feat(web): RegisterPage avatar uses transferStore + waitForTransfer helper

Replaces the legacy /api/uploads call in RegisterPage with the tus-based
transferStore path. Extends Transfer to persist the server-assigned
filename (not just attachmentId) since downstream consumers store
attachment.filename on the user/space record.

- transferStore: rename setAttachmentId -> setAttachmentRef(id, attachmentId, filename)
  and add attachmentFilename field to Transfer
- both startUpload + resumeUpload onSuccess paths now record filename
- new utils/waitForTransfer.ts: waitForTransferAttachment(transferId)
  returns {attachmentId, filename}, with immediate-terminal handling
- RegisterPage: silent (tray:false) upload via transferStore, awaits
  the helper, passes the server filename to api.users.update

packages/web/src/components/auth/RegisterPage.tsx

@@ -7,6 +7,8 @@ import { AVATAR_GRADIENT_MAP } from '../../utils/gradients';
 import { AVATAR_COLORS } from '@backspace/shared';
 import type { AvatarColor, CheckInviteResponse, InstanceInfoResponse } from '@backspace/shared';
 import { api, RateLimitError } from '../../api/client';
+import { useTransferStore } from '../../stores/transferStore';
+import { waitForTransferAttachment } from '../../utils/waitForTransfer';
 
 // Single-source regex for extracting a bare invite token from a pasted full URL.
 // Token format: 22 chars base64url ([A-Za-z0-9_-]).
@@ -355,8 +357,9 @@ export function RegisterPage() {
       let finalUser = response.user;
       if (!skip && avatarFile) {
         try {
-          const attachment = await api.uploads.upload(avatarFile);
-          finalUser = await api.users.update({ avatar: attachment.filename });
+          const tid = await useTransferStore.getState().startUpload(avatarFile, { tray: false });
+          const { filename } = await waitForTransferAttachment(tid);
+          finalUser = await api.users.update({ avatar: filename });
         } catch {
           // Avatar upload failed — user can set it later in settings
         }

packages/web/src/stores/transferStore.test.ts

@@ -93,18 +93,19 @@ describe('transferStore basics', () => {
     expect(t.error).toEqual({ message: 'boom', permanent: true });
   });
 
-  it('setTusUrl + setAttachmentId stores the metadata', () => {
+  it('setTusUrl + setAttachmentRef stores the metadata', () => {
     const id = useTransferStore.getState().createTransfer({
       type: 'upload',
       file: { name: 'a', size: 1, mimetype: 'image/png' },
       tray: true,
     });
     useTransferStore.getState().setTusUrl(id, '/api/files/abc', 5_000);
-    useTransferStore.getState().setAttachmentId(id, 'att-9');
+    useTransferStore.getState().setAttachmentRef(id, 'att-9', 'server-name.png');
     const t = useTransferStore.getState().get(id)!;
     expect(t.tusUploadUrl).toBe('/api/files/abc');
     expect(t.tusExpiresAt).toBe(5_000);
     expect(t.attachmentId).toBe('att-9');
+    expect(t.attachmentFilename).toBe('server-name.png');
   });
 
   it('remove drops a transfer; idempotent on missing id', () => {

packages/web/src/stores/transferStore.ts

@@ -29,6 +29,7 @@ export interface Transfer {
   tusExpiresAt?: number;
   fileHandleId?: string;
   attachmentId?: string;
+  attachmentFilename?: string;
   uploaderUserId?: string;
 
   // Download-specific
@@ -59,7 +60,7 @@ interface TransferStoreActions {
   updateProgress: (id: string, loaded: number) => void;
   setError: (id: string, error: TransferError) => void;
   setTusUrl: (id: string, url: string, expiresAt: number) => void;
-  setAttachmentId: (id: string, attachmentId: string) => void;
+  setAttachmentRef: (id: string, attachmentId: string, filename: string) => void;
   remove: (id: string) => void;
 
   startUpload: (file: Blob, opts: { channelId?: string; tray?: boolean; origin?: string; fileHandleId?: string }) => Promise<string>;
@@ -181,11 +182,11 @@ export const useTransferStore = create<TransferStore>()(
         return { transfers: next };
       }),
 
-      setAttachmentId: (id, attachmentId) => set((s) => {
+      setAttachmentRef: (id, attachmentId, filename) => set((s) => {
         const t = s.transfers.get(id);
         if (!t) return s;
         const next = new Map(s.transfers);
-        next.set(id, { ...t, attachmentId });
+        next.set(id, { ...t, attachmentId, attachmentFilename: filename });
         return { transfers: next };
       }),
 
@@ -245,7 +246,7 @@ export const useTransferStore = create<TransferStore>()(
             try {
               const body = payload.lastResponse?.getBody?.() ?? '';
               const att = JSON.parse(body) as Attachment;
-              get().setAttachmentId(id, att.id);
+              get().setAttachmentRef(id, att.id, att.filename);
               get().setState_(id, 'completed');
               get().updateProgress(id, fileLike.size);
             } catch (e) {
@@ -346,7 +347,7 @@ export const useTransferStore = create<TransferStore>()(
             try {
               const body = payload.lastResponse?.getBody?.() ?? '';
               const att = JSON.parse(body) as Attachment;
-              get().setAttachmentId(id, att.id);
+              get().setAttachmentRef(id, att.id, att.filename);
               get().setState_(id, 'completed');
             } catch (e) {
               const msg = e instanceof Error ? e.message : 'Resume completed but parse failed';

packages/web/src/stores/transferStore.upload.test.ts

@@ -68,7 +68,7 @@ describe('transferStore.startUpload', () => {
     if (typeof localStorage !== 'undefined') localStorage.clear();
   });
 
-  it('drives a transfer through tus → completed with attachmentId', async () => {
+  it('drives a transfer through tus → completed with attachmentId + attachmentFilename', async () => {
     const file = new File([new Uint8Array(100)], 'a.png', { type: 'image/png' });
     const id = await useTransferStore.getState().startUpload(file, { channelId: 'ch-1', tray: true });
     expect(startMock).toHaveBeenCalledTimes(1);
@@ -76,6 +76,7 @@ describe('transferStore.startUpload', () => {
     expect(t).toBeDefined();
     expect(t!.state).toBe('completed');
     expect(t!.attachmentId).toBe('att-9');
+    expect(t!.attachmentFilename).toBe('a.png');
     expect(t!.tusUploadUrl).toBe('/api/files/abc-123');
     expect(t!.tusExpiresAt).toBeGreaterThan(Date.now());
   });

packages/web/src/utils/waitForTransfer.ts

@@ -0,0 +1,38 @@
+import { useTransferStore } from '../stores/transferStore';
+
+export interface TransferAttachmentRef {
+  attachmentId: string;
+  filename: string;
+}
+
+/**
+ * Wait for a transferStore upload to reach a terminal state.
+ * Resolves with the server-assigned attachmentId + filename on success.
+ * Rejects on failure or abort.
+ *
+ * Handles the already-terminal case synchronously (resolves/rejects immediately
+ * without subscribing) and unsubscribes after the first terminal observation.
+ */
+export function waitForTransferAttachment(transferId: string): Promise<TransferAttachmentRef> {
+  return new Promise<TransferAttachmentRef>((resolve, reject) => {
+    const check = (): boolean => {
+      const t = useTransferStore.getState().transfers.get(transferId);
+      if (!t) return false;
+      if (t.state === 'completed' && t.attachmentId && t.attachmentFilename) {
+        resolve({ attachmentId: t.attachmentId, filename: t.attachmentFilename });
+        return true;
+      }
+      if (t.state === 'failed' || t.state === 'aborted') {
+        reject(new Error(t.error?.message ?? 'Upload failed'));
+        return true;
+      }
+      return false;
+    };
+
+    if (check()) return;
+
+    const unsub = useTransferStore.subscribe(() => {
+      if (check()) unsub();
+    });
+  });
+}