perf(P6B.T7): WebP thumbnails for image attachments (320px max, thumb-first render)

apps/desktop/src/lib/useConversationMessages.ts

@@ -16,6 +16,7 @@ import { bytesToPgHex, pgBytesToBytes } from '@chat-app/shared/supabase';
 import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
 
 import { decryptBatch as decryptBatchWorker } from './decryptWorker';
+import { generateWebPThumb } from './imageCompress';
 import {
   loadCachedMessages,
   persistMessages,
@@ -632,6 +633,12 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
           throw new Error('attachment exceeds max size (10 MB)');
         }
         const dims = await readImageDimensions(file);
+        // Phase 6B: generate a small WebP preview thumb so the receiver's
+        // bubble loads fast (typical 320×240 WebP is 10–30KB vs the full
+        // image's 1–10MB). `generateWebPThumb` short-circuits to null on
+        // non-images, animated formats, and small files — and on failure;
+        // the upload helper then just skips the second upload.
+        const thumbBlob = await generateWebPThumb(file);
         const res = await encryptAndUploadAttachment({
           client: supabase,
           conversationId,
@@ -640,6 +647,7 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
           sizeBytes: file.size,
           ...(dims.width !== undefined ? { width: dims.width } : {}),
           ...(dims.height !== undefined ? { height: dims.height } : {}),
+          ...(thumbBlob ? { thumbBlob } : {}),
         });
         // Stamp the view-once flag on each handle the caller requested it
         // for. The flag rides inside the encrypted payload (so peers can