refactor(web): 拆 lib/api.ts 789→109 barrel + lib/api/ 8域文件(纯搬移零逻辑)

- lib/api/{core,auth,chat,sessions,personas,admin,adminChannels,adminSystem}.ts
- api.ts 改纯 barrel 显式 re-export(export type for types, isolatedModules); 导出名 77→77, 36处导入点零改动
- 代码行多重集比对一致(仅 request/limitQuery 各加一 export 供兄弟模块); 每文件≤500/函数≤80
- 前端 build 绿(165 modules)

frontend/web/src/lib/api/sessions.ts

@@ -0,0 +1,86 @@
+import type { ChatMessage, Mode, SessionMeta } from "../types";
+import { request } from "./core";
+
+/** One chat message as returned by GET /api/v1/sessions/{id}/messages. Mirrors
+ *  the `chat_messages` row; `mode`/`mood`/`image`/`thinking` are optional. */
+export interface MessageDto {
+  id: string;
+  sessionId: string;
+  role: "user" | "assistant" | "system";
+  content: string;
+  mode?: Mode;
+  mood?: string;
+  image?: string;
+  thinking?: string;
+  /** Source-platform tag (design/16 §4.4): "web" or an IM channel platform. */
+  platform?: string;
+  /** Concrete client/device that produced the message (design/16 §4.5). */
+  deviceId?: string;
+  /** Sender display name of a third-party message (design/16 §4.6). Blank for the owner. */
+  senderName?: string;
+  createdAt: number;
+}
+
+/** Map a wire message into a display ChatMessage (carrying its sessionId). */
+function toChatMessage(m: MessageDto): ChatMessage {
+  return {
+    id: m.id,
+    sessionId: m.sessionId,
+    role: m.role,
+    content: m.content,
+    mode: m.mode,
+    mood: m.mood,
+    image: m.image,
+    thinking: m.thinking,
+    platform: m.platform,
+    deviceId: m.deviceId,
+    senderName: m.senderName,
+    createdAt: m.createdAt,
+  };
+}
+
+/** GET /api/v1/sessions — the main + secondary sessions for this web account. */
+export function fetchSessions(): Promise<SessionMeta[]> {
+  return request<SessionMeta[]>("/sessions");
+}
+
+/** POST /api/v1/sessions — creates a new secondary session. */
+export function createSubSession(title?: string): Promise<SessionMeta> {
+  return request<SessionMeta>("/sessions", {
+    method: "POST",
+    body: JSON.stringify(title ? { title } : {}),
+  });
+}
+
+/** GET /api/v1/sessions/{id}/messages?before=&limit=&platform= — hot-paginated
+ *  history, optionally filtered to one source platform (design/16 §4.4). The wire
+ *  returns newest-first, but callers render chronologically (oldest first), so we
+ *  reverse here: page 1 is the most recent `limit` messages in display order, and
+ *  `before` (the oldest message's createdAt) walks upward. The Web client omits
+ *  `platform` for the full shared main session; an IM adapter passes its own
+ *  platform to see only its lane. */
+export async function fetchMessages(
+  sessionId: string,
+  before?: number,
+  limit = 50,
+  platform?: string
+): Promise<ChatMessage[]> {
+  const qs = new URLSearchParams();
+  qs.set("limit", String(limit));
+  if (before !== undefined) qs.set("before", String(before));
+  if (platform) qs.set("platform", platform);
+  const list = await request<MessageDto[]>(
+    `/sessions/${encodeURIComponent(sessionId)}/messages?${qs.toString()}`
+  );
+  return list.map(toChatMessage).reverse();
+}
+
+/** DELETE /api/v1/sessions/{id} — removes a secondary session (and its messages). */
+export function deleteSession(
+  sessionId: string
+): Promise<{ id: string; deleted: true }> {
+  return request<{ id: string; deleted: true }>(
+    `/sessions/${encodeURIComponent(sessionId)}`,
+    { method: "DELETE" }
+  );
+}