fix: restore reviewable migration evidence

proxy/sse_event.go

@@ -0,0 +1,65 @@
+package proxy
+
+import (
+	"bytes"
+	"encoding/json"
+	"strings"
+)
+
+type sseEventTracker struct {
+	buf      []byte
+	terminal bool
+}
+
+func (t *sseEventTracker) Write(p []byte) {
+	t.buf = append(t.buf, p...)
+	for {
+		end, separator := completeSSEEvent(t.buf)
+		if end < 0 {
+			return
+		}
+		event := t.buf[:end]
+		t.buf = t.buf[end+separator:]
+		if terminalSSEEvent(event) {
+			t.terminal = true
+		}
+	}
+}
+
+func (t *sseEventTracker) Complete() bool { return len(t.buf) == 0 }
+
+func completeSSEEvent(buf []byte) (int, int) {
+	lf := bytes.Index(buf, []byte("\n\n"))
+	crlf := bytes.Index(buf, []byte("\r\n\r\n"))
+	if crlf >= 0 && (lf < 0 || crlf < lf) {
+		return crlf, 4
+	}
+	if lf >= 0 {
+		return lf, 2
+	}
+	return -1, 0
+}
+
+func terminalSSEEvent(event []byte) bool {
+	var data strings.Builder
+	for _, line := range strings.Split(strings.ReplaceAll(string(event), "\r\n", "\n"), "\n") {
+		if !strings.HasPrefix(line, "data:") {
+			continue
+		}
+		if data.Len() > 0 {
+			data.WriteByte('\n')
+		}
+		data.WriteString(strings.TrimSpace(strings.TrimPrefix(line, "data:")))
+	}
+	payload := data.String()
+	if payload == "[DONE]" {
+		return true
+	}
+	var envelope struct {
+		Type string `json:"type"`
+	}
+	if json.Unmarshal([]byte(payload), &envelope) != nil {
+		return false
+	}
+	return envelope.Type == "message_stop" || envelope.Type == "response.completed"
+}