feat(FN-3053): consolidate mock helpers across CLI, dashboard, and engine p

The merge consolidates mock helpers across packages by creating a new shared `mockCoreEngine.ts` in the CLI package and strengthening the core/engine helpers, then migrating both CLI command tests and the dashboard's `AgentsView` tests to use the canonical helpers. It also publishes SSE architecture

Fusion-Task-Id: FN-3053

packages/cli/src/test/mockCoreEngine.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it, vi } from "vitest";
+import {
+  createCliCoreMock,
+  createCliEngineMock,
+  resetCliCoreEngineMockState,
+} from "./mockCoreEngine";
+
+describe("cli test mock helpers", () => {
+  it("creates stable fallback functions for missing callable exports", async () => {
+    const module = await createCliCoreMock(async () => ({ known: vi.fn() }));
+
+    const first = module.missingThing as ReturnType<typeof vi.fn>;
+    const second = module.missingThing as ReturnType<typeof vi.fn>;
+    expect(first).toBe(second);
+
+    first("x");
+    expect(first).toHaveBeenCalledWith("x");
+
+    resetCliCoreEngineMockState();
+    expect(first).not.toHaveBeenCalled();
+  });
+
+  it("keeps real non-function exports while allowing callable overrides", async () => {
+    const module = await createCliEngineMock(
+      async () => ({ VERSION: "1.0.0", factory: () => "real" }),
+      {},
+      { factory: vi.fn().mockReturnValue("mocked") },
+    );
+
+    expect(module.VERSION).toBe("1.0.0");
+    expect((module.factory as () => string)()).toBe("mocked");
+  });
+});

packages/cli/src/test/mockCoreEngine.ts

@@ -0,0 +1,59 @@
+/**
+ * Canonical @fusion/core and @fusion/engine mock helpers for CLI command tests.
+ *
+ * When a new commonly-mocked export is added, update defaults here instead of
+ * copying large inline export lists into command suites.
+ */
+import { vi, type Mock } from "vitest";
+
+type AnyModule = Record<string, unknown>;
+type AnyMock = Mock;
+
+const fallbackFns = new Map<string, AnyMock>();
+
+function getFallback(name: string): AnyMock {
+  if (!fallbackFns.has(name)) {
+    fallbackFns.set(name, vi.fn());
+  }
+  return fallbackFns.get(name)!;
+}
+
+function withFallbackFunctions(actual: AnyModule, mocked: AnyModule): AnyModule {
+  return new Proxy(mocked, {
+    get(target, prop, receiver) {
+      if (typeof prop !== "string") return Reflect.get(target, prop, receiver);
+      if (Reflect.has(target, prop)) return Reflect.get(target, prop, receiver);
+      if (["then", "catch", "finally"].includes(prop)) return undefined;
+
+      const actualValue = actual[prop];
+      if (typeof actualValue === "function" || actualValue === undefined) {
+        const fn = getFallback(prop);
+        target[prop] = fn;
+        return fn;
+      }
+      return actualValue;
+    },
+  });
+}
+
+export async function createCliCoreMock(
+  importActual: () => Promise<AnyModule>,
+  defaults: AnyModule = {},
+  overrides: AnyModule = {},
+): Promise<AnyModule> {
+  const actual = await importActual();
+  return withFallbackFunctions(actual, { ...actual, ...defaults, ...overrides });
+}
+
+export async function createCliEngineMock(
+  importActual: () => Promise<AnyModule>,
+  defaults: AnyModule = {},
+  overrides: AnyModule = {},
+): Promise<AnyModule> {
+  const actual = await importActual();
+  return withFallbackFunctions(actual, { ...actual, ...defaults, ...overrides });
+}
+
+export function resetCliCoreEngineMockState(): void {
+  for (const fn of fallbackFns.values()) fn.mockReset();
+}