fix(sse): stop scanner sender when stream context cancels

internal/sse/stream.go

@@ -29,15 +29,29 @@ func StartParsedLinePump(ctx context.Context, body io.Reader, thinkingEnabled bo
 			eof  bool
 		}
 		lineCh := make(chan scanItem, 1)
+		stopScanner := make(chan struct{})
+		defer close(stopScanner)
 		go func() {
+			sendScanItem := func(item scanItem) bool {
+				select {
+				case lineCh <- item:
+					return true
+				case <-ctx.Done():
+					return false
+				case <-stopScanner:
+					return false
+				}
+			}
+			defer close(lineCh)
 			scanner := bufio.NewScanner(body)
 			scanner.Buffer(make([]byte, 0, scannerBufferSize), maxScannerLineSize)
 			for scanner.Scan() {
 				line := append([]byte{}, scanner.Bytes()...)
-				lineCh <- scanItem{line: line}
+				if !sendScanItem(scanItem{line: line}) {
+					return
+				}
 			}
-			lineCh <- scanItem{err: scanner.Err(), eof: true}
-			close(lineCh)
+			_ = sendScanItem(scanItem{err: scanner.Err(), eof: true})
 		}()
 
 		ticker := time.NewTicker(maxFlushWait)