diff --git a/frontend/src/components/comm/blocks/BlockRenderer.tsx b/frontend/src/components/comm/blocks/BlockRenderer.tsx
index dc1f43c..f3c4823 100644
--- a/frontend/src/components/comm/blocks/BlockRenderer.tsx
+++ b/frontend/src/components/comm/blocks/BlockRenderer.tsx
@@ -6,14 +6,8 @@ import ImageBlock from './ImageBlock';
 import AudioBlock from './AudioBlock';
 import VideoBlock from './VideoBlock';
 import FileBlock from './FileBlock';
-import ActionCardBlock from './ActionCardBlock';
-import ContactCardBlock from './ContactCardBlock';
-import MiniAppBlock from './MiniAppBlock';
-import AgentResultBlock from './AgentResultBlock';
-import ApprovalRequestBlock from './ApprovalRequestBlock';
-import TaskCardBlock from './TaskCardBlock';
-import WorkflowCardBlock from './WorkflowCardBlock';
-import KnowledgeCardBlock from './KnowledgeCardBlock';
+import { getBlockComponent } from './registry';
+import './registrations'; // plugin-contributed block registrations
 
 interface BlockRendererProps {
   blocks: MessageBlock[];
@@ -51,29 +45,20 @@ const BlockRenderer: React.FC<BlockRendererProps> = ({ blocks }) => {
               return <VideoBlock block={block} />;
             case 'file':
               return <FileBlock block={block} />;
-            case 'action_card':
-              return <ActionCardBlock block={block} />;
-            case 'contact_card':
-              return <ContactCardBlock block={block} />;
-            case 'miniapp':
-              return <MiniAppBlock block={block} />;
-            case 'agent_result':
-              return <AgentResultBlock block={block} />;
-            case 'approval_request':
-              return <ApprovalRequestBlock block={block} />;
-            case 'task_card':
-              return <TaskCardBlock block={block} />;
-            case 'workflow_card':
-              return <WorkflowCardBlock block={block} />;
-            case 'knowledge_card':
-              return <KnowledgeCardBlock block={block} />;
-            default:
+            default: {
+              // Plugin-contributed block types (Block H / HC-F)
+              const Contributed = getBlockComponent(block.block_type);
+              if (Contributed) {
+                const ContributedBlock = Contributed as React.FC<{ block: MessageBlock }>;
+                return <ContributedBlock block={block} />;
+              }
               // Fallback for unknown block types
               return (
                 <div className="text-xs text-secondary-400 italic p-2 rounded bg-secondary-50">
                   Unbekannter Block-Typ: {block.block_type}
                 </div>
               );
+            }
           }
         };
 
diff --git a/frontend/src/components/comm/blocks/registrations.ts b/frontend/src/components/comm/blocks/registrations.ts
new file mode 100644
index 0000000..2046b76
--- /dev/null
+++ b/frontend/src/components/comm/blocks/registrations.ts
@@ -0,0 +1,26 @@
+/**
+ * Plugin block registrations.
+ *
+ * Currently a static import list; the dynamic plugin loader (ARCH-019 fix)
+ * will replace this file with manifest-driven registration. Plugins register
+ * their block renderers via ``registerBlockType`` with an owner tag so that
+ * ``unregisterBlockTypes(owner)`` can clean up on deactivation.
+ */
+import { registerBlockType } from './registry';
+import ActionCardBlock from './ActionCardBlock';
+import ContactCardBlock from './ContactCardBlock';
+import MiniAppBlock from './MiniAppBlock';
+import AgentResultBlock from './AgentResultBlock';
+import ApprovalRequestBlock from './ApprovalRequestBlock';
+import TaskCardBlock from './TaskCardBlock';
+import WorkflowCardBlock from './WorkflowCardBlock';
+import KnowledgeCardBlock from './KnowledgeCardBlock';
+
+registerBlockType('action_card', ActionCardBlock, 'core-comm');
+registerBlockType('contact_card', ContactCardBlock, 'contacts');
+registerBlockType('miniapp', MiniAppBlock, 'kommunikation');
+registerBlockType('agent_result', AgentResultBlock, 'automation');
+registerBlockType('approval_request', ApprovalRequestBlock, 'core-approvals');
+registerBlockType('task_card', TaskCardBlock, 'tasks');
+registerBlockType('workflow_card', WorkflowCardBlock, 'workflows');
+registerBlockType('knowledge_card', KnowledgeCardBlock, 'knowledge');
diff --git a/frontend/src/components/comm/blocks/registry.ts b/frontend/src/components/comm/blocks/registry.ts
new file mode 100644
index 0000000..534d408
--- /dev/null
+++ b/frontend/src/components/comm/blocks/registry.ts
@@ -0,0 +1,36 @@
+/**
+ * Message block type registry.
+ *
+ * Core owns the base block types; plugins can contribute additional block
+ * renderers via ``registerBlockType`` / ``unregisterBlockTypes`` during their
+ * frontend activation lifecycle (Block H / HC-F).
+ */
+import type { ComponentType } from 'react';
+import type { MessageBlock } from '@/store/commStore';
+
+export type BlockComponent = ComponentType<{ block: MessageBlock }>;
+
+const _registry = new Map<string, BlockComponent>();
+
+export function registerBlockType(blockType: string, component: BlockComponent, owner = ''): void {
+  if (_registry.has(blockType)) {
+    // eslint-disable-next-line no-console
+    console.warn(`[blockRegistry] block type '${blockType}' re-registered by '${owner || 'unknown'}' — overwriting`);
+  }
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  (component as any).__block_owner__ = owner;
+  _registry.set(blockType, component);
+}
+
+export function unregisterBlockTypes(owner: string): void {
+  for (const [key, component] of _registry.entries()) {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    if ((component as any).__block_owner__ === owner) {
+      _registry.delete(key);
+    }
+  }
+}
+
+export function getBlockComponent(blockType: string): BlockComponent | undefined {
+  return _registry.get(blockType);
+}