fix(plugins): support export default { activate }, cleanup partiel et erreurs visibles

Le loader accepte désormais aussi la forme export default { activate }
en plus de l'export nommé, les subscriptions partiellement établies
sont nettoyées en cas d'échec d'activation, et une erreur de
runtime-catalog est remontée visuellement dans PluginsPanel avec un
badge Invalide/Isolé sur les plugins concernés (#116/#120).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/features/plugins/plugins.test.tsx

@@ -7,6 +7,7 @@ import { describe, it, expect } from "vitest";
 import { render, screen, waitFor, fireEvent, within } from "@testing-library/react";
 
 import { MockPluginGateway, MockSystemGateway } from "@/adapters/mock";
+import type { PluginInstallResult, PluginRuntimeContributionCatalog } from "@/domain";
 import type { Gateways } from "@/ports";
 import { DIProvider } from "@/app/di";
 import { PluginRuntimeRegistry } from "@/plugins/runtime";
@@ -38,6 +39,44 @@ function renderPanel(
   };
 }
 
+function renderPanelWithLiveRuntime(plugin: MockPluginGateway, system = new MockSystemGateway()) {
+  const gateways = { plugin, system } as unknown as Gateways;
+  return render(
+    <DIProvider gateways={gateways}>
+      <PluginRuntimeProvider>
+        <PluginsPanel />
+      </PluginRuntimeProvider>
+    </DIProvider>,
+  );
+}
+
+class InvalidInstallPluginGateway extends MockPluginGateway {
+  async installFromDirectory(path: string): Promise<PluginInstallResult> {
+    const plugin = {
+      id: "dev.idea.fixtures.missing-main",
+      displayName: "Missing Main Plugin",
+      version: "0.1.0",
+      sourceKind: "directory" as const,
+      sourceLabel: path,
+      lifecycleState: "invalid" as const,
+      enabled: false,
+      pendingUninstall: false,
+      restartRequired: false,
+      trustLevel: "full" as const,
+      contributionSummary: { topLevelMenus: 1, menuItems: 1, layouts: 0, mcpServers: 0 },
+      error: "plugin main asset is missing: dist/index.js",
+    };
+    this._seedPlugin(plugin);
+    return { plugin, restartRequired: false };
+  }
+}
+
+class FailingRuntimeCatalogPluginGateway extends MockPluginGateway {
+  async listRuntimeContributions(): Promise<PluginRuntimeContributionCatalog> {
+    throw { code: "INVALID", message: "runtime catalog failed" };
+  }
+}
+
 describe("PluginsPanel", () => {
   it("shows an empty state with no plugins installed", async () => {
     renderPanel();
@@ -57,6 +96,15 @@ describe("PluginsPanel", () => {
     expect(screen.getByText(/Cannot use import statement outside a module/)).toBeTruthy();
   });
 
+  it("keeps the Plugins panel rendered when the runtime catalog fetch fails", async () => {
+    renderPanelWithLiveRuntime(new FailingRuntimeCatalogPluginGateway());
+
+    expect(await screen.findByText("Aucun plugin installé.")).toBeTruthy();
+    expect(screen.getByText("Certains plugins installés n'ont pas pu être chargés.")).toBeTruthy();
+    expect(screen.getByText("<runtime-catalog>")).toBeTruthy();
+    expect(screen.getByText(/runtime catalog failed/)).toBeTruthy();
+  });
+
   it("installs from an archive via the review dialog, mentioning full-trust", async () => {
     renderPanel();
     await screen.findByText("Aucun plugin installé.");
@@ -74,6 +122,21 @@ describe("PluginsPanel", () => {
     expect(screen.getByText("Activé")).toBeTruthy();
   });
 
+  it("renders an invalid plugin returned after install as isolated, without replacing the panel", async () => {
+    renderPanel(new InvalidInstallPluginGateway());
+    await screen.findByText("Aucun plugin installé.");
+
+    fireEvent.click(screen.getByRole("button", { name: "Installer depuis un dossier…" }));
+    const dialog = await screen.findByRole("dialog");
+    fireEvent.click(within(dialog).getByRole("button", { name: "Installer" }));
+
+    expect(await screen.findByText("Missing Main Plugin")).toBeTruthy();
+    expect(screen.getByText("Invalide")).toBeTruthy();
+    expect(screen.getByText("plugin main asset is missing: dist/index.js")).toBeTruthy();
+    expect(screen.getByRole("button", { name: "Isolé" }).hasAttribute("disabled")).toBe(true);
+    expect(screen.queryByRole("button", { name: "Activer" })).toBeNull();
+  });
+
   it("disables an installed plugin after confirmation", async () => {
     const plugin = new MockPluginGateway();
     plugin._seedPlugin({