feat(chat): add activeAgentId to track current agent state

Add activeAgentId field to chat state to track which agent is currently active. This enables UI to reflect the active agent state and handle agent-specific interactions.

src/renderer/src/store/runtime.ts

@@ -7,6 +7,8 @@ export interface ChatState {
   isMultiSelectMode: boolean
   selectedMessageIds: string[]
   activeTopic: Topic | null
+  /** UI state. null represents no active agent, may active assistant  */
+  activeAgentId: string | null
   /** topic ids that are currently being renamed */
   renamingTopics: string[]
   /** topic ids that are newly renamed */
@@ -78,6 +80,7 @@ const initialState: RuntimeState = {
     isMultiSelectMode: false,
     selectedMessageIds: [],
     activeTopic: null,
+    activeAgentId: null,
     renamingTopics: [],
     newlyRenamedTopics: []
   },
@@ -142,6 +145,9 @@ const runtimeSlice = createSlice({
     setActiveTopic: (state, action: PayloadAction<Topic>) => {
       state.chat.activeTopic = action.payload
     },
+    setActiveAgentId: (state, action: PayloadAction<string>) => {
+      state.chat.activeAgentId = action.payload
+    },
     setRenamingTopics: (state, action: PayloadAction<string[]>) => {
       state.chat.renamingTopics = action.payload
     },
@@ -180,6 +186,7 @@ export const {
   toggleMultiSelectMode,
   setSelectedMessageIds,
   setActiveTopic,
+  setActiveAgentId,
   setRenamingTopics,
   setNewlyRenamedTopics,
   // WebSearch related actions