QA: replace qa-lab-runtime with qa-runtime

Introduce a tiny generic qa-runtime seam for shared live-lane helpers and
repoint qa-matrix to it. This keeps the qa-lab host split while removing
the host-owned runtime name from runner code.

Drop the old qa-lab-runtime shim/export now that nothing consumes it and
keep the plugin-sdk surface aligned with the new seam.

src/plugin-sdk/qa-runtime.test.ts

@@ -0,0 +1,47 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const loadBundledPluginPublicSurfaceModuleSync = vi.hoisted(() => vi.fn());
+
+vi.mock("./facade-runtime.js", () => ({
+  loadBundledPluginPublicSurfaceModuleSync,
+}));
+
+describe("plugin-sdk qa-runtime", () => {
+  beforeEach(() => {
+    loadBundledPluginPublicSurfaceModuleSync.mockReset();
+  });
+
+  it("stays cold until the runtime seam is used", async () => {
+    const module = await import("./qa-runtime.js");
+
+    expect(loadBundledPluginPublicSurfaceModuleSync).not.toHaveBeenCalled();
+    expect(typeof module.loadQaRuntimeModule).toBe("function");
+    expect(typeof module.isQaRuntimeAvailable).toBe("function");
+  });
+
+  it("loads the qa-lab runtime public surface through the generic seam", async () => {
+    const runtimeSurface = {
+      defaultQaRuntimeModelForMode: vi.fn(),
+      startQaLiveLaneGateway: vi.fn(),
+    };
+    loadBundledPluginPublicSurfaceModuleSync.mockReturnValue(runtimeSurface);
+
+    const module = await import("./qa-runtime.js");
+
+    expect(module.loadQaRuntimeModule()).toBe(runtimeSurface);
+    expect(loadBundledPluginPublicSurfaceModuleSync).toHaveBeenCalledWith({
+      dirName: "qa-lab",
+      artifactBasename: "runtime-api.js",
+    });
+  });
+
+  it("reports the runtime as unavailable when the qa-lab surface is missing", async () => {
+    loadBundledPluginPublicSurfaceModuleSync.mockImplementation(() => {
+      throw new Error("Unable to resolve bundled plugin public surface qa-lab/runtime-api.js");
+    });
+
+    const module = await import("./qa-runtime.js");
+
+    expect(module.isQaRuntimeAvailable()).toBe(false);
+  });
+});

src/plugin-sdk/qa-runtime.ts

@@ -0,0 +1,39 @@
+import { loadBundledPluginPublicSurfaceModuleSync } from "./facade-runtime.js";
+
+type QaRuntimeSurface = {
+  defaultQaRuntimeModelForMode: (
+    mode: string,
+    options?: {
+      alternate?: boolean;
+      preferredLiveModel?: string;
+    },
+  ) => string;
+  startQaLiveLaneGateway: (...args: unknown[]) => Promise<unknown>;
+};
+
+function isMissingQaRuntimeError(error: unknown) {
+  return (
+    error instanceof Error &&
+    (error.message === "Unable to resolve bundled plugin public surface qa-lab/runtime-api.js" ||
+      error.message.startsWith("Unable to open bundled plugin public surface "))
+  );
+}
+
+export function loadQaRuntimeModule(): QaRuntimeSurface {
+  return loadBundledPluginPublicSurfaceModuleSync<QaRuntimeSurface>({
+    dirName: "qa-lab",
+    artifactBasename: "runtime-api.js",
+  });
+}
+
+export function isQaRuntimeAvailable(): boolean {
+  try {
+    loadQaRuntimeModule();
+    return true;
+  } catch (error) {
+    if (isMissingQaRuntimeError(error)) {
+      return false;
+    }
+    throw error;
+  }
+}