Record source project when adding ExCS projects

app/models/project.rb

@@ -18,6 +18,8 @@ module Origins
   belongs_to :lesson, optional: true
   belongs_to :parent, optional: true, class_name: :Project, foreign_key: :remixed_from_id, inverse_of: :remixes
   has_many :remixes, dependent: :nullify, class_name: :Project, foreign_key: :remixed_from_id, inverse_of: :parent
+  belongs_to :source_project, optional: true, class_name: :Project, inverse_of: :derived_projects
+  has_many :derived_projects, dependent: :nullify, class_name: :Project, foreign_key: :source_project_id, inverse_of: :source_project
   has_many :components, -> { order(default: :desc, name: :asc) }, dependent: :destroy, inverse_of: :project
   has_one :scratch_component, dependent: :destroy, inverse_of: :project, required: false
   has_many :scratch_assets, dependent: :destroy

db/migrate/20260828095502_add_source_project_to_projects.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class AddSourceProjectToProjects < ActiveRecord::Migration[8.1]
+  def change
+    add_reference :projects, :source_project,
+      type: :uuid,
+      foreign_key: { to_table: :projects, on_delete: :nullify }
+  end
+end

lib/concepts/lesson/operations/create.rb

@@ -43,7 +43,10 @@ def attributes_for_copy(source_project, project_params)
           name: project_params[:name].presence || source_project.name,
           user_id: project_params[:user_id],
           school_id: project_params[:school_id],
-          lesson_id: project_params[:lesson_id]
+          lesson_id: project_params[:lesson_id],
+          source_project_id: source_project.id,
+          remixed_from_id: nil,
+          remix_origin: nil
         }
       end
     end

spec/concepts/lesson/create_copy_spec.rb

@@ -109,6 +109,22 @@
     expect(copied_component.content).to eq(original_component.content)
   end
 
+  context 'when copying a lesson whose project has a source_project' do
+    let!(:source_project) { create(:project, :with_components) }
+    let!(:original_project) { create(:project, :with_components, source_project:) }
+
+    before do
+      lesson.project = original_project
+      lesson.save!
+    end
+
+    it 'copies the source_project to the new project' do
+      response = described_class.call(lesson:, lesson_params:)
+      copied_project = response[:lesson].reload.project
+      expect(copied_project.source_project_id).to eq(source_project.id)
+    end
+  end
+
   context 'when the project is a Scratch project' do
     let(:copied_teacher_id) { SecureRandom.uuid }
     let(:lesson_params) { { user_id: copied_teacher_id } }

spec/concepts/lesson/create_spec.rb

@@ -265,6 +265,10 @@
       expect(lesson_project.name).to eq('My digital canvas')
     end
 
+    it 'records the source project id on the lesson project' do
+      expect(lesson_project.source_project_id).to eq(source_project.id)
+    end
+
     it 'does not change the source project' do
       expect { response }.not_to(change { source_project.reload.attributes })
     end
@@ -274,6 +278,25 @@
       expect { response }.not_to change(ScratchAsset, :count)
     end
 
+    context 'when the source project is itself a remix' do
+      let(:source_project_fr) do
+        create(:scratch_project, identifier: source_project_en.identifier, locale: 'fr-FR', user_id: nil,
+                                 name: 'Ma toile numérique', origin: Project::Origins::EXPERIENCE_CS,
+                                 instructions: 'Instructions en français',
+                                 remixed_from_id: create(:project).id,
+                                 remix_origin: 'example.com')
+          .tap { |project| project.scratch_component.update!(content: french_content) }
+      end
+
+      it 'does not inherit remixed_from_id from the source project' do
+        expect(lesson_project.remixed_from_id).to be_nil
+      end
+
+      it 'does not inherit remix_origin from the source project' do
+        expect(lesson_project.remix_origin).to be_nil
+      end
+    end
+
     context 'when the source project has no origin' do
       let(:source_project) do
         create(:scratch_project, identifier: 'not-backfilled-yet', locale: 'en', user_id: nil, origin: nil)

spec/concepts/project/create_remix_spec.rb

@@ -186,6 +186,21 @@
       end
     end
 
+    context 'when remixing a project that has a source_project' do
+      let!(:source_project) { create(:project, :with_components) }
+      let!(:original_project) { create(:project, :with_components, source_project:) }
+
+      it 'copies the source_project to the remix' do
+        remixed_project = create_remix[:project]
+        expect(remixed_project.source_project_id).to eq(source_project.id)
+      end
+
+      it 'sets remixed_from_id to the immediate parent, not the source project' do
+        remixed_project = create_remix[:project]
+        expect(remixed_project.remixed_from_id).to eq(original_project.id)
+      end
+    end
+
     context 'when user_id is not present' do
       let(:user_id) { nil }
       let(:params) { { project_id: original_project.identifier } }

spec/models/project_spec.rb

@@ -9,10 +9,12 @@
     it { is_expected.to belong_to(:school).optional(true) }
     it { is_expected.to belong_to(:lesson).optional(true) }
     it { is_expected.to belong_to(:parent).optional(true) }
+    it { is_expected.to belong_to(:source_project).optional(true) }
     it { is_expected.to have_many(:remixes).dependent(:nullify) }
     it { is_expected.to have_many(:components) }
     it { is_expected.to have_many(:scratch_assets).dependent(:destroy) }
     it { is_expected.to have_many(:project_errors).dependent(:nullify) }
+    it { is_expected.to have_many(:derived_projects).dependent(:nullify) }
     it { is_expected.to have_many_attached(:images) }
     it { is_expected.to have_many_attached(:videos) }
     it { is_expected.to have_many_attached(:audio) }
@@ -68,6 +70,11 @@
       expect(invalid_project).not_to be_valid
     end
 
+    it 'is valid without a source project' do
+      valid_project = build(:project, source_project: nil)
+      expect(valid_project).to be_valid
+    end
+
     it 'allows a public Code Classroom Blocks project to have instructions' do
       project = build(
         :project,
@@ -230,6 +237,18 @@
     end
   end
 
+  describe 'source project lineage' do
+    let(:source_project) { create(:project) }
+
+    it 'nullifies source_project_id on derived projects when the source project is destroyed' do
+      project = create(:project, source_project:)
+
+      source_project.destroy!
+
+      expect(project.reload.source_project_id).to be_nil
+    end
+  end
+
   describe '#public_experience_cs_project?' do
     it 'returns true for public Experience CS project types', :aggregate_failures do
       project_types = [described_class::Types::SCRATCH, described_class::Types::CODE_EDITOR_SCRATCH]