fix: resolve @file virtual-file URLs to absolute in HTML renderer

frontend/src/components/data-table/renderers.tsx

@@ -164,13 +164,17 @@ export const DataTableBody = <TData,>({
       );
 
       const title = cell.getHoverTitle?.() ?? undefined;
+      const isCellSelected = cell.getIsSelected?.() || false;
       return (
         <TableCell
           tabIndex={0}
           {...getCellDomProps(cell.id)}
           key={cell.id}
           className={cn(
-            "whitespace-pre truncate max-w-[300px] outline-hidden border-r border-r-border/75",
+            "whitespace-pre truncate max-w-[300px] border-r border-r-border/75",
+            isCellSelected
+              ? "outline outline-2 outline-(--blue-7) -outline-offset-2"
+              : "outline-hidden",
             cell.column.getColumnWrapping &&
               cell.column.getColumnWrapping?.() === "wrap" &&
               COLUMN_WRAPPING_STYLES,

frontend/src/plugins/core/RenderHTML.tsx

@@ -18,6 +18,7 @@ import { Tooltip } from "@/components/ui/tooltip";
 import { DocHoverTarget } from "@/core/documentation/DocHoverTarget";
 import { hasTrustedNotebookContext } from "@/core/static/export-context";
 import { Logger } from "@/utils/Logger";
+import { getRuntimeManager } from "@/core/runtime/config";
 import { sanitizeHtml, useSanitizeHtml } from "./sanitize";
 
 type ReplacementFn = NonNullable<HTMLReactParserOptions["replace"]>;
@@ -32,6 +33,39 @@ interface Options {
   alwaysSanitizeHtml?: boolean;
   additionalReplacements?: ReplacementFn[];
 }
+// Resolve a virtual file URL (./@file/... or @file/...) to an absolute URL
+// using the runtime base, ensuring a trailing slash so the notebook-ID path
+// segment is never dropped during relative resolution.
+function resolveVirtualFileUrl(src: string): string {
+  const base = getRuntimeManager().httpURL;
+  if (!base.pathname.endsWith("/")) {
+    base.pathname += "/";
+  }
+  return new URL(src.replace(/^\.\//, ""), base).toString();
+}
+
+// Rewrite relative @file virtual-file URLs to absolute URLs so they resolve
+// correctly even when the page URL has no trailing slash (e.g., molab edit mode).
+// The virtual file URL is generated as "./@file/SIZE-filename" (relative). When
+// the page URL has no trailing slash (e.g., /notebooks/nb_xxx), the browser
+// resolves "./@file/..." to "/notebooks/@file/..." — dropping the notebook ID.
+// We fix this by resolving against the runtime base URL with a guaranteed
+// trailing slash, making the URL unambiguous.
+const VIRTUAL_FILE_SRC_TAGS = new Set(["img", "source", "audio", "video"]);
+const replaceVirtualFileSrc = (domNode: DOMNode): JSX.Element | undefined => {
+  if (
+    domNode instanceof Element &&
+    VIRTUAL_FILE_SRC_TAGS.has(domNode.name) &&
+    domNode.attribs?.src
+  ) {
+    const src = domNode.attribs.src;
+    if (src.includes("/@file/") || src.startsWith("@file/")) {
+      const absoluteSrc = resolveVirtualFileUrl(src);
+      domNode.attribs.src = absoluteSrc;
+      return undefined;
+    }
+  }
+};
 
 const replaceValidTags = (domNode: DOMNode) => {
   // Don't render invalid tags
@@ -87,6 +121,13 @@ const replaceValidIframes = (domNode: DOMNode) => {
       if (key.startsWith('"') && key.endsWith('"')) {
         key = key.slice(1, -1);
       }
+      // Rewrite relative @file URLs to absolute (same fix as replaceVirtualFileSrc)
+      if (
+        key === "src" &&
+        (value.includes("/@file/") || value.startsWith("@file/"))
+      ) {
+        value = resolveVirtualFileUrl(value);
+      }
       element.setAttribute(key, value);
     });
     return <div dangerouslySetInnerHTML={{ __html: element.outerHTML }} />;
@@ -275,6 +316,7 @@ function parseHtml({
   additionalReplacements = [],
 }: Pick<Options, "html" | "additionalReplacements">) {
   const renderFunctions: ReplacementFn[] = [
+    replaceVirtualFileSrc,
     replaceValidTags,
     replaceValidIframes,
     replaceSrcScripts,

frontend/src/plugins/core/__test__/renderHTML-sanitization.test.tsx

@@ -129,3 +129,44 @@ describe("renderHTML sanitization integration", () => {
     );
   });
 });
+
+describe("replaceVirtualFileSrc - virtual file URL rewriting", () => {
+  test("rewrites ./@file/ img src to absolute URL", () => {
+    const html = '<img src="./@file/12345-abc.png" alt="test">';
+    const { container } = render(
+      renderHTML({ html, alwaysSanitizeHtml: false }),
+    );
+    const img = container.querySelector("img");
+    expect(img).not.toBeNull();
+    // Should be absolute, not relative
+    expect(img?.getAttribute("src")).not.toMatch(/^\.\//);
+    expect(img?.getAttribute("src")).toContain("/@file/12345-abc.png");
+  });
+
+  test("rewrites @file/ img src (no leading ./) to absolute URL", () => {
+    const html = '<img src="@file/12345-abc.png" alt="test">';
+    const { container } = render(
+      renderHTML({ html, alwaysSanitizeHtml: false }),
+    );
+    const img = container.querySelector("img");
+    expect(img?.getAttribute("src")).toContain("/@file/12345-abc.png");
+  });
+
+  test("does not rewrite non-@file img src", () => {
+    const html = '<img src="https://example.com/image.png" alt="test">';
+    const { container } = render(
+      renderHTML({ html, alwaysSanitizeHtml: false }),
+    );
+    const img = container.querySelector("img");
+    expect(img?.getAttribute("src")).toBe("https://example.com/image.png");
+  });
+
+  test("does not rewrite data: URL img src", () => {
+    const html = '<img src="data:image/png;base64,abc==" alt="test">';
+    const { container } = render(
+      renderHTML({ html, alwaysSanitizeHtml: false }),
+    );
+    const img = container.querySelector("img");
+    expect(img?.getAttribute("src")).toBe("data:image/png;base64,abc==");
+  });
+});