refactor(scripts): scoped parent query + parent picker for multi-parent templates

Two caveats from the script-scope rollout addressed:

1. ITemplateEngineRepository.GetTemplatesComposingAsync — a scoped
   query that returns only the templates referencing a given template
   via Compositions, eager-loaded with their Attributes / Scripts /
   Compositions. Replaces the GetAllTemplatesAsync + filter pattern
   in TemplateEdit so the Monaco metadata fetch doesn't pull the
   entire template catalog to find one parent.

2. Multi-parent picker. The previous implementation suppressed Parent
   assistance entirely when more than one template composes the open
   one. Now TemplateEdit collects every parent into _editorParents
   and renders a small `select` above the script editor when there
   are >1, letting the user choose which parent's metadata drives
   Parent.Attributes / Parent.CallScript completion + diagnostics.
   Single-parent templates skip the picker (no UI change). Zero
   parents (root template) hide the picker and surface no Parent
   assistance.

Browser-verified on the Sensor Module template (composed by both Pump
and Variable Speed Motor): picker shows both options, switching
updates the editor's parent metadata immediately via the existing
GetContext callback.

Test counts unchanged (159 / 199); the new repo method is exercised
end-to-end by the parent-picker browser path.

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

@@ -94,7 +94,22 @@
         = Array.Empty<ScadaLink.CentralUI.ScriptAnalysis.DiagnosticMarker>();
     private IReadOnlyList<ScadaLink.CentralUI.ScriptAnalysis.CompositionContext> _editorChildren
         = Array.Empty<ScadaLink.CentralUI.ScriptAnalysis.CompositionContext>();
-    private ScadaLink.CentralUI.ScriptAnalysis.CompositionContext? _editorParent;
+
+    /// <summary>
+    /// One entry per template that composes this one (in the design-time
+    /// graph). Populated by <see cref="LoadEditorParentsAsync"/>; the user
+    /// picks one via <see cref="_selectedParentIndex"/> when multiple exist.
+    /// </summary>
+    private List<ScadaLink.CentralUI.ScriptAnalysis.CompositionContext> _editorParents
+        = new();
+
+    /// <summary>Index into <see cref="_editorParents"/>; -1 when none.</summary>
+    private int _selectedParentIndex = -1;
+
+    private ScadaLink.CentralUI.ScriptAnalysis.CompositionContext? ActiveEditorParent =>
+        _selectedParentIndex >= 0 && _selectedParentIndex < _editorParents.Count
+            ? _editorParents[_selectedParentIndex]
+            : null;
 
     private bool _showCompForm;
     private int _compComposedTemplateId;
@@ -129,12 +144,14 @@
             _scripts = (await TemplateEngineRepository.GetScriptsByTemplateIdAsync(Id)).ToList();
             _compositions = (await TemplateEngineRepository.GetCompositionsByTemplateIdAsync(Id)).ToList();
 
-            // Editor metadata: child compositions + parent (if exactly one).
+            // Editor metadata: child compositions + every parent that
-            // Powers Attributes["X"] / Children["Y"].Attributes["Z"] /
+            // composes this template. Powers Attributes["X"] /
-            // Parent.Attributes["W"] completion + SCADA006 / SCADA007 diagnostics
+            // Children["Y"].Attributes["Z"] / Parent.Attributes["W"]
-            // in the Monaco editor.
+            // completion + SCADA006 / SCADA007 diagnostics in the Monaco
+            // editor.
             _editorChildren = await BuildChildContextsAsync(_compositions);
-            _editorParent = await TryGetParentContextAsync(Id);
+            _editorParents = await BuildParentContextsAsync(Id);
+            _selectedParentIndex = _editorParents.Count > 0 ? 0 : -1;
 
             _validationResult = null;
         }
@@ -667,6 +684,21 @@
                         </div>
                         <div class="col-12">
                             <label class="form-label">Code</label>
+                            @if (_editorParents.Count > 1)
+                            {
+                                <div class="small text-muted mb-2">
+                                    Parent context for editor:
+                                    <select class="form-select form-select-sm d-inline-block w-auto ms-1"
+                                            value="@_selectedParentIndex"
+                                            @onchange="OnParentContextChanged">
+                                        @foreach (var (parent, idx) in _editorParents.Select((p, i) => (p, i)))
+                                        {
+                                            <option value="@idx">@parent.Name</option>
+                                        }
+                                    </select>
+                                    <span class="ms-2">(this template is composed by @_editorParents.Count parents; pick one for <code>Parent.*</code> assistance)</span>
+                                </div>
+                            }
                             <MonacoEditor @ref="_scriptEditor" Value="@_scriptCode" ValueChanged="@(v => _scriptCode = v)"
                                           Language="csharp" Height="320px"
                                           DeclaredParameters="@ScriptParameterNames.Parse(_scriptParameters)"
@@ -674,7 +706,7 @@
                                           SiblingScripts="@(_scripts.Select(s => ScadaLink.CentralUI.ScriptAnalysis.ScriptShapeParser.Parse(s.Name, s.ParameterDefinitions, s.ReturnDefinition)).ToArray())"
                                           SelfAttributes="@(_attributes.Select(a => new ScadaLink.CentralUI.ScriptAnalysis.AttributeShape(a.Name, MapDataType(a.DataType))).ToArray())"
                                           Children="@_editorChildren"
-                                          Parent="@_editorParent"
+                                          Parent="@ActiveEditorParent"
                                           MarkersChanged="@(m => { _scriptMarkers = m; StateHasChanged(); })" />
                             <ProblemsPanel Markers="@_scriptMarkers" OnNavigate="@(m => _scriptEditor?.RevealLineAsync(m.StartLineNumber, m.StartColumn) ?? Task.CompletedTask)" />
                         </div>
@@ -999,13 +1031,12 @@
         return result;
     }
 
-    private async Task<ScadaLink.CentralUI.ScriptAnalysis.CompositionContext?> TryGetParentContextAsync(int templateId)
+    private async Task<List<ScadaLink.CentralUI.ScriptAnalysis.CompositionContext>> BuildParentContextsAsync(int templateId)
     {
-        var all = await TemplateEngineRepository.GetAllTemplatesAsync();
+        var parents = await TemplateEngineRepository.GetTemplatesComposingAsync(templateId);
-        var parents = all.Where(t => t.Compositions.Any(c => c.ComposedTemplateId == templateId)).ToList();
+        return parents
-        if (parents.Count != 1) return null; // ambiguous or root — suppress Parent assistance
+            .Select(p => BuildCompositionContext(p.Name, p))
-        var p = await TemplateEngineRepository.GetTemplateWithChildrenAsync(parents[0].Id);
+            .ToList();
-        return p == null ? null : BuildCompositionContext(p.Name, p);
     }
 
     private static ScadaLink.CentralUI.ScriptAnalysis.CompositionContext BuildCompositionContext(
@@ -1022,6 +1053,12 @@
         return new ScadaLink.CentralUI.ScriptAnalysis.CompositionContext(label, attrs, scripts);
     }
 
+    private void OnParentContextChanged(ChangeEventArgs e)
+    {
+        if (int.TryParse(e.Value?.ToString(), out var idx) && idx >= 0 && idx < _editorParents.Count)
+            _selectedParentIndex = idx;
+    }
+
     private static string MapDataType(ScadaLink.Commons.Types.Enums.DataType dt) => dt switch
     {
         ScadaLink.Commons.Types.Enums.DataType.Boolean => "Boolean",

src/ScadaLink.Commons/Interfaces/Repositories/ITemplateEngineRepository.cs

@@ -10,6 +10,13 @@ public interface ITemplateEngineRepository
     Task<Template?> GetTemplateByIdAsync(int id, CancellationToken cancellationToken = default);
     Task<Template?> GetTemplateWithChildrenAsync(int id, CancellationToken cancellationToken = default);
     Task<IReadOnlyList<Template>> GetAllTemplatesAsync(CancellationToken cancellationToken = default);
+    /// <summary>
+    /// Returns every template that contains a composition referencing
+    /// <paramref name="composedTemplateId"/>. Each result is eager-loaded with
+    /// its Attributes / Scripts / Compositions so the caller can build a
+    /// CompositionContext without a follow-up round-trip per parent.
+    /// </summary>
+    Task<IReadOnlyList<Template>> GetTemplatesComposingAsync(int composedTemplateId, CancellationToken cancellationToken = default);
     Task AddTemplateAsync(Template template, CancellationToken cancellationToken = default);
     Task UpdateTemplateAsync(Template template, CancellationToken cancellationToken = default);
     Task DeleteTemplateAsync(int id, CancellationToken cancellationToken = default);

src/ScadaLink.ConfigurationDatabase/Repositories/TemplateEngineRepository.cs

@@ -50,6 +50,16 @@ public class TemplateEngineRepository : ITemplateEngineRepository
             .ToListAsync(cancellationToken);
     }
 
+    public async Task<IReadOnlyList<Template>> GetTemplatesComposingAsync(int composedTemplateId, CancellationToken cancellationToken = default)
+    {
+        return await _context.Templates
+            .Where(t => t.Compositions.Any(c => c.ComposedTemplateId == composedTemplateId))
+            .Include(t => t.Attributes)
+            .Include(t => t.Scripts)
+            .Include(t => t.Compositions)
+            .ToListAsync(cancellationToken);
+    }
+
     public async Task AddTemplateAsync(Template template, CancellationToken cancellationToken = default)
     {
         await _context.Templates.AddAsync(template, cancellationToken);