Support comment updates and multipart post uploads

docs/FRONTEND_INTEGRATION.md

@@ -105,6 +105,8 @@ Supported filters:
   - `read`, `type`, `resourceType`, `sortOrder`
 - `GET /comments/post/:postId`
   - `page`, `limit`, `sortOrder`
+- `PATCH /comments/:commentId`
+  - JSON body: `content`, `mentionUsernames`
 
 ## WebSocket auth
 
@@ -171,6 +173,34 @@ Posts and comments support:
 
 The backend also extracts `@username` from `content` automatically and emits mention notifications for matched users.
 
+## Posts Upload Contract
+
+Post creation and updates now require `multipart/form-data` for all post payloads, including text-only posts and posts that use external media links.
+
+- `POST /posts`
+- `PATCH /posts/:postId`
+- `POST /posts/reels`
+
+Send media uploads as files:
+
+- `imageFiles`
+- `videoFile`
+- `audioFile`
+
+Send link-based fields as text fields inside the same form-data payload:
+
+- `imageUrls`
+- `videoUrl`
+- `audioUrl`
+- `thumbnailUrl`
+
+Array fields may be sent either as repeated form keys or JSON text:
+
+- `taggedUserIds`
+- `mentionUsernames`
+- `imageUrls`
+- `waveformPeaks`
+
 ## Marketplace split
 
 Marketplace is now separated from musical instruments at the API contract level: