diff --git a/ZB.MOM.WW.LocalDb/src/ZB.MOM.WW.LocalDb/Internal/LocalDbSchema.cs b/ZB.MOM.WW.LocalDb/src/ZB.MOM.WW.LocalDb/Internal/LocalDbSchema.cs
index b0b5528..a704ab1 100644
--- a/ZB.MOM.WW.LocalDb/src/ZB.MOM.WW.LocalDb/Internal/LocalDbSchema.cs
+++ b/ZB.MOM.WW.LocalDb/src/ZB.MOM.WW.LocalDb/Internal/LocalDbSchema.cs
@@ -14,6 +14,8 @@ internal static class LocalDbSchema
           hlc_high_water INTEGER NOT NULL DEFAULT 0,
           schema_version INTEGER NOT NULL
         );
+        -- AUTOINCREMENT: seq must never be reused after row pruning, or peer watermarks/acks would
+        -- silently skip/misattribute rows sharing a reused seq value.
         CREATE TABLE IF NOT EXISTS __localdb_oplog (
           seq INTEGER PRIMARY KEY AUTOINCREMENT,
           table_name TEXT NOT NULL,
@@ -91,7 +93,9 @@ internal static class LocalDbSchema
         using var cmd = connection.CreateCommand();
         cmd.CommandText = "SELECT node_id, hlc_high_water FROM __localdb_meta WHERE id = 1";
         using var reader = cmd.ExecuteReader();
-        reader.Read();
+        if (!reader.Read())
+            throw new InvalidOperationException(
+                "LocalDb schema not initialized: __localdb_meta is empty. Call EnsureCreated first.");
         return (reader.GetString(0), reader.GetInt64(1));
     }
 
diff --git a/ZB.MOM.WW.LocalDb/tests/ZB.MOM.WW.LocalDb.Tests/HybridLogicalClockTests.cs b/ZB.MOM.WW.LocalDb/tests/ZB.MOM.WW.LocalDb.Tests/HybridLogicalClockTests.cs
index d16a6e3..5ea98fa 100644
--- a/ZB.MOM.WW.LocalDb/tests/ZB.MOM.WW.LocalDb.Tests/HybridLogicalClockTests.cs
+++ b/ZB.MOM.WW.LocalDb/tests/ZB.MOM.WW.LocalDb.Tests/HybridLogicalClockTests.cs
@@ -1,3 +1,4 @@
+using System.Collections.Concurrent;
 using ZB.MOM.WW.LocalDb.Hlc;
 
 namespace ZB.MOM.WW.LocalDb.Tests;
@@ -87,4 +88,20 @@ public sealed class HybridLogicalClockTests
         Assert.Equal(ms + 1, HybridLogicalClock.PhysicalMs(next));
         Assert.Equal(0, HybridLogicalClock.Counter(next));
     }
+
+    [Fact]
+    public void Next_ConcurrentCallers_NoDuplicates_StrictlyIncreasing()
+    {
+        var clock = new HybridLogicalClock();
+        var results = new ConcurrentBag<long>();
+
+        Parallel.For(0, 8, _ =>
+        {
+            for (var i = 0; i < 1000; i++)
+                results.Add(clock.Next());
+        });
+
+        Assert.Equal(8000, results.Count);
+        Assert.Equal(8000, results.Distinct().Count());
+    }
 }
diff --git a/ZB.MOM.WW.LocalDb/tests/ZB.MOM.WW.LocalDb.Tests/LocalDbSchemaTests.cs b/ZB.MOM.WW.LocalDb/tests/ZB.MOM.WW.LocalDb.Tests/LocalDbSchemaTests.cs
index 55598e8..cef4ec3 100644
--- a/ZB.MOM.WW.LocalDb/tests/ZB.MOM.WW.LocalDb.Tests/LocalDbSchemaTests.cs
+++ b/ZB.MOM.WW.LocalDb/tests/ZB.MOM.WW.LocalDb.Tests/LocalDbSchemaTests.cs
@@ -54,6 +54,9 @@ public sealed class LocalDbSchemaTests : IDisposable
                      "__localdb_row_version", "__localdb_applying", "__localdb_dead_letter"
                  })
             Assert.Contains(expected, tables);
+
+        Assert.Equal(1, ScalarLong(conn,
+            "SELECT count(*) FROM sqlite_master WHERE type='index' AND name='__localdb_oplog_hlc'"));
     }
 
     [Fact]