feat(kol): add SSE streaming for prompt assist

- Extract assist runtime (prompt building, response parsing, finalize)
  from the worker into kol_assist_runtime so the sync streaming path
  and the async task path share the same logic.
- Add POST /kol/manage/assist/stream as a Server-Sent Events endpoint
  emitting start/delta/completed/error events, and wire it to a
  streamAssist helper on kolManageApi that reports ApiClientError with
  the server's error envelope.
- Stream generated content live in KolPromptEditor and KolGenerateView,
  switching KolPromptEditArea to a boolean aiBusy flag and refining the
  generator page layout.
- Add KolAssistStreamEvent to shared types.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/admin-web/src/lib/api.ts

@@ -1,4 +1,4 @@
-import { createApiClient } from "@geo/http-client";
+import { ApiClientError, createApiClient } from "@geo/http-client";
 import type {
   ApiEnvelope,
   ArticleDetail,
@@ -29,6 +29,7 @@ import type {
   KnowledgeTextItemRequest,
   KnowledgeURLItemRequest,
   KolAssistRequest,
+  KolAssistStreamEvent,
   KolAssistSubmitResponse,
   KolAssistTask,
   KolPackageSummary,
@@ -384,6 +385,27 @@ export const kolManageApi = {
       body,
     );
   },
+  streamAssist(
+    body: KolAssistRequest,
+    handlers: {
+      onEvent: (event: KolAssistStreamEvent) => void;
+      onClose?: () => void;
+    },
+    signal: AbortSignal,
+  ) {
+    return subscribeSSE<KolAssistStreamEvent>(
+      "/api/tenant/kol/manage/assist/stream",
+      {
+        method: "POST",
+        headers: {
+          "Content-Type": "application/json",
+        },
+        body: JSON.stringify(body),
+      },
+      handlers,
+      signal,
+    );
+  },
   getAssist(id: string) {
     return apiClient.get<KolAssistTask>(`/api/tenant/kol/manage/assist/${id}`);
   },
@@ -701,7 +723,7 @@ async function subscribeSSE<TEvent extends SSEEventShape>(
   });
 
   if (!response.ok) {
-    throw new Error(`stream request failed with status ${response.status}`);
+    throw await buildSSERequestError(response);
   }
   if (!response.body) {
     throw new Error("stream response body is empty");
@@ -730,6 +752,44 @@ async function subscribeSSE<TEvent extends SSEEventShape>(
   }
 }
 
+type SSEErrorEnvelope = {
+  code?: number;
+  message?: string;
+  detail?: string;
+  request_id?: string;
+};
+
+async function buildSSERequestError(response: Response): Promise<ApiClientError> {
+  try {
+    const payload = (await response.clone().json()) as SSEErrorEnvelope | null;
+    if (payload && typeof payload === "object" && !Array.isArray(payload)) {
+      return new ApiClientError({
+        message: payload.message ?? "unknown_error",
+        code: payload.code,
+        status: response.status,
+        detail: payload.detail,
+        requestId: payload.request_id,
+      });
+    }
+  } catch {
+    // Ignore JSON parse errors and fall back to a generic error below.
+  }
+
+  let detail: string | undefined;
+  try {
+    const text = (await response.text()).trim();
+    detail = text || undefined;
+  } catch {
+    detail = undefined;
+  }
+
+  return new ApiClientError({
+    message: "unknown_error",
+    status: response.status,
+    detail: detail ?? `stream request failed with status ${response.status}`,
+  });
+}
+
 export const brandsApi = {
   list() {
     return apiClient.get<Brand[]>("/api/tenant/brands");