feat(FN-5413): add null description persist regression test

Added a regression test for null description persistence in the core task store and a CLI patch changeset to ship the fix.

Fusion-Task-Id: FN-5413

.changeset/fn-5413-null-description-persist.md

@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": patch
+---
+
+Coerce null or undefined `task.description` values to an empty string when persisting TaskStore rows.

packages/core/src/__tests__/store-create.test.ts

@@ -35,6 +35,27 @@ describe("TaskStore", () => {
   const createSourceIssueFixture = () => harness.createSourceIssueFixture();
   const insertLogEntryWithTimestamp = (...args: any[]) => (harness as any).insertLogEntryWithTimestamp(...args);
 
+  describe("FN-5413 null description coercion", () => {
+    it.each([
+      ["undefined", undefined],
+      ["null", null],
+    ])("coerces %s description to empty string on persist", async (_label, description) => {
+      const created = await store.createTask({
+        description: "Initial description",
+      });
+
+      const task = await store.getTask(created.id);
+      (task as Task & { description?: string | null }).description = description;
+
+      expect(() => {
+        (store as unknown as { upsertTaskWithFtsRecovery: (task: Task) => void }).upsertTaskWithFtsRecovery(task);
+      }).not.toThrow();
+
+      const persisted = await store.getTask(created.id);
+      expect(persisted.description).toBe("");
+    });
+  });
+
   describe("breakIntoSubtasks task creation flag", () => {
     it("persists breakIntoSubtasks=true when explicitly requested", async () => {
       const task = await store.createTask({