feat(web): image and file message attachments (send + render)

- lib/api/upload.ts: POST /v0/file/u/ (docs/IM-前后端对接文档.md:460-461) --
  a separate surface from /v1/im/*, at the tenant's file base URL, auth'd
  with X-MeetingIM-Auth: token <token> rather than Authorization: Bearer
  (matches upstream Tinode's own LargeFileHelper convention).
- lib/tinode/attachments.ts: sendImage/sendFile. Files <= the inband limit
  go in directly as base64 (Drafty.insertImage's `bits` field / attachFile's
  `data` field) with no upload round trip; larger ones upload first and
  reference the returned URL. Simplified from the old app's urlPromise
  dance (optimistic local preview while the upload runs in the background)
  by just awaiting the upload before creating the message -- less
  optimistic, meaningfully simpler.
- AttachmentPreview.tsx: image/file bubble rendering. Externally-referenced
  (non-inline) attachments need an authenticated fetch into a blob URL,
  not a plain <img src>/<a href> -- GET /v0/file/s/{file_id} requires the
  same custom auth header uploads do, which a bare element can't attach.
- drafty.tsx: wired the 'IM'/'EX' Drafty style-tag cases to these.

Verified end to end: sent a real inline image (confirmed the exact IM
entity shape in the outgoing WS packet, and that the <img> decoded and
loaded from its own base64 data) and a real inline file (rendered with the
correct icon/size/download affordance).

Known gap: voice messages (MediaRecorder + AU entities) not built yet --
meaningfully more complex (hold-to-record gesture, audio encoding,
duration/waveform) and deliberately left for a following pass rather than
rushed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/lib/api/client.ts

@@ -113,7 +113,7 @@ export function currentTenantCode(): string {
 }
 
 /** Set by tinode-web.jsx-equivalent login/reconnect code; tab-lifetime, independent of "remember me". */
-function authToken(): string {
+export function authToken(): string {
   return sessionStorage.getItem('im-session-token') || '';
 }
 

web/src/lib/api/upload.ts

@@ -0,0 +1,50 @@
+// The file HTTP endpoint (docs/IM-前后端对接文档.md:62,460-461) is a SEPARATE surface from
+// /v1/im/* -- it lives at the tenant's `file` base URL, and authenticates with a different header
+// (`X-MeetingIM-Auth: token <token>`) than the REST API's `Authorization: Bearer`, matching
+// upstream Tinode's own LargeFileHelper convention. The token value is the same session token
+// either way, just carried differently.
+import { authToken, fileBase } from './client';
+
+export interface UploadedFile {
+  url: string;
+  name: string;
+  size: number;
+  mime: string;
+}
+
+export async function uploadFile(file: File, topic?: string): Promise<UploadedFile> {
+  const form = new FormData();
+  form.append('file', file);
+  if (topic) {
+    form.append('purpose', 'chat_file');
+    form.append('topic', topic);
+  }
+  const res = await fetch(`${fileBase()}/u/`, {
+    method: 'POST',
+    headers: { 'X-MeetingIM-Auth': `token ${authToken()}` },
+    body: form,
+  });
+  const text = await res.text();
+  let payload: { ctrl?: { code: number; text?: string; params?: UploadedFile } } = {};
+  try {
+    payload = JSON.parse(text);
+  } catch {
+    throw new Error('文件上传失败：服务器返回异常');
+  }
+  if (!res.ok || !payload.ctrl || payload.ctrl.code >= 300 || !payload.ctrl.params) {
+    throw new Error(payload.ctrl?.text || '文件上传失败');
+  }
+  return payload.ctrl.params;
+}
+
+/**
+ * Absolute download URL for a file reference returned by uploadFile() or a received attachment.
+ * The upload response's `url` (e.g. "/v0/file/s/file123") is already rooted at the tenant's file
+ * origin, not relative to fileBase() (which itself already ends in "/v0/file") -- so this strips
+ * fileBase() down to just its origin before appending, rather than concatenating the two paths.
+ */
+export function fileDownloadUrl(refUrl: string): string {
+  if (refUrl.startsWith('http')) return refUrl;
+  const origin = fileBase().replace(/\/v0\/file.*$/, '');
+  return `${origin}${refUrl}`;
+}

web/src/lib/messages/drafty.tsx

@@ -2,6 +2,8 @@ import { Fragment, type ReactNode } from 'react';
 
 import { Drafty, type DraftyContent } from 'tinode-sdk';
 
+import { FileAttachment, ImageAttachment } from '@/features/messages/AttachmentPreview';
+
 /**
  * Bubble content renderer for the Drafty style tags this app currently sends/receives. Grown
  * incrementally alongside composer features -- IM/VD/AU/QQ/TC/VC/BN/FM land when their respective
@@ -55,6 +57,10 @@ function formatNode(
         </a>
       );
     }
+    case 'IM':
+      return <ImageAttachment key={key} data={data || {}} />;
+    case 'EX':
+      return <FileAttachment key={key} data={data || {}} />;
     case 'QQ':
       // Drafty.quote() has no `key`/`data` of its own (tinode.dev.js:2160-2168) -- it's a plain style
       // span wrapping mention(header,uid) + linebreak + body, all already rendered into `children`.

web/src/lib/tinode/attachments.ts

@@ -0,0 +1,64 @@
+import { Drafty, type Topic } from 'tinode-sdk';
+
+import { uploadFile } from '@/lib/api/upload';
+import { MAX_INBAND_ATTACHMENT_SIZE } from '@/lib/config';
+
+function fileToBase64(file: File): Promise<string> {
+  return new Promise((resolve, reject) => {
+    const reader = new FileReader();
+    reader.onload = () => resolve((reader.result as string).split(',')[1] ?? '');
+    reader.onerror = () => reject(reader.error);
+    reader.readAsDataURL(file);
+  });
+}
+
+function imageDimensions(file: File): Promise<{ width: number; height: number }> {
+  return new Promise((resolve) => {
+    const url = URL.createObjectURL(file);
+    const img = new Image();
+    img.onload = () => {
+      resolve({ width: img.naturalWidth, height: img.naturalHeight });
+      URL.revokeObjectURL(url);
+    };
+    img.onerror = () => {
+      resolve({ width: 0, height: 0 });
+      URL.revokeObjectURL(url);
+    };
+    img.src = url;
+  });
+}
+
+/**
+ * Small files go inline as base64 (Drafty.insertImage's `bits` field) -- no upload round trip at
+ * all. Larger ones upload first, then reference the returned URL (`refurl`). Simplified from the
+ * old app's own urlPromise dance (which inserts an optimistic local preview immediately and lets
+ * the upload happen in the background): this awaits the upload before creating the message at all,
+ * trading that "shows immediately while uploading" nicety for meaningfully simpler code.
+ */
+export async function sendImage(topic: Topic, file: File): Promise<unknown> {
+  const { width, height } = await imageDimensions(file);
+  const content =
+    file.size <= MAX_INBAND_ATTACHMENT_SIZE
+      ? Drafty.insertImage(undefined, 0, { mime: file.type, bits: await fileToBase64(file), width, height, filename: file.name, size: file.size })
+      : Drafty.insertImage(undefined, 0, {
+          mime: file.type,
+          refurl: (await uploadFile(file, topic.name)).url,
+          width,
+          height,
+          filename: file.name,
+          size: file.size,
+        });
+  const msg = topic.createMessage(content, false);
+  msg.head = Object.assign(msg.head || {}, { 'x-im-type': 'image' });
+  return topic.publishDraft(msg, Promise.resolve());
+}
+
+export async function sendFile(topic: Topic, file: File): Promise<unknown> {
+  const content =
+    file.size <= MAX_INBAND_ATTACHMENT_SIZE
+      ? Drafty.attachFile(undefined, { mime: file.type, data: await fileToBase64(file), filename: file.name, size: file.size })
+      : Drafty.attachFile(undefined, { mime: file.type, refurl: (await uploadFile(file, topic.name)).url, filename: file.name, size: file.size });
+  const msg = topic.createMessage(content, false);
+  msg.head = Object.assign(msg.head || {}, { 'x-im-type': 'file' });
+  return topic.publishDraft(msg, Promise.resolve());
+}