new MotelySearchSettings<ThrowingFilterDesc.ThrowingFilter>(new ThrowingFilterDesc())
+            .WithListSearch(seeds, seeds.Length)
+            .WithThreadCount(Math.Max(2, Environment.ProcessorCount))
+            .WithQuietMode(true);
+
+        using var search = settings.CreateSearch();
+        var run = search.RunSearchAsync();
+        var winner = await Task.WhenAny(run, Task.Delay(TimeSpan.FromSeconds(5)));
+        Assert.Same(run, winner); // didn't hang
+        var ex = await Assert.ThrowsAnyAsync<Exception>(() => run);
+        Assert.Contains("boom from worker", FlattenMessages(ex));
+    }
+
+    [Fact]
+    public void RunSearchUntilCompletion_MultiThread_SurfacesWorkerException()
+    {
+        var seeds = Enumerable.Range(0, 1024).Select(i => $"S{i:D7}").ToArray();
+        var settings = new MotelySearchSettings<ThrowingFilterDesc.ThrowingFilter>(new ThrowingFilterDesc())
+            .WithListSearch(seeds, seeds.Length)
+            .WithThreadCount(Math.Max(2, Environment.ProcessorCount))
+            .WithQuietMode(true);
+
+        using var search = settings.CreateSearch();
+        // Sync surface: previously the throw was lost and SignalSearchCompleted()
+        // marked the search "clean". Now the first error rethrows.
+        var ex = Assert.ThrowsAny<Exception>(() => search.RunSearchUntilCompletion());
+        Assert.Contains("boom from worker", FlattenMessages(ex));
+    }
+
+    private static string FlattenMessages(Exception ex)
+    {
+        var msgs = new List<string>();
+        for (var current = ex; current is not null; current = current.InnerException)
+            msgs.Add(current.Message);
+        if (ex is AggregateException agg)
+            foreach (var inner in agg.Flatten().InnerExceptions)
+                msgs.Add(inner.Message);
+        return string.Join(" | ", msgs);
+    }
+}
diff --git a/Motely/MotelySearch.cs b/Motely/MotelySearch.cs
index 9f2f942d..0e7a6a27 100644
--- a/Motely/MotelySearch.cs
+++ b/Motely/MotelySearch.cs
@@ -1095,10 +1095,28 @@ public void RunSearchUntilCompletion()
             throw new InvalidOperationException("Search has already been started.");
         _elapsedTime.Start();
 
+        Exception? firstError = null;
+
+        void RunWorkerSafe(int idx)
+        {
+            try
+            {
+                RunWorkerBody(_plans[idx]);
+            }
+            catch (OperationCanceledException) when (_cancellationToken.IsCancellationRequested)
+            {
+                // cooperative cancellation
+            }
+            catch (Exception ex)
+            {
+                Interlocked.CompareExchange(ref firstError, ex, null);
+            }
+        }
+
         if (_threadCount == 1)
         {
             // Single-threaded: run directly on this thread
-            RunWorkerBody(_plans[0]);
+            RunWorkerSafe(0);
         }
         else
         {
@@ -1107,7 +1125,7 @@ public void RunSearchUntilCompletion()
             for (int i = 0; i < _threadCount; i++)
             {
                 int threadIdx = i;
-                threads[i] = new Thread(() => RunWorkerBody(_plans[threadIdx]))
+                threads[i] = new Thread(() => RunWorkerSafe(threadIdx))
                 {
                     Name = $"Motely Search Thread {threadIdx}",
                     IsBackground = true
@@ -1121,6 +1139,15 @@ public void RunSearchUntilCompletion()
             }
         }
 
+        if (firstError is not null)
+        {
+            // Tell awaiters about the failure, then rethrow on the caller for the
+            // sync surface. Without this, a failed worker used to look like a clean
+            // completion to anyone waiting on _completionSource.
+            _completionSource.TrySetException(firstError);
+            throw firstError;
+        }
+
         SignalSearchCompleted();
     }
 
@@ -1195,48 +1222,85 @@ private void BeginSearch(CancellationToken cancellationToken)
     /// Starts search threads without blocking the caller.
     /// Completion is signaled via <see cref="_completionSource"/>.
     /// </summary>
+    /// <remarks>
+    /// Both paths off-thread the worker bodies. The single-thread case used to run
+    /// synchronously on the caller, which broke <see cref="RunSearchAsync"/>: the Task
+    /// only returned after the search had already completed, so any code that did
+    /// <c>await search.RunSearchAsync()</c> on the same thread deadlocked. The
+    /// multi-thread case used to swallow worker exceptions silently — if a worker
+    /// threw, <see cref="_completionSource"/> never moved and the caller hung forever.
+    /// Every worker is now wrapped so the first exception is captured and surfaced
+    /// through <see cref="_completionSource"/> once the last worker drops out.
+    /// </remarks>
     private void StartSearchThreads()
     {
-        // what the fuck - pifreak
-        // //ObjectDisposedException.ThrowIf(Volatile.Read(ref _isDisposed) != 0, this);
-
         _elapsedTime.Start();
 
-        if (_threadCount == 1)
+        int totalWorkers = _threadCount;
+        WorkerCoordinator coordinator = new(this, totalWorkers);
+
+        for (int i = 0; i < totalWorkers; i++)
         {
+            int threadIdx = i;
+            var thread = new Thread(() => coordinator.RunWorker(threadIdx))
+            {
+                Name = totalWorkers == 1
+                    ? "Motely Search Thread"
+                    : $"Motely Search Thread {threadIdx}",
+                IsBackground = true,
+            };
+            thread.Start();
+        }
+    }
 
-                try
-                {
-                    RunWorkerBody(_plans[0]);
-                    SignalSearchCompleted();
-                }
-                catch (Exception ex)
-                {
-                    _completionSource.TrySetException(ex);
-                }
+    /// <summary>
+    /// Tracks the running worker count and routes the first thrown exception back
+    /// through <see cref="_completionSource"/>. One instance per search.
+    /// </summary>
+    private sealed class WorkerCoordinator
+    {
+        private readonly MotelySearch<TBaseFilter> _owner;
+        private int _remaining;
+        private Exception? _firstError;
+
+        public WorkerCoordinator(MotelySearch<TBaseFilter> owner, int totalWorkers)
+        {
+            _owner = owner;
+            _remaining = totalWorkers;
         }
-        else
+
+        public void RunWorker(int idx)
         {
-            int remaining = _threadCount;
-            for (int i = 0; i < _threadCount; i++)
+            try
             {
-                int threadIdx = i;
-                var thread = new Thread(() =>
+                _owner.RunWorkerBody(_owner._plans[idx]);
+            }
+            catch (OperationCanceledException) when (_owner._cancellationToken.IsCancellationRequested)
+            {
+                // honour cooperative cancellation — no error
+            }
+            catch (Exception ex)
+            {
+                Interlocked.CompareExchange(ref _firstError, ex, null);
+            }
+            finally
+            {
+                if (Interlocked.Decrement(ref _remaining) == 0)
                 {
-                    RunWorkerBody(_plans[threadIdx]);
-                    if (Interlocked.Decrement(ref remaining) == 0)
+                    Thread.MemoryBarrier();
+                    var err = Volatile.Read(ref _firstError);
+                    if (err is not null)
+                    {
+                        _owner._completionSource.TrySetException(err);
+                    }
+                    else
                     {
-                        Thread.MemoryBarrier();
                         bool completed =
-                            Volatile.Read(ref _isDisposed) == 0 && !_cancellationToken.IsCancellationRequested;
-                        _completionSource.TrySetResult(completed);
+                            Volatile.Read(ref _owner._isDisposed) == 0
+                            && !_owner._cancellationToken.IsCancellationRequested;
+                        _owner._completionSource.TrySetResult(completed);
                     }
-                })
-                {
-                    Name = $"Motely Search Thread {threadIdx}",
-                    IsBackground = true
-                };
-                thread.Start();
+                }
             }
         }
     }