diff --git a/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/InstanceActor.cs b/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/InstanceActor.cs
index c8bd3afa..64c65d3c 100644
--- a/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/InstanceActor.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/InstanceActor.cs
@@ -948,10 +948,31 @@ public class InstanceActor : ReceiveActor
             if (_resolvedAttributeByName.TryGetValue(kvp.Key, out var resolved)
                 && IsListAttribute(resolved))
             {
+                // NJ-4: decode the stored List override (both old array-of-strings
+                // and native-typed forms decode) and re-persist the native form if
+                // the stored value is still in the OLD form. Re-encoding the decoded
+                // list and comparing to the stored string detects old-form values
+                // (native → native is byte-identical, so a native value is a no-op).
+                // The re-persist is fire-and-forget and never throws into the actor.
                 var decoded = DecodeAttributeValue(resolved, kvp.Value);
                 _attributes[kvp.Key] = decoded;
                 if (decoded is null && !string.IsNullOrEmpty(kvp.Value))
+                {
                     _attributeQualities[kvp.Key] = "Bad";
+                }
+                else if (decoded is not null)
+                {
+                    var native = AttributeValueCodec.Encode(decoded);
+                    if (native != kvp.Value)   // stored value was old-form → normalize on disk
+                    {
+                        var key = kvp.Key;
+                        _storage.SetStaticOverrideAsync(_instanceUniqueName, key, native!)
+                            .ContinueWith(t => _logger.LogWarning(t.Exception?.GetBaseException(),
+                                "Failed to normalize static override {Instance}.{Attr} to native JSON",
+                                _instanceUniqueName, key),
+                                TaskContinuationOptions.OnlyOnFaulted);
+                    }
+                }
             }
             else
             {
diff --git a/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Actors/InstanceActorTests.cs b/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Actors/InstanceActorTests.cs
index f93a238e..72dbb49c 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Actors/InstanceActorTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Actors/InstanceActorTests.cs
@@ -1016,4 +1016,159 @@ public class InstanceActorTests : TestKit, IDisposable
         Assert.Single(overrides);
         Assert.Equal("[]", overrides["Labels"]);
     }
+
+    // ── NJ-4: old-form List static override normalization on load ────────────
+
+    /// <summary>
+    /// NJ-4: an OLD array-of-strings static override (<c>["10","20"]</c>) for an
+    /// Int32 List attribute must be re-persisted in the native form (<c>[10,20]</c>)
+    /// when the actor loads it at startup. The in-memory read still returns the
+    /// typed list {10,20}; the on-disk value is normalized to native JSON.
+    /// </summary>
+    [Fact]
+    public async Task InstanceActor_OldFormListOverride_NormalizedToNativeOnLoad()
+    {
+        await _storage.SetStaticOverrideAsync("Pump-OldForm", "Counts", "[\"10\",\"20\"]");
+
+        var config = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Pump-OldForm",
+            Attributes =
+            [
+                new ResolvedAttribute
+                {
+                    CanonicalName = "Counts", Value = "[1,2]",
+                    DataType = "List", ElementDataType = "Int32"
+                }
+            ]
+        };
+
+        var actor = CreateInstanceActor("Pump-OldForm", config);
+
+        // Wait for the async override load (PipeTo) + fire-and-forget normalization.
+        await Task.Delay(1000);
+
+        // In-memory read returns the typed list, decoded from the old form.
+        actor.Tell(new GetAttributeRequest("corr-of", "Pump-OldForm", "Counts", DateTimeOffset.UtcNow));
+        var response = ExpectMsg<GetAttributeResponse>(TimeSpan.FromSeconds(5));
+        Assert.True(response.Found);
+        var list = Assert.IsType<List<int>>(response.Value);
+        Assert.Equal(new[] { 10, 20 }, list);
+
+        // The on-disk override has been normalized to the native form.
+        var overrides = await _storage.GetStaticOverridesAsync("Pump-OldForm");
+        Assert.Single(overrides);
+        Assert.Equal("[10,20]", overrides["Counts"]);
+    }
+
+    /// <summary>
+    /// NJ-4: a NATIVE-form static override (<c>[10,20]</c>) is already canonical, so
+    /// load-time normalization must be a no-op — the on-disk value is unchanged
+    /// (idempotent: native → native is byte-identical, so no re-persist occurs).
+    /// </summary>
+    [Fact]
+    public async Task InstanceActor_NativeFormListOverride_NotRePersistedOnLoad()
+    {
+        await _storage.SetStaticOverrideAsync("Pump-Native", "Counts", "[10,20]");
+
+        var config = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Pump-Native",
+            Attributes =
+            [
+                new ResolvedAttribute
+                {
+                    CanonicalName = "Counts", Value = "[1,2]",
+                    DataType = "List", ElementDataType = "Int32"
+                }
+            ]
+        };
+
+        var actor = CreateInstanceActor("Pump-Native", config);
+        await Task.Delay(1000);
+
+        actor.Tell(new GetAttributeRequest("corr-nat", "Pump-Native", "Counts", DateTimeOffset.UtcNow));
+        var response = ExpectMsg<GetAttributeResponse>(TimeSpan.FromSeconds(5));
+        Assert.True(response.Found);
+        var list = Assert.IsType<List<int>>(response.Value);
+        Assert.Equal(new[] { 10, 20 }, list);
+
+        // The native value is left untouched on disk.
+        var overrides = await _storage.GetStaticOverridesAsync("Pump-Native");
+        Assert.Single(overrides);
+        Assert.Equal("[10,20]", overrides["Counts"]);
+    }
+
+    /// <summary>
+    /// NJ-4: a scalar static override is unaffected by the List normalization path —
+    /// its on-disk value is left exactly as stored (no native re-encode).
+    /// </summary>
+    [Fact]
+    public async Task InstanceActor_ScalarOverride_NotTouchedByListNormalization()
+    {
+        await _storage.SetStaticOverrideAsync("Pump-ScalarOf", "Temperature", "200.0");
+
+        var config = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Pump-ScalarOf",
+            Attributes =
+            [
+                new ResolvedAttribute { CanonicalName = "Temperature", Value = "100.0", DataType = "Double" }
+            ]
+        };
+
+        var actor = CreateInstanceActor("Pump-ScalarOf", config);
+        await Task.Delay(1000);
+
+        actor.Tell(new GetAttributeRequest("corr-sof", "Pump-ScalarOf", "Temperature", DateTimeOffset.UtcNow));
+        var response = ExpectMsg<GetAttributeResponse>(TimeSpan.FromSeconds(5));
+        Assert.True(response.Found);
+        Assert.Equal("200.0", response.Value);
+
+        var overrides = await _storage.GetStaticOverridesAsync("Pump-ScalarOf");
+        Assert.Single(overrides);
+        Assert.Equal("200.0", overrides["Temperature"]);
+    }
+
+    /// <summary>
+    /// NJ-4: a malformed stored List override (truncated JSON) must NOT crash the
+    /// actor and must NOT be re-persisted — it loads with Bad quality (as today),
+    /// the actor stays alive, and the poison on-disk value is left unchanged.
+    /// </summary>
+    [Fact]
+    public async Task InstanceActor_MalformedListOverride_BadQuality_NotRePersisted()
+    {
+        await _storage.SetStaticOverrideAsync("Pump-BadOf", "Counts", "[\"a\"");
+
+        var config = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Pump-BadOf",
+            Attributes =
+            [
+                new ResolvedAttribute
+                {
+                    CanonicalName = "Counts", Value = "[1,2]",
+                    DataType = "List", ElementDataType = "Int32"
+                }
+            ]
+        };
+
+        var actor = CreateInstanceActor("Pump-BadOf", config);
+        Watch(actor);
+        await Task.Delay(1000);
+
+        actor.Tell(new GetAttributeRequest("corr-bof", "Pump-BadOf", "Counts", DateTimeOffset.UtcNow));
+        var response = ExpectMsg<GetAttributeResponse>(TimeSpan.FromSeconds(5));
+        Assert.True(response.Found);
+        Assert.Equal("Bad", response.Quality);
+        Assert.Null(response.Value);
+
+        // The actor must still be alive — no crash from the normalization path.
+        ExpectNoTerminated(actor, TimeSpan.FromMilliseconds(500));
+
+        // The malformed value must NOT have been re-persisted (left exactly as stored).
+        var overrides = await _storage.GetStaticOverridesAsync("Pump-BadOf");
+        Assert.Single(overrides);
+        Assert.Equal("[\"a\"", overrides["Counts"]);
+    }
 }