diff --git a/.changeset/encode-artifact-download-path.md b/.changeset/encode-artifact-download-path.md
new file mode 100644
index 000000000..9efa812d8
--- /dev/null
+++ b/.changeset/encode-artifact-download-path.md
@@ -0,0 +1,5 @@
+---
+'@truefoundry/trueforge-ui': patch
+---
+
+Encode sandbox artifact paths when building file-download links, so names containing spaces, `#`, `?`, `&`, `%` or non-ASCII characters resolve to the intended file instead of a truncated or misparsed URL.
diff --git a/packages/trueforge-ui/src/atoms/ChatFileDownload.tsx b/packages/trueforge-ui/src/atoms/ChatFileDownload.tsx
index 19c0a1eb1..c7e7b2457 100644
--- a/packages/trueforge-ui/src/atoms/ChatFileDownload.tsx
+++ b/packages/trueforge-ui/src/atoms/ChatFileDownload.tsx
@@ -18,6 +18,12 @@ export type ChatFileDownloadProps = {
   readOnly?: boolean;
 };
 
+// Artifact paths are model-authored, so a name may carry characters that change what the
+// URL means. Encode per segment so `/` keeps its structural role and the rest stays literal.
+function encodeArtifactPath(path: string): string {
+  return path.split('/').map(encodeURIComponent).join('/');
+}
+
 export function ChatFileDownload({ files, fileDownloadBaseUrl, onDownloadArtifact, readOnly }: ChatFileDownloadProps) {
   const [downloadingPath, setDownloadingPath] = useState<string | null>(null);
 
@@ -49,7 +55,7 @@ export function ChatFileDownload({ files, fileDownloadBaseUrl, onDownloadArtifac
             );
           }
 
-          const href = fileDownloadBaseUrl ? `${fileDownloadBaseUrl}${path}` : undefined;
+          const href = fileDownloadBaseUrl ? `${fileDownloadBaseUrl}${encodeArtifactPath(path)}` : undefined;
           const canDownload = Boolean(onDownloadArtifact || href);
           const isDownloading = downloadingPath === path;
 
diff --git a/packages/trueforge-ui/test/atoms/ChatFileDownload.test.tsx b/packages/trueforge-ui/test/atoms/ChatFileDownload.test.tsx
index e0aa91908..a004f5c46 100644
--- a/packages/trueforge-ui/test/atoms/ChatFileDownload.test.tsx
+++ b/packages/trueforge-ui/test/atoms/ChatFileDownload.test.tsx
@@ -30,6 +30,32 @@ describe('ChatFileDownload', () => {
     expect(screen.getByRole('link', { name: 'Download data.csv' })).toHaveAttribute('href', '/downloads/data.csv');
   });
 
+  it('encodes artifact names that would otherwise break or rewrite the URL', () => {
+    render(
+      <ChatFileDownload
+        files={[
+          { name: 'my report#final,v2.csv', path: '/tmp/my report#final,v2.csv' },
+          { name: 'a&b?c%d.txt', path: '/tmp/a&b?c%d.txt' },
+          { name: 'ünïcode.txt', path: '/tmp/ünïcode.txt' },
+        ]}
+        fileDownloadBaseUrl="https://files.example.com"
+      />,
+    );
+
+    expect(screen.getByRole('link', { name: 'Download my report#final,v2.csv' })).toHaveAttribute(
+      'href',
+      'https://files.example.com/tmp/my%20report%23final%2Cv2.csv',
+    );
+    expect(screen.getByRole('link', { name: 'Download a&b?c%d.txt' })).toHaveAttribute(
+      'href',
+      'https://files.example.com/tmp/a%26b%3Fc%25d.txt',
+    );
+    expect(screen.getByRole('link', { name: 'Download ünïcode.txt' })).toHaveAttribute(
+      'href',
+      'https://files.example.com/tmp/%C3%BCn%C3%AFcode.txt',
+    );
+  });
+
   it('shows per-file progress and suppresses duplicate artifact downloads', async () => {
     let resolveDownload: (() => void) | undefined;
     const downloadPromise = new Promise<void>(resolve => {