fix: optimize Gemini stream parsing to support real-time streaming of JSON arrays

internal/providers/gemini_test.go

@@ -3,6 +3,7 @@ package providers
 import (
 	"encoding/json"
 	"reflect"
+	"strings"
 	"testing"
 
 	"gophergate/internal/models"
@@ -209,3 +210,57 @@ func TestEmitGeminiChunk_ToolCalls(t *testing.T) {
 		t.Fatalf("expected response on channel")
 	}
 }
+
+func TestStreamGeminiJSONArrayStream(t *testing.T) {
+	input := `[
+		{
+			"candidates": [
+				{
+					"content": {
+						"parts": [
+							{"text": "Hello"}
+						]
+					}
+				}
+			]
+		},
+		{
+			"candidates": [
+				{
+					"content": {
+						"parts": [
+							{"text": " world"}
+						]
+					}
+				}
+			],
+			"usageMetadata": {
+				"promptTokenCount": 5,
+				"candidatesTokenCount": 2,
+				"totalTokenCount": 7
+			}
+		}
+	]`
+
+	ch := make(chan *models.ChatCompletionStreamResponse, 5)
+	defer close(ch)
+
+	streamGeminiJSONArrayStream(strings.NewReader(input), ch, "gemini-2.5-flash")
+
+	var texts []string
+	for i := 0; i < 2; i++ {
+		select {
+		case resp := <-ch:
+			if len(resp.Choices) > 0 && resp.Choices[0].Delta.Content != nil {
+				texts = append(texts, *resp.Choices[0].Delta.Content)
+			}
+		default:
+			t.Fatalf("expected chunk %d", i+1)
+		}
+	}
+
+	joined := strings.Join(texts, "")
+	if joined != "Hello world" {
+		t.Errorf("expected 'Hello world', got %q", joined)
+	}
+}