fix(web): hide stale upload error banner when previewing other files (#994)

The upload-failure banner in FileWorkspace renders unconditionally inside
ws-body, so a failed upload's error message stayed pinned above any file
the user opened next. The banner is information about the Design Files
upload surface, not the active file viewer; once the user clicks an
existing file in the list, the message becomes unrelated stale state.

Scope the banner to activeTab === DESIGN_FILES_TAB so previewing any
file hides it. The error stays in state, so returning to the Design
Files tab brings it back: the failed upload is still unaddressed and we
do not want to silently drop that signal entirely.

Co-authored-by: Nagendhra <nagendhra405@gmail.com>

apps/web/src/components/FileWorkspace.tsx

@@ -621,7 +621,28 @@ export function FileWorkspace({
         ) : null}
       </div>
       <div className="ws-body">
-        {uploadError ? <div className="viewer-empty">{uploadError}</div> : null}
+        {/* Keep the failure banner visible across tab switches so the
+            partial-success case (some files succeed and auto-open while
+            others fail) doesn't silently drop the failure signal. The
+            banner now carries an explicit dismiss button so the user
+            can clear the stale message themselves, which is what #786
+            was really asking for: a way to drop the message rather than
+            have it pinned above an unrelated file preview forever. The
+            next upload also clears it via setUploadError(null) at the
+            top of uploadFiles(). */}
+        {uploadError ? (
+          <div className="viewer-empty viewer-empty-dismissible">
+            <span>{uploadError}</span>
+            <button
+              type="button"
+              className="ghost"
+              aria-label={t('common.close')}
+              onClick={() => setUploadError(null)}
+            >
+              {t('common.close')}
+            </button>
+          </div>
+        ) : null}
         {activeTab === DESIGN_FILES_TAB ? (
           <DesignFilesPanel
             key={projectId}

apps/web/src/index.css

@@ -8692,6 +8692,17 @@ button.ghost.mcp-copy-btn:hover:not(:disabled) {
   color: var(--text-muted);
   font-size: 13px;
 }
+/* Compact horizontal variant for the upload-failure banner: the message
+   sits inline next to a dismiss button so the user can clear the stale
+   notice without changing tabs. Issue #786. */
+.viewer-empty.viewer-empty-dismissible {
+  padding: 12px 16px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: 12px;
+  text-align: left;
+}
 .document-preview {
   max-width: 860px;
   margin: 0 auto;