feat(chat): stream and persist local answer UI with final report references

src/chat/answer-stream-projection.ts

@@ -0,0 +1,57 @@
+import type { UIMessageChunk } from "ai";
+
+/** Canonical parts are projected independently of an attached browser response. */
+export function createAnswerStreamProjection(options: {
+  messageId: string;
+  sessionId: string;
+  write: (chunk: UIMessageChunk) => void;
+  onChange: () => void;
+}) {
+  const parts: Record<string, unknown>[] = [];
+  let segment = 0;
+  let textId = "answer";
+  let currentText: Record<string, unknown> | undefined;
+  let finished = false;
+  const endText = () => {
+    if (!currentText) return;
+    currentText.state = "done";
+    options.write({ type: "text-end", id: textId });
+    currentText = undefined;
+    textId = `answer-${++segment}`;
+  };
+  const appendText = (delta: string) => {
+    if (!delta || finished) return;
+    if (!currentText) {
+      currentText = { type: "text", text: "", state: "streaming" };
+      parts.push(currentText);
+      options.write({ type: "text-start", id: textId });
+    }
+    currentText.text = `${String(currentText.text)}${delta}`;
+    options.write({ type: "text-delta", id: textId, delta });
+    options.write({ type: "data-stream_token", transient: true, data: {
+      session_id: options.sessionId, message_id: options.messageId, content: delta,
+    } } as UIMessageChunk);
+    options.onChange();
+  };
+  const appendData = (event: string, data: Record<string, unknown>) => {
+    if (finished) return;
+    if (event === "answer_ui") endText();
+    const type = `data-${event}`;
+    const id = [data.id, data.request_id, data.envelope_id, data.block_id].find((value): value is string => typeof value === "string");
+    const existing = id === undefined ? -1 : parts.findIndex((part) => part.type === type && part.id === id);
+    const part = id ? { type, id, data } : { type, data };
+    if (existing >= 0) parts[existing] = part;
+    else parts.push(part);
+    options.write(part as UIMessageChunk);
+    options.onChange();
+  };
+  const finish = (finishReason: "stop" | "error" = "stop") => {
+    if (finished) return;
+    if (!parts.length) appendText("Agent 已完成处理。");
+    endText();
+    finished = true;
+    options.onChange();
+    options.write({ type: "finish", finishReason });
+  };
+  return { parts, appendText, appendData, finish, get finished() { return finished; } };
+}