fix: handle read_file on directories gracefully (EISDIR fallback)

src/handlers/filesystem-handlers.ts

@@ -171,7 +171,7 @@ export async function handleReadFile(args: unknown): Promise<ServerResult> {
             const textContent = typeof fileResult.content === 'string'
                 ? fileResult.content
                 : fileResult.content.toString('utf8');
-            const fileType = resolvePreviewFileType(resolvedFilePath);
+            const fileType = fileResult.metadata?.isDirectory ? 'directory' as const : resolvePreviewFileType(resolvedFilePath);
             return {
                 content: [{ type: "text", text: textContent }],
                 structuredContent: {
@@ -326,9 +326,15 @@ export async function handleListDirectory(args: unknown): Promise<ServerResult>
         const duration = Date.now() - startTime;
 
         const resultText = entries.join('\n');
+        const resolvedPath = resolveAbsolutePath(parsed.path);
 
         return {
             content: [{ type: "text", text: resultText }],
+            structuredContent: {
+                fileName: path.basename(resolvedPath),
+                filePath: resolvedPath,
+                fileType: 'directory' as const,
+            },
         };
     } catch (error) {
         const errorMessage = error instanceof Error ? error.message : String(error);

src/server.ts

@@ -522,6 +522,7 @@ server.setRequestHandler(ListToolsRequestSchema, async () => {
                         ${PATH_GUIDANCE}
                         ${CMD_PREFIX_DESCRIPTION}`,
                 inputSchema: zodToJsonSchema(ListDirectoryArgsSchema),
+                _meta: buildUiToolMeta(FILE_PREVIEW_RESOURCE_URI, true),
                 annotations: {
                     title: "List Directory Contents",
                     readOnlyHint: true,

src/tools/filesystem.ts

@@ -369,6 +369,40 @@ export async function readFileFromDisk(
     // Get file extension for telemetry
     const fileExtension = getFileExtension(validPath);
 
+    // Check if path is a directory — return listing instead of EISDIR error
+    try {
+        const stats = await fs.stat(validPath);
+        if (stats.isDirectory()) {
+            const dirListOp = async () => {
+                const entries = await listDirectory(validPath);
+                const listing = entries.join('\n');
+                return {
+                    content: `This is a directory, not a file. Use the list_directory tool instead of read_file for directories.\n\n${listing}`,
+                    mimeType: 'text/plain',
+                    metadata: { isImage: false, isDirectory: true }
+                } as FileResult;
+            };
+            const dirResult = await withTimeout(
+                dirListOp(),
+                FILE_OPERATION_TIMEOUTS.FILE_READ,
+                'Directory listing fallback',
+                null
+            );
+            if (dirResult === null) {
+                throw new Error(`Directory listing timed out for: ${filePath}`);
+            }
+            return dirResult;
+        }
+    } catch (error) {
+        // If stat itself failed, fall through to the read path which will produce a proper error.
+        // But if this was a directory-listing error, re-throw — don't let it fall into the file-read path.
+        const err = error as NodeJS.ErrnoException;
+        if (err.message?.includes('Directory listing') || err.message?.includes('list_directory')) {
+            throw error;
+        }
+        // stat() failed (e.g. ENOENT) — fall through to the read path below
+    }
+
     // Check file size before attempting to read
     try {
         const stats = await fs.stat(validPath);