Fix the issue where the sender and receiver (without requesting existing files) have inconsistent states in resumeable file transfer with broken connections

frontend/lib/fileReceiver.ts

@@ -15,6 +15,7 @@ import {
   FileHandlers,
   FileMeta,
   FileRequest,
+  FolderComplete,
 } from "@/types/webrtc";
 
 /**
@@ -255,6 +256,24 @@ class FileReceiver {
       }
     }
     this.currentFolderName = null;
+
+    // After the loop, the receiver has requested all necessary files.
+    // Send a completion message to the sender to sync the final state.
+    const folderComplete: FolderComplete = {
+      type: "FolderComplete",
+      folderName: folderName,
+    };
+
+    if (this.peerId) {
+      this.webrtcConnection.sendData(
+        JSON.stringify(folderComplete),
+        this.peerId
+      );
+      this.log(
+        "log",
+        `Sent folderComplete message for ${folderName} to peer ${this.peerId}`
+      );
+    }
   }
   // endregion
 

frontend/lib/fileSender.ts

@@ -12,7 +12,9 @@ import {
   WebRTCMessage,
   PeerState,
   FolderMeta,
+  FileAck,
   FileRequest,
+  FolderComplete,
 } from "@/types/webrtc";
 
 class FileSender {
@@ -97,9 +99,21 @@ class FileSender {
       case "fileAck":
         peerState.isSending = false;
         this.log("log", `Received file-finish ack from peer ${peerId}`, {
-          fileId: (message as any).fileId,
+          fileId: (message as FileAck).fileId,
         });
         break;
+      case "folderComplete":
+        const folderName = (message as FolderComplete).folderName;
+        this.log(
+          "log",
+          `Received folderComplete message for ${folderName} from peer ${peerId}`
+        );
+        // The receiver has confirmed the folder is complete.
+        // Force the progress to 100% for the sender's UI.
+        if (this.pendingFolerMeta[folderName]) {
+          peerState.progressCallback?.(folderName, 1, 0);
+        }
+        break;
       default:
         this.log("warn", `Unknown signaling message type received`, {
           type: message.type,
@@ -295,7 +309,7 @@ class FileSender {
       // This is more robust and correct for resumed transfers.
       let folderTotalSent = 0;
       if (folderMeta) {
-        folderMeta.fileIds.forEach(fId => {
+        folderMeta.fileIds.forEach((fId) => {
           folderTotalSent += peerState.totalBytesSent[fId] || 0;
         });
       }

frontend/types/webrtc.ts

@@ -51,13 +51,19 @@ export interface FileEnd {
   fileId: string;
 }
 
+export interface FolderComplete {
+  type: "FolderComplete";
+  folderName: string;
+}
+
 export type WebRTCMessage =
   | fileMetadata
   | FileRequest
   | FileAck
   | StringMetadata
   | StringChunk
-  | FileEnd;
+  | FileEnd
+  | FolderComplete;
 
 export interface FolderMeta {
   totalSize: number;