refactor(block-h): ai sidebar tabs resolve via plugin-contributable registry

frontend/src/components/layout/AISidebar.tsx

@@ -5,6 +5,7 @@ import { SuggestionList } from '@/components/ai/SuggestionSidebar';
 import { ImprovementPanel } from '@/components/ai/ImprovementPanel';
 import { createSession, fetchSessions } from '@/api/ai';
 import { useUIStore } from '@/store/uiStore';
+import { getContributedTabs } from './sidebarTabs';
 import { useTranslation } from 'react-i18next';
 import { useUsers, useGroups } from '@/api/hooks';
 import { Avatar } from '@/components/ui/Avatar';
@@ -35,7 +36,7 @@ const chevronRightIcon = (
 );
 
 interface TabDef {
-  key: 'proactive' | 'chat' | 'notifications' | 'team' | 'chatroom';
+  key: string;
   label: string;
   icon: (cls: string) => React.ReactNode;
   testId: string;
@@ -139,6 +140,13 @@ export function AISidebar() {
     { key: 'notifications', label: t('topbar.notifications'), icon: bellIcon, testId: 'ai-sidebar-tab-notifications' },
     { key: 'team', label: 'Team', icon: teamIcon, testId: 'ai-sidebar-tab-team' },
     { key: 'chatroom', label: 'Chat', icon: chatBubbleIcon, testId: 'ai-sidebar-tab-chatroom' },
+    // Plugin-contributed tabs (Block H / HC-G)
+    ...getContributedTabs().map((ct) => ({
+      key: ct.key,
+      label: ct.label,
+      icon: ct.icon,
+      testId: ct.testId,
+    })),
   ];
 
   const activeTab = tabs.find((tab) => tab.key === aiSidebarTab) || tabs[0];
@@ -209,6 +217,12 @@ export function AISidebar() {
     if (aiSidebarTab === 'chatroom') {
       return <ChatPanel />;
     }
+    // Plugin-contributed tabs (Block H / HC-G)
+    const contributed = getContributedTabs().find((ct) => ct.key === aiSidebarTab);
+    if (contributed) {
+      const ContributedComponent = contributed.component;
+      return <ContributedComponent />;
+    }
     // chat tab
     if (loading) {
       return (

frontend/src/components/layout/sidebarTabs.ts

@@ -0,0 +1,42 @@
+/**
+ * AI sidebar tab registry.
+ *
+ * Core owns the base tabs (chat/proactive/notifications/team/chatroom);
+ * plugins contribute additional tabs via ``registerSidebarTab`` during their
+ * frontend activation lifecycle (Block H / HC-G). Contributed tabs render a
+ * generic container component provided by the plugin.
+ */
+import type { ComponentType } from 'react';
+
+type IconFn = (className: string) => JSX.Element;
+
+export interface ContributedTab {
+  key: string;
+  label: string;
+  icon: IconFn;
+  testId: string;
+  component: ComponentType;
+}
+
+const _tabs = new Map<string, ContributedTab>();
+
+export function registerSidebarTab(tab: ContributedTab): void {
+  if (_tabs.has(tab.key)) {
+    // eslint-disable-next-line no-console
+    console.warn(`[sidebarTabs] tab '${tab.key}' re-registered — overwriting`);
+  }
+  _tabs.set(tab.key, tab);
+}
+
+export function unregisterSidebarTabs(owner: string): void {
+  for (const [key, tab] of _tabs.entries()) {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    if ((tab.component as any).__sidebar_owner__ === owner) {
+      _tabs.delete(key);
+    }
+  }
+}
+
+export function getContributedTabs(): ContributedTab[] {
+  return Array.from(_tabs.values());
+}

frontend/src/store/uiStore.ts

@@ -2,7 +2,9 @@ import { create } from 'zustand';
 
 export type Theme = 'light' | 'dark' | 'system';
 export type Locale = 'de' | 'en';
-export type AISidebarTab = 'proactive' | 'chat' | 'notifications' | 'team' | 'chatroom';
+// Plugin-contributed tabs add arbitrary keys (Block H / HC-G) — the union
+// keeps autocomplete for the base tabs while allowing any string key.
+export type AISidebarTab = 'proactive' | 'chat' | 'notifications' | 'team' | 'chatroom' | (string & {});
 
 export interface Toast {
   id: string;