fall back to first agent if last used agent is not available

packages/opencode/src/cli/cmd/tui/context/local.tsx

@@ -57,7 +57,7 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
           return agents()
         },
         current() {
-          return agents().find((x) => x.name === agentStore.current)!
+          return agents().find((x) => x.name === agentStore.current) ?? agents()[0]
         },
         set(name: string) {
           if (!agents().some((x) => x.name === name))