fix: add Transfer-Encoding chunked to SSE responses (#1619)

Author: guoyangzhen

packages/server/src/server/streamableHttp.ts

@@ -450,6 +450,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
         const headers: Record<string, string> = {
             'Content-Type': 'text/event-stream',
             'Cache-Control': 'no-cache, no-transform',
+            'Transfer-Encoding': 'chunked',
             Connection: 'keep-alive'
         };
 
@@ -503,6 +504,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
             const headers: Record<string, string> = {
                 'Content-Type': 'text/event-stream',
                 'Cache-Control': 'no-cache, no-transform',
+                'Transfer-Encoding': 'chunked',
                 Connection: 'keep-alive'
             };
 
@@ -751,6 +753,7 @@ export class WebStandardStreamableHTTPServerTransport implements Transport {
             const headers: Record<string, string> = {
                 'Content-Type': 'text/event-stream',
                 'Cache-Control': 'no-cache',
+                'Transfer-Encoding': 'chunked',
                 Connection: 'keep-alive'
             };