fix(plugins): isole les menus plugin et durcit hello-plugin SDK contre la rechute #120

Requalification Architect du 2026-08-01: le crash INTERFACE INTERROMPUE au
chargement d'un plugin (menu + item) remonte via ProjectsView -> usePluginMenus
-> MenuBar jusqu'à RootErrorBoundary, quel que soit le plugin (ancien ou
reconstruit via SDK).

- usePluginMenus isole la résolution/conversion des contributions plugin :
  toute erreur retombe sur [] au lieu de propager.
- ProjectsView sépare les menus natifs des menus enrichis par plugin et rend
  MenuBar derrière une error boundary locale (fallback menus natifs seuls).
- hello-plugin (SDK) et les tests d'installation associés durcis en cohérence.

Bookkeeping ticket #120 uniquement (issue.md, carnet.md) ; les fichiers
counter.json/index.json et le dossier tickets/122/ restent hors commit car
une collision de numérotation #122 existe entre cette base et
feature/ticket120-hello-plugin-install-path-audit (deux tickets différents
revendiquent #122) — à arbitrer avant de committer le bookkeeping global.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/features/projects/ProjectsView.tsx

@@ -33,7 +33,14 @@
  * open; the project tab bar (`role="tablist"`) is always present.
  */
 
-import { useEffect, useMemo, useState, type ReactNode } from "react";
+import {
+  Component,
+  useEffect,
+  useMemo,
+  useState,
+  type ErrorInfo,
+  type ReactNode,
+} from "react";
 
 import type { Agent, DomainEvent, LayoutInfo } from "@/domain";
 import { LayoutGrid, LayoutTabs } from "@/features/layout";
@@ -109,6 +116,41 @@ interface PendingConversationOpen {
   conversationId: string;
 }
 
+interface PluginMenuRenderBoundaryProps {
+  resetKey: string;
+  fallbackMenus: MenuBarMenu[];
+  children: ReactNode;
+}
+
+class PluginMenuRenderBoundary extends Component<
+  PluginMenuRenderBoundaryProps,
+  { hasError: boolean }
+> {
+  state = { hasError: false };
+
+  static getDerivedStateFromError(): { hasError: boolean } {
+    return { hasError: true };
+  }
+
+  componentDidCatch(error: Error, errorInfo: ErrorInfo): void {
+    console.error("[plugins] menu render failed; using native menus only", {
+      error,
+      componentStack: errorInfo.componentStack,
+    });
+  }
+
+  componentDidUpdate(prevProps: PluginMenuRenderBoundaryProps): void {
+    if (prevProps.resetKey !== this.props.resetKey && this.state.hasError) {
+      this.setState({ hasError: false });
+    }
+  }
+
+  render(): ReactNode {
+    if (this.state.hasError) return <MenuBar menus={this.props.fallbackMenus} />;
+    return this.props.children;
+  }
+}
+
 function isTerminalBackgroundTaskEvent(
   event: DomainEvent,
 ): event is Extract<DomainEvent, { type: "backgroundTaskChanged" }> {
@@ -546,22 +588,43 @@ export function ProjectsView() {
     return items;
   }
 
+  const nativePanelItems: MenuBarItem[] = panelOrder.map((panel) => ({
+    id: panel,
+    label: PANEL_TITLE[panel],
+    active: placementOf(placements, panel) !== "closed",
+    onSelect: () => {},
+    submenu: placementSubmenu(panel),
+  }));
+  const nativeSettingsItems: MenuBarItem[] = SETTINGS_SECTIONS.map((section) => ({
+    id: section,
+    label: SETTINGS_SECTION_LABEL[section],
+    active: settingsSection === section,
+    onSelect: () => {
+      setSettingsSection(section);
+      dismissFloating();
+    },
+  }));
+  const pluginPanelItems = pluginMenus.itemsFor("panels");
+  const pluginSettingsItems = pluginMenus.itemsFor("settings");
+  const nativeMenus: MenuBarMenu[] = [
+    {
+      id: "panels",
+      label: "Panneaux",
+      items: nativePanelItems,
+    },
+    {
+      id: "settings",
+      label: "Paramètres",
+      items: nativeSettingsItems,
+    },
+  ];
   const menus: MenuBarMenu[] = [
     {
       id: "panels",
       label: "Panneaux",
       // Native items first, plugin-contributed items after in their own
       // (discreetly-labelled) group (#43, F3, carnet §7.2).
-      items: [
-        ...panelOrder.map((panel) => ({
-          id: panel,
-          label: PANEL_TITLE[panel],
-          active: placementOf(placements, panel) !== "closed",
-          onSelect: () => {},
-          submenu: placementSubmenu(panel),
-        })),
-        ...pluginMenus.itemsFor("panels"),
-      ],
+      items: [...nativePanelItems, ...pluginPanelItems],
     },
     // Top-level plugin menus render between Panneaux and Paramètres (#43,
     // carnet §0 UX decision + §7.1).
@@ -572,20 +635,14 @@ export function ProjectsView() {
       // One entry per section (#68). The entries name sections and mark the open
       // one; closing lives in the view ("Fermer les paramètres"), so no label
       // alternates. Plugin-contributed items are appended after (#43, F3).
-      items: [
-        ...SETTINGS_SECTIONS.map((section) => ({
-          id: section,
-          label: SETTINGS_SECTION_LABEL[section],
-          active: settingsSection === section,
-          onSelect: () => {
-            setSettingsSection(section);
-            dismissFloating();
-          },
-        })),
-        ...pluginMenus.itemsFor("settings"),
-      ],
+      items: [...nativeSettingsItems, ...pluginSettingsItems],
     },
   ];
+  const pluginMenuResetKey = [
+    pluginMenus.topLevelMenus.map((menu) => menu.id).join(","),
+    pluginPanelItems.map((item) => item.id).join(","),
+    pluginSettingsItems.map((item) => item.id).join(","),
+  ].join("|");
 
   // The create-project form + known-projects list. Rendered inline in the
   // welcome area (no active project) or inside the Projects floating window.
@@ -810,7 +867,12 @@ export function ProjectsView() {
       />
 
       {/* ── Menu bar (replaces the former left sidebar) ── */}
-      <MenuBar menus={menus} />
+      <PluginMenuRenderBoundary
+        resetKey={pluginMenuResetKey}
+        fallbackMenus={nativeMenus}
+      >
+        <MenuBar menus={menus} />
+      </PluginMenuRenderBoundary>
 
       {/* ── Chrome row: left dock │ main │ right dock (#22). Docks are in-flow
           resizable columns, not overlays — they sit beside the main surface. */}