fix: Implement proactive packet flushing based on Content-Length to resolve UI update lag

internal/capture/local.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"os/exec"
+	"strconv"
 	"strings"
 	"sync"
 
@@ -133,6 +134,7 @@ func (c *LocalCapturer) processStream(r io.Reader) {
 	var buffer strings.Builder
 	inSIPMessage := false
 	var msgNetInfo *NetInfo
+	contentLength := -1
 
 	for scanner.Scan() {
 		c.mu.Lock()
@@ -192,11 +194,38 @@ func (c *LocalCapturer) processStream(r io.Reader) {
 			}
 
 			inSIPMessage = true
+			contentLength = -1 // Reset for new message
 		}
 
 		if inSIPMessage {
 			buffer.WriteString(line)
 			buffer.WriteString("\r\n")
+
+			// Check for Content-Length
+			lowerLine := strings.ToLower(line)
+			if strings.HasPrefix(lowerLine, "content-length:") || strings.HasPrefix(lowerLine, "l:") {
+				parts := strings.Split(line, ":")
+				if len(parts) >= 2 {
+					val := strings.TrimSpace(parts[1])
+					if val != "" {
+						if cl, err := strconv.Atoi(val); err == nil {
+							contentLength = cl
+						}
+					}
+				}
+			}
+
+			// Check for end of headers (empty line)
+			if line == "" {
+				// If Content-Length is 0 (or not found, treating as 0 for safety in this context usually 0 for BYE/ACK)
+				// Flush immediately
+				if contentLength <= 0 {
+					c.parseAndEmit(buffer.String(), msgNetInfo)
+					buffer.Reset()
+					inSIPMessage = false
+					contentLength = -1
+				}
+			}
 		}
 	}