Protect referenced feeder structures from deletion

tests/distribution-board-subtree-project-command.repository.test.ts

@@ -291,6 +291,43 @@ describe("distribution-board subtree project command", () => {
     }
   });
 
+  it("blocks deleting a board subtree that feeds another board", () => {
+    const context = createTestDatabase();
+    try {
+      const upstream = createPopulatedBoard(context);
+      const downstream = new DistributionBoardFixtureRepository(
+        context.db
+      ).createWithCircuitListAndDefaultSections("project-1", "Unterverteiler");
+      context.db
+        .update(distributionBoards)
+        .set({
+          boardNumber: "UV-03",
+          feedingDistributionBoardId: upstream.id,
+        })
+        .where(eq(distributionBoards.id, downstream.id))
+        .run();
+      const repository =
+        new DistributionBoardSubtreeProjectCommandRepository(context.db);
+      const snapshot = repository.capture("project-1", upstream.id);
+
+      assert.throws(
+        () =>
+          repository.execute({
+            projectId: "project-1",
+            expectedRevision: 0,
+            source: "user",
+            command:
+              createDistributionBoardDeleteSubtreeProjectCommand(snapshot),
+          }),
+        /Speist UV-03 – erst Einspeisung ändern\./
+      );
+      assert.deepEqual(repository.capture("project-1", upstream.id), snapshot);
+      assert.equal(context.db.select().from(projectRevisions).all().length, 0);
+    } finally {
+      context.close();
+    }
+  });
+
   it("rolls back a cascaded deletion when history persistence fails", () => {
     const context = createTestDatabase();
     try {