feat: improve agent activity UI and fix status update propagation

**Agent Activity UI Improvements:**
- Create typed discriminated unions for SessionNotification updates
- Add AgentActivity component with specialized rendering for each update type
- Group consecutive text chunks into single messages (like main chat)
- Add collapsible tool call rendering with input/output details
- Add plan rendering with task status indicators
- Add fallback rendering for unknown activity types (badge + drawer)

**Agent Status Update Fix:**
- Fix agent killing not updating UI status
- Session now detects status change notifications and emits agent_status messages
- Agent manager delays agent deletion to allow status updates to propagate
- Frontend agent_status handler now receives proper updates

**Technical Details:**
- Created /packages/app/src/types/agent-activity.ts with typed session updates
- Created /packages/app/src/components/agent-activity.tsx with activity renderers
- Updated AgentStreamView to use grouped activities with useMemo
- Modified session.ts subscribeToAgent to emit agent_status on status changes
- Modified agent-manager.ts killAgent to delay deletion for status propagation

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

packages/server/src/server/acp/agent-manager.ts

@@ -349,6 +349,9 @@ export class AgentManager {
     }
 
     agent.status = "killed";
+
+    // Notify subscribers BEFORE removing from manager
+    // This ensures subscribers can still query agent info
     this.notifySubscribers(agentId);
 
     // Kill the process
@@ -361,8 +364,11 @@ export class AgentManager {
       }
     }, 5000);
 
-    // Remove from manager
-    this.agents.delete(agentId);
+    // Remove from manager after a small delay to allow status updates to propagate
+    setTimeout(() => {
+      this.agents.delete(agentId);
+      console.log(`[Agent ${agentId}] Removed from manager`);
+    }, 100);
   }
 
   /**

packages/server/src/server/session.ts

@@ -145,6 +145,41 @@ export class Session {
             notification: update.notification,
           },
         });
+
+        // Check if this is a status change notification
+        // The agent manager sends custom notifications with status field
+        const notification = update.notification as any;
+        if (notification && notification.sessionUpdate && notification.sessionUpdate.status) {
+          const status = notification.sessionUpdate.status;
+
+          // Get current agent info
+          try {
+            const info = this.agentManager!.listAgents().find(a => a.id === agentId);
+            if (info) {
+              // Emit agent_status message
+              this.emit({
+                type: "agent_status",
+                payload: {
+                  agentId,
+                  status,
+                  info: {
+                    id: info.id,
+                    status: info.status,
+                    createdAt: info.createdAt.toISOString(),
+                    type: info.type,
+                    sessionId: info.sessionId,
+                    error: info.error,
+                    currentModeId: info.currentModeId,
+                    availableModes: info.availableModes,
+                  },
+                },
+              });
+              console.log(`[Session ${this.clientId}] Agent ${agentId} status changed to: ${status}`);
+            }
+          } catch (error) {
+            console.error(`[Session ${this.clientId}] Failed to get agent info for status update:`, error);
+          }
+        }
       }
     );