refactor(ui/design): replace JSON inputs with structured editors

Two new shared components in Components/Shared:
  - ParameterListEditor: table of rows (name + type + item type + required + remove)
  - ReturnTypeEditor: single type (+ item type when List)

Both round-trip the same JSON shape already stored on the entity:
  parameters: [{"name":"x","type":"String","required":true},...]
  return:     {"type":"List","itemType":"Integer"} | null

Type set follows the Inbound API validator (Boolean, Integer, Float,
String, Object, List). Legacy values normalize on read — Int32 / int64
/ Double / Decimal / lowercase string / etc all coalesce to the new
set so existing rows render correctly. Re-saving persists the
normalized form.

Applied to:
  - SharedScriptForm
  - TemplateEdit Add Script form (also surfaces ParameterDefinitions
    + ReturnDefinition which the entity supported but the form was
    never wiring through)
  - ApiMethodForm

Graceful degradation: invalid JSON is shown with a "Start fresh"
escape hatch instead of crashing the form.

src/ScadaLink.CentralUI/Components/Pages/Design/ApiMethodForm.razor

@@ -29,14 +29,12 @@
                     <input type="number" class="form-control" @bind="_timeoutSeconds" min="1" />
                 </div>
                 <div class="mb-3">
-                    <label class="form-label">Params (JSON)</label>
-                    <input type="text" class="form-control" @bind="_params"
-                           placeholder='[{"name":"id","type":"Int32"}]' />
+                    <label class="form-label">Parameters</label>
+                    <ParameterListEditor Json="@_params" JsonChanged="@(v => _params = v)" />
                 </div>
                 <div class="mb-3">
-                    <label class="form-label">Returns (JSON)</label>
-                    <input type="text" class="form-control" @bind="_returns"
-                           placeholder='{"type":"Boolean"}' />
+                    <label class="form-label">Return value</label>
+                    <ReturnTypeEditor Json="@_returns" JsonChanged="@(v => _returns = v)" />
                 </div>
                 <div class="mb-3">
                     <label class="form-label">Script</label>

src/ScadaLink.CentralUI/Components/Pages/Design/SharedScriptForm.razor

@@ -29,25 +29,13 @@
                     <input type="text" class="form-control form-control-sm" @bind="_formName"
                            disabled="@(Id.HasValue)" />
                 </div>
-                <div class="mb-2">
-                    <label class="form-label small">
-                        Parameters (JSON)
-                        <span class="text-muted" title='JSON array of {name, type} objects. Example: [{"name":"id","type":"Int32"},{"name":"label","type":"String"}]'>
-                            <i class="bi bi-question-circle"></i>
-                        </span>
-                    </label>
-                    <input type="text" class="form-control form-control-sm" @bind="_formParameters"
-                           placeholder='e.g. [{"name":"x","type":"Int32"}]' />
+                <div class="mb-3">
+                    <label class="form-label small">Parameters</label>
+                    <ParameterListEditor Json="@_formParameters" JsonChanged="@(v => _formParameters = v)" />
                 </div>
-                <div class="mb-2">
-                    <label class="form-label small">
-                        Return Definition (JSON)
-                        <span class="text-muted" title='JSON object with a type field. Example: {"type":"Boolean"} or {"type":"List","itemType":"Int32"}'>
-                            <i class="bi bi-question-circle"></i>
-                        </span>
-                    </label>
-                    <input type="text" class="form-control form-control-sm" @bind="_formReturn"
-                           placeholder='e.g. {"type":"Boolean"}' />
+                <div class="mb-3">
+                    <label class="form-label small">Return value</label>
+                    <ReturnTypeEditor Json="@_formReturn" JsonChanged="@(v => _formReturn = v)" />
                 </div>
                 <div class="mb-2">
                     <label class="form-label small">Code</label>

src/ScadaLink.CentralUI/Components/Pages/Design/TemplateEdit.razor

@@ -85,6 +85,8 @@
     private string _scriptCode = string.Empty;
     private string? _scriptTriggerType;
     private string? _scriptTriggerConfig;
+    private string? _scriptParameters;
+    private string? _scriptReturn;
     private bool _scriptIsLocked;
     private string? _scriptFormError;
 
@@ -615,7 +617,7 @@
     {
         <div class="d-flex justify-content-between align-items-center mb-2">
             <h5 class="mb-0">Scripts</h5>
-            <button class="btn btn-primary btn-sm" @onclick="() => { _showScriptForm = true; _scriptFormError = null; _scriptName = string.Empty; _scriptCode = string.Empty; _scriptTriggerType = null; _scriptTriggerConfig = null; _scriptIsLocked = false; }">Add Script</button>
+            <button class="btn btn-primary btn-sm" @onclick="() => { _showScriptForm = true; _scriptFormError = null; _scriptName = string.Empty; _scriptCode = string.Empty; _scriptTriggerType = null; _scriptTriggerConfig = null; _scriptParameters = null; _scriptReturn = null; _scriptIsLocked = false; }">Add Script</button>
         </div>
 
         @if (_showScriptForm)
@@ -636,6 +638,14 @@
                             <label class="form-label">Trigger Config (JSON)</label>
                             <input type="text" class="form-control" @bind="_scriptTriggerConfig" />
                         </div>
+                        <div class="col-12">
+                            <label class="form-label">Parameters</label>
+                            <ParameterListEditor Json="@_scriptParameters" JsonChanged="@(v => _scriptParameters = v)" />
+                        </div>
+                        <div class="col-12">
+                            <label class="form-label">Return value</label>
+                            <ReturnTypeEditor Json="@_scriptReturn" JsonChanged="@(v => _scriptReturn = v)" />
+                        </div>
                         <div class="col-12">
                             <div class="form-check">
                                 <input class="form-check-input" type="checkbox" @bind="_scriptIsLocked" id="scriptLocked" />
@@ -884,6 +894,8 @@
         {
             TriggerType = _scriptTriggerType?.Trim(),
             TriggerConfiguration = _scriptTriggerConfig?.Trim(),
+            ParameterDefinitions = _scriptParameters,
+            ReturnDefinition = _scriptReturn,
             IsLocked = _scriptIsLocked
         };
 

src/ScadaLink.CentralUI/Components/Shared/ParameterListEditor.razor

@@ -0,0 +1,203 @@
+@namespace ScadaLink.CentralUI.Components.Shared
+@using System.Text.Json
+
+@if (_parseError != null)
+{
+    <div class="alert alert-warning py-2 small mb-2">
+        Could not parse existing parameter JSON: <code>@_parseError</code>
+        <button class="btn btn-link btn-sm p-0 ms-2" type="button" @onclick="StartFresh">Start fresh</button>
+    </div>
+}
+
+@if (_rows.Count > 0)
+{
+    <div class="table-responsive">
+        <table class="table table-sm align-middle mb-2">
+            <thead class="table-light">
+                <tr>
+                    <th>Name</th>
+                    <th style="width: 160px;">Type</th>
+                    <th style="width: 160px;">Item type</th>
+                    <th class="text-center" style="width: 100px;">Required</th>
+                    <th style="width: 50px;"></th>
+                </tr>
+            </thead>
+            <tbody>
+                @foreach (var row in _rows)
+                {
+                    var r = row;
+                    <tr @key="r">
+                        <td>
+                            <input class="form-control form-control-sm" @bind="r.Name" @bind:event="oninput" @bind:after="Emit"
+                                   placeholder="e.g. id" aria-label="Parameter name" />
+                        </td>
+                        <td>
+                            <select class="form-select form-select-sm" @bind="r.Type" @bind:after="Emit"
+                                    aria-label="Parameter type">
+                                @foreach (var t in Types)
+                                {
+                                    <option value="@t">@t</option>
+                                }
+                            </select>
+                        </td>
+                        <td>
+                            @if (r.Type == "List")
+                            {
+                                <select class="form-select form-select-sm" @bind="r.ItemType" @bind:after="Emit"
+                                        aria-label="List item type">
+                                    @foreach (var t in ItemTypes)
+                                    {
+                                        <option value="@t">@t</option>
+                                    }
+                                </select>
+                            }
+                            else
+                            {
+                                <span class="text-muted small">—</span>
+                            }
+                        </td>
+                        <td class="text-center">
+                            <input type="checkbox" class="form-check-input" @bind="r.Required" @bind:after="Emit"
+                                   aria-label="Required" />
+                        </td>
+                        <td>
+                            <button type="button" class="btn btn-link btn-sm p-0 text-danger"
+                                    @onclick="() => Remove(r)"
+                                    aria-label="@($"Remove parameter {r.Name}")">✕</button>
+                        </td>
+                    </tr>
+                }
+            </tbody>
+        </table>
+    </div>
+}
+else if (_parseError == null)
+{
+    <p class="text-muted small fst-italic mb-2">No parameters defined.</p>
+}
+
+<button type="button" class="btn btn-outline-secondary btn-sm" @onclick="Add">+ Add parameter</button>
+
+@code {
+    [Parameter] public string? Json { get; set; }
+    [Parameter] public EventCallback<string?> JsonChanged { get; set; }
+
+    private static readonly string[] Types = { "Boolean", "Integer", "Float", "String", "Object", "List" };
+    private static readonly string[] ItemTypes = { "Boolean", "Integer", "Float", "String", "Object" };
+
+    private List<ParamRow> _rows = new();
+    private string? _parseError;
+    private string? _lastSeenJson;
+
+    protected override void OnParametersSet()
+    {
+        if (Json != _lastSeenJson)
+        {
+            _lastSeenJson = Json;
+            ParseFromJson();
+        }
+    }
+
+    private void ParseFromJson()
+    {
+        _parseError = null;
+        _rows = new();
+        if (string.IsNullOrWhiteSpace(Json)) return;
+
+        try
+        {
+            using var doc = JsonDocument.Parse(Json);
+            if (doc.RootElement.ValueKind != JsonValueKind.Array)
+            {
+                _parseError = "Expected a JSON array of parameter objects.";
+                return;
+            }
+
+            foreach (var el in doc.RootElement.EnumerateArray())
+            {
+                var name = el.TryGetProperty("name", out var n) ? n.GetString() ?? "" : "";
+                var rawType = el.TryGetProperty("type", out var t) ? t.GetString() ?? "String" : "String";
+                var rawItem = el.TryGetProperty("itemType", out var it) ? it.GetString() ?? "String" : "String";
+                var required = !el.TryGetProperty("required", out var rq) || rq.ValueKind != JsonValueKind.False;
+                _rows.Add(new ParamRow
+                {
+                    Name = name,
+                    Type = NormalizeType(rawType),
+                    ItemType = NormalizeType(rawItem),
+                    Required = required
+                });
+            }
+        }
+        catch (JsonException ex)
+        {
+            _parseError = ex.Message;
+        }
+    }
+
+    private static string NormalizeType(string raw)
+    {
+        if (string.IsNullOrEmpty(raw)) return "String";
+        return raw.ToLowerInvariant() switch
+        {
+            "boolean" or "bool" => "Boolean",
+            "integer" or "int" or "int32" or "int64" or "int16" or "byte" or "sbyte" or "uint32" or "uint64" or "uint16" => "Integer",
+            "float" or "double" or "single" or "decimal" => "Float",
+            "string" or "datetime" => "String",
+            "object" => "Object",
+            "list" => "List",
+            _ => raw
+        };
+    }
+
+    private async Task StartFresh()
+    {
+        _parseError = null;
+        _rows = new();
+        await Emit();
+    }
+
+    private async Task Add()
+    {
+        _rows.Add(new ParamRow { Type = "String", ItemType = "String", Required = true });
+        await Emit();
+    }
+
+    private async Task Remove(ParamRow row)
+    {
+        _rows.Remove(row);
+        await Emit();
+    }
+
+    private async Task Emit()
+    {
+        var json = SerializeToJson();
+        _lastSeenJson = json;
+        await JsonChanged.InvokeAsync(json);
+    }
+
+    private string? SerializeToJson()
+    {
+        if (_rows.Count == 0) return null;
+        var list = new List<Dictionary<string, object>>();
+        foreach (var r in _rows)
+        {
+            var obj = new Dictionary<string, object>
+            {
+                ["name"] = r.Name,
+                ["type"] = r.Type,
+            };
+            if (r.Type == "List") obj["itemType"] = r.ItemType;
+            if (!r.Required) obj["required"] = false;
+            list.Add(obj);
+        }
+        return JsonSerializer.Serialize(list);
+    }
+
+    private class ParamRow
+    {
+        public string Name { get; set; } = "";
+        public string Type { get; set; } = "String";
+        public string ItemType { get; set; } = "String";
+        public bool Required { get; set; } = true;
+    }
+}

src/ScadaLink.CentralUI/Components/Shared/ReturnTypeEditor.razor

@@ -0,0 +1,117 @@
+@namespace ScadaLink.CentralUI.Components.Shared
+@using System.Text.Json
+
+@if (_parseError != null)
+{
+    <div class="alert alert-warning py-2 small mb-2">
+        Could not parse existing return JSON: <code>@_parseError</code>
+        <button class="btn btn-link btn-sm p-0 ms-2" type="button" @onclick="StartFresh">Start fresh</button>
+    </div>
+}
+
+<div class="row g-2 align-items-end">
+    <div class="col-md-3">
+        <label class="form-label small">Type</label>
+        <select class="form-select form-select-sm" @bind="_type" @bind:after="Emit" aria-label="Return type">
+            <option value="">(no return value)</option>
+            @foreach (var t in Types)
+            {
+                <option value="@t">@t</option>
+            }
+        </select>
+    </div>
+    @if (_type == "List")
+    {
+        <div class="col-md-3">
+            <label class="form-label small">Item type</label>
+            <select class="form-select form-select-sm" @bind="_itemType" @bind:after="Emit" aria-label="List item type">
+                @foreach (var t in ItemTypes)
+                {
+                    <option value="@t">@t</option>
+                }
+            </select>
+        </div>
+    }
+</div>
+
+@code {
+    [Parameter] public string? Json { get; set; }
+    [Parameter] public EventCallback<string?> JsonChanged { get; set; }
+
+    private static readonly string[] Types = { "Boolean", "Integer", "Float", "String", "Object", "List" };
+    private static readonly string[] ItemTypes = { "Boolean", "Integer", "Float", "String", "Object" };
+
+    private string _type = "";
+    private string _itemType = "String";
+    private string? _parseError;
+    private string? _lastSeenJson;
+
+    protected override void OnParametersSet()
+    {
+        if (Json != _lastSeenJson)
+        {
+            _lastSeenJson = Json;
+            ParseFromJson();
+        }
+    }
+
+    private void ParseFromJson()
+    {
+        _parseError = null;
+        _type = "";
+        _itemType = "String";
+        if (string.IsNullOrWhiteSpace(Json)) return;
+
+        try
+        {
+            using var doc = JsonDocument.Parse(Json);
+            if (doc.RootElement.ValueKind != JsonValueKind.Object)
+            {
+                _parseError = "Expected a JSON object with a type field.";
+                return;
+            }
+            _type = doc.RootElement.TryGetProperty("type", out var t) ? NormalizeType(t.GetString() ?? "") : "";
+            _itemType = doc.RootElement.TryGetProperty("itemType", out var it) ? NormalizeType(it.GetString() ?? "String") : "String";
+        }
+        catch (JsonException ex)
+        {
+            _parseError = ex.Message;
+        }
+    }
+
+    private static string NormalizeType(string raw)
+    {
+        if (string.IsNullOrEmpty(raw)) return "";
+        return raw.ToLowerInvariant() switch
+        {
+            "boolean" or "bool" => "Boolean",
+            "integer" or "int" or "int32" or "int64" or "int16" or "byte" or "sbyte" or "uint32" or "uint64" or "uint16" => "Integer",
+            "float" or "double" or "single" or "decimal" => "Float",
+            "string" or "datetime" => "String",
+            "object" => "Object",
+            "list" => "List",
+            _ => raw
+        };
+    }
+
+    private async Task StartFresh()
+    {
+        _parseError = null;
+        _type = "";
+        _itemType = "String";
+        await Emit();
+    }
+
+    private async Task Emit()
+    {
+        string? json = null;
+        if (!string.IsNullOrEmpty(_type))
+        {
+            var obj = new Dictionary<string, object> { ["type"] = _type };
+            if (_type == "List") obj["itemType"] = _itemType;
+            json = JsonSerializer.Serialize(obj);
+        }
+        _lastSeenJson = json;
+        await JsonChanged.InvokeAsync(json);
+    }
+}