fix: release HTTP connections after POST responses (modelcontextprotocol#1214)

Co-authored-by: Konstantin Konstantinov <KKonstantinov@users.noreply.github.com>

Author: mattzcarey

src/client/sse.ts

@@ -281,6 +281,9 @@ export class SSEClientTransport implements Transport {
 
                 throw new Error(`Error POSTing to endpoint (HTTP ${response.status}): ${text}`);
             }
+
+            // Release connection - POST responses don't have content we need
+            await response.body?.cancel();
         } catch (error) {
             this.onerror?.(error as Error);
             throw error;

src/client/streamableHttp.ts

@@ -592,8 +592,12 @@ export class StreamableHTTPClientTransport implements Transport {
                         this.onmessage?.(msg);
                     }
                 } else {
+                    await response.body?.cancel();
                     throw new StreamableHTTPError(-1, `Unexpected content type: ${contentType}`);
                 }
+            } else {
+                // No requests in message but got 200 OK - still need to release connection
+                await response.body?.cancel();
             }
         } catch (error) {
             this.onerror?.(error as Error);