Bundle workerd JSON schema validator in server shim

Author: mattzcarey

.changeset/workerd-shim-vendors-cfworker.md

@@ -0,0 +1,5 @@
+---
+"@modelcontextprotocol/server": patch
+---
+
+Bundle the workerd/browser JSON Schema validator dependency into the server package's workerd shim output. Workers consumers no longer need to install `@cfworker/json-schema` separately when conditional exports select the edge-safe shim, while Node consumers continue to resolve the Node shim and do not add the validator to the Node runtime path.

packages/server/test/server/barrelClean.test.ts

@@ -8,6 +8,7 @@ import { beforeAll, describe, expect, test } from 'vitest';
 const pkgDir = join(dirname(fileURLToPath(import.meta.url)), '../..');
 const distDir = join(pkgDir, 'dist');
 const NODE_ONLY = /\b(child_process|cross-spawn|node:stream|node:child_process)\b/;
+const CFWORKER_JSON_SCHEMA_IMPORT = /from\s+["']@cfworker\/json-schema["']/;
 
 function chunkImportsOf(entryPath: string): string[] {
     const visited = new Set<string>();
@@ -53,4 +54,15 @@ describe('@modelcontextprotocol/server root entry is browser-safe', () => {
         const stdio = readFileSync(join(distDir, 'stdio.mjs'), 'utf8');
         expect(stdio).toMatch(/\bStdioServerTransport\b/);
     });
+
+    test('workerd shim vendors @cfworker/json-schema instead of requiring consumers to install it', () => {
+        const workerdShim = readFileSync(join(distDir, 'shimsWorkerd.mjs'), 'utf8');
+        expect(workerdShim).not.toMatch(CFWORKER_JSON_SCHEMA_IMPORT);
+
+        for (const chunk of chunkImportsOf(join(distDir, 'shimsWorkerd.mjs'))) {
+            expect({ chunk, content: readFileSync(chunk, 'utf8') }).not.toEqual(
+                expect.objectContaining({ content: expect.stringMatching(CFWORKER_JSON_SCHEMA_IMPORT) })
+            );
+        }
+    });
 });

packages/server/tsdown.config.ts

@@ -31,9 +31,16 @@ export default defineConfig({
             }
         }
     },
-    // 5. Vendoring Strategy - Bundle the code for this specific package into the output,
-    //    but treat all other dependencies as external (require/import).
-    noExternal: ['@modelcontextprotocol/core'],
+    // 5. Vendoring Strategy - Bundle this package's core implementation into the output,
+    //    but treat most dependencies as external (require/import).
+    //
+    //    The workerd/browser `_shims` entry defaults JSON Schema validation to
+    //    CfWorkerJsonSchemaValidator. Bundle @cfworker/json-schema into that shim's chunk so
+    //    Workers consumers get the edge-safe default automatically when conditional exports select
+    //    the workerd/browser shim. Node consumers still resolve `_shims` to shimsNode and the root
+    //    entry only imports `_shims` as a self-reference, so this does not add @cfworker/json-schema
+    //    to the Node runtime path.
+    noExternal: ['@modelcontextprotocol/core', '@cfworker/json-schema'],
 
     // 6. External packages - keep self-reference imports external for runtime resolution
     external: ['@modelcontextprotocol/server/_shims']