diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/DeviceModal.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/DeviceModal.razor
index aee2778e..eaebf206 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/DeviceModal.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/DeviceModal.razor
@@ -108,13 +108,19 @@
     private bool _enabled = true;
     private string _deviceConfigJson = "{}";
 
-    /// <summary>Parameters handed to the DynamicComponent-rendered device form. Rebuilt on every render —
-    /// see DriverConfigModal for why this must not be cached.</summary>
-    private Dictionary<string, object> _deviceFormParameters => new()
-    {
-        ["DeviceConfigJson"] = _deviceConfigJson,
-        ["DeviceConfigJsonChanged"] = EventCallback.Factory.Create<string>(this, v => _deviceConfigJson = v),
-    };
+    /// <summary>Parameters handed to the DynamicComponent-rendered device form. Cached on the value it
+    /// carries and rebuilt when that changes (never build-once: see DriverConfigModal), with the callback
+    /// created once (R04 H2).</summary>
+    private Dictionary<string, object> _deviceFormParameters => _deviceFormParameterCache.Get(
+        [_deviceConfigJson],
+        () => new()
+        {
+            ["DeviceConfigJson"] = _deviceConfigJson,
+            ["DeviceConfigJsonChanged"] = _deviceConfigJsonChanged ??=
+                EventCallback.Factory.Create<string>(this, v => _deviceConfigJson = v),
+        });
+    private readonly ParameterDictionaryCache _deviceFormParameterCache = new();
+    private EventCallback<string>? _deviceConfigJsonChanged;
     private byte[] _rowVersion = [];
     private string _parentDriverConfig = "{}";
 
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/DriverConfigModal.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/DriverConfigModal.razor
index d15c8a8c..8c3e7047 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/DriverConfigModal.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/DriverConfigModal.razor
@@ -111,16 +111,24 @@
     private string _name = "";
     private string _driverConfigJson = "{}";
 
-    /// <summary>Parameters handed to the DynamicComponent-rendered driver form. Rebuilt on every render so
-    /// the child receives the CURRENT json — a cached dictionary would pin the value captured at first
-    /// render and silently strand every subsequent edit.</summary>
-    private Dictionary<string, object> _formParameters => new()
-    {
-        ["DriverConfigJson"] = _driverConfigJson,
-        ["DriverConfigJsonChanged"] = EventCallback.Factory.Create<string>(this, v => _driverConfigJson = v),
-        ["ResilienceConfig"] = _resilienceConfig!,
-        ["ResilienceConfigChanged"] = EventCallback.Factory.Create<string?>(this, v => _resilienceConfig = v),
-    };
+    /// <summary>Parameters handed to the DynamicComponent-rendered driver form. The child must receive the
+    /// CURRENT json — a build-once dictionary would pin the value captured at first render and silently
+    /// strand every subsequent edit — so the cache is keyed on the values it carries and rebuilt only when
+    /// one changes; the callbacks are created once and reused (R04 H2).</summary>
+    private Dictionary<string, object> _formParameters => _formParameterCache.Get(
+        [_driverConfigJson, _resilienceConfig],
+        () => new()
+        {
+            ["DriverConfigJson"] = _driverConfigJson,
+            ["DriverConfigJsonChanged"] = _driverConfigJsonChanged ??=
+                EventCallback.Factory.Create<string>(this, v => _driverConfigJson = v),
+            ["ResilienceConfig"] = _resilienceConfig!,
+            ["ResilienceConfigChanged"] = _resilienceConfigChanged ??=
+                EventCallback.Factory.Create<string?>(this, v => _resilienceConfig = v),
+        });
+    private readonly ParameterDictionaryCache _formParameterCache = new();
+    private EventCallback<string>? _driverConfigJsonChanged;
+    private EventCallback<string?>? _resilienceConfigChanged;
     private string? _resilienceConfig;
     private byte[] _rowVersion = [];
 
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/ParameterDictionaryCache.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/ParameterDictionaryCache.cs
new file mode 100644
index 00000000..4a2e5f19
--- /dev/null
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/ParameterDictionaryCache.cs
@@ -0,0 +1,50 @@
+namespace ZB.MOM.WW.OtOpcUa.AdminUI.Components.Shared;
+
+/// <summary>
+///     Caches a <c>DynamicComponent</c> parameter dictionary (R04 H2) and rebuilds it only when one of the
+///     values it carries changed. The modals used to build a new dictionary, and new
+///     <c>EventCallback</c>s, on every render. A plain build-once cache is wrong: it would pin the JSON
+///     captured at first render and silently strand every later edit — so the cache is keyed on the
+///     current values, and the callbacks it hands out are created once by the caller and reused.
+///     <para>Note the limit: Blazor's change detection treats any <c>EventCallback</c> parameter as
+///     possibly changed, so a hosted form still sees <c>SetParametersAsync</c> on each parent render. The
+///     per-form <c>_lastParsed</c> guards remain load-bearing; this removes the per-render allocations and
+///     gives the child a stable dictionary and callback identity.</para>
+/// </summary>
+public sealed class ParameterDictionaryCache
+{
+    private object?[]? _keyValues;
+    private Dictionary<string, object>? _cached;
+
+    /// <summary>Returns the cached dictionary when <paramref name="keyValues"/> equal the previous call's,
+    /// otherwise builds, caches and returns a new one.</summary>
+    /// <param name="keyValues">The values the dictionary carries (compared with <see cref="object.Equals(object, object)"/>).</param>
+    /// <param name="build">Builds the dictionary from the current state.</param>
+    /// <returns>The parameter dictionary.</returns>
+    public Dictionary<string, object> Get(object?[] keyValues, Func<Dictionary<string, object>> build)
+    {
+        if (_cached is not null && _keyValues is not null && Same(_keyValues, keyValues)) return _cached;
+
+        _cached = build();
+        _keyValues = (object?[])keyValues.Clone();
+        return _cached;
+    }
+
+    /// <summary>Drops the cached dictionary (e.g. on modal close) so the next <see cref="Get"/> rebuilds.</summary>
+    public void Reset()
+    {
+        _cached = null;
+        _keyValues = null;
+    }
+
+    private static bool Same(object?[] a, object?[] b)
+    {
+        if (a.Length != b.Length) return false;
+        for (var i = 0; i < a.Length; i++)
+        {
+            if (!Equals(a[i], b[i])) return false;
+        }
+
+        return true;
+    }
+}
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Raw/RawTagModal.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Raw/RawTagModal.razor
index 474922f4..b9909392 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Raw/RawTagModal.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Raw/RawTagModal.razor
@@ -217,15 +217,23 @@
         }
     }
 
-    /// <summary>Parameters handed to the typed TagConfig editor. Internal so tests can assert them.</summary>
-    internal IDictionary<string, object> BuildEditorParameters() => new Dictionary<string, object>
-    {
-        ["ConfigJson"] = _form.TagConfig,
-        ["ConfigJsonChanged"] = EventCallback.Factory.Create<string>(this, v => _form.TagConfig = v),
-        ["DriverType"] = DriverType ?? "",
-        // Live accessor, not a snapshot: the picker reads it when the operator clicks Browse.
-        ["GetDriverConfigJson"] = (Func<string>)(() => _mergedConfigJson ?? "{}"),
-    };
+    /// <summary>Parameters handed to the typed TagConfig editor. Internal so tests can assert them. Cached
+    /// on the values it carries and rebuilt when one changes (never build-once, which would pin the first
+    /// render's TagConfig); the callback and accessor are created once (R04 H2).</summary>
+    internal IDictionary<string, object> BuildEditorParameters() => _editorParameterCache.Get(
+        [_form.TagConfig, DriverType ?? ""],
+        () => new Dictionary<string, object>
+        {
+            ["ConfigJson"] = _form.TagConfig,
+            ["ConfigJsonChanged"] = _configJsonChanged ??=
+                EventCallback.Factory.Create<string>(this, v => _form.TagConfig = v),
+            ["DriverType"] = DriverType ?? "",
+            // Live accessor, not a snapshot: the picker reads it when the operator clicks Browse.
+            ["GetDriverConfigJson"] = _getDriverConfigJson ??= () => _mergedConfigJson ?? "{}",
+        });
+    private readonly ParameterDictionaryCache _editorParameterCache = new();
+    private EventCallback<string>? _configJsonChanged;
+    private Func<string>? _getDriverConfigJson;
 
     private async Task SaveAsync()
     {
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Raw/ParameterDictionaryCacheTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Raw/ParameterDictionaryCacheTests.cs
new file mode 100644
index 00000000..7bbe3c0b
--- /dev/null
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Raw/ParameterDictionaryCacheTests.cs
@@ -0,0 +1,87 @@
+using Microsoft.AspNetCore.Components;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.AdminUI.Components.Shared;
+
+namespace ZB.MOM.WW.OtOpcUa.AdminUI.Tests.Raw;
+
+/// <summary>
+///     R04 H2: the modals' DynamicComponent parameter dictionaries are reused across renders while their
+///     values are unchanged, and rebuilt — carrying the current value — the moment one changes. The second
+///     half is the regression a naive build-once cache would introduce (stale JSON stranding every edit).
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class ParameterDictionaryCacheTests
+{
+    [Fact]
+    public void Unchanged_values_return_the_same_dictionary()
+    {
+        var cache = new ParameterDictionaryCache();
+        var builds = 0;
+        var json = "{}";
+        Dictionary<string, object> Build() { builds++; return new() { ["Json"] = json }; }
+
+        var first = cache.Get([json], Build);
+        cache.Get([json], Build).ShouldBeSameAs(first);
+        builds.ShouldBe(1);
+    }
+
+    [Fact]
+    public void A_changed_value_rebuilds_with_the_current_value()
+    {
+        var cache = new ParameterDictionaryCache();
+        var json = "{}";
+        Dictionary<string, object> Build() => new() { ["Json"] = json };
+
+        cache.Get([json], Build)["Json"].ShouldBe("{}");
+        json = "{\"a\":1}";
+        cache.Get([json], Build)["Json"].ShouldBe("{\"a\":1}");
+    }
+
+    [Fact]
+    public void Null_values_compare_and_reset_forces_a_rebuild()
+    {
+        var cache = new ParameterDictionaryCache();
+        var builds = 0;
+        Dictionary<string, object> Build() { builds++; return new(); }
+
+        cache.Get(["x", null], Build);
+        cache.Get(["x", null], Build);
+        builds.ShouldBe(1);
+
+        cache.Reset();
+        cache.Get(["x", null], Build);
+        builds.ShouldBe(2);
+    }
+
+    [Fact]
+    public void Modals_build_their_parameters_through_the_cache_with_reused_callbacks()
+    {
+        foreach (var (path, cacheField) in new[]
+                 {
+                     (new[] { "Components", "Shared", "Drivers", "DriverConfigModal.razor" }, "_formParameterCache.Get("),
+                     (new[] { "Components", "Shared", "Drivers", "DeviceModal.razor" }, "_deviceFormParameterCache.Get("),
+                     (new[] { "Components", "Shared", "Raw", "RawTagModal.razor" }, "_editorParameterCache.Get("),
+                 })
+        {
+            var src = AdminUiSource.Read(path);
+            src.ShouldContain(cacheField, customMessage: path[^1]);
+            // Every EventCallback is created behind a ??= so it is made once per component.
+            var all = System.Text.RegularExpressions.Regex.Matches(src, @"EventCallback\.Factory\.Create").Count;
+            var once = System.Text.RegularExpressions.Regex.Matches(src, @"\?\?=\s*EventCallback\.Factory\.Create").Count;
+            all.ShouldBeGreaterThan(0, path[^1]);
+            once.ShouldBe(all, path[^1]);
+        }
+    }
+
+    [Fact]
+    public void RawTagModal_reuses_its_callback_across_renders()
+    {
+        var modal = new ZB.MOM.WW.OtOpcUa.AdminUI.Components.Shared.Raw.RawTagModal();
+        var first = modal.BuildEditorParameters();
+        var second = modal.BuildEditorParameters();
+
+        second.ShouldBeSameAs(first);
+        ((EventCallback<string>)first["ConfigJsonChanged"]).HasDelegate.ShouldBeTrue();
+    }
+}