feat(filesystem): add append_file

src/filesystem/README.md

@@ -113,6 +113,15 @@ The server's directory access control follows this flow:
   - Returns detailed diff and match information for dry runs, otherwise applies changes
   - Best Practice: Always use dryRun first to preview changes before applying them
 
+- **append_file**
+  - Append content to existing file or create new file if it doesn't exist
+  - Inputs:
+    - `path` (string): File location
+    - `content` (string): Content to append
+  - Features:
+    - Creates file if it doesn't exist
+    - Appends content to the end of the file
+
 - **create_directory**
   - Create new directory or ensure it exists
   - Input: `path` (string)

src/filesystem/index.ts

@@ -147,6 +147,11 @@ const EditFileArgsSchema = z.object({
   dryRun: z.boolean().default(false).describe('Preview changes using git-style diff format')
 });
 
+const AppendFileArgsSchema = z.object({
+  path: z.string(),
+  content: z.string(),
+});
+
 const CreateDirectoryArgsSchema = z.object({
   path: z.string(),
 });
@@ -548,6 +553,13 @@ server.setRequestHandler(ListToolsRequestSchema, async () => {
           "Only works within allowed directories.",
         inputSchema: zodToJsonSchema(EditFileArgsSchema) as ToolInput,
       },
+      {
+        name: "append_file",
+        description:
+          "Appends content to a file. If the file does not exist, it will be created. " +
+          "Only works within allowed directories.",
+        inputSchema: zodToJsonSchema(AppendFileArgsSchema) as ToolInput,
+      },
       {
         name: "create_directory",
         description:
@@ -769,6 +781,19 @@ server.setRequestHandler(CallToolRequestSchema, async (request) => {
         };
       }
 
+      case "append_file": {
+        const parsed = AppendFileArgsSchema.safeParse(args);
+        if (!parsed.success) {
+          throw new Error(`Invalid arguments for append_file: ${parsed.error}`);
+        }
+
+        const validPath = await validatePath(parsed.data.path);
+        await fs.appendFile(validPath, parsed.data.content, "utf-8");
+        return {
+          content: [{ type: "text", text: `Successfully appended to ${parsed.data.path}` }],
+        };
+      }
+
       case "create_directory": {
         const parsed = CreateDirectoryArgsSchema.safeParse(args);
         if (!parsed.success) {