feat(FN-2709): migrate Hermes runtime plugin to pi-ai streaming client

- Replace Hermes pi module integration with pi-ai session streaming and updated runtime adapter contracts
- Remove legacy engine guard scaffolding and add hermes-stream-client coverage for streaming behavior
- Rewrite plugin and engine e2e tests to align with the new runtime flow and regenerate dist artifacts
- Update Hermes runtime README and package metadata to document pi-ai execution expectations

plugins/fusion-plugin-hermes-runtime/vitest.config.ts

@@ -1,39 +1,14 @@
-import { fileURLToPath } from "node:url";
 import { defineConfig } from "vitest/config";
 
 const requestedMaxWorkers = Number.parseInt(process.env.VITEST_MAX_WORKERS ?? "2", 10);
 const maxWorkers = Math.max(1, Math.min(4, Number.isFinite(requestedMaxWorkers) ? requestedMaxWorkers : 2));
 process.env.VITEST_MAX_WORKERS = String(maxWorkers);
 
-const engineGuardStub = fileURLToPath(new URL("./src/__tests__/engine-guard-stub.ts", import.meta.url));
-
 export default defineConfig({
-  resolve: {
-    alias: {
-      "@fusion/engine": fileURLToPath(new URL("../../packages/engine/src/index.ts", import.meta.url)),
-    },
-  },
   test: {
     include: ["src/**/*.test.ts"],
     pool: "threads",
     maxWorkers,
     poolOptions: { threads: { minThreads: 1, maxThreads: maxWorkers }, forks: { minForks: 1, maxForks: maxWorkers } },
-    // ── Engine guard ──────────────────────────────────────────────────────
-    // This setup file installs a vi.mock("@fusion/engine") that throws if
-    // the real engine is loaded. All plugin tests must mock "../pi-module.js"
-    // (the seam) to prevent the real @fusion/engine import chain.
-    //
-    // If you introduce a test that genuinely needs @fusion/engine:
-    //   1. Create a setup-test-isolation.ts (HOME override) following the
-    //      pattern in packages/core/src/__tests__/setup-test-isolation.ts
-    //   2. Add it to setupFiles BEFORE this guard
-    //   3. Add a vi.mock("@fusion/engine", ...) override in the test file
-    //      or a dedicated setup file to replace the throwing mock
-    setupFiles: ["./src/__tests__/setup-engine-guard.ts"],
-    alias: {
-      // Resolve @fusion/engine to a local test stub so Vitest can register the
-      // guard mock without requiring built dist artifacts from packages/engine.
-      "@fusion/engine": engineGuardStub,
-    },
   },
 });