fix(admin): filter usage logs by request id

backend/internal/handler/admin/usage_handler.go

@@ -110,6 +110,7 @@ func (h *UsageHandler) List(c *gin.Context) {
 	}
 
 	model := c.Query("model")
+	requestID := strings.TrimSpace(c.Query("request_id"))
 	billingMode := strings.TrimSpace(c.Query("billing_mode"))
 
 	var requestType *int16
@@ -176,6 +177,7 @@ func (h *UsageHandler) List(c *gin.Context) {
 		APIKeyID:          apiKeyID,
 		AccountID:         accountID,
 		GroupID:           groupID,
+		RequestID:         requestID,
 		Model:             model,
 		ModelFilterSource: usagestats.ModelSourceRequested,
 		RequestType:       requestType,

backend/internal/handler/admin/usage_handler_request_type_test.go

@@ -107,6 +107,18 @@ func TestAdminUsageListExactTotalTrue(t *testing.T) {
 	require.True(t, repo.listFilters.ExactTotal)
 }
 
+func TestAdminUsageListRequestIDFilter(t *testing.T) {
+	repo := &adminUsageRepoCapture{}
+	router := newAdminUsageRequestTypeTestRouter(repo)
+
+	req := httptest.NewRequest(http.MethodGet, "/admin/usage?request_id=req-0123", nil)
+	rec := httptest.NewRecorder()
+	router.ServeHTTP(rec, req)
+
+	require.Equal(t, http.StatusOK, rec.Code)
+	require.Equal(t, "req-0123", repo.listFilters.RequestID)
+}
+
 func TestAdminUsageListInvalidExactTotal(t *testing.T) {
 	repo := &adminUsageRepoCapture{}
 	router := newAdminUsageRequestTypeTestRouter(repo)