fix(aistudio): strip usage metadata from non-final stream chunks

internal/runtime/executor/aistudio_executor.go

@@ -150,14 +150,16 @@ func (e *AistudioExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth
 			case wsrelay.MessageTypeStreamChunk:
 				if len(event.Payload) > 0 {
 					appendAPIResponseChunk(ctx, e.cfg, bytes.Clone(event.Payload))
-					if detail, ok := parseGeminiStreamUsage(event.Payload); ok {
+					filtered := filterAistudioUsageMetadata(event.Payload)
+					if detail, ok := parseGeminiStreamUsage(filtered); ok {
 						reporter.publish(ctx, detail)
 					}
-				}
-				lines := sdktranslator.TranslateStream(ctx, body.toFormat, opts.SourceFormat, req.Model, bytes.Clone(opts.OriginalRequest), translatedReq, bytes.Clone(event.Payload), &param)
+					lines := sdktranslator.TranslateStream(ctx, body.toFormat, opts.SourceFormat, req.Model, bytes.Clone(opts.OriginalRequest), translatedReq, bytes.Clone(filtered), &param)
 					for i := range lines {
 						out <- cliproxyexecutor.StreamChunk{Payload: []byte(lines[i])}
 					}
+					break
+				}
 			case wsrelay.MessageTypeStreamEnd:
 				return
 			case wsrelay.MessageTypeHTTPResp:
@@ -281,3 +283,62 @@ func (e *AistudioExecutor) buildEndpoint(model, action, alt string) string {
 	}
 	return base
 }
+
+// filterAistudioUsageMetadata removes usageMetadata from intermediate SSE events so that
+// only the terminal chunk retains token statistics.
+func filterAistudioUsageMetadata(payload []byte) []byte {
+	if len(payload) == 0 {
+		return payload
+	}
+
+	lines := bytes.Split(payload, []byte("\n"))
+	modified := false
+	for idx, line := range lines {
+		trimmed := bytes.TrimSpace(line)
+		if len(trimmed) == 0 || !bytes.HasPrefix(trimmed, []byte("data:")) {
+			continue
+		}
+		dataIdx := bytes.Index(line, []byte("data:"))
+		if dataIdx < 0 {
+			continue
+		}
+		rawJSON := bytes.TrimSpace(line[dataIdx+5:])
+		cleaned, changed := stripUsageMetadataFromJSON(rawJSON)
+		if !changed {
+			continue
+		}
+		var rebuilt []byte
+		rebuilt = append(rebuilt, line[:dataIdx]...)
+		rebuilt = append(rebuilt, []byte("data:")...)
+		if len(cleaned) > 0 {
+			rebuilt = append(rebuilt, ' ')
+			rebuilt = append(rebuilt, cleaned...)
+		}
+		lines[idx] = rebuilt
+		modified = true
+	}
+	if !modified {
+		return payload
+	}
+	return bytes.Join(lines, []byte("\n"))
+}
+
+// stripUsageMetadataFromJSON drops usageMetadata when no finishReason is present.
+func stripUsageMetadataFromJSON(rawJSON []byte) ([]byte, bool) {
+	jsonBytes := bytes.TrimSpace(rawJSON)
+	if len(jsonBytes) == 0 || !gjson.ValidBytes(jsonBytes) {
+		return rawJSON, false
+	}
+	finishReason := gjson.GetBytes(jsonBytes, "candidates.0.finishReason")
+	if finishReason.Exists() && finishReason.String() != "" {
+		return rawJSON, false
+	}
+	if !gjson.GetBytes(jsonBytes, "usageMetadata").Exists() {
+		return rawJSON, false
+	}
+	cleaned, err := sjson.DeleteBytes(jsonBytes, "usageMetadata")
+	if err != nil {
+		return rawJSON, false
+	}
+	return cleaned, true
+}