feat(FN-2855): route scheduled tasks using effective node resolution

- Add an effective node resolver with task override, project default, and local fallback precedence.
- Wire scheduler dispatch to persist effectiveNodeId/effectiveNodeSource and log resolved node routing.
- Add coverage for effective node resolution and scheduler node routing integration behavior.
- Stabilize workspace test resolution by adding @fusion/core and @fusion/plugin-sdk aliases across Vitest configs.

packages/engine/src/__tests__/effective-node.test.ts

@@ -0,0 +1,67 @@
+import { describe, expect, it } from "vitest";
+import { resolveEffectiveNode } from "../effective-node.js";
+
+describe("resolveEffectiveNode", () => {
+  it("uses task override when both task and project default are set", () => {
+    expect(resolveEffectiveNode({ nodeId: "node-task" }, { defaultNodeId: "node-project" })).toEqual({
+      nodeId: "node-task",
+      source: "task-override",
+    });
+  });
+
+  it("uses project default when task override is not set", () => {
+    expect(resolveEffectiveNode({ nodeId: undefined }, { defaultNodeId: "node-project" })).toEqual({
+      nodeId: "node-project",
+      source: "project-default",
+    });
+  });
+
+  it("uses local when neither task override nor project default is set", () => {
+    expect(resolveEffectiveNode({ nodeId: undefined }, { defaultNodeId: undefined })).toEqual({
+      nodeId: undefined,
+      source: "local",
+    });
+  });
+
+  it("treats empty task override as unset and falls through to project default", () => {
+    expect(resolveEffectiveNode({ nodeId: "" }, { defaultNodeId: "node-project" })).toEqual({
+      nodeId: "node-project",
+      source: "project-default",
+    });
+  });
+
+  it("treats null task nodeId as unset", () => {
+    expect(resolveEffectiveNode({ nodeId: null as unknown as string }, { defaultNodeId: "node-project" })).toEqual({
+      nodeId: "node-project",
+      source: "project-default",
+    });
+  });
+
+  it("treats empty project default as unset and falls through to local", () => {
+    expect(resolveEffectiveNode({ nodeId: undefined }, { defaultNodeId: "" })).toEqual({
+      nodeId: undefined,
+      source: "local",
+    });
+  });
+
+  it("treats null project default as unset", () => {
+    expect(resolveEffectiveNode({ nodeId: undefined }, { defaultNodeId: null as unknown as string })).toEqual({
+      nodeId: undefined,
+      source: "local",
+    });
+  });
+
+  it("uses local when both task and project values are empty", () => {
+    expect(resolveEffectiveNode({ nodeId: "" }, { defaultNodeId: "" })).toEqual({
+      nodeId: undefined,
+      source: "local",
+    });
+  });
+
+  it("uses task override when set even if project default is empty", () => {
+    expect(resolveEffectiveNode({ nodeId: "node-task" }, { defaultNodeId: "" })).toEqual({
+      nodeId: "node-task",
+      source: "task-override",
+    });
+  });
+});