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__/scheduler-node-routing.test.ts

@@ -0,0 +1,130 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import type { Task, TaskStore } from "@fusion/core";
+import { Scheduler } from "../scheduler.js";
+import { existsSync } from "node:fs";
+import { readFile } from "node:fs/promises";
+import { schedulerLog } from "../logger.js";
+
+vi.mock("node:fs", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("node:fs")>();
+  return {
+    ...actual,
+    existsSync: vi.fn(),
+  };
+});
+
+vi.mock("node:fs/promises", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("node:fs/promises")>();
+  return {
+    ...actual,
+    readFile: vi.fn(),
+  };
+});
+
+vi.mock("../logger.js", () => ({
+  schedulerLog: {
+    log: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+  },
+}));
+
+function createMockTask(overrides: Partial<Task> = {}): Task {
+  return {
+    id: "FN-100",
+    description: "Node routing task",
+    column: "todo",
+    dependencies: [],
+    steps: [],
+    currentStep: 0,
+    log: [],
+    createdAt: "2026-01-01T00:00:00Z",
+    updatedAt: "2026-01-01T00:00:00Z",
+    prompt: "",
+    ...overrides,
+  } as Task;
+}
+
+function createMockStore(task: Task, settings: Record<string, unknown> = {}): TaskStore {
+  return {
+    listTasks: vi.fn().mockResolvedValue([task]),
+    getSettings: vi.fn().mockResolvedValue(settings),
+    getTask: vi.fn().mockResolvedValue(task),
+    updateTask: vi.fn().mockResolvedValue(undefined),
+    moveTask: vi.fn().mockResolvedValue(undefined),
+    parseFileScopeFromPrompt: vi.fn().mockResolvedValue([]),
+    logEntry: vi.fn().mockResolvedValue(undefined),
+    getRootDir: vi.fn().mockReturnValue("/tmp/test"),
+    getTasksDir: vi.fn().mockReturnValue("/tmp/test/.fusion/tasks"),
+    on: vi.fn(),
+    off: vi.fn(),
+  } as unknown as TaskStore;
+}
+
+describe("Scheduler node routing", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    vi.mocked(existsSync).mockReturnValue(true);
+    vi.mocked(readFile).mockResolvedValue("# Task\nNode routing");
+  });
+
+  it("stores task override as effective node", async () => {
+    const task = createMockTask({ id: "FN-101", nodeId: "node-task" });
+    const store = createMockStore(task, { maxConcurrent: 1, maxWorktrees: 1, defaultNodeId: "node-project" });
+    const scheduler = new Scheduler(store);
+    (scheduler as unknown as { running: boolean }).running = true;
+
+    await scheduler.schedule();
+
+    expect(store.updateTask).toHaveBeenCalledWith(task.id, expect.objectContaining({
+      effectiveNodeId: "node-task",
+      effectiveNodeSource: "task-override",
+    }));
+    expect(store.logEntry).toHaveBeenCalledWith(task.id, "Node routing resolved: node-task (source: task-override)");
+    expect(schedulerLog.log).toHaveBeenCalledWith("Task FN-101 routed to node=node-task (source=task-override)");
+  });
+
+  it("uses project default when task nodeId is unset", async () => {
+    const task = createMockTask({ id: "FN-102", nodeId: undefined });
+    const store = createMockStore(task, { maxConcurrent: 1, maxWorktrees: 1, defaultNodeId: "node-project" });
+    const scheduler = new Scheduler(store);
+    (scheduler as unknown as { running: boolean }).running = true;
+
+    await scheduler.schedule();
+
+    expect(store.updateTask).toHaveBeenCalledWith(task.id, expect.objectContaining({
+      effectiveNodeId: "node-project",
+      effectiveNodeSource: "project-default",
+    }));
+    expect(store.logEntry).toHaveBeenCalledWith(task.id, "Node routing resolved: node-project (source: project-default)");
+  });
+
+  it("uses local when neither task nor project default are set", async () => {
+    const task = createMockTask({ id: "FN-103", nodeId: undefined });
+    const store = createMockStore(task, { maxConcurrent: 1, maxWorktrees: 1 });
+    const scheduler = new Scheduler(store, { nodeHealthMonitor: undefined });
+    (scheduler as unknown as { running: boolean }).running = true;
+
+    await scheduler.schedule();
+
+    expect(store.updateTask).toHaveBeenCalledWith(task.id, expect.objectContaining({
+      effectiveNodeId: null,
+      effectiveNodeSource: "local",
+    }));
+    expect(store.logEntry).toHaveBeenCalledWith(task.id, "Node routing resolved: local (source: local)");
+    expect(schedulerLog.log).toHaveBeenCalledWith("Task FN-103 routed to node=local (source=local)");
+  });
+
+  it("accepts nodeHealthMonitor option at construction", () => {
+    const task = createMockTask();
+    const store = createMockStore(task);
+
+    const scheduler = new Scheduler(store, {
+      nodeHealthMonitor: {
+        getNodeHealth: vi.fn(),
+      } as unknown as import("../node-health-monitor.js").NodeHealthMonitor,
+    });
+
+    expect(scheduler).toBeDefined();
+  });
+});