Q47: task parents cannot form a cycle

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/task-hierarchy.test.ts

@@ -0,0 +1,36 @@
+import { randomUUID } from "node:crypto";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { describe, expect, test } from "vitest";
+import { DatabaseConnection } from "../../src/main/database/connection";
+import { OrganizationService } from "../../src/main/services/organization-service";
+import { RISK_LEVEL, TASK_PRIORITY, TASK_STATUS } from "../../src/shared/domain";
+
+describe("task hierarchy", () => {
+  test("a task cannot become its own parent or the child of its own descendant", () => {
+    const connection = new DatabaseConnection(join(tmpdir(), `ac-tree-${randomUUID()}.db`));
+    const organization = new OrganizationService(connection.db);
+    let orgId = "";
+    const ids: Record<string, string> = {};
+    connection.transaction(() => {
+      orgId = organization.createOrganization({ organizationName: "Acme", employeeName: "Dana", mission: "m", goal: "g" });
+      for (const title of ["A", "B", "C"]) {
+        ids[title] = organization.createTask({
+          orgId, title, description: "d", status: TASK_STATUS.BACKLOG, assigneeAgentId: null,
+          risk: RISK_LEVEL.LOW, projectId: null, goalId: null, workspaceId: null, priority: TASK_PRIORITY.NORMAL, requiresFilesystem: false,
+        });
+      }
+    });
+    const reparent = (title: string, parent: string | null) => organization.updateTask({
+      orgId, taskId: ids[title], title, description: "d", assigneeAgentId: null, risk: RISK_LEVEL.LOW, priority: TASK_PRIORITY.NORMAL, parentTaskId: parent,
+    });
+    reparent("B", ids.A);
+    reparent("C", ids.B);
+    expect(() => reparent("A", ids.A)).toThrow('"A" cannot be its own parent.');
+    expect(() => reparent("A", ids.C)).toThrow('"A" cannot sit under "C": "C" is already beneath "A".');
+    expect(connection.db.prepare("select parent_task_id from tasks where id = ?").get(ids.A)).toEqual({ parent_task_id: null });
+    reparent("C", ids.A);
+    reparent("C", null);
+    connection.close();
+  });
+});