fix(filesystem): address review feedback from #3016 (#3031)

Address two items from Camila's review:

1. Use blob type for non-image/non-audio media files, restoring the
   original behavior. This matches the previous implementation which
   used blob as the fallback for unknown binary types. Use type
   assertion to satisfy the SDK's type constraints.

2. Reuse ReadTextFileArgsSchema.shape in the deprecated read_file tool
   instead of redefining the schema inline.

Author: domdomegg

src/filesystem/index.ts

@@ -3,6 +3,7 @@
 import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
 import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
 import {
+  CallToolResult,
   RootsListChangedNotificationSchema,
   type Root,
 } from "@modelcontextprotocol/sdk/types.js";
@@ -199,11 +200,7 @@ server.registerTool(
   {
     title: "Read File (Deprecated)",
     description: "Read the complete contents of a file as text. DEPRECATED: Use read_text_file instead.",
-    inputSchema: {
-      path: z.string(),
-      tail: z.number().optional().describe("If provided, returns only the last N lines of the file"),
-      head: z.number().optional().describe("If provided, returns only the first N lines of the file")
-    },
+    inputSchema: ReadTextFileArgsSchema.shape,
     outputSchema: {
       content: z.array(z.object({
         type: z.literal("text"),
@@ -253,7 +250,7 @@ server.registerTool(
     },
     outputSchema: {
       content: z.array(z.object({
-        type: z.enum(["image", "audio"]),
+        type: z.enum(["image", "audio", "blob"]),
         data: z.string(),
         mimeType: z.string()
       }))
@@ -278,17 +275,15 @@ server.registerTool(
     const mimeType = mimeTypes[extension] || "application/octet-stream";
     const data = await readFileAsBase64Stream(validPath);
 
-    if (mimeType.startsWith("audio/")) {
-      return {
-        content: [{ type: "audio" as const, data, mimeType }],
-      };
-    } else {
-      // For all other media types including images and unknown types, return as image
-      // (MCP ImageContent can handle any base64-encoded binary data with appropriate mimeType)
-      return {
-        content: [{ type: "image" as const, data, mimeType }],
-      };
-    }
+    const type = mimeType.startsWith("image/")
+      ? "image"
+      : mimeType.startsWith("audio/")
+        ? "audio"
+        // Fallback for other binary types, not officially supported by the spec but has been used for some time
+        : "blob";
+    return {
+      content: [{ type, data, mimeType }],
+    } as unknown as CallToolResult;
   }
 );