feat(infra/llm): Gemini client with stream + count_tokens via google.golang.org/genai

internal/infra/llm/gemini_test.go

@@ -0,0 +1,55 @@
+package llm
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// Gemini SSE 行格式：每行 "data: {json}\n"，body 内含完整 candidates。
+const geminiStreamFixture = `data: {"candidates":[{"content":{"parts":[{"text":"Hello"}],"role":"model"},"finishReason":null}],"usageMetadata":{"promptTokenCount":10,"candidatesTokenCount":1}}
+
+data: {"candidates":[{"content":{"parts":[{"text":" world"}],"role":"model"},"finishReason":"STOP"}],"usageMetadata":{"promptTokenCount":10,"candidatesTokenCount":2}}
+
+`
+
+func TestGemini_Stream_TextDelta(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = w.Write([]byte(geminiStreamFixture))
+	}))
+	defer srv.Close()
+
+	c, _ := NewGemini("k", srv.URL)
+	ch, err := c.Stream(context.Background(), "gemini-2.0-flash", Request{
+		Messages:        []Message{{Role: RoleUser, Blocks: []ContentBlock{{Type: "text", Text: "hi"}}}},
+		MaxOutputTokens: 100,
+	})
+	require.NoError(t, err)
+
+	var deltas []string
+	var sawUsage, sawDone bool
+	for ev := range ch {
+		switch ev.Type {
+		case EventTextDelta:
+			deltas = append(deltas, ev.Text)
+		case EventUsage:
+			sawUsage = true
+			require.Equal(t, 10, ev.Usage.PromptTokens)
+		case EventDone:
+			sawDone = true
+		}
+	}
+	require.Equal(t, "Hello world", strings.Join(deltas, ""))
+	require.True(t, sawUsage)
+	require.True(t, sawDone)
+}
+
+func TestGemini_Provider(t *testing.T) {
+	c, _ := NewGemini("k", "http://localhost")
+	require.Equal(t, "gemini", c.Provider())
+}