diff --git a/packages/ui/src/components/layout/SidebarFilesTree.tsx b/packages/ui/src/components/layout/SidebarFilesTree.tsx
index 2736e675..8d56c831 100644
--- a/packages/ui/src/components/layout/SidebarFilesTree.tsx
+++ b/packages/ui/src/components/layout/SidebarFilesTree.tsx
@@ -43,6 +43,7 @@ import { opencodeClient } from '@/lib/opencode/client';
 import { FileTypeIcon } from '@/components/icons/FileTypeIcon';
 import { Icon } from "@/components/icon/Icon";
 import { getContextFileOpenFailureMessage, validateContextFileOpen } from '@/lib/contextFileOpenGuard';
+import { isFilesystemError } from '@/lib/api/files-errors';
 import { isBrowserClientRuntime } from '@/lib/desktop';
 import { useI18n } from '@/lib/i18n';
 
@@ -54,6 +55,40 @@ type FileNode = {
   relativePath?: string;
 };
 
+type UploadConflicts = {
+  directory: string;
+  files: File[];
+  runtimeKey: string;
+  workspaceRoot: string;
+};
+
+type UploadOutcome = 'uploaded' | 'conflict' | 'failed';
+
+const MAX_PARALLEL_UPLOADS = 3;
+
+const hasExternalFiles = (dataTransfer: DataTransfer): boolean => (
+  Array.from(dataTransfer.types).includes('Files')
+);
+
+const getExternalFiles = (dataTransfer: DataTransfer): File[] => {
+  const items = Array.from(dataTransfer.items);
+  if (items.length === 0) return Array.from(dataTransfer.files);
+
+  return items.flatMap((item) => {
+    if (item.kind !== 'file' || item.webkitGetAsEntry()?.isDirectory) return [];
+    const file = item.getAsFile();
+    return file ? [file] : [];
+  });
+};
+
+const getUploadName = (file: File): string | null => {
+  const name = file.name;
+  if (!name || name === '.' || name === '..' || name.includes('/') || name.includes('\\')) {
+    return null;
+  }
+  return name;
+};
+
 const sortNodes = (items: FileNode[]) =>
   items.slice().sort((a, b) => {
     if (a.type !== b.type) {
@@ -93,6 +128,22 @@ const getRelativePath = (root: string, path: string): string => {
   return normalizedPath.slice(normalizedRoot.length + 1);
 };
 
+const getDropTargetLabel = (root: string, target: string): string => {
+  const relativePath = getRelativePath(root, target);
+  if (relativePath !== '.') return relativePath;
+
+  const normalizedRoot = normalizePath(root);
+  return normalizedRoot.split('/').filter(Boolean).pop() ?? normalizedRoot;
+};
+
+const getParentPath = (value: string): string => {
+  const normalized = normalizePath(value);
+  const separatorIndex = normalized.lastIndexOf('/');
+  if (separatorIndex < 0) return '';
+  if (separatorIndex === 0) return '/';
+  return normalized.slice(0, separatorIndex);
+};
+
 const isAbsolutePath = (value: string): boolean => {
   return value.startsWith('/') || value.startsWith('//') || /^[A-Za-z]:\//.test(value);
 };
@@ -194,6 +245,8 @@ interface FileRowProps {
   isBrowserClient: boolean;
   status?: FileStatus | null;
   badge?: { modified: number; added: number } | null;
+  isDropTarget: boolean;
+  canUpload: boolean;
   permissions: {
     canRename: boolean;
     canCreateFile: boolean;
@@ -206,6 +259,8 @@ interface FileRowProps {
   onToggle: (path: string) => void;
   onRevealPath: (path: string) => void;
   onOpenDialog: (type: 'createFile' | 'createFolder' | 'rename' | 'delete', data: { path: string; name?: string; type?: 'file' | 'directory' }) => void;
+  onSetDropTarget: (path: string | null) => void;
+  onDropFiles: (directory: string, dataTransfer: DataTransfer) => void;
 }
 
 const FileRow: React.FC<FileRowProps> = ({
@@ -216,15 +271,20 @@ const FileRow: React.FC<FileRowProps> = ({
   isBrowserClient,
   status,
   badge,
+  isDropTarget,
+  canUpload,
   permissions,
   downloadFile,
   onSelect,
   onToggle,
   onRevealPath,
   onOpenDialog,
+  onSetDropTarget,
+  onDropFiles,
 }) => {
   const { t } = useI18n();
   const isDir = node.type === 'directory';
+  const uploadDirectory = isDir ? node.path : getParentPath(node.path);
   const { canRename, canCreateFile, canCreateFolder, canDelete, canReveal } = permissions;
   const canDownload = !isDir && Boolean(downloadFile);
   const canRevealPath = canReveal && !isBrowserClient;
@@ -333,9 +393,40 @@ const FileRow: React.FC<FileRowProps> = ({
     e.dataTransfer.effectAllowed = 'copy';
   }, [node.path, root]);
 
+  const handleExternalDragOver = React.useCallback((event: React.DragEvent) => {
+    if (!canUpload || !uploadDirectory || !hasExternalFiles(event.dataTransfer)) return;
+    event.preventDefault();
+    event.stopPropagation();
+    event.dataTransfer.dropEffect = 'copy';
+    onSetDropTarget(uploadDirectory);
+  }, [canUpload, onSetDropTarget, uploadDirectory]);
+
+  const handleExternalDragLeave = React.useCallback((event: React.DragEvent) => {
+    if (!canUpload || !uploadDirectory || !hasExternalFiles(event.dataTransfer)) return;
+    if (event.relatedTarget instanceof Node && event.currentTarget.contains(event.relatedTarget)) return;
+    event.stopPropagation();
+    onSetDropTarget(null);
+  }, [canUpload, onSetDropTarget, uploadDirectory]);
+
+  const handleExternalDrop = React.useCallback((event: React.DragEvent) => {
+    if (!canUpload || !uploadDirectory || !hasExternalFiles(event.dataTransfer)) return;
+    event.preventDefault();
+    event.stopPropagation();
+    onDropFiles(uploadDirectory, event.dataTransfer);
+  }, [canUpload, onDropFiles, uploadDirectory]);
+
   return (
     <ContextMenu open={rightClickOpen} onOpenChange={setRightClickOpen}>
-      <ContextMenuTrigger render={<div className="group relative flex items-center" onContextMenu={handleContextMenu} />}>
+      <ContextMenuTrigger render={(
+        <div
+          className="group relative flex items-center"
+          onContextMenu={handleContextMenu}
+          onDragEnter={handleExternalDragOver}
+          onDragOver={handleExternalDragOver}
+          onDragLeave={handleExternalDragLeave}
+          onDrop={handleExternalDrop}
+        />
+      )}>
       <button
         type="button"
         onClick={handleInteraction}
@@ -344,7 +435,9 @@ const FileRow: React.FC<FileRowProps> = ({
         onDragStart={handleDragStart}
         className={cn(
           'flex w-full items-center gap-1.5 rounded-md px-2 py-1 text-left text-foreground transition-colors pr-8 select-none',
-          isActive ? 'bg-interactive-selection/70' : 'hover:bg-interactive-hover/40',
+          isDropTarget
+            ? 'bg-interactive-selection ring-2 ring-inset ring-primary'
+            : (isActive ? 'bg-interactive-selection/70' : 'hover:bg-interactive-hover/40'),
           'cursor-grab active:cursor-grabbing'
         )}
       >
@@ -415,12 +508,16 @@ const areFileRowPropsEqual = (prev: FileRowProps, next: FileRowProps): boolean =
   && prev.isBrowserClient === next.isBrowserClient
   && prev.status === next.status
   && prev.badge === next.badge
+  && prev.isDropTarget === next.isDropTarget
+  && prev.canUpload === next.canUpload
   && prev.permissions === next.permissions
   && prev.downloadFile === next.downloadFile
   && prev.onSelect === next.onSelect
   && prev.onToggle === next.onToggle
   && prev.onRevealPath === next.onRevealPath
   && prev.onOpenDialog === next.onOpenDialog
+  && prev.onSetDropTarget === next.onSetDropTarget
+  && prev.onDropFiles === next.onDropFiles
 );
 
 const MemoizedFileRow = React.memo(FileRow, areFileRowPropsEqual);
@@ -444,6 +541,12 @@ export const SidebarFilesTree: React.FC = () => {
   const searchInputRef = React.useRef<HTMLInputElement>(null);
   const [searchResults, setSearchResults] = React.useState<FileNode[]>([]);
   const [searching, setSearching] = React.useState(false);
+  const [dropTarget, setDropTarget] = React.useState<string | null>(null);
+  const [isUploading, setIsUploading] = React.useState(false);
+  const [uploadConflicts, setUploadConflicts] = React.useState<UploadConflicts | null>(null);
+  const uploadingRef = React.useRef(false);
+  const rootRef = React.useRef(root);
+  rootRef.current = root;
 
   const [childrenByDir, setChildrenByDir] = React.useState<Record<string, FileNode[]>>({});
   const [loadErrorsByDir, setLoadErrorsByDir] = React.useState<Record<string, string>>({});
@@ -457,6 +560,8 @@ export const SidebarFilesTree: React.FC = () => {
   // combining the two means the tree re-paints with cached data instead
   // of blanking out and re-listing every directory.
   React.useEffect(() => {
+    setDropTarget(null);
+    setUploadConflicts(null);
     if (!root) {
       setChildrenByDir({});
       setLoadErrorsByDir({});
@@ -544,6 +649,7 @@ export const SidebarFilesTree: React.FC = () => {
   const canRename = Boolean(files.rename);
   const canDelete = Boolean(files.delete);
   const canReveal = Boolean(files.revealPath);
+  const canUpload = Boolean(files.uploadFile);
 
   const fileRowPermissions = React.useMemo(
     () => ({ canRename, canCreateFile, canCreateFolder, canDelete, canReveal }),
@@ -897,6 +1003,101 @@ export const SidebarFilesTree: React.FC = () => {
     }
   }, [loadDirectory, root, toggleExpandedPath]);
 
+  const uploadDroppedFiles = React.useCallback(async (
+    directory: string,
+    droppedFiles: File[],
+    overwrite = false,
+  ) => {
+    const uploadFile = files.uploadFile;
+    if (!uploadFile || droppedFiles.length === 0 || uploadingRef.current || !root) return;
+
+    const operationRoot = root;
+    const operationRuntime = getRuntimeKey();
+    uploadingRef.current = true;
+    setIsUploading(true);
+    setDropTarget(directory);
+    if (overwrite) setUploadConflicts(null);
+
+    const outcomes: UploadOutcome[] = [];
+    for (let index = 0; index < droppedFiles.length; index += MAX_PARALLEL_UPLOADS) {
+      const batch = droppedFiles.slice(index, index + MAX_PARALLEL_UPLOADS);
+      const batchOutcomes = await Promise.all(batch.map(async (file): Promise<UploadOutcome> => {
+        const name = getUploadName(file);
+        if (!name || getRuntimeKey() !== operationRuntime) return 'failed';
+
+        try {
+          const result = await uploadFile(normalizePath(`${directory}/${name}`), file, {
+            directory: operationRoot,
+            overwrite,
+          });
+          return result.success ? 'uploaded' : 'failed';
+        } catch (error) {
+          if (!overwrite && isFilesystemError(error) && error.reason === 'already-exists') {
+            return 'conflict';
+          }
+          return 'failed';
+        }
+      }));
+      outcomes.push(...batchOutcomes);
+    }
+
+    const uploadedCount = outcomes.filter((outcome) => outcome === 'uploaded').length;
+    const failedCount = outcomes.filter((outcome) => outcome === 'failed').length;
+    const conflictingFiles = droppedFiles.filter((_, index) => outcomes[index] === 'conflict');
+    const isCurrentDestination = rootRef.current === operationRoot && getRuntimeKey() === operationRuntime;
+
+    try {
+      if (uploadedCount > 0 && isCurrentDestination) {
+        await refreshDirectory(directory);
+      }
+      if (uploadedCount > 0) {
+        toast.success(t(conflictingFiles.length > 0
+          ? 'sidebarFilesTree.toast.uploadedWithoutConflicts'
+          : 'sidebarFilesTree.toast.uploaded'));
+      }
+      if (failedCount > 0) {
+        toast.error(t('sidebarFilesTree.toast.uploadFailed'));
+      }
+      if (conflictingFiles.length > 0 && isCurrentDestination) {
+        setUploadConflicts({
+          directory,
+          files: conflictingFiles,
+          runtimeKey: operationRuntime,
+          workspaceRoot: operationRoot,
+        });
+      }
+    } finally {
+      uploadingRef.current = false;
+      setIsUploading(false);
+      setDropTarget(null);
+    }
+  }, [files.uploadFile, refreshDirectory, root, t]);
+
+  const handleDropFiles = React.useCallback((directory: string, dataTransfer: DataTransfer) => {
+    const droppedFiles = getExternalFiles(dataTransfer);
+    if (droppedFiles.length === 0) return;
+    void uploadDroppedFiles(directory, droppedFiles);
+  }, [uploadDroppedFiles]);
+
+  const handleRootDragOver = React.useCallback((event: React.DragEvent) => {
+    if (!canUpload || uploadingRef.current || !root || !hasExternalFiles(event.dataTransfer)) return;
+    event.preventDefault();
+    event.dataTransfer.dropEffect = 'copy';
+    setDropTarget(root);
+  }, [canUpload, root]);
+
+  const handleRootDragLeave = React.useCallback((event: React.DragEvent) => {
+    if (!hasExternalFiles(event.dataTransfer)) return;
+    if (event.relatedTarget instanceof Node && event.currentTarget.contains(event.relatedTarget)) return;
+    setDropTarget(null);
+  }, []);
+
+  const handleRootDrop = React.useCallback((event: React.DragEvent) => {
+    if (!canUpload || uploadingRef.current || !root || !hasExternalFiles(event.dataTransfer)) return;
+    event.preventDefault();
+    handleDropFiles(root, event.dataTransfer);
+  }, [canUpload, handleDropFiles, root]);
+
   // --- Dialog submit (matching FilesView) ---
 
   const handleDialogSubmit = React.useCallback(async (e?: React.FormEvent) => {
@@ -1056,12 +1257,16 @@ export const SidebarFilesTree: React.FC = () => {
             isBrowserClient={isBrowserClient}
             status={!isDir ? getFileStatus(node.path) : undefined}
             badge={isDir ? getFolderBadge(node.path) : undefined}
+            isDropTarget={isDir && dropTarget === node.path}
+            canUpload={canUpload && !isUploading}
             permissions={fileRowPermissions}
             downloadFile={files.downloadFile}
             onSelect={handleOpenFile}
             onToggle={toggleDirectory}
             onRevealPath={handleRevealPath}
             onOpenDialog={handleOpenDialog}
+            onSetDropTarget={setDropTarget}
+            onDropFiles={handleDropFiles}
           />
           {isDir && isExpanded && (
             <ul className="flex flex-col gap-1 ml-3 pl-3 border-l border-border/40 relative">
@@ -1084,6 +1289,7 @@ export const SidebarFilesTree: React.FC = () => {
 
   const hasTree = Boolean(root && childrenByDir[root]);
   const rootLoadError = root ? loadErrorsByDir[root] : null;
+  const dropTargetLabel = dropTarget ? getDropTargetLabel(root, dropTarget) : '';
 
   return (
     <section className="flex h-full min-h-0 flex-col overflow-hidden">
@@ -1182,7 +1388,15 @@ export const SidebarFilesTree: React.FC = () => {
         </div>
       </div>
 
-      <ScrollableOverlay outerClassName="flex-1 min-h-0" className="p-2">
+      <div className="relative flex-1 min-h-0">
+        <ScrollableOverlay
+          outerClassName="h-full min-h-0"
+          className={cn('p-2', dropTarget === root && 'bg-interactive-selection/10')}
+          onDragEnter={handleRootDragOver}
+          onDragOver={handleRootDragOver}
+          onDragLeave={handleRootDragLeave}
+          onDrop={handleRootDrop}
+        >
         <ul className="flex flex-col">
           {searching ? (
             <li className="flex items-center gap-1.5 px-2 py-1 typography-meta text-muted-foreground">
@@ -1235,7 +1449,52 @@ export const SidebarFilesTree: React.FC = () => {
             <li className="px-2 py-1 typography-meta text-muted-foreground">{t('sidebarFilesTree.state.loading')}</li>
           )}
         </ul>
-      </ScrollableOverlay>
+        </ScrollableOverlay>
+        {dropTarget ? (
+          <div className="pointer-events-none absolute left-2 right-2 top-2 z-50 flex items-center gap-2 rounded-md border border-primary bg-background/95 px-2 py-1.5 shadow-sm">
+            <Icon name={isUploading ? 'loader-4' : 'folder-received'} className={cn('size-4 flex-shrink-0', isUploading && 'animate-spin')} />
+            <span className="min-w-0 truncate typography-meta" title={dropTargetLabel}>
+              {t(isUploading ? 'sidebarFilesTree.drop.uploading' : 'sidebarFilesTree.drop.target', { path: dropTargetLabel })}
+            </span>
+          </div>
+        ) : null}
+      </div>
+
+      <Dialog open={Boolean(uploadConflicts)} onOpenChange={(open: boolean) => !open && setUploadConflicts(null)}>
+        <DialogContent>
+          <DialogHeader>
+            <DialogTitle>{t('sidebarFilesTree.dialog.uploadConflicts.title')}</DialogTitle>
+            <DialogDescription>
+              {t('sidebarFilesTree.dialog.uploadConflicts.description', { path: uploadConflicts?.directory ?? '' })}
+            </DialogDescription>
+          </DialogHeader>
+          <ScrollableOverlay outerClassName="max-h-52" className="flex flex-col gap-1 pr-2">
+            {uploadConflicts?.files.map((file, index) => (
+              <div key={`${file.name}-${file.size}-${index}`} className="truncate rounded-md bg-muted px-2 py-1 typography-meta" title={file.name}>
+                {file.name}
+              </div>
+            ))}
+          </ScrollableOverlay>
+          <DialogFooter>
+            <Button variant="outline" onClick={() => setUploadConflicts(null)} disabled={isUploading}>
+              {t('sidebarFilesTree.dialog.cancel')}
+            </Button>
+            <Button
+              onClick={() => {
+                if (!uploadConflicts) return;
+                if (uploadConflicts.runtimeKey !== getRuntimeKey() || uploadConflicts.workspaceRoot !== root) {
+                  setUploadConflicts(null);
+                  return;
+                }
+                void uploadDroppedFiles(uploadConflicts.directory, uploadConflicts.files, true);
+              }}
+              disabled={isUploading}
+            >
+              {t('sidebarFilesTree.dialog.uploadConflicts.replace')}
+            </Button>
+          </DialogFooter>
+        </DialogContent>
+      </Dialog>
 
       {/* CRUD dialogs (matching FilesView) */}
       <Dialog open={!!activeDialog} onOpenChange={(open) => !open && setActiveDialog(null)}>
diff --git a/packages/ui/src/lib/api/files-errors.test.ts b/packages/ui/src/lib/api/files-errors.test.ts
index 6d54d837..7c5ca4ec 100644
--- a/packages/ui/src/lib/api/files-errors.test.ts
+++ b/packages/ui/src/lib/api/files-errors.test.ts
@@ -25,4 +25,9 @@ describe('FilesystemError', () => {
     expect(parseFilesystemErrorReason('made-up')).toBe('unknown');
     expect(parseFilesystemErrorReason(undefined)).toBe('unknown');
   });
+
+  test('recognizes filesystem errors created across runtime boundaries', () => {
+    expect(isFilesystemError({ reason: 'already-exists' })).toBe(true);
+    expect(isFilesystemError({ reason: 409 })).toBe(false);
+  });
 });
diff --git a/packages/ui/src/lib/api/files-errors.ts b/packages/ui/src/lib/api/files-errors.ts
index bdac478a..7daee473 100644
--- a/packages/ui/src/lib/api/files-errors.ts
+++ b/packages/ui/src/lib/api/files-errors.ts
@@ -1,5 +1,6 @@
 export type FilesystemErrorReason =
   | 'os-permission'
+  | 'already-exists'
   | 'not-found'
   | 'not-directory'
   | 'invalid-response'
@@ -30,6 +31,7 @@ export const isFilesystemError = (error: unknown): error is FilesystemError => (
 export const parseFilesystemErrorReason = (value: unknown): FilesystemErrorReason => {
   switch (value) {
     case 'os-permission':
+    case 'already-exists':
     case 'not-found':
     case 'not-directory':
     case 'invalid-response':
diff --git a/packages/ui/src/lib/api/types.ts b/packages/ui/src/lib/api/types.ts
index 0a146327..58f126cb 100644
--- a/packages/ui/src/lib/api/types.ts
+++ b/packages/ui/src/lib/api/types.ts
@@ -606,6 +606,7 @@ export interface FilesAPI {
   readFile?(path: string, options?: FileReadOptions): Promise<{ content: string; path: string }>;
   readFileBinary?(path: string, options?: FileReadOptions): Promise<{ dataUrl: string; path: string }>;
   writeFile?(path: string, content: string): Promise<{ success: boolean; path: string }>;
+  uploadFile?(path: string, file: Blob, options?: { overwrite?: boolean; directory?: string }): Promise<{ success: boolean; path: string }>;
   delete?(path: string): Promise<{ success: boolean }>;
   rename?(oldPath: string, newPath: string): Promise<{ success: boolean; path: string }>;
   revealPath?(path: string): Promise<{ success: boolean }>;
diff --git a/packages/ui/src/lib/i18n/messages/de.ts b/packages/ui/src/lib/i18n/messages/de.ts
index 21b72195..125994af 100644
--- a/packages/ui/src/lib/i18n/messages/de.ts
+++ b/packages/ui/src/lib/i18n/messages/de.ts
@@ -1172,6 +1172,14 @@ export const dict = {
   'sidebarFilesTree.toast.writeNotSupported': 'Schreiben nicht unterstützt',
   'sidebarFilesTree.toast.fileCreated': 'Datei erstellt',
   'sidebarFilesTree.toast.operationFailed': 'Operation fehlgeschlagen',
+  'sidebarFilesTree.toast.uploaded': 'Dateien hochgeladen',
+  'sidebarFilesTree.toast.uploadedWithoutConflicts': 'Dateien ohne Konflikte wurden hochgeladen',
+  'sidebarFilesTree.toast.uploadFailed': 'Einige Dateien konnten nicht hochgeladen werden',
+  'sidebarFilesTree.drop.target': 'In {path} hochladen',
+  'sidebarFilesTree.drop.uploading': 'Dateien werden in {path} hochgeladen',
+  'sidebarFilesTree.dialog.uploadConflicts.title': 'Vorhandene Dateien ersetzen?',
+  'sidebarFilesTree.dialog.uploadConflicts.description': 'Dateien mit diesen Namen sind in {path} bereits vorhanden. Das Ersetzen kann nicht rückgängig gemacht werden.',
+  'sidebarFilesTree.dialog.uploadConflicts.replace': 'Ersetzen',
   'sidebarFilesTree.toast.folderNameRequired': 'Ordnername ist erforderlich',
   'sidebarFilesTree.toast.folderCreated': 'Ordner erstellt',
   'sidebarFilesTree.toast.nameRequired': 'Name ist erforderlich',
diff --git a/packages/ui/src/lib/i18n/messages/en.ts b/packages/ui/src/lib/i18n/messages/en.ts
index eb82405d..41d8bfab 100644
--- a/packages/ui/src/lib/i18n/messages/en.ts
+++ b/packages/ui/src/lib/i18n/messages/en.ts
@@ -1322,6 +1322,14 @@ export const dict = {
   'sidebarFilesTree.toast.writeNotSupported': 'Write not supported',
   'sidebarFilesTree.toast.fileCreated': 'File created',
   'sidebarFilesTree.toast.operationFailed': 'Operation failed',
+  'sidebarFilesTree.toast.uploaded': 'Files uploaded',
+  'sidebarFilesTree.toast.uploadedWithoutConflicts': 'Files without conflicts were uploaded',
+  'sidebarFilesTree.toast.uploadFailed': 'Some files could not be uploaded',
+  'sidebarFilesTree.drop.target': 'Upload to {path}',
+  'sidebarFilesTree.drop.uploading': 'Uploading files to {path}',
+  'sidebarFilesTree.dialog.uploadConflicts.title': 'Replace existing files?',
+  'sidebarFilesTree.dialog.uploadConflicts.description': 'Files with these names already exist in {path}. Replacing them cannot be undone.',
+  'sidebarFilesTree.dialog.uploadConflicts.replace': 'Replace',
   'sidebarFilesTree.toast.folderNameRequired': 'Folder name is required',
   'sidebarFilesTree.toast.folderCreated': 'Folder created',
   'sidebarFilesTree.toast.nameRequired': 'Name is required',
diff --git a/packages/ui/src/lib/i18n/messages/es.ts b/packages/ui/src/lib/i18n/messages/es.ts
index 0aa85137..3c7aebb1 100644
--- a/packages/ui/src/lib/i18n/messages/es.ts
+++ b/packages/ui/src/lib/i18n/messages/es.ts
@@ -1288,6 +1288,14 @@ export const dict: Record<I18nKey, string> = {
   "sidebarFilesTree.toast.writeNotSupported": "La escritura no es compatible",
   "sidebarFilesTree.toast.fileCreated": "Archivo creado",
   "sidebarFilesTree.toast.operationFailed": "No se pudo completar la operación",
+  "sidebarFilesTree.toast.uploaded": "Archivos subidos",
+  "sidebarFilesTree.toast.uploadedWithoutConflicts": "Se subieron los archivos sin conflictos",
+  "sidebarFilesTree.toast.uploadFailed": "No se pudieron subir algunos archivos",
+  "sidebarFilesTree.drop.target": "Subir a {path}",
+  "sidebarFilesTree.drop.uploading": "Subiendo archivos a {path}",
+  "sidebarFilesTree.dialog.uploadConflicts.title": "¿Reemplazar los archivos existentes?",
+  "sidebarFilesTree.dialog.uploadConflicts.description": "Ya existen archivos con estos nombres en {path}. El reemplazo no se puede deshacer.",
+  "sidebarFilesTree.dialog.uploadConflicts.replace": "Reemplazar",
   "sidebarFilesTree.toast.folderNameRequired": "El nombre de carpeta es obligatorio",
   "sidebarFilesTree.toast.folderCreated": "Carpeta creada",
   "sidebarFilesTree.toast.nameRequired": "El nombre es obligatorio",
diff --git a/packages/ui/src/lib/i18n/messages/fr.ts b/packages/ui/src/lib/i18n/messages/fr.ts
index ddb5aa56..e2c0f1bd 100644
--- a/packages/ui/src/lib/i18n/messages/fr.ts
+++ b/packages/ui/src/lib/i18n/messages/fr.ts
@@ -1089,6 +1089,14 @@ export const dict = {
   'sidebarFilesTree.toast.writeNotSupported': 'Écriture non prise en charge',
   'sidebarFilesTree.toast.fileCreated': 'Fichier créé',
   'sidebarFilesTree.toast.operationFailed': 'L\'opération a échoué',
+  'sidebarFilesTree.toast.uploaded': 'Fichiers téléversés',
+  'sidebarFilesTree.toast.uploadedWithoutConflicts': 'Les fichiers sans conflit ont été téléversés',
+  'sidebarFilesTree.toast.uploadFailed': 'Certains fichiers n’ont pas pu être téléversés',
+  'sidebarFilesTree.drop.target': 'Téléverser dans {path}',
+  'sidebarFilesTree.drop.uploading': 'Téléversement des fichiers dans {path}',
+  'sidebarFilesTree.dialog.uploadConflicts.title': 'Remplacer les fichiers existants ?',
+  'sidebarFilesTree.dialog.uploadConflicts.description': 'Des fichiers portant ces noms existent déjà dans {path}. Leur remplacement est irréversible.',
+  'sidebarFilesTree.dialog.uploadConflicts.replace': 'Remplacer',
   'sidebarFilesTree.toast.folderNameRequired': 'Le nom du dossier est requis',
   'sidebarFilesTree.toast.folderCreated': 'Dossier créé',
   'sidebarFilesTree.toast.nameRequired': 'Le nom est requis',
diff --git a/packages/ui/src/lib/i18n/messages/ja.ts b/packages/ui/src/lib/i18n/messages/ja.ts
index 3992ba78..f231df35 100644
--- a/packages/ui/src/lib/i18n/messages/ja.ts
+++ b/packages/ui/src/lib/i18n/messages/ja.ts
@@ -1318,6 +1318,14 @@ export const dict: Record<I18nKey, string> = {
   'sidebarFilesTree.toast.writeNotSupported': '書き込みはサポートされていません',
   'sidebarFilesTree.toast.fileCreated': 'ファイルを作成しました',
   'sidebarFilesTree.toast.operationFailed': '操作に失敗しました',
+  'sidebarFilesTree.toast.uploaded': 'ファイルをアップロードしました',
+  'sidebarFilesTree.toast.uploadedWithoutConflicts': '競合のないファイルをアップロードしました',
+  'sidebarFilesTree.toast.uploadFailed': '一部のファイルをアップロードできませんでした',
+  'sidebarFilesTree.drop.target': '{path} にアップロード',
+  'sidebarFilesTree.drop.uploading': '{path} にファイルをアップロードしています',
+  'sidebarFilesTree.dialog.uploadConflicts.title': '既存のファイルを置き換えますか？',
+  'sidebarFilesTree.dialog.uploadConflicts.description': '同じ名前のファイルが {path} に既に存在します。置き換えは元に戻せません。',
+  'sidebarFilesTree.dialog.uploadConflicts.replace': '置き換える',
   'sidebarFilesTree.toast.folderNameRequired': 'フォルダ名が必要です',
   'sidebarFilesTree.toast.folderCreated': 'フォルダを作成しました',
   'sidebarFilesTree.toast.nameRequired': '名前が必要です',
diff --git a/packages/ui/src/lib/i18n/messages/ko.ts b/packages/ui/src/lib/i18n/messages/ko.ts
index dde3d0f1..4d924744 100644
--- a/packages/ui/src/lib/i18n/messages/ko.ts
+++ b/packages/ui/src/lib/i18n/messages/ko.ts
@@ -1324,6 +1324,14 @@ export const dict: Record<I18nKey, string> = {
   'sidebarFilesTree.toast.writeNotSupported': '쓰기를 지원하지 않음',
   'sidebarFilesTree.toast.fileCreated': '파일 생성됨',
   'sidebarFilesTree.toast.operationFailed': '작업 실패',
+  'sidebarFilesTree.toast.uploaded': '파일을 업로드했습니다',
+  'sidebarFilesTree.toast.uploadedWithoutConflicts': '충돌하지 않은 파일을 업로드했습니다',
+  'sidebarFilesTree.toast.uploadFailed': '일부 파일을 업로드하지 못했습니다',
+  'sidebarFilesTree.drop.target': '{path}에 업로드',
+  'sidebarFilesTree.drop.uploading': '{path}에 파일 업로드 중',
+  'sidebarFilesTree.dialog.uploadConflicts.title': '기존 파일을 교체할까요?',
+  'sidebarFilesTree.dialog.uploadConflicts.description': '같은 이름의 파일이 {path}에 이미 있습니다. 교체 작업은 취소할 수 없습니다.',
+  'sidebarFilesTree.dialog.uploadConflicts.replace': '교체',
   'sidebarFilesTree.toast.folderNameRequired': '폴더 이름 필수',
   'sidebarFilesTree.toast.folderCreated': '폴더 생성됨',
   'sidebarFilesTree.toast.nameRequired': '이름 필수',
diff --git a/packages/ui/src/lib/i18n/messages/pl.ts b/packages/ui/src/lib/i18n/messages/pl.ts
index d0c85d40..91123a37 100644
--- a/packages/ui/src/lib/i18n/messages/pl.ts
+++ b/packages/ui/src/lib/i18n/messages/pl.ts
@@ -2845,6 +2845,14 @@ export const dict: Record<I18nKey, string> = {
   'sidebarFilesTree.toast.folderNameRequired': 'Nazwa folderu jest wymagana',
   'sidebarFilesTree.toast.nameRequired': 'Nazwa jest wymagana',
   'sidebarFilesTree.toast.operationFailed': 'Operacja nie powiodła się',
+  'sidebarFilesTree.toast.uploaded': 'Pliki przesłano',
+  'sidebarFilesTree.toast.uploadedWithoutConflicts': 'Przesłano pliki bez konfliktów',
+  'sidebarFilesTree.toast.uploadFailed': 'Nie udało się przesłać niektórych plików',
+  'sidebarFilesTree.drop.target': 'Prześlij do {path}',
+  'sidebarFilesTree.drop.uploading': 'Przesyłanie plików do {path}',
+  'sidebarFilesTree.dialog.uploadConflicts.title': 'Zastąpić istniejące pliki?',
+  'sidebarFilesTree.dialog.uploadConflicts.description': 'Pliki o tych nazwach już istnieją w {path}. Zastąpienia nie można cofnąć.',
+  'sidebarFilesTree.dialog.uploadConflicts.replace': 'Zastąp',
   'sidebarFilesTree.toast.pathCopied': 'Ścieżka skopiowana',
   'sidebarFilesTree.toast.renameNotSupported': 'Zmiana nazwy nie jest obsługiwana',
   'sidebarFilesTree.toast.renamedSuccessfully': 'Zmieniono nazwę pomyślnie',
diff --git a/packages/ui/src/lib/i18n/messages/pt-BR.ts b/packages/ui/src/lib/i18n/messages/pt-BR.ts
index 8275d93c..925ef6eb 100644
--- a/packages/ui/src/lib/i18n/messages/pt-BR.ts
+++ b/packages/ui/src/lib/i18n/messages/pt-BR.ts
@@ -1288,6 +1288,14 @@ export const dict: Record<I18nKey, string> = {
   "sidebarFilesTree.toast.writeNotSupported": "A escrita não é compatível",
   "sidebarFilesTree.toast.fileCreated": "Arquivo criado",
   "sidebarFilesTree.toast.operationFailed": "Não foi possível completar a operación",
+  "sidebarFilesTree.toast.uploaded": "Arquivos enviados",
+  "sidebarFilesTree.toast.uploadedWithoutConflicts": "Os arquivos sem conflitos foram enviados",
+  "sidebarFilesTree.toast.uploadFailed": "Não foi possível enviar alguns arquivos",
+  "sidebarFilesTree.drop.target": "Enviar para {path}",
+  "sidebarFilesTree.drop.uploading": "Enviando arquivos para {path}",
+  "sidebarFilesTree.dialog.uploadConflicts.title": "Substituir arquivos existentes?",
+  "sidebarFilesTree.dialog.uploadConflicts.description": "Já existem arquivos com esses nomes em {path}. A substituição não pode ser desfeita.",
+  "sidebarFilesTree.dialog.uploadConflicts.replace": "Substituir",
   "sidebarFilesTree.toast.folderNameRequired": "O nome de pasta é obrigatório",
   "sidebarFilesTree.toast.folderCreated": "Pasta criada",
   "sidebarFilesTree.toast.nameRequired": "O nome é obrigatório",
diff --git a/packages/ui/src/lib/i18n/messages/uk.ts b/packages/ui/src/lib/i18n/messages/uk.ts
index 3173b933..d27adfb2 100644
--- a/packages/ui/src/lib/i18n/messages/uk.ts
+++ b/packages/ui/src/lib/i18n/messages/uk.ts
@@ -1288,6 +1288,14 @@ export const dict: Record<I18nKey, string> = {
   "sidebarFilesTree.toast.writeNotSupported": "Запис не підтримується",
   "sidebarFilesTree.toast.fileCreated": "Файл створено",
   "sidebarFilesTree.toast.operationFailed": "Операція не вдалася",
+  "sidebarFilesTree.toast.uploaded": "Файли завантажено",
+  "sidebarFilesTree.toast.uploadedWithoutConflicts": "Файли без конфліктів завантажено",
+  "sidebarFilesTree.toast.uploadFailed": "Деякі файли не вдалося завантажити",
+  "sidebarFilesTree.drop.target": "Завантажити в {path}",
+  "sidebarFilesTree.drop.uploading": "Завантаження файлів у {path}",
+  "sidebarFilesTree.dialog.uploadConflicts.title": "Замінити наявні файли?",
+  "sidebarFilesTree.dialog.uploadConflicts.description": "Файли з такими назвами вже існують у {path}. Заміну неможливо скасувати.",
+  "sidebarFilesTree.dialog.uploadConflicts.replace": "Замінити",
   "sidebarFilesTree.toast.folderNameRequired": "Потрібно вказати назву папки",
   "sidebarFilesTree.toast.folderCreated": "Папку створено",
   "sidebarFilesTree.toast.nameRequired": "Потрібно вказати назву",
diff --git a/packages/ui/src/lib/i18n/messages/zh-CN.ts b/packages/ui/src/lib/i18n/messages/zh-CN.ts
index 58cca12a..df562496 100644
--- a/packages/ui/src/lib/i18n/messages/zh-CN.ts
+++ b/packages/ui/src/lib/i18n/messages/zh-CN.ts
@@ -1288,6 +1288,14 @@ export const dict: Record<I18nKey, string> = {
   'sidebarFilesTree.toast.writeNotSupported': '不支持写入',
   'sidebarFilesTree.toast.fileCreated': '文件已创建',
   'sidebarFilesTree.toast.operationFailed': '操作失败',
+  'sidebarFilesTree.toast.uploaded': '文件已上传',
+  'sidebarFilesTree.toast.uploadedWithoutConflicts': '无冲突的文件已上传',
+  'sidebarFilesTree.toast.uploadFailed': '部分文件无法上传',
+  'sidebarFilesTree.drop.target': '上传到 {path}',
+  'sidebarFilesTree.drop.uploading': '正在将文件上传到 {path}',
+  'sidebarFilesTree.dialog.uploadConflicts.title': '替换现有文件？',
+  'sidebarFilesTree.dialog.uploadConflicts.description': '{path} 中已存在同名文件。替换后无法撤销。',
+  'sidebarFilesTree.dialog.uploadConflicts.replace': '替换',
   'sidebarFilesTree.toast.folderNameRequired': '文件夹名不能为空',
   'sidebarFilesTree.toast.folderCreated': '文件夹已创建',
   'sidebarFilesTree.toast.nameRequired': '名称不能为空',
diff --git a/packages/ui/src/lib/i18n/messages/zh-TW.ts b/packages/ui/src/lib/i18n/messages/zh-TW.ts
index 98202726..d908d97b 100644
--- a/packages/ui/src/lib/i18n/messages/zh-TW.ts
+++ b/packages/ui/src/lib/i18n/messages/zh-TW.ts
@@ -1300,6 +1300,14 @@ export const dict: Record<I18nKey, string> = {
   'sidebarFilesTree.toast.writeNotSupported': '不支援寫入',
   'sidebarFilesTree.toast.fileCreated': '檔案已建立',
   'sidebarFilesTree.toast.operationFailed': '操作失敗',
+  'sidebarFilesTree.toast.uploaded': '檔案已上傳',
+  'sidebarFilesTree.toast.uploadedWithoutConflicts': '無衝突的檔案已上傳',
+  'sidebarFilesTree.toast.uploadFailed': '部分檔案無法上傳',
+  'sidebarFilesTree.drop.target': '上傳至 {path}',
+  'sidebarFilesTree.drop.uploading': '正在將檔案上傳至 {path}',
+  'sidebarFilesTree.dialog.uploadConflicts.title': '取代現有檔案？',
+  'sidebarFilesTree.dialog.uploadConflicts.description': '{path} 中已有同名檔案。取代後無法復原。',
+  'sidebarFilesTree.dialog.uploadConflicts.replace': '取代',
   'sidebarFilesTree.toast.folderNameRequired': '資料夾名稱不能為空',
   'sidebarFilesTree.toast.folderCreated': '資料夾已建立',
   'sidebarFilesTree.toast.nameRequired': '名稱不能為空',
diff --git a/packages/web/server/lib/fs/DOCUMENTATION.md b/packages/web/server/lib/fs/DOCUMENTATION.md
index f184e8c1..cdf2fd62 100644
--- a/packages/web/server/lib/fs/DOCUMENTATION.md
+++ b/packages/web/server/lib/fs/DOCUMENTATION.md
@@ -16,6 +16,7 @@ Own filesystem API behavior for the web server runtime, including workspace-boun
     - `GET /api/fs/raw`
     - `GET /api/fs/serve/:path(*)`
     - `POST /api/fs/write`
+    - `POST /api/fs/upload`
     - `POST /api/fs/delete`
     - `POST /api/fs/rename`
     - `POST /api/fs/reveal`
@@ -38,3 +39,4 @@ Own filesystem API behavior for the web server runtime, including workspace-boun
 - Read-only routes authorize the requested path against the workspace before resolving symlinks. A symlink reached through the workspace may therefore target a file outside it, while a directly requested outside path still requires an exact-path grant. Write routes keep canonical-target boundary checks.
 - If adding new `/api/fs/*` endpoints, add them in `routes.js` and extend this document.
 - `GET /api/fs/list` may resolve symlinks with `realpath` to read directory contents, but the response `path` and each entry `path` must stay in the caller's requested path space (`path.join(requestedPath, name)`). Returning real paths breaks file-tree expansion for directories reached through workspace symlinks.
+- `POST /api/fs/upload` accepts one `application/octet-stream` body (up to 100 MB) with `path` and optional `overwrite=true` query parameters. It rejects existing files with `409` unless overwrite is explicit, and resolves the destination parent before writing so uploads cannot escape through workspace symlinks.
diff --git a/packages/web/server/lib/fs/routes.js b/packages/web/server/lib/fs/routes.js
index 20cc32b7..7888742c 100644
--- a/packages/web/server/lib/fs/routes.js
+++ b/packages/web/server/lib/fs/routes.js
@@ -139,6 +139,29 @@ const FILE_MIME_MAP = Object.freeze({
 });
 
 const MAX_SERVE_BYTES = 100 * 1024 * 1024;
+const MAX_UPLOAD_BYTES = 100 * 1024 * 1024;
+
+const readUploadBody = async (req) => {
+  const declaredSize = Number.parseInt(req.headers?.['content-length'] || '0', 10);
+  if (Number.isFinite(declaredSize) && declaredSize > MAX_UPLOAD_BYTES) {
+    req.resume?.();
+    return null;
+  }
+
+  const chunks = [];
+  let size = 0;
+  for await (const chunk of req) {
+    const buffer = Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk);
+    size += buffer.length;
+    if (size > MAX_UPLOAD_BYTES) {
+      req.resume?.();
+      return null;
+    }
+    chunks.push(buffer);
+  }
+
+  return Buffer.concat(chunks, size);
+};
 
 // Only deterministic, side-effect-free git plumbing path queries are cacheable.
 // Anything outside this allowlist (including any non-git command) runs normally
@@ -1041,6 +1064,83 @@ export const registerFsRoutes = (app, dependencies) => {
     }
   });
 
+  app.post('/api/fs/upload', async (req, res) => {
+    const filePath = typeof req.query?.path === 'string' ? req.query.path.trim() : '';
+    const overwrite = req.query?.overwrite === 'true';
+    if (!filePath) {
+      return res.status(400).json({ error: 'Path is required' });
+    }
+    if (!String(req.headers?.['content-type'] || '').toLowerCase().startsWith('application/octet-stream')) {
+      return res.status(415).json({ error: 'Content-Type must be application/octet-stream' });
+    }
+
+    try {
+      const resolved = await resolveWorkspacePathFromContext({
+        req,
+        targetPath: filePath,
+        resolveProjectDirectory,
+        path,
+        os,
+        normalizeDirectoryPath,
+        openchamberUserConfigRoot,
+      });
+      if (!resolved.ok) {
+        return res.status(400).json({ error: resolved.error });
+      }
+
+      const canonicalBase = await fsPromises.realpath(resolved.base).catch(() => path.resolve(resolved.base));
+      const requestedParent = path.dirname(resolved.resolved);
+      const canonicalParent = await fsPromises.realpath(requestedParent);
+      if (!isPathWithinRoot(canonicalParent, canonicalBase, path, os)) {
+        return res.status(403).json({ error: 'Access denied' });
+      }
+
+      const existingPath = await fsPromises.realpath(resolved.resolved).catch((error) => {
+        if (error && typeof error === 'object' && error.code === 'ENOENT') {
+          return null;
+        }
+        throw error;
+      });
+      const writePath = existingPath || path.join(canonicalParent, path.basename(resolved.resolved));
+      if (!isPathWithinRoot(writePath, canonicalBase, path, os)) {
+        return res.status(403).json({ error: 'Access denied' });
+      }
+
+      const body = await readUploadBody(req);
+      if (!body) {
+        return res.status(413).json({ error: `File exceeds maximum size of ${MAX_UPLOAD_BYTES} bytes` });
+      }
+
+      if (!overwrite) {
+        await fsPromises.writeFile(writePath, body, { flag: 'wx' });
+      } else {
+        const tmp = `${writePath}.tmp-${process.pid}-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
+        try {
+          await fsPromises.writeFile(tmp, body, { flag: 'wx' });
+          await fsPromises.rename(tmp, writePath);
+        } catch (error) {
+          await fsPromises.unlink(tmp).catch(() => {});
+          throw error;
+        }
+      }
+
+      return res.json({ success: true, path: resolved.resolved });
+    } catch (error) {
+      const err = error;
+      if (err && typeof err === 'object' && err.code === 'EEXIST') {
+        return res.status(409).json({ error: 'File already exists', reason: 'already-exists' });
+      }
+      if (err && typeof err === 'object' && err.code === 'ENOENT') {
+        return res.status(404).json({ error: 'Destination directory not found', reason: 'not-found' });
+      }
+      if (isOsPermissionError(err)) {
+        return sendOsPermissionDenied(res, 'Access denied');
+      }
+      console.error('Failed to upload file:', error);
+      return res.status(500).json({ error: (error && error.message) || 'Failed to upload file' });
+    }
+  });
+
   app.post('/api/fs/delete', async (req, res) => {
     const { path: targetPath } = req.body || {};
     if (!targetPath || typeof targetPath !== 'string') {
diff --git a/packages/web/server/lib/fs/routes.test.js b/packages/web/server/lib/fs/routes.test.js
index b238c559..dbda0a27 100644
--- a/packages/web/server/lib/fs/routes.test.js
+++ b/packages/web/server/lib/fs/routes.test.js
@@ -140,6 +140,26 @@ const registerWrite = (fsPromises) => {
   return getRoute('POST', '/api/fs/write');
 };
 
+const registerUpload = (fsPromises) => {
+  const { app, getRoute } = createRouteRegistry();
+  registerFsRoutes(app, {
+    os: { homedir: () => '/home/user' },
+    path: path.posix,
+    fsPromises: {
+      realpath: async (targetPath) => targetPath,
+      ...fsPromises,
+    },
+    spawn: vi.fn(),
+    crypto: { randomUUID: () => 'job-0' },
+    normalizeDirectoryPath: (p) => p,
+    resolveProjectDirectory: async () => ({ directory: '/repo' }),
+    buildAugmentedPath: () => '/usr/bin',
+    resolveGitBinaryForSpawn: () => 'git',
+    openchamberUserConfigRoot: '/home/user/.config',
+  });
+  return getRoute('POST', '/api/fs/upload');
+};
+
 const registerRead = (fsPromises) => {
   const { app, getRoute } = createRouteRegistry();
   registerFsRoutes(app, {
@@ -233,6 +253,22 @@ const callWrite = async (handler, body) => {
   return res;
 };
 
+const callUpload = async (handler, { body = Buffer.from('upload'), path: filePath = '/repo/file.bin', overwrite = false } = {}) => {
+  const res = createMockResponse();
+  const req = {
+    headers: {
+      'content-type': 'application/octet-stream',
+      'content-length': String(body.length),
+    },
+    query: { path: filePath, overwrite: overwrite ? 'true' : undefined },
+    async *[Symbol.asyncIterator]() {
+      yield body;
+    },
+  };
+  await handler(req, res);
+  return res;
+};
+
 const callRead = async (handler, query) => {
   const res = createMockResponse();
   await handler({ query }, res);
@@ -340,6 +376,95 @@ describe('fs write', () => {
   });
 });
 
+describe('fs upload', () => {
+  it('creates a binary file without overwriting existing content', async () => {
+    const fsPromises = {
+      writeFile: vi.fn(async () => undefined),
+      rename: vi.fn(async () => undefined),
+      unlink: vi.fn(async () => undefined),
+    };
+    const handler = registerUpload(fsPromises);
+
+    const res = await callUpload(handler, { body: Buffer.from([0, 1, 2, 255]) });
+
+    expect(res.body).toEqual({ success: true, path: '/repo/file.bin' });
+    expect(fsPromises.writeFile).toHaveBeenCalledWith(
+      '/repo/file.bin',
+      Buffer.from([0, 1, 2, 255]),
+      { flag: 'wx' },
+    );
+    expect(fsPromises.rename).not.toHaveBeenCalled();
+  });
+
+  it('returns a conflict instead of silently replacing an existing file', async () => {
+    const error = Object.assign(new Error('exists'), { code: 'EEXIST' });
+    const fsPromises = {
+      writeFile: vi.fn(async () => { throw error; }),
+    };
+    const handler = registerUpload(fsPromises);
+
+    const res = await callUpload(handler);
+
+    expect(res.statusCode).toBe(409);
+    expect(res.body).toEqual({ error: 'File already exists', reason: 'already-exists' });
+  });
+
+  it('atomically replaces a file only when overwrite is explicit', async () => {
+    const fsPromises = {
+      writeFile: vi.fn(async () => undefined),
+      rename: vi.fn(async () => undefined),
+      unlink: vi.fn(async () => undefined),
+    };
+    const handler = registerUpload(fsPromises);
+
+    const res = await callUpload(handler, { overwrite: true });
+
+    expect(res.body).toEqual({ success: true, path: '/repo/file.bin' });
+    const tmp = fsPromises.writeFile.mock.calls[0][0];
+    expect(tmp).toMatch(/^\/repo\/file\.bin\.tmp-/);
+    expect(fsPromises.writeFile).toHaveBeenCalledWith(tmp, Buffer.from('upload'), { flag: 'wx' });
+    expect(fsPromises.rename).toHaveBeenCalledWith(tmp, '/repo/file.bin');
+  });
+
+  it('rejects a destination parent that resolves outside the workspace', async () => {
+    const fsPromises = {
+      realpath: vi.fn(async (targetPath) => targetPath === '/repo/link' ? '/outside' : targetPath),
+      writeFile: vi.fn(async () => undefined),
+    };
+    const handler = registerUpload(fsPromises);
+
+    const res = await callUpload(handler, { path: '/repo/link/file.bin' });
+
+    expect(res.statusCode).toBe(403);
+    expect(res.body).toEqual({ error: 'Access denied' });
+    expect(fsPromises.writeFile).not.toHaveBeenCalled();
+  });
+
+  it('rejects streamed bodies larger than 100 MB', async () => {
+    const fsPromises = {
+      writeFile: vi.fn(async () => undefined),
+    };
+    const handler = registerUpload(fsPromises);
+    const chunk = Buffer.alloc(1024 * 1024);
+    const req = {
+      headers: { 'content-type': 'application/octet-stream' },
+      query: { path: '/repo/file.bin' },
+      async *[Symbol.asyncIterator]() {
+        for (let index = 0; index < 101; index += 1) {
+          yield chunk;
+        }
+      },
+    };
+    const res = createMockResponse();
+
+    await handler(req, res);
+
+    expect(res.statusCode).toBe(413);
+    expect(res.body).toEqual({ error: `File exceeds maximum size of ${100 * 1024 * 1024} bytes` });
+    expect(fsPromises.writeFile).not.toHaveBeenCalled();
+  });
+});
+
 describe('fs read', () => {
   it('reads workspace files through symlinks that resolve outside the workspace', async () => {
     const fsPromises = {
diff --git a/packages/web/src/api/files.test.ts b/packages/web/src/api/files.test.ts
index beb88c9c..f353acfa 100644
--- a/packages/web/src/api/files.test.ts
+++ b/packages/web/src/api/files.test.ts
@@ -92,6 +92,39 @@ describe('createWebFilesAPI', () => {
     });
   });
 
+  it('uploads binary file contents to the active workspace', async () => {
+    const { createWebFilesAPI } = await import('./files');
+    const api = createWebFilesAPI({ urls, getDirectory: () => '/workspace' });
+    const file = new Blob([new Uint8Array([0, 1, 255])]);
+    runtimeFetchMock.mockResolvedValueOnce(Response.json({ success: true, path: '/workspace/image.bin' }));
+
+    await api.uploadFile?.('/workspace/image.bin', file, { directory: '/workspace' });
+
+    expect(runtimeFetchMock).toHaveBeenLastCalledWith('/api/fs/upload', {
+      method: 'POST',
+      query: { path: '/workspace/image.bin', overwrite: undefined },
+      headers: {
+        'Content-Type': 'application/octet-stream',
+        'x-opencode-directory': '/workspace',
+      },
+      body: file,
+    });
+  });
+
+  it('preserves upload conflict details for explicit overwrite handling', async () => {
+    const { createWebFilesAPI } = await import('./files');
+    const api = createWebFilesAPI({ urls, getDirectory: () => '/workspace' });
+    runtimeFetchMock.mockResolvedValueOnce(Response.json(
+      { error: 'File already exists', reason: 'already-exists' },
+      { status: 409 },
+    ));
+
+    await expect(api.uploadFile?.('/workspace/file.txt', new Blob(['new']))).rejects.toMatchObject({
+      reason: 'already-exists',
+      status: 409,
+    });
+  });
+
   it('opens the native share sheet for downloads in the Capacitor app', async () => {
     const { createWebFilesAPI } = await import('./files');
     const api = createWebFilesAPI({ urls, getDirectory: () => '/workspace' });
diff --git a/packages/web/src/api/files.ts b/packages/web/src/api/files.ts
index 6655d365..696c6f60 100644
--- a/packages/web/src/api/files.ts
+++ b/packages/web/src/api/files.ts
@@ -7,6 +7,7 @@ import type {
 import {
   FilesystemError,
   parseFilesystemErrorReason,
+  type FilesystemErrorReason,
 } from '@openchamber/ui/lib/api/files-errors';
 import { runtimeFetch } from '@openchamber/ui/lib/runtime-fetch';
 
@@ -31,6 +32,13 @@ type WebDirectoryListResponse = {
   entries?: WebDirectoryEntry[];
 };
 
+type WebFileUploadResponse = {
+  success?: boolean;
+  path?: string;
+  error?: string;
+  reason?: FilesystemErrorReason;
+};
+
 const toDirectoryListResult = (fallbackDirectory: string, payload: WebDirectoryListResponse): DirectoryListResult => {
   if (!payload || !Array.isArray(payload.entries)) {
     throw new FilesystemError('Directory listing returned an invalid response', {
@@ -222,6 +230,36 @@ export const createWebFilesAPI = ({ getDirectory }: WebFilesAPIOptions): FilesAP
     };
   },
 
+  async uploadFile(path: string, file: Blob, options): Promise<{ success: boolean; path: string }> {
+    const target = normalizePath(path);
+    const response = await runtimeFetch('/api/fs/upload', {
+      method: 'POST',
+      query: {
+        path: target,
+        overwrite: options?.overwrite ? 'true' : undefined,
+      },
+      headers: {
+        'Content-Type': 'application/octet-stream',
+        ...directoryHeaders(getDirectory, options?.directory),
+      },
+      body: file,
+    });
+
+    if (!response.ok) {
+      const error: WebFileUploadResponse = await response.json().catch(() => ({ error: response.statusText }));
+      throw new FilesystemError(error.error || 'Failed to upload file', {
+        reason: parseFilesystemErrorReason(error.reason),
+        status: response.status,
+      });
+    }
+
+    const result: WebFileUploadResponse = await response.json().catch(() => ({}));
+    return {
+      success: Boolean(result.success),
+      path: result.path ? normalizePath(result.path) : target,
+    };
+  },
+
   async delete(path: string): Promise<{ success: boolean }> {
     const target = normalizePath(path);
     const response = await runtimeFetch('/api/fs/delete', {