diff --git a/static/js/chat.js b/static/js/chat.js
index 713d85322..d7b19dd85 100644
--- a/static/js/chat.js
+++ b/static/js/chat.js
@@ -292,6 +292,9 @@ import { wireArrowUpRecall, getLastUserMessageFromChatHistory } from './composer
 
     // If currently streaming, stop it
     if (isStreaming) {
+      if (fileHandlerModule.isUploading && fileHandlerModule.isUploading()) {
+        fileHandlerModule.cancelUpload && fileHandlerModule.cancelUpload();
+      }
       // Cancel server-side research if in progress
       const _cancelSid = sessionModule.getCurrentSessionId();
       if (_cancelSid && _researchingStreamIds.has(_cancelSid)) {
@@ -687,6 +690,15 @@ import { wireArrowUpRecall, getLastUserMessageFromChatHistory } from './composer
       } catch(e) {
         console.error('upload failed', e);
       }
+      if (_pendingAttachInfo && !ids.length && !(_pendingRegenAttachments && _pendingRegenAttachments.length)) {
+        if (_userMsgEl && _userMsgEl.parentNode) _userMsgEl.remove();
+        if (fileHandlerModule.wasLastUploadCancelled && !fileHandlerModule.wasLastUploadCancelled()) {
+          uiModule.showError && uiModule.showError('Upload failed. Attachment kept so you can retry.');
+        }
+        updateSubmitButton('idle', submitBtn);
+        _releaseSendFlag();
+        return;
+      }
 
       // Carry over the original message's file-ids on a regenerate so the new
       // send still references the same photos / docs (and picks up the user's
diff --git a/static/js/fileHandler.js b/static/js/fileHandler.js
index d59e8d601..529075bc7 100644
--- a/static/js/fileHandler.js
+++ b/static/js/fileHandler.js
@@ -15,6 +15,9 @@ let uploaded = [];
 let _lastUploadedMeta = [];
 let API_BASE = '';
 let _uploadSpinners = [];
+let _uploadAbortCtrl = null;
+let _uploading = false;
+let _lastUploadCancelled = false;
 const _previewUrls = new WeakMap();
 
 const MAX_FILES = 10;
@@ -130,6 +133,7 @@ function _createChip(f, idx) {
  * Remove a pending file by index
  */
 export function removePending(idx) {
+  if (_uploading) cancelUpload();
   _revokePreviewUrl(pendingFiles[idx]);
   pendingFiles.splice(idx, 1);
   renderAttachStrip();
@@ -140,6 +144,7 @@ export function removePending(idx) {
  */
 export async function uploadPending() {
   if (pendingFiles.length === 0) return [];
+  _lastUploadCancelled = false;
 
   // The message bubble is shown immediately, but the upload can take a moment —
   // dim the chips and overlay a whirlpool so it's clear the files are still
@@ -164,11 +169,19 @@ export async function uploadPending() {
 
   const fd = new FormData();
   pendingFiles.forEach(f => fd.append('files', f, f.name || 'paste.png'));
+  _uploadAbortCtrl = new AbortController();
+  _uploading = true;
+  const timeoutId = setTimeout(() => {
+    if (_uploadAbortCtrl && !_uploadAbortCtrl.signal.aborted) {
+      try { _uploadAbortCtrl.abort(); } catch (_) {}
+    }
+  }, 120000);
 
   try {
     const res = await fetch(`${API_BASE}/api/upload`, {
       method: 'POST',
-      body: fd
+      body: fd,
+      signal: _uploadAbortCtrl.signal,
     });
     if (!res.ok) {
       // Surface the failure instead of swallowing it. Previously a non-OK
@@ -193,7 +206,18 @@ export async function uploadPending() {
     // returned shape as `ids` for backward-compatibility with existing call sites.
     _lastUploadedMeta = uploaded;
     return uploaded.map(x => x.id);
+  } catch (e) {
+    if (e && e.name === 'AbortError') {
+      _lastUploadCancelled = true;
+      _showToast('Upload cancelled');
+      return [];
+    }
+    _showToast('Upload failed: ' + (e?.message || 'network error'));
+    return [];
   } finally {
+    clearTimeout(timeoutId);
+    _uploading = false;
+    _uploadAbortCtrl = null;
     _uploadSpinners.forEach(sp => { try { sp.stop && sp.stop(); } catch (_) {} });
     _uploadSpinners = [];
     if (strip) strip.classList.remove('attach-uploading');
@@ -266,6 +290,7 @@ export function getPendingInfo() {
  * Clear all pending files
  */
 export function clearPending() {
+  if (_uploading) cancelUpload();
   pendingFiles.forEach(_revokePreviewUrl);
   pendingFiles = [];
   renderAttachStrip();
@@ -276,6 +301,21 @@ export function getLastUploadedMeta() {
   return _lastUploadedMeta;
 }
 
+export function isUploading() {
+  return _uploading;
+}
+
+export function wasLastUploadCancelled() {
+  return _lastUploadCancelled;
+}
+
+export function cancelUpload() {
+  _lastUploadCancelled = true;
+  if (_uploadAbortCtrl && !_uploadAbortCtrl.signal.aborted) {
+    try { _uploadAbortCtrl.abort(); } catch (_) {}
+  }
+}
+
 var escapeHtml = uiModule.esc;
 
 const fileHandlerModule = {
@@ -290,6 +330,9 @@ const fileHandlerModule = {
   getPendingRaw,
   clearPending,
   getLastUploadedMeta,
+  isUploading,
+  wasLastUploadCancelled,
+  cancelUpload,
 };
 
 export default fileHandlerModule;