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/engine/src/test/mockCore.ts

@@ -1,21 +1,45 @@
 /**
  * Canonical @fusion/core mock helper for engine tests.
  *
- * Prefer extending this helper over suite-local full export lists.
+ * Prefer extending this helper over suite-local full export lists; this is the
+ * first place to update when new @fusion/core exports are consumed by engine tests.
  */
-import type { Mock } from "vitest";
+import { vi, type Mock } from "vitest";
 
 type AnyModule = Record<string, unknown>;
 
+const fallbackFns = new Map<string, Mock>();
+
+function getFallback(name: string): Mock {
+  if (!fallbackFns.has(name)) fallbackFns.set(name, vi.fn());
+  return fallbackFns.get(name)!;
+}
+
 export async function createEngineCoreMock(
   importActual: () => Promise<AnyModule>,
   overrides: AnyModule = {},
 ): Promise<AnyModule> {
   const actual = await importActual();
-  return {
-    ...actual,
-    ...overrides,
-  };
+  const merged = { ...actual, ...overrides };
+  return new Proxy(merged, {
+    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 function resetEngineCoreMockState(): void {
+  for (const fn of fallbackFns.values()) fn.mockReset();
 }
 
 export type MockFn = Mock;