fix(list_directory): include listing in structuredContent (#496)

list_directory put the [DIR]/[FILE] listing only in the text content
array; its structuredContent carried just { fileName, filePath,
fileType: 'directory' } with no entries. Clients that render from the
text content (chat file-preview widget) worked, but structuredContent-
only consumers (e.g. Cowork) received an empty directory object and
rendered "directory empty".

Bring list_directory in line with the read_file structuredContent
convention by adding `sourceTool: 'list_directory'` and `content`
(the listing text). Chat is unaffected — it still reads the same text
from the content array — while structuredContent consumers now get the
listing.

No change to the model-facing content array.

Author: wonderwhy-er

src/handlers/filesystem-handlers.ts

@@ -361,6 +361,11 @@ export async function handleListDirectory(args: unknown): Promise<ServerResult>
                 fileName: path.basename(resolvedPath),
                 filePath: resolvedPath,
                 fileType: 'directory' as const,
+                sourceTool: 'list_directory',
+                // Carry the listing in structuredContent too. Chat reads the text
+                // content array, but structuredContent-only consumers (e.g. Cowork)
+                // render from here and would otherwise show an empty directory.
+                content: resultText,
             },
         };
     } catch (error) {