feat(frontend): Zustand session store + applyEvent

frontend/src/store/sessionStore.ts

@@ -0,0 +1,44 @@
+import { create } from "zustand";
+import type { StreamEvent, WidgetDescriptor } from "../api/types";
+
+interface Entry {
+  role: "assistant";
+  text: string;
+}
+
+interface SessionState {
+  pendingWidget: WidgetDescriptor | null;
+  transcript: Entry[];
+  toasts: { level: string; text: string }[];
+  lastSystemEvent: StreamEvent | null;
+  applyEvent: (e: StreamEvent) => void;
+  clearPending: () => void;
+  resetSession: () => void;
+}
+
+const empty = {
+  pendingWidget: null,
+  transcript: [] as Entry[],
+  toasts: [] as { level: string; text: string }[],
+  lastSystemEvent: null,
+};
+
+export const useSessionStore = create<SessionState>((set) => ({
+  ...empty,
+  applyEvent: (e) =>
+    set((st) => {
+      if (e.type === "ui_request") return { pendingWidget: e.ui_request };
+      if (e.type === "text_delta") {
+        const t = [...st.transcript];
+        const last = t.at(-1);
+        if (last && !st.pendingWidget) t[t.length - 1] = { role: "assistant", text: last.text + e.text };
+        else t.push({ role: "assistant", text: e.text });
+        return { transcript: t };
+      }
+      if (e.type === "info") return { toasts: [...st.toasts, { level: e.level ?? "info", text: e.text }] };
+      if (e.type === "system_event") return { lastSystemEvent: e };
+      return {};
+    }),
+  clearPending: () => set({ pendingWidget: null }),
+  resetSession: () => set({ ...empty }),
+}));