Slice 1 follow-up: component-render interaction tests (CR-1/CR-2)

- vite: add @testing-library/svelte's svelteTesting() plugin so component
  render()/mount() resolves Svelte's browser build under vitest/jsdom
- dep: @testing-library/user-event for realistic interaction tests
- app: 7 component-render tests driving App.svelte through a fake socket
  (catalog render, subscribe-on-click, unsub/sub ordering, aria-current,
  error banner, action invoke)

Verified green: svelte-check 0/0, vitest 91 passed, biome clean, vite build ok.

4 files changed, 268 insertions, 6 deletions

diff --git a/bun.lock b/bun.lock
index a9725c7..6689953 100644
--- a/bun.lock
+++ b/bun.lock
@@ -12,6 +12,7 @@
         "@sveltejs/vite-plugin-svelte": "^5.0.0",
         "@testing-library/jest-dom": "^6.6.0",
         "@testing-library/svelte": "^5.2.0",
+        "@testing-library/user-event": "^14.6.1",
         "@tsconfig/svelte": "^5.0.0",
         "jsdom": "^25.0.0",
         "svelte": "^5.0.0",
@@ -191,6 +192,8 @@
 
     "@testing-library/svelte-core": ["@testing-library/[email protected]", "", { "peerDependencies": { "svelte": "^3 || ^4 || ^5 || ^5.0.0-next.0" } }, "sha512-VkUePoLV6oOYwSUvX6ShA8KLnJqZiYMIbP2JW2t0GLWLkJxKGvuH5qrrZBV/X7cXFnLGuFQEC7RheYiZOW68KQ=="],
 
+    "@testing-library/user-event": ["@testing-library/[email protected]", "", { "peerDependencies": { "@testing-library/dom": ">=7.21.4" } }, "sha512-vq7fv0rnt+QTXgPxr5Hjc210p6YKq2kmdziLgnsZGgLJ9e6VAShx1pACLuRjd/AS/sr7phAR58OIIpf0LlmQNw=="],
+
     "@tsconfig/svelte": ["@tsconfig/[email protected]", "", {}, "sha512-UkNnw1/oFEfecR8ypyHIQuWYdkPvHiwcQ78sh+ymIiYoF+uc5H1UBetbjyqT+vgGJ3qQN6nhucJviX6HesWtKQ=="],
 
     "@types/aria-query": ["@types/[email protected]", "", {}, "sha512-rfT93uj5s0PRL7EzccGMs3brplhcrghnDoV26NqKhCAS1hVo+WdNsPvE/yb6ilfr5hi2MEk6d5EWJTKdxg8jVw=="],
diff --git a/package.json b/package.json
index 244baf1..cf856d3 100644
--- a/package.json
+++ b/package.json
@@ -21,6 +21,7 @@
 		"@sveltejs/vite-plugin-svelte": "^5.0.0",
 		"@testing-library/jest-dom": "^6.6.0",
 		"@testing-library/svelte": "^5.2.0",
+		"@testing-library/user-event": "^14.6.1",
 		"@tsconfig/svelte": "^5.0.0",
 		"jsdom": "^25.0.0",
 		"svelte": "^5.0.0",
diff --git a/src/app/App.test.ts b/src/app/App.test.ts
new file mode 100644
index 0000000..ce37586
--- /dev/null
+++ b/src/app/App.test.ts
@@ -0,0 +1,259 @@
+import type { SurfaceServerMessage } from "@dispatch/ui-contract";
+import { render, screen } from "@testing-library/svelte";
+import userEvent from "@testing-library/user-event";
+import { describe, expect, it } from "vitest";
+import type { WebSocketLike } from "../adapters/ws";
+import App from "./App.svelte";
+import { createAppStore } from "./store.svelte";
+
+interface FakeSocket extends WebSocketLike {
+	sent: string[];
+	resolveOpen(): void;
+	feedMessage(data: SurfaceServerMessage): void;
+}
+
+function fakeSocket(): FakeSocket {
+	let onopen: (() => void) | null = null;
+	let onmessage: ((ev: { data: string }) => void) | null = null;
+	const sent: string[] = [];
+
+	const ws: FakeSocket = {
+		send(data: string) {
+			sent.push(data);
+		},
+		close() {},
+		get onopen() {
+			return onopen;
+		},
+		set onopen(fn) {
+			onopen = fn;
+		},
+		get onmessage() {
+			return onmessage;
+		},
+		set onmessage(fn) {
+			onmessage = fn;
+		},
+		get onclose() {
+			return null;
+		},
+		set onclose(_fn) {},
+		resolveOpen() {
+			onopen?.();
+		},
+		feedMessage(msg: SurfaceServerMessage) {
+			onmessage?.({ data: JSON.stringify(msg) });
+		},
+		sent,
+	};
+	return ws;
+}
+
+function sentMessages(ws: FakeSocket) {
+	return ws.sent.map((s) => JSON.parse(s));
+}
+
+describe("App component interaction tests", () => {
+	it("renders empty state when catalog is empty", () => {
+		const ws = fakeSocket();
+		const store = createAppStore({ socketFactory: () => ws });
+		ws.resolveOpen();
+
+		render(App, { props: { store } });
+
+		expect(screen.getByText("No surfaces available")).toBeInTheDocument();
+
+		store.dispose();
+	});
+
+	it("renders a catalog button per entry after a catalog message", () => {
+		const ws = fakeSocket();
+		const store = createAppStore({ socketFactory: () => ws });
+		ws.resolveOpen();
+
+		ws.feedMessage({
+			type: "catalog",
+			catalog: [
+				{ id: "s1", region: "sidebar", title: "Surface One" },
+				{ id: "s2", region: "panel", title: "Surface Two" },
+			],
+		});
+
+		render(App, { props: { store } });
+
+		const buttons = screen.getAllByRole("button");
+		expect(buttons).toHaveLength(2);
+		expect(buttons[0]).toHaveTextContent("Surface One");
+		expect(buttons[1]).toHaveTextContent("Surface Two");
+
+		store.dispose();
+	});
+
+	it("clicking a catalog entry subscribes and renders its surface", async () => {
+		const ws = fakeSocket();
+		const store = createAppStore({ socketFactory: () => ws });
+		ws.resolveOpen();
+
+		ws.feedMessage({
+			type: "catalog",
+			catalog: [{ id: "s1", region: "sidebar", title: "Surface One" }],
+		});
+
+		render(App, { props: { store } });
+
+		const user = userEvent.setup();
+		const button = screen.getByRole("button", { name: /Surface One/ });
+		ws.sent.length = 0;
+		await user.click(button);
+
+		const msgs = sentMessages(ws);
+		const subscribe = msgs.find(
+			(m: { type: string; surfaceId: string }) => m.type === "subscribe" && m.surfaceId === "s1",
+		);
+		expect(subscribe).toBeTruthy();
+
+		ws.feedMessage({
+			type: "surface",
+			spec: {
+				id: "s1",
+				region: "sidebar",
+				title: "Surface One",
+				fields: [{ kind: "stat", label: "Tokens", value: "1,234" }],
+			},
+		});
+
+		expect(await screen.findByRole("heading", { name: "Surface One" })).toBeInTheDocument();
+		expect(await screen.findByText("Tokens")).toBeInTheDocument();
+		expect(await screen.findByText("1,234")).toBeInTheDocument();
+
+		store.dispose();
+	});
+
+	it("clicking a different entry unsubscribes the previous then subscribes the new", async () => {
+		const ws = fakeSocket();
+		const store = createAppStore({ socketFactory: () => ws });
+		ws.resolveOpen();
+
+		ws.feedMessage({
+			type: "catalog",
+			catalog: [
+				{ id: "s1", region: "sidebar", title: "Surface One" },
+				{ id: "s2", region: "panel", title: "Surface Two" },
+			],
+		});
+
+		render(App, { props: { store } });
+
+		const user = userEvent.setup();
+		await user.click(screen.getByRole("button", { name: /Surface One/ }));
+		ws.sent.length = 0;
+
+		await user.click(screen.getByRole("button", { name: /Surface Two/ }));
+
+		const msgs = sentMessages(ws) as Array<{ type: string; surfaceId: string }>;
+		const unsubIdx = msgs.findIndex((m) => m.type === "unsubscribe" && m.surfaceId === "s1");
+		const subIdx = msgs.findIndex((m) => m.type === "subscribe" && m.surfaceId === "s2");
+		expect(unsubIdx).toBeGreaterThanOrEqual(0);
+		expect(subIdx).toBeGreaterThanOrEqual(0);
+		expect(unsubIdx).toBeLessThan(subIdx);
+
+		store.dispose();
+	});
+
+	it("selected catalog button reflects aria-current", async () => {
+		const ws = fakeSocket();
+		const store = createAppStore({ socketFactory: () => ws });
+		ws.resolveOpen();
+
+		ws.feedMessage({
+			type: "catalog",
+			catalog: [
+				{ id: "s1", region: "sidebar", title: "Surface One" },
+				{ id: "s2", region: "panel", title: "Surface Two" },
+			],
+		});
+
+		render(App, { props: { store } });
+
+		const user = userEvent.setup();
+		const btn1 = screen.getByRole("button", { name: /Surface One/ });
+		const btn2 = screen.getByRole("button", { name: /Surface Two/ });
+
+		await user.click(btn1);
+		expect(btn1).toHaveAttribute("aria-current", "true");
+		expect(btn2).not.toHaveAttribute("aria-current");
+
+		await user.click(btn2);
+		expect(btn2).toHaveAttribute("aria-current", "true");
+		expect(btn1).not.toHaveAttribute("aria-current");
+
+		store.dispose();
+	});
+
+	it("an error message renders the alert banner", () => {
+		const ws = fakeSocket();
+		const store = createAppStore({ socketFactory: () => ws });
+		ws.resolveOpen();
+
+		ws.feedMessage({
+			type: "error",
+			message: "Something went wrong",
+		});
+
+		render(App, { props: { store } });
+
+		const alert = screen.getByRole("alert");
+		expect(alert).toHaveTextContent("Something went wrong");
+
+		store.dispose();
+	});
+
+	it("invoking a field action sends an invoke", async () => {
+		const ws = fakeSocket();
+		const store = createAppStore({ socketFactory: () => ws });
+		ws.resolveOpen();
+
+		ws.feedMessage({
+			type: "catalog",
+			catalog: [{ id: "s1", region: "sidebar", title: "Surface One" }],
+		});
+
+		render(App, { props: { store } });
+
+		const user = userEvent.setup();
+		await user.click(screen.getByRole("button", { name: /Surface One/ }));
+
+		ws.feedMessage({
+			type: "surface",
+			spec: {
+				id: "s1",
+				region: "sidebar",
+				title: "Surface One",
+				fields: [
+					{
+						kind: "toggle",
+						label: "Dark Mode",
+						value: false,
+						action: { actionId: "toggle-dark" },
+					},
+				],
+			},
+		});
+
+		ws.sent.length = 0;
+		const checkbox = await screen.findByRole("checkbox", { name: "Dark Mode" });
+		await user.click(checkbox);
+
+		const msgs = sentMessages(ws);
+		const invoke = msgs.find(
+			(m: { type: string; surfaceId: string; actionId: string; payload: unknown }) =>
+				m.type === "invoke" &&
+				m.surfaceId === "s1" &&
+				m.actionId === "toggle-dark" &&
+				m.payload === true,
+		);
+		expect(invoke).toBeTruthy();
+
+		store.dispose();
+	});
+});
diff --git a/vite.config.ts b/vite.config.ts
index fab62a0..5ff83cd 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -1,10 +1,14 @@
 import { svelte } from "@sveltejs/vite-plugin-svelte";
+import { svelteTesting } from "@testing-library/svelte/vite";
 import { defineConfig } from "vitest/config";
 
 // Dev server on the reserved FRONTEND_PORT (24204). Vitest config lives here too
 // (jsdom + globals) so component tests run without extra config.
 export default defineConfig({
-	plugins: [svelte()],
+	// svelteTesting() forces Svelte's `browser` resolve condition under vitest so
+	// component render()/mount() works in jsdom (a plain test.resolve.conditions
+	// does not propagate to Vite's SSR resolution — sveltejs/svelte#11394).
+	plugins: [svelte(), svelteTesting()],
 	// Bind all interfaces + accept any Host header so the dev server is reachable over a LAN /
 	// Tailscale. Safe for LOCAL-NETWORK-ONLY use (NOT internet-exposed): `allowedHosts: true`
 	// disables Vite's DNS-rebinding host check. (The WS URL still runs in the browser — set
@@ -14,10 +18,5 @@ export default defineConfig({
 		environment: "jsdom",
 		globals: true,
 		setupFiles: ["./vitest-setup.ts"],
-		// Svelte 5's exports map resolves `svelte` → server build under the default
-		// condition; force the browser build so component tests can mount().
-		resolve: {
-			conditions: ["browser"],
-		},
 	},
 });