refactor(tasks): drop in-memory task dedup, rely on unique index

The duplicate task rows getTasksForProjects deduplicated came from the
LEFT JOIN multiplying when duplicate task_positions rows existed. The new
unique index on (task_id, project_view_id) removes the root cause at the
SQL layer (the migration also runs before serving), so the join can no
longer multiply. Revert getTasksForProjects and getRawTasksForProjects to
their pre-dedup shape.

pkg/models/kanban.go

@@ -257,7 +257,7 @@ func GetTasksInBucketsForView(s *xorm.Session, view *ProjectView, projects []*Pr
 			}
 		}
 
-		ts, total, err := getRawTasksForProjects(s, projects, auth, opts)
+		ts, _, total, err := getRawTasksForProjects(s, projects, auth, opts)
 		if err != nil {
 			return nil, err
 		}

pkg/models/project.go

@@ -1370,7 +1370,7 @@ func (p *Project) Delete(s *xorm.Session, a web.Auth) (err error) {
 
 	// Delete all tasks on that project
 	// Using the loop to make sure all related entities to all tasks are properly deleted as well.
-	tasks, _, err := getRawTasksForProjects(s, []*Project{p}, a, &taskSearchOptions{})
+	tasks, _, _, err := getRawTasksForProjects(s, []*Project{p}, a, &taskSearchOptions{})
 	if err != nil {
 		return
 	}

pkg/models/task_collection_test.go

@@ -1898,7 +1898,7 @@ func TestTaskSearchWithExpandSubtasks(t *testing.T) {
 		expand: []TaskCollectionExpandable{TaskCollectionExpandSubtasks},
 	}
 
-	tasks, _, err := getRawTasksForProjects(s, []*Project{project}, &user.User{ID: 15}, opts)
+	tasks, _, _, err := getRawTasksForProjects(s, []*Project{project}, &user.User{ID: 15}, opts)
 	require.NoError(t, err)
 	require.NotEmpty(t, tasks)
 }

pkg/models/task_search_bench_test.go

@@ -139,7 +139,7 @@ func BenchmarkTaskSearch(b *testing.B) {
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		s := db.NewSession()
-		resultSlice, _, err := getRawTasksForProjects(s, projects, auth, opts)
+		resultSlice, _, _, err := getRawTasksForProjects(s, projects, auth, opts)
 		if len(resultSlice) == 0 {
 			b.Fatalf("no results found for needle %q", needle)
 		}

pkg/models/tasks.go

@@ -288,11 +288,11 @@ func getTaskIndexFromSearchString(s string) (index int64) {
 	return
 }
 
-func getRawTasksForProjects(s *xorm.Session, projects []*Project, a web.Auth, opts *taskSearchOptions) (tasks []*Task, totalItems int64, err error) {
+func getRawTasksForProjects(s *xorm.Session, projects []*Project, a web.Auth, opts *taskSearchOptions) (tasks []*Task, resultCount int, totalItems int64, err error) {
 
 	// If the user does not have any projects, don't try to get any tasks
 	if len(projects) == 0 {
-		return nil, 0, nil
+		return nil, 0, 0, nil
 	}
 
 	// Get all project IDs and get the tasks
@@ -324,18 +324,17 @@ func getRawTasksForProjects(s *xorm.Session, projects []*Project, a web.Auth, op
 	}
 	tasks, totalItems, err = dbSearcher.Search(opts)
 
-	return tasks, totalItems, err
+	return tasks, len(tasks), totalItems, err
 }
 
 func getTasksForProjects(s *xorm.Session, projects []*Project, a web.Auth, opts *taskSearchOptions, view *ProjectView) (tasks []*Task, resultCount int, totalItems int64, err error) {
-	tasks, totalItems, err = getRawTasksForProjects(s, projects, a, opts)
+	tasks, resultCount, totalItems, err = getRawTasksForProjects(s, projects, a, opts)
 	if err != nil {
 		return nil, 0, 0, err
 	}
 
-	rawTasks := tasks
-	taskMap := make(map[int64]*Task, len(rawTasks))
-	for _, t := range rawTasks {
+	taskMap := make(map[int64]*Task, len(tasks))
+	for _, t := range tasks {
 		taskMap[t.ID] = t
 	}
 
@@ -344,22 +343,7 @@ func getTasksForProjects(s *xorm.Session, projects []*Project, a web.Auth, opts
 		return nil, 0, 0, err
 	}
 
-	// A task can appear more than once in the raw result when it has duplicate
-	// task_positions rows for the view (the LEFT JOIN multiplies it). Return one
-	// entry per task, in the original sort order, referencing the enriched map
-	// value so its identifier and other data are set. totalItems already counts
-	// distinct tasks, so this also aligns the page size with it.
-	tasks = make([]*Task, 0, len(taskMap))
-	seen := make(map[int64]bool, len(taskMap))
-	for _, t := range rawTasks {
-		if seen[t.ID] {
-			continue
-		}
-		seen[t.ID] = true
-		tasks = append(tasks, taskMap[t.ID])
-	}
-
-	return tasks, len(tasks), totalItems, err
+	return tasks, resultCount, totalItems, err
 }
 
 // GetTaskByIDSimple returns a raw task without extra data by the task ID