Revert "fix(server): application/json header for notifictions" (modelcontextprotocol#1388)

Author: mattzcarey

.changeset/strong-hairs-study.md .changeset/heavy-walls-swim.md.changeset/strong-hairs-study.md renamed to .changeset/heavy-walls-swim.md

@@ -2,4 +2,4 @@
 '@modelcontextprotocol/server': patch
 ---
 
-add application/json header for notifications
+reverting application/json in notifications

packages/middleware/node/test/streamableHttp.test.ts

@@ -657,7 +657,6 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
             const response = await sendPostRequest(baseUrl, batchNotifications, sessionId);
 
             expect(response.status).toBe(202);
-            expect(response.headers.get('content-type')).toBe('application/json');
         });
 
         it('should handle batch request messages with SSE stream for responses', async () => {

packages/server/src/server/streamableHttp.ts

@@ -667,12 +667,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
                 for (const message of messages) {
                     this.onmessage?.(message, { authInfo: options?.authInfo, requestInfo });
                 }
-                return new Response(null, {
-                    status: 202,
-                    headers: {
-                        'Content-Type': 'application/json'
-                    }
-                });
+                return new Response(null, { status: 202 });
             }
 
             // The default behavior is to use SSE streaming