修复接续流的增量bug

internal/sse/dedupe.go

@@ -0,0 +1,22 @@
+package sse
+
+import "strings"
+
+// TrimContinuationOverlap removes the already-seen prefix when DeepSeek
+// continue rounds resend the full fragment snapshot instead of only the new
+// suffix. Non-overlapping chunks are returned unchanged.
+func TrimContinuationOverlap(existing, incoming string) string {
+	if incoming == "" {
+		return ""
+	}
+	if existing == "" {
+		return incoming
+	}
+	if strings.HasPrefix(incoming, existing) {
+		return incoming[len(existing):]
+	}
+	if strings.HasPrefix(existing, incoming) {
+		return ""
+	}
+	return incoming
+}