fix(backend): keep workspace completion metadata honest

backend/internal/logic/projects/workspace_test.go

@@ -3,6 +3,7 @@ package projects
 import (
 	"encoding/json"
 	"fmt"
+	"os"
 	"testing"
 	"time"
 
@@ -63,7 +64,7 @@ func TestWorkspaceUsesIdentitiesUTCTimesAndProjectScopedTags(t *testing.T) {
 	require.Equal(t, "UI", workspace.Tasks[0].Tag)
 	require.Equal(t, nextRun.UTC(), *workspace.Tasks[0].Due)
 	require.Equal(t, createdAt.UTC(), workspace.Tasks[0].CreatedAt)
-	require.Equal(t, updatedAt.UTC(), *workspace.Tasks[0].CompletedAt)
+	require.Nil(t, workspace.Tasks[0].CompletedAt)
 
 	require.Len(t, workspace.AISessions, 1)
 	require.Equal(t, session.Identity, workspace.AISessions[0].ID)
@@ -93,6 +94,34 @@ func TestWorkspaceUsesIdentitiesUTCTimesAndProjectScopedTags(t *testing.T) {
 	require.NotContains(t, string(payload), "duration")
 }
 
+func TestWorkspaceDoneTaskDoesNotInventCompletedAt(t *testing.T) {
+	database := newTestDB(t)
+	service := NewService()
+	require.NoError(t, database.Create(&models.SenlinAgentUser{Email: "owner@example.com", DisplayName: "Owner", PasswordHash: "hash"}).Error)
+	project, err := service.CreateProject(1, "Alpha", "")
+	require.NoError(t, err)
+	createdAt := time.Date(2026, 7, 20, 1, 0, 0, 0, time.UTC)
+	updatedAt := createdAt.Add(2 * time.Hour)
+	require.NoError(t, database.Create(&models.SenlinAgentTask{
+		ProjectID: project.ID, CreatedBy: 1, Title: "Done", Status: "done", CreatedAt: createdAt, UpdatedAt: updatedAt,
+	}).Error)
+
+	workspace, err := service.Workspace(1, project.Identity)
+
+	require.NoError(t, err)
+	require.Len(t, workspace.Tasks, 1)
+	require.Nil(t, workspace.Tasks[0].CompletedAt)
+	payload, err := json.Marshal(workspace.Tasks[0])
+	require.NoError(t, err)
+	require.Contains(t, string(payload), `"completedAt":null`)
+}
+
+func TestWorkspaceFileDoesNotOwnDashboard(t *testing.T) {
+	source, err := os.ReadFile("workspace.go")
+	require.NoError(t, err)
+	require.NotContains(t, string(source), "func (s *Service) Dashboard")
+}
+
 func TestWorkspaceRejectsProjectOwnedByAnotherUserByIdentity(t *testing.T) {
 	newTestDB(t)
 	service := NewService()