feat(agent-model): add per-agent model override with default-reset UX and runtime sync (#651)

src/stores/agents.ts

@@ -6,6 +6,7 @@ import type { AgentSummary, AgentsSnapshot } from '@/types/agent';
 interface AgentsState {
   agents: AgentSummary[];
   defaultAgentId: string;
+  defaultModelRef: string | null;
   configuredChannelTypes: string[];
   channelOwners: Record<string, string>;
   channelAccountOwners: Record<string, string>;
@@ -14,6 +15,7 @@ interface AgentsState {
   fetchAgents: () => Promise<void>;
   createAgent: (name: string, options?: { inheritWorkspace?: boolean }) => Promise<void>;
   updateAgent: (agentId: string, name: string) => Promise<void>;
+  updateAgentModel: (agentId: string, modelRef: string | null) => Promise<void>;
   deleteAgent: (agentId: string) => Promise<void>;
   assignChannel: (agentId: string, channelType: ChannelType) => Promise<void>;
   removeChannel: (agentId: string, channelType: ChannelType) => Promise<void>;
@@ -24,6 +26,7 @@ function applySnapshot(snapshot: AgentsSnapshot | undefined) {
   return snapshot ? {
     agents: snapshot.agents ?? [],
     defaultAgentId: snapshot.defaultAgentId ?? 'main',
+    defaultModelRef: snapshot.defaultModelRef ?? null,
     configuredChannelTypes: snapshot.configuredChannelTypes ?? [],
     channelOwners: snapshot.channelOwners ?? {},
     channelAccountOwners: snapshot.channelAccountOwners ?? {},
@@ -33,6 +36,7 @@ function applySnapshot(snapshot: AgentsSnapshot | undefined) {
 export const useAgentsStore = create<AgentsState>((set) => ({
   agents: [],
   defaultAgentId: 'main',
+  defaultModelRef: null,
   configuredChannelTypes: [],
   channelOwners: {},
   channelAccountOwners: {},
@@ -83,6 +87,23 @@ export const useAgentsStore = create<AgentsState>((set) => ({
     }
   },
 
+  updateAgentModel: async (agentId: string, modelRef: string | null) => {
+    set({ error: null });
+    try {
+      const snapshot = await hostApiFetch<AgentsSnapshot & { success?: boolean }>(
+        `/api/agents/${encodeURIComponent(agentId)}/model`,
+        {
+          method: 'PUT',
+          body: JSON.stringify({ modelRef }),
+        }
+      );
+      set(applySnapshot(snapshot));
+    } catch (error) {
+      set({ error: String(error) });
+      throw error;
+    }
+  },
+
   deleteAgent: async (agentId: string) => {
     set({ error: null });
     try {