fix: CREATE OR REPLACE IMAGE COLLECTION fails with "already exists" (issue #436)

Three layers were missing support for CreateOrReplace:

- ast: added CreateOrReplace bool field to CreateImageCollectionStmt
- visitor: read OR REPLACE from parent createStatement via
  findParentCreateStatement(), same pattern used by business events
- executor: when CreateOrReplace is set and collection exists, delete it
  before creating; otherwise return the existing "already exists" error

Added tests for both the plain-create conflict case and the
create-or-replace delete+recreate path.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ako

mdl/ast/ast_imagecollection.go

@@ -12,10 +12,11 @@ type ImageItem struct {
 //
 //	CREATE IMAGE COLLECTION Module.Name [EXPORT LEVEL 'Public'] [COMMENT '...'] [(IMAGE "name" FROM FILE 'path', ...)]
 type CreateImageCollectionStmt struct {
-	Name        QualifiedName
-	ExportLevel string // "Hidden" (default) or "Public"
-	Comment     string
-	Images      []ImageItem
+	Name            QualifiedName
+	CreateOrReplace bool
+	ExportLevel     string // "Hidden" (default) or "Public"
+	Comment         string
+	Images          []ImageItem
 }
 
 func (s *CreateImageCollectionStmt) isStatement() {}

mdl/executor/cmd_imagecollections.go

@@ -29,7 +29,12 @@ func execCreateImageCollection(ctx *ExecContext, s *ast.CreateImageCollectionStm
 	// Check if image collection already exists
 	existing := findImageCollection(ctx, s.Name.Module, s.Name.Name)
 	if existing != nil {
-		return mdlerrors.NewAlreadyExists("image collection", s.Name.Module+"."+s.Name.Name)
+		if !s.CreateOrReplace {
+			return mdlerrors.NewAlreadyExists("image collection", s.Name.Module+"."+s.Name.Name)
+		}
+		if err := ctx.Backend.DeleteImageCollection(string(existing.ID)); err != nil {
+			return mdlerrors.NewBackend("delete existing image collection", err)
+		}
 	}
 
 	// Build ImageCollection

mdl/executor/cmd_imagecollections_mock_test.go

@@ -105,3 +105,67 @@ func TestDescribeImageCollection_Mock(t *testing.T) {
 	out := buf.String()
 	assertContainsStr(t, out, "create or replace image collection")
 }
+
+func TestCreateImageCollection_AlreadyExists_Error(t *testing.T) {
+	mod := mkModule("MyModule")
+	existing := &types.ImageCollection{
+		BaseElement: model.BaseElement{ID: nextID("ic")},
+		ContainerID: mod.ID,
+		Name:        "Icons",
+	}
+	h := mkHierarchy(mod)
+	withContainer(h, existing.ContainerID, mod.ID)
+
+	mb := &mock.MockBackend{
+		IsConnectedFunc:          func() bool { return true },
+		ListModulesFunc:          func() ([]*model.Module, error) { return []*model.Module{mod}, nil },
+		ListImageCollectionsFunc: func() ([]*types.ImageCollection, error) { return []*types.ImageCollection{existing}, nil },
+	}
+	ctx, _ := newMockCtx(t, withBackend(mb), withHierarchy(h))
+
+	err := execCreateImageCollection(ctx, &ast.CreateImageCollectionStmt{
+		Name: ast.QualifiedName{Module: "MyModule", Name: "Icons"},
+	})
+	assertError(t, err)
+}
+
+func TestCreateImageCollection_CreateOrReplace_DeletesAndRecreates(t *testing.T) {
+	mod := mkModule("MyModule")
+	existing := &types.ImageCollection{
+		BaseElement: model.BaseElement{ID: nextID("ic")},
+		ContainerID: mod.ID,
+		Name:        "Icons",
+	}
+	h := mkHierarchy(mod)
+	withContainer(h, existing.ContainerID, mod.ID)
+
+	deleted := false
+	created := false
+	mb := &mock.MockBackend{
+		IsConnectedFunc:          func() bool { return true },
+		ListModulesFunc:          func() ([]*model.Module, error) { return []*model.Module{mod}, nil },
+		ListImageCollectionsFunc: func() ([]*types.ImageCollection, error) { return []*types.ImageCollection{existing}, nil },
+		DeleteImageCollectionFunc: func(id string) error {
+			deleted = true
+			return nil
+		},
+		CreateImageCollectionFunc: func(ic *types.ImageCollection) error {
+			created = true
+			return nil
+		},
+	}
+	ctx, buf := newMockCtx(t, withBackend(mb), withHierarchy(h))
+
+	err := execCreateImageCollection(ctx, &ast.CreateImageCollectionStmt{
+		Name:            ast.QualifiedName{Module: "MyModule", Name: "Icons"},
+		CreateOrReplace: true,
+	})
+	assertNoError(t, err)
+	if !deleted {
+		t.Error("expected existing collection to be deleted")
+	}
+	if !created {
+		t.Error("expected new collection to be created")
+	}
+	assertContainsStr(t, buf.String(), "Created image collection")
+}

mdl/visitor/visitor_imagecollection.go

@@ -46,5 +46,10 @@ func (b *Builder) ExitCreateImageCollectionStatement(ctx *parser.CreateImageColl
 		}
 	}
 
+	createStmt := findParentCreateStatement(ctx)
+	if createStmt != nil && createStmt.OR() != nil && (createStmt.REPLACE() != nil || createStmt.MODIFY() != nil) {
+		stmt.CreateOrReplace = true
+	}
+
 	b.statements = append(b.statements, stmt)
 }