feat(template-engine): contained names for composition-derived templates

A composition-derived template now stores its contained name — the
composition slot's InstanceName (e.g. "Pump"), unique only within its
owner — instead of the dotted global path ("Motor Controller.Pump").
The qualified hierarchical name is computed on read.

- TemplateNaming.QualifiedName: walks the OwnerCompositionId chain to
  build the dotted path; null-safe, cycle-guarded.
- TemplateConfiguration: the unique index on Template.Name becomes
  filtered (WHERE IsDerived = 0) — base templates stay globally unique;
  derived templates' uniqueness is the existing (TemplateId,
  InstanceName) index on TemplateComposition.
- Migration ContainedDerivedTemplateNames: rewrites derived rows to the
  contained name; Down rebuilds the dotted names via a recursive CTE
  before restoring the global index.
- TemplateService: composition create/rename store the contained name;
  the dotted-name collision pre-checks and cascade-rename are removed
  (a slot rename no longer touches nested derived templates).
- TemplateEdit: title shows the contained name; the qualified path is a
  breadcrumb subtitle; "composed inside" uses the owner's qualified name.

TDD: 4 TemplateNaming tests + updated composition tests. TemplateEngine
293, ConfigurationDatabase 114, CentralUI 316 green. Migration applied to
the dev cluster and verified in the browser (Motor Controller.Pump now
titled "Pump"; nested Motor Controller.Pump.TempSensor resolves).

Design: docs/plans/2026-05-18-contained-template-names-design.md

docs/plans/2026-05-18-contained-template-names-design.md

@@ -1,7 +1,7 @@
 # Contained Names for Composition-Derived Templates — Design
 
 **Date:** 2026-05-18
-**Status:** Approved (brainstorming) — implementation to follow
+**Status:** Implemented
 
 ## Context
 

docs/requirements/Component-TemplateEngine.md

@@ -81,6 +81,18 @@ When a template composes a feature module, members from that module are addresse
 - The composing template's own members (not from a module) have no prefix — they are top-level names.
 - Naming collision detection operates on canonical names, so two modules can define the same member name as long as their module instance names differ.
 
+### Derived template naming
+
+A composition slot is materialized as its own *derived* template. A derived
+template stores a **contained name** — the composition slot's instance name
+(e.g. `Pump`), unique only within its owner. The **qualified name**
+(`Motor Controller.Pump`, or `Motor Controller.Pump.TempSensor` when nested) is
+*computed* on read by walking the owner-composition chain — it is not stored.
+Only base (user-authored) templates are globally unique by name; a derived
+template's uniqueness is the slot-name uniqueness within its owner. The Central
+UI shows the contained name as the template title and the qualified path as a
+breadcrumb.
+
 ## Override Granularity
 
 Override and lock rules apply per entity type at the following granularity:

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

@@ -236,7 +236,7 @@
                     <a href="/design/templates/@_baseTemplate.Id"><code>@_baseTemplate.Name</code></a>
                     @if (_ownerTemplate != null && _ownerComposition != null)
                     {
-                        <span class="ms-1">— composed inside <a href="/design/templates/@_ownerTemplate.Id"><code>@_ownerTemplate.Name</code></a> as <code>@_ownerComposition.InstanceName</code>.</span>
+                        <span class="ms-1">— composed inside <a href="/design/templates/@_ownerTemplate.Id"><code>@QualifiedTemplateName(_ownerTemplate)</code></a> as <code>@_ownerComposition.InstanceName</code>.</span>
                     }
                 </div>
             </div>
@@ -248,6 +248,12 @@
                 {
                     <span class="text-muted ms-2">inherits @(_templates.FirstOrDefault(t => t.Id == _selectedTemplate.ParentTemplateId)?.Name)</span>
                 }
+                @if (_selectedTemplate.IsDerived)
+                {
+                    @* Derived templates store a contained name; show the full
+                       qualified path as a breadcrumb subtitle. *@
+                    <div class="text-muted small font-monospace">@QualifiedTemplateName(_selectedTemplate)</div>
+                }
             </div>
             <div>
                 <button class="btn btn-outline-info btn-sm me-1" @onclick="RunValidation" disabled="@_validating">
@@ -1701,6 +1707,18 @@
         else { _toast.ShowError(result.Error); }
     }
 
+    /// <summary>
+    /// Computes a template's qualified (hierarchical) name from the loaded
+    /// template set — the stored name for a base template, the dotted
+    /// owner-chain path for a composition-derived one.
+    /// </summary>
+    private string QualifiedTemplateName(Template template)
+    {
+        var byId = _templates.ToDictionary(t => t.Id);
+        var compById = _templates.SelectMany(t => t.Compositions).ToDictionary(c => c.Id);
+        return TemplateNaming.QualifiedName(template, byId, compById);
+    }
+
     // ---- Editor metadata builders ----
 
     private async Task<IReadOnlyList<ScadaLink.CentralUI.ScriptAnalysis.CompositionContext>> BuildChildContextsAsync(

src/ScadaLink.ConfigurationDatabase/Configurations/TemplateConfiguration.cs

@@ -17,7 +17,12 @@ public class TemplateConfiguration : IEntityTypeConfiguration<Template>
         builder.Property(t => t.Description)
             .HasMaxLength(2000);
 
-        builder.HasIndex(t => t.Name).IsUnique();
+        // Only base (user-authored) templates are globally unique by name.
+        // Derived templates store their *contained* name (the composition slot's
+        // InstanceName), unique only within the owner — enforced by the
+        // (TemplateId, InstanceName) index on TemplateComposition — so they are
+        // excluded from this index via a filter.
+        builder.HasIndex(t => t.Name).IsUnique().HasFilter("[IsDerived] = 0");
 
         // Self-referencing parent template (inheritance)
         builder.HasOne<Template>()

src/ScadaLink.ConfigurationDatabase/Migrations/20260518214444_ContainedDerivedTemplateNames.cs

@@ -0,0 +1,81 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace ScadaLink.ConfigurationDatabase.Migrations
+{
+    /// <summary>
+    /// Moves composition-derived templates to AVEVA-style contained names: a
+    /// derived template stores only its slot name (e.g. <c>Pump</c>), not the
+    /// dotted qualified path (<c>Motor Controller.Pump</c>). The qualified name
+    /// is computed on read by walking the OwnerComposition chain. The unique
+    /// index on Template.Name becomes filtered to base templates only —
+    /// derived templates' uniqueness is the (TemplateId, InstanceName) index on
+    /// TemplateComposition.
+    /// </summary>
+    public partial class ContainedDerivedTemplateNames : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            // Drop the global unique index first: derived rows are about to be
+            // renamed to contained names that may duplicate one another or a
+            // base template.
+            migrationBuilder.DropIndex(
+                name: "IX_Templates_Name",
+                table: "Templates");
+
+            // Collapse every derived template's dotted name to its contained
+            // name — the owning composition slot's InstanceName.
+            migrationBuilder.Sql(@"
+                UPDATE t
+                SET t.Name = c.InstanceName
+                FROM Templates t
+                INNER JOIN TemplateCompositions c ON c.Id = t.OwnerCompositionId
+                WHERE t.IsDerived = 1;");
+
+            // Recreate the uniqueness guarantee for base templates only.
+            migrationBuilder.CreateIndex(
+                name: "IX_Templates_Name",
+                table: "Templates",
+                column: "Name",
+                unique: true,
+                filter: "[IsDerived] = 0");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropIndex(
+                name: "IX_Templates_Name",
+                table: "Templates");
+
+            // Rebuild the dotted qualified names so the global unique index can
+            // be restored — derived templates' contained names are not globally
+            // unique. The recursive CTE walks the OwnerComposition chain down
+            // from each base template.
+            migrationBuilder.Sql(@"
+                WITH q AS (
+                    SELECT t.Id, CAST(t.Name AS NVARCHAR(MAX)) AS Qualified
+                    FROM Templates t
+                    WHERE t.IsDerived = 0
+                    UNION ALL
+                    SELECT t.Id, CAST(q.Qualified + N'.' + c.InstanceName AS NVARCHAR(MAX))
+                    FROM Templates t
+                    INNER JOIN TemplateCompositions c ON c.Id = t.OwnerCompositionId
+                    INNER JOIN q ON q.Id = c.TemplateId
+                )
+                UPDATE t
+                SET t.Name = q.Qualified
+                FROM Templates t
+                INNER JOIN q ON q.Id = t.Id
+                WHERE t.IsDerived = 1;");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_Templates_Name",
+                table: "Templates",
+                column: "Name",
+                unique: true);
+        }
+    }
+}

src/ScadaLink.ConfigurationDatabase/Migrations/ScadaLinkDbContextModelSnapshot.cs

@@ -900,7 +900,8 @@ namespace ScadaLink.ConfigurationDatabase.Migrations
                     b.HasIndex("FolderId");
 
                     b.HasIndex("Name")
-                        .IsUnique();
+                        .IsUnique()
+                        .HasFilter("[IsDerived] = 0");
 
                     b.HasIndex("ParentTemplateId");
 

src/ScadaLink.TemplateEngine/TemplateNaming.cs

@@ -0,0 +1,53 @@
+using ScadaLink.Commons.Entities.Templates;
+
+namespace ScadaLink.TemplateEngine;
+
+/// <summary>
+/// Resolves the hierarchical ("qualified") name of a composition-derived
+/// template. A derived template stores only its <em>contained</em> name — the
+/// owning composition slot's <c>InstanceName</c>, unique only within that owner.
+/// The qualified path (<c>Owner.Slot.Slot…</c>) is computed on demand by
+/// walking the <see cref="Template.OwnerCompositionId"/> chain up to the base
+/// template.
+/// </summary>
+public static class TemplateNaming
+{
+    /// <summary>
+    /// Returns the dotted hierarchical name of <paramref name="template"/>. For
+    /// a base (non-derived) template this is just its stored name. The walk is
+    /// null-safe: if any owner link is missing from the supplied lookups it
+    /// stops and falls back to the stored contained name, and a cycle (which
+    /// the composition graph should never contain) is broken defensively.
+    /// </summary>
+    public static string QualifiedName(
+        Template template,
+        IReadOnlyDictionary<int, Template> byId,
+        IReadOnlyDictionary<int, TemplateComposition> compById)
+    {
+        ArgumentNullException.ThrowIfNull(template);
+        ArgumentNullException.ThrowIfNull(byId);
+        ArgumentNullException.ThrowIfNull(compById);
+
+        return Resolve(template, byId, compById, new HashSet<int>());
+    }
+
+    private static string Resolve(
+        Template template,
+        IReadOnlyDictionary<int, Template> byId,
+        IReadOnlyDictionary<int, TemplateComposition> compById,
+        HashSet<int> visited)
+    {
+        // Base template, broken owner link, or a cycle → the stored name is the
+        // best (and contained) answer.
+        if (!template.IsDerived
+            || template.OwnerCompositionId is not { } compId
+            || !compById.TryGetValue(compId, out var composition)
+            || !byId.TryGetValue(composition.TemplateId, out var owner)
+            || !visited.Add(template.Id))
+        {
+            return template.Name;
+        }
+
+        return $"{Resolve(owner, byId, compById, visited)}.{composition.InstanceName}";
+    }
+}

src/ScadaLink.TemplateEngine/TemplateService.cs

@@ -598,20 +598,9 @@ public class TemplateService
         if (collisions.Count > 0)
             return Result<TemplateComposition>.Failure(string.Join(" ", collisions));
 
-        // Derived template name uses dot-separated path: "<parent>.<slot>". The
+        // No global name pre-check: derived templates store their contained
-        // cascade may create additional derived templates one level per slot
+        // (slot) name, which need only be unique within the owner — and that is
-        // (composing $Sensor with a Probe1 slot into $Pump produces both
+        // already enforced above and by the (TemplateId, InstanceName) index.
-        // $Pump.TempSensor and $Pump.TempSensor.Probe1). Pre-check every name
-        // the cascade is about to introduce so a deep collision aborts before
-        // any rows mutate.
-        var byId = allTemplates.ToDictionary(t => t.Id);
-        var cascadeNames = EnumerateCascadeNames(template.Name, instanceName, baseTemplate, byId).ToList();
-        var existingNames = allTemplates.Select(t => t.Name).ToHashSet(StringComparer.Ordinal);
-        var nameCollision = cascadeNames.FirstOrDefault(n => existingNames.Contains(n));
-        if (nameCollision != null)
-            return Result<TemplateComposition>.Failure(
-                $"Cannot create derived template '{nameCollision}': a template with that name already exists.");
-
         var composition = await CreateCascadedCompositionAsync(template, baseTemplate, instanceName, user, cancellationToken);
         await _auditService.LogAsync(user, "Create", "TemplateComposition", "0", instanceName, composition, cancellationToken);
         await _repository.SaveChangesAsync(cancellationToken);
@@ -633,8 +622,10 @@ public class TemplateService
         string user,
         CancellationToken cancellationToken)
     {
-        var derivedName = $"{outerTemplate.Name}.{instanceName}";
+        // A derived template stores its contained name — the slot's instance
-        var derived = BuildDerivedTemplate(source, derivedName);
+        // name, unique within its owner. The qualified path is computed on read
+        // (see TemplateNaming.QualifiedName).
+        var derived = BuildDerivedTemplate(source, instanceName);
 
         await _repository.AddTemplateAsync(derived, cancellationToken);
         await _repository.SaveChangesAsync(cancellationToken);
@@ -664,19 +655,6 @@ public class TemplateService
         return composition;
     }
 
-    private static IEnumerable<string> EnumerateCascadeNames(
-        string outerName, string instanceName, Template source, IReadOnlyDictionary<int, Template> byId)
-    {
-        var derivedName = $"{outerName}.{instanceName}";
-        yield return derivedName;
-        foreach (var comp in source.Compositions)
-        {
-            if (!byId.TryGetValue(comp.ComposedTemplateId, out var child)) continue;
-            foreach (var name in EnumerateCascadeNames(derivedName, comp.InstanceName, child, byId))
-                yield return name;
-        }
-    }
-
     public async Task<Result<TemplateComposition>> RenameCompositionAsync(
         int compositionId,
         string newInstanceName,
@@ -700,33 +678,15 @@ public class TemplateService
             return Result<TemplateComposition>.Failure(
                 $"Slot name '{newInstanceName}' already exists on '{owner.Name}'.");
 
+        // The derived template stores the slot's contained name, so renaming
+        // the slot renames just that one template. Nested derived templates
+        // keep their own contained names — an ancestor slot rename never
+        // touches them, and the qualified path is recomputed on read.
         var derived = await _repository.GetTemplateByIdAsync(composition.ComposedTemplateId, cancellationToken);
         if (derived != null && derived.IsDerived && derived.OwnerCompositionId == compositionId)
         {
-            var newDerivedName = $"{owner.Name}.{newInstanceName}";
+            derived.Name = newInstanceName;
-            var allTemplates = await _repository.GetAllTemplatesAsync(cancellationToken);
+            await _repository.UpdateTemplateAsync(derived, cancellationToken);
-
-            // The cascade of derived templates created by AddComposition follows a
-            // dotted path (Pump.TempSensor and the nested Pump.TempSensor.Probe1).
-            // Renaming the slot must rename every derived template in that cascade
-            // so the dotted-path naming invariant holds — pre-check every new name
-            // the cascade will introduce before any row mutates.
-            var renames = new List<(Template Template, string NewName)>();
-            await CollectCascadeRenamesAsync(derived, newDerivedName, renames, cancellationToken);
-
-            var renamedIds = renames.Select(r => r.Template.Id).ToHashSet();
-            foreach (var (_, newName) in renames)
-            {
-                if (allTemplates.Any(t => !renamedIds.Contains(t.Id) && t.Name == newName))
-                    return Result<TemplateComposition>.Failure(
-                        $"Cannot rename derived template to '{newName}': a template with that name already exists.");
-            }
-
-            foreach (var (template, newName) in renames)
-            {
-                template.Name = newName;
-                await _repository.UpdateTemplateAsync(template, cancellationToken);
-            }
         }
 
         composition.InstanceName = newInstanceName;
@@ -763,30 +723,6 @@ public class TemplateService
         return Result<bool>.Success(true);
     }
 
-    /// <summary>
-    /// Recursively collects the (template, new name) pairs for a renamed derived
-    /// template and every cascaded inner derived template beneath it. Each inner
-    /// derived's new name is re-derived from its renamed parent and the slot's
-    /// instance name (mirroring the cascade <see cref="CreateCascadedCompositionAsync"/>
-    /// builds and the recursion in <see cref="CascadeDeleteDerivedAsync"/>).
-    /// </summary>
-    private async Task CollectCascadeRenamesAsync(
-        Template derived,
-        string newName,
-        List<(Template Template, string NewName)> renames,
-        CancellationToken cancellationToken)
-    {
-        renames.Add((derived, newName));
-
-        foreach (var child in derived.Compositions.ToList())
-        {
-            var childDerived = await _repository.GetTemplateByIdAsync(child.ComposedTemplateId, cancellationToken);
-            if (childDerived != null && childDerived.IsDerived && childDerived.OwnerCompositionId == child.Id)
-                await CollectCascadeRenamesAsync(
-                    childDerived, $"{newName}.{child.InstanceName}", renames, cancellationToken);
-        }
-    }
-
     /// <summary>
     /// Recursively deletes a derived template along with the cascade of inner
     /// derived templates the compose flow created. Each composition row on the

tests/ScadaLink.TemplateEngine.Tests/TemplateNamingTests.cs

@@ -0,0 +1,87 @@
+using ScadaLink.Commons.Entities.Templates;
+
+namespace ScadaLink.TemplateEngine.Tests;
+
+/// <summary>
+/// Coverage for <see cref="TemplateNaming.QualifiedName"/> — the computed
+/// hierarchical name of a composition-derived template. Derived templates store
+/// only their contained name (the composition slot's <c>InstanceName</c>); the
+/// dotted path is resolved on read by walking the <c>OwnerCompositionId</c> chain.
+/// </summary>
+public class TemplateNamingTests
+{
+    private static (Dictionary<int, Template> byId, Dictionary<int, TemplateComposition> compById)
+        BuildGraph(params Template[] templates)
+    {
+        var byId = templates.ToDictionary(t => t.Id);
+        var compById = templates
+            .SelectMany(t => t.Compositions)
+            .ToDictionary(c => c.Id);
+        return (byId, compById);
+    }
+
+    [Fact]
+    public void QualifiedName_BaseTemplate_IsJustItsName()
+    {
+        var motorController = new Template("Motor Controller") { Id = 4 };
+        var (byId, compById) = BuildGraph(motorController);
+
+        Assert.Equal("Motor Controller", TemplateNaming.QualifiedName(motorController, byId, compById));
+    }
+
+    [Fact]
+    public void QualifiedName_OneLevelDerived_PrefixesTheOwner()
+    {
+        // Motor Controller composes the Pump template into a slot named "Pump".
+        var motorController = new Template("Motor Controller") { Id = 4 };
+        motorController.Compositions.Add(
+            new TemplateComposition("Pump") { Id = 1014, TemplateId = 4, ComposedTemplateId = 2018 });
+        var derivedPump = new Template("Pump")
+        {
+            Id = 2018, IsDerived = true, OwnerCompositionId = 1014
+        };
+        var (byId, compById) = BuildGraph(motorController, derivedPump);
+
+        Assert.Equal("Motor Controller.Pump", TemplateNaming.QualifiedName(derivedPump, byId, compById));
+    }
+
+    [Fact]
+    public void QualifiedName_NestedDerived_WalksTheWholeChain()
+    {
+        // Motor Controller -> Pump slot -> TempSensor slot.
+        var motorController = new Template("Motor Controller") { Id = 4 };
+        motorController.Compositions.Add(
+            new TemplateComposition("Pump") { Id = 1014, TemplateId = 4, ComposedTemplateId = 2018 });
+
+        var derivedPump = new Template("Pump")
+        {
+            Id = 2018, IsDerived = true, OwnerCompositionId = 1014
+        };
+        derivedPump.Compositions.Add(
+            new TemplateComposition("TempSensor") { Id = 1015, TemplateId = 2018, ComposedTemplateId = 2019 });
+
+        var derivedTempSensor = new Template("TempSensor")
+        {
+            Id = 2019, IsDerived = true, OwnerCompositionId = 1015
+        };
+        var (byId, compById) = BuildGraph(motorController, derivedPump, derivedTempSensor);
+
+        Assert.Equal(
+            "Motor Controller.Pump.TempSensor",
+            TemplateNaming.QualifiedName(derivedTempSensor, byId, compById));
+    }
+
+    [Fact]
+    public void QualifiedName_DerivedWithMissingOwnerLink_FallsBackToStoredName()
+    {
+        // Defensive: a derived template whose owner composition is not in the
+        // lookup must not throw — it falls back to the stored contained name.
+        var orphan = new Template("TempSensor")
+        {
+            Id = 2019, IsDerived = true, OwnerCompositionId = 9999
+        };
+        var (byId, compById) = BuildGraph(orphan);
+
+        Assert.Equal("TempSensor", TemplateNaming.QualifiedName(orphan, byId, compById));
+    }
+}

tests/ScadaLink.TemplateEngine.Tests/TemplateServiceTests.cs

@@ -359,7 +359,7 @@ public class TemplateServiceTests
         Assert.Equal("myModule", result.Value.InstanceName);
         Assert.NotNull(captured);
         Assert.True(captured!.IsDerived);
-        Assert.Equal("Parent.myModule", captured.Name);
+        Assert.Equal("myModule", captured.Name); // contained (slot) name, not the qualified path
         Assert.Equal(2, captured.ParentTemplateId);
         Assert.Single(captured.Attributes);
         Assert.True(captured.Attributes.First().IsInherited);
@@ -372,13 +372,13 @@ public class TemplateServiceTests
     [Fact]
     public async Task AddComposition_CascadesChildCompositions()
     {
-        // $Probe (base) → $Sensor.Probe1 (derived) ← $Sensor composes "Probe1"
+        // $Probe (base) → $Sensor's "Probe1" derived ← $Sensor composes "Probe1"
-        // Composing $Sensor into $Pump as "TempSensor" should produce:
+        // Composing $Sensor into $Pump as "TempSensor" should produce two derived
-        //   $Pump.TempSensor (derived from $Sensor)
+        // templates whose stored names are their *contained* names (the slot
-        //   $Pump.TempSensor.Probe1 (derived from $Sensor.Probe1)
+        // names) — "TempSensor" and "Probe1" — plus a composition row on the
-        // plus a composition row on $Pump.TempSensor pointing at the new inner derived.
+        // TempSensor derived pointing at the new inner derived.
         var probe = new Template("Probe") { Id = 10 };
-        var sensorProbe1 = new Template("Sensor.Probe1") { Id = 11, IsDerived = true, ParentTemplateId = 10, OwnerCompositionId = 1 };
+        var sensorProbe1 = new Template("Probe1") { Id = 11, IsDerived = true, ParentTemplateId = 10, OwnerCompositionId = 1 };
         var sensor = new Template("Sensor") { Id = 2 };
         sensor.Compositions.Add(new TemplateComposition("Probe1") { Id = 1, TemplateId = 2, ComposedTemplateId = 11 });
         var pump = new Template("Pump") { Id = 1 };
@@ -403,9 +403,9 @@ public class TemplateServiceTests
 
         Assert.True(result.IsSuccess);
         Assert.Equal(2, captured.Count);
-        Assert.Equal("Pump.TempSensor", captured[0].Name);
+        Assert.Equal("TempSensor", captured[0].Name);
         Assert.Equal(2, captured[0].ParentTemplateId);
-        Assert.Equal("Pump.TempSensor.Probe1", captured[1].Name);
+        Assert.Equal("Probe1", captured[1].Name);
         Assert.Equal(11, captured[1].ParentTemplateId);
         Assert.Equal(2, capturedCompositions.Count);
         Assert.Equal("TempSensor", capturedCompositions[0].InstanceName);
@@ -428,9 +428,13 @@ public class TemplateServiceTests
     }
 
     [Fact]
-    public async Task AddComposition_DerivedNameCollision_Fails()
+    public async Task AddComposition_DerivedContainedName_NeedNotBeGloballyUnique()
     {
-        var existing = new Template("Parent.myModule") { Id = 99 };
+        // A derived template's stored name is its contained (slot) name, which
+        // is only unique within its owner — it may freely coincide with an
+        // unrelated base template's name. Composing a module as the slot
+        // "myModule" succeeds even though a base template "myModule" exists.
+        var existing = new Template("myModule") { Id = 99 };
         var moduleTemplate = new Template("Module") { Id = 2 };
         var template = new Template("Parent") { Id = 1 };
 
@@ -439,92 +443,67 @@ public class TemplateServiceTests
         _repoMock.Setup(r => r.GetAllTemplatesAsync(It.IsAny<CancellationToken>()))
             .ReturnsAsync(new List<Template> { template, moduleTemplate, existing });
 
+        var captured = new List<Template>();
+        _repoMock.Setup(r => r.AddTemplateAsync(It.IsAny<Template>(), It.IsAny<CancellationToken>()))
+            .Callback<Template, CancellationToken>((t, _) => captured.Add(t))
+            .Returns(Task.CompletedTask);
+
         var result = await _service.AddCompositionAsync(1, 2, "myModule", "admin");
 
-        Assert.True(result.IsFailure);
+        Assert.True(result.IsSuccess);
-        Assert.Contains("already exists", result.Error);
+        Assert.Single(captured);
+        Assert.Equal("myModule", captured[0].Name);
     }
 
     [Fact]
     public async Task RenameComposition_RenamesSlotAndDerivedTemplate()
     {
+        // The derived template's stored name is the slot's contained name, so
+        // renaming the slot renames the derived template to the new short name.
         var composition = new TemplateComposition("OldSlot") { Id = 50, TemplateId = 1, ComposedTemplateId = 77 };
         var owner = new Template("Pump") { Id = 1 };
         owner.Compositions.Add(composition);
-        var derived = new Template("Pump.OldSlot") { Id = 77, IsDerived = true, OwnerCompositionId = 50, ParentTemplateId = 2 };
+        var derived = new Template("OldSlot") { Id = 77, IsDerived = true, OwnerCompositionId = 50, ParentTemplateId = 2 };
 
         _repoMock.Setup(r => r.GetTemplateCompositionByIdAsync(50, It.IsAny<CancellationToken>())).ReturnsAsync(composition);
         _repoMock.Setup(r => r.GetTemplateByIdAsync(1, It.IsAny<CancellationToken>())).ReturnsAsync(owner);
         _repoMock.Setup(r => r.GetTemplateByIdAsync(77, It.IsAny<CancellationToken>())).ReturnsAsync(derived);
-        _repoMock.Setup(r => r.GetAllTemplatesAsync(It.IsAny<CancellationToken>()))
-            .ReturnsAsync(new List<Template> { owner, derived });
 
         var result = await _service.RenameCompositionAsync(50, "NewSlot", "admin");
 
         Assert.True(result.IsSuccess);
         Assert.Equal("NewSlot", result.Value.InstanceName);
-        Assert.Equal("Pump.NewSlot", derived.Name);
+        Assert.Equal("NewSlot", derived.Name);
     }
 
     [Fact]
-    public async Task RenameComposition_CascadesRenameToNestedDerivedTemplates()
+    public async Task RenameComposition_RenamesOnlyTheSlotsOwnDerivedTemplate()
     {
-        // Pump.TempSensor is the slot-owned derived; Pump.TempSensor.Probe1 is a
+        // With contained names, a nested derived template's name is its own
-        // cascaded inner derived under it. Renaming the TempSensor slot to
+        // slot name and is unaffected by renaming an ancestor slot. Renaming
-        // MainSensor must rename BOTH derived templates so the dotted-path
+        // the TempSensor slot to MainSensor renames only that derived template;
-        // naming invariant holds: Pump.MainSensor and Pump.MainSensor.Probe1.
+        // the inner "Probe1" derived is left untouched.
         var innerComp = new TemplateComposition("Probe1") { Id = 51, TemplateId = 77, ComposedTemplateId = 78 };
-        var innerDerived = new Template("Pump.TempSensor.Probe1") { Id = 78, IsDerived = true, OwnerCompositionId = 51, ParentTemplateId = 11 };
+        var innerDerived = new Template("Probe1") { Id = 78, IsDerived = true, OwnerCompositionId = 51, ParentTemplateId = 11 };
         var composition = new TemplateComposition("TempSensor") { Id = 50, TemplateId = 1, ComposedTemplateId = 77 };
         var owner = new Template("Pump") { Id = 1 };
         owner.Compositions.Add(composition);
-        var derived = new Template("Pump.TempSensor") { Id = 77, IsDerived = true, OwnerCompositionId = 50, ParentTemplateId = 2 };
+        var derived = new Template("TempSensor") { Id = 77, IsDerived = true, OwnerCompositionId = 50, ParentTemplateId = 2 };
         derived.Compositions.Add(innerComp);
 
         _repoMock.Setup(r => r.GetTemplateCompositionByIdAsync(50, It.IsAny<CancellationToken>())).ReturnsAsync(composition);
         _repoMock.Setup(r => r.GetTemplateByIdAsync(1, It.IsAny<CancellationToken>())).ReturnsAsync(owner);
         _repoMock.Setup(r => r.GetTemplateByIdAsync(77, It.IsAny<CancellationToken>())).ReturnsAsync(derived);
         _repoMock.Setup(r => r.GetTemplateByIdAsync(78, It.IsAny<CancellationToken>())).ReturnsAsync(innerDerived);
-        _repoMock.Setup(r => r.GetAllTemplatesAsync(It.IsAny<CancellationToken>()))
-            .ReturnsAsync(new List<Template> { owner, derived, innerDerived });
 
         var result = await _service.RenameCompositionAsync(50, "MainSensor", "admin");
 
         Assert.True(result.IsSuccess);
         Assert.Equal("MainSensor", result.Value.InstanceName);
-        Assert.Equal("Pump.MainSensor", derived.Name);
+        Assert.Equal("MainSensor", derived.Name);
-        Assert.Equal("Pump.MainSensor.Probe1", innerDerived.Name);
+        Assert.Equal("Probe1", innerDerived.Name);
         _repoMock.Verify(r => r.UpdateTemplateAsync(
-            It.Is<Template>(t => t.Id == 78), It.IsAny<CancellationToken>()), Times.Once);
+            It.Is<Template>(t => t.Id == 78), It.IsAny<CancellationToken>()), Times.Never);
-    }
-
-    [Fact]
-    public async Task RenameComposition_NestedCascadeNameCollision_Fails()
-    {
-        // A pre-existing template occupies the name the nested cascade would
-        // produce (Pump.MainSensor.Probe1). The rename must abort before any
-        // row mutates, so the full cascade name set must be pre-checked.
-        var innerComp = new TemplateComposition("Probe1") { Id = 51, TemplateId = 77, ComposedTemplateId = 78 };
-        var innerDerived = new Template("Pump.TempSensor.Probe1") { Id = 78, IsDerived = true, OwnerCompositionId = 51, ParentTemplateId = 11 };
-        var composition = new TemplateComposition("TempSensor") { Id = 50, TemplateId = 1, ComposedTemplateId = 77 };
-        var owner = new Template("Pump") { Id = 1 };
-        owner.Compositions.Add(composition);
-        var derived = new Template("Pump.TempSensor") { Id = 77, IsDerived = true, OwnerCompositionId = 50, ParentTemplateId = 2 };
-        derived.Compositions.Add(innerComp);
-        var collider = new Template("Pump.MainSensor.Probe1") { Id = 99 };
-
-        _repoMock.Setup(r => r.GetTemplateCompositionByIdAsync(50, It.IsAny<CancellationToken>())).ReturnsAsync(composition);
-        _repoMock.Setup(r => r.GetTemplateByIdAsync(1, It.IsAny<CancellationToken>())).ReturnsAsync(owner);
-        _repoMock.Setup(r => r.GetTemplateByIdAsync(77, It.IsAny<CancellationToken>())).ReturnsAsync(derived);
-        _repoMock.Setup(r => r.GetTemplateByIdAsync(78, It.IsAny<CancellationToken>())).ReturnsAsync(innerDerived);
-        _repoMock.Setup(r => r.GetAllTemplatesAsync(It.IsAny<CancellationToken>()))
-            .ReturnsAsync(new List<Template> { owner, derived, innerDerived, collider });
-
-        var result = await _service.RenameCompositionAsync(50, "MainSensor", "admin");
-
-        Assert.True(result.IsFailure);
-        Assert.Contains("already exists", result.Error);
-        _repoMock.Verify(r => r.UpdateTemplateAsync(It.IsAny<Template>(), It.IsAny<CancellationToken>()), Times.Never);
     }
 
     [Fact]