feat(tasks): assign tasks in shared lists, unified people search, list avatars

- Tasks in shared task lists can be assigned to one or more people with access
  (task_assignees); assignments are pruned whenever access is lost
- UserAutocomplete: type-to-search everywhere, nothing before typing, max 3 results,
  first match preselected
- Task list and list tabs: avatar stack of members and round monochrome counter
- Shared list items remember who added them (list_items.created_by)
- Doku/ui-patterns.md documents the shared UI patterns

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/storage/sqlite.go

@@ -398,6 +398,13 @@ func (s *Store) migrate() error {
 		"CREATE TABLE IF NOT EXISTS block_tags (tag TEXT NOT NULL, document_id TEXT NOT NULL, block_id TEXT NOT NULL, PRIMARY KEY(tag, block_id), FOREIGN KEY(document_id) REFERENCES documents(id) ON DELETE CASCADE, FOREIGN KEY(block_id) REFERENCES blocks(id) ON DELETE CASCADE);",
 		"CREATE INDEX IF NOT EXISTS idx_block_tags_tag ON block_tags(tag);",
 		"CREATE INDEX IF NOT EXISTS idx_block_tags_doc ON block_tags(document_id);",
+
+		// Task assignments: who a task in a shared task list is assigned to
+		"CREATE TABLE IF NOT EXISTS task_assignees (task_id TEXT NOT NULL, user_id TEXT NOT NULL, created_at TEXT NOT NULL, PRIMARY KEY(task_id, user_id), FOREIGN KEY(task_id) REFERENCES thoughts(id) ON DELETE CASCADE);",
+		"CREATE INDEX IF NOT EXISTS idx_task_assignees_user ON task_assignees(user_id);",
+
+		// Who added an item to a (shopping) list
+		"ALTER TABLE list_items ADD COLUMN created_by TEXT NOT NULL DEFAULT '';",
 	}
 	for _, q := range columnMigrations {
 		_, _ = s.db.Exec(q)
@@ -812,6 +819,7 @@ func (s *Store) UpdateUserPassword(userID, passwordHash string) error {
 
 func (s *Store) DeleteUser(userID string) error {
 	_, _ = s.db.Exec(`DELETE FROM revoked_tokens WHERE user_id = ?`, userID)
+	_, _ = s.db.Exec(`DELETE FROM task_assignees WHERE user_id = ?`, userID)
 	_, err := s.db.Exec(`DELETE FROM users WHERE id = ?`, userID)
 	return err
 }
@@ -956,6 +964,7 @@ func scanThought(rows interface {
 		t.DocID = parts[0]
 		t.BlockID = parts[1]
 	}
+	t.Assignees = []string{}
 	t.Subtasks = []domain.SubTask{}
 	if subtasksStr != "" && subtasksStr != "null" {
 		_ = json.Unmarshal([]byte(subtasksStr), &t.Subtasks)
@@ -980,7 +989,12 @@ func (s *Store) GetThoughtByID(userID, thoughtID string) (*domain.Thought, error
 		 FROM thoughts WHERE id = ? AND (user_id = ? OR task_list_id IN (`+s.accessibleTaskListIDsQuery()+`))`,
 		thoughtID, userID, userID, userID, userID, userID,
 	)
-	return scanThought(row)
+	t, err := scanThought(row)
+	if err != nil {
+		return nil, err
+	}
+	t.Assignees = s.getTaskAssignees(t.ID)
+	return t, nil
 }
 
 func (s *Store) GetThoughts(userID, statusFilter string, limit int) ([]domain.Thought, error) {
@@ -1055,6 +1069,7 @@ func (s *Store) GetTasks(userID string, taskListID string) ([]domain.Thought, er
 		}
 	}
 	_ = rows.Close()
+	s.attachTaskAssignees(result)
 	return result, nil
 }
 
@@ -1190,7 +1205,7 @@ func (s *Store) UpdateThoughtTriage(userID, thoughtID, action, convertTo, target
 		} else if convertTo == "list_item" && targetListID != "" {
 			newStatus = domain.StatusConverted
 			convertedType = "list_item"
-			item, err := s.CreateListItem(targetListID, thought.Content, "", "", 0)
+			item, err := s.CreateListItem(targetListID, thought.Content, "", "", 0, userID)
 			if err == nil && item != nil {
 				convertedRefID = item.ID
 			}
@@ -1208,6 +1223,9 @@ func (s *Store) UpdateThoughtTriage(userID, thoughtID, action, convertTo, target
 	if err != nil {
 		return nil, err
 	}
+	if taskListID != thought.TaskListID {
+		s.PruneTaskAssignees()
+	}
 
 	return s.GetThoughtByID(userID, thoughtID)
 }
@@ -1285,6 +1303,10 @@ func (s *Store) UpdateThoughtDetails(userID, thoughtID string, content *string,
 	if err != nil {
 		return nil, err
 	}
+	if taskListID != nil {
+		s.PruneTaskAssignees()
+		thought.Assignees = s.getTaskAssignees(thoughtID)
+	}
 	return thought, nil
 }
 
@@ -3625,6 +3647,7 @@ func (s *Store) GetAllListsForUser(userID string) ([]domain.SharedList, error) {
 	for i := range lists {
 		lists[i].Items, _ = s.GetListItems(lists[i].ID)
 		lists[i].Shares, _ = s.GetListShares(lists[i].ID)
+		lists[i].Members = s.getListMembers(lists[i].ID, lists[i].UserID)
 	}
 	return lists, nil
 }
@@ -3673,9 +3696,38 @@ func (s *Store) GetListByID(userID, listID string) (*domain.SharedList, error) {
 	l.Role = effectiveRole
 	l.Items, _ = s.GetListItems(l.ID)
 	l.Shares, _ = s.GetListShares(l.ID)
+	l.Members = s.getListMembers(l.ID, l.UserID)
 	return &l, nil
 }
 
+// getListMembers returns the owner and everyone a list is shared with (directly or via a team).
+func (s *Store) getListMembers(listID, ownerID string) []domain.TaskListMember {
+	members := make([]domain.TaskListMember, 0)
+	rows, err := s.db.Query(
+		`SELECT id, display_name, email, avatar_url FROM users WHERE id IN (
+		    SELECT user_id FROM lists WHERE id = ?
+		    UNION SELECT target_id FROM list_shares WHERE list_id = ? AND target_type = 'user'
+		    UNION SELECT user_id FROM team_members WHERE team_id IN (SELECT target_id FROM list_shares WHERE list_id = ? AND target_type = 'team')
+		 ) ORDER BY display_name`,
+		listID, listID, listID,
+	)
+	if err != nil {
+		return members
+	}
+	defer rows.Close()
+	for rows.Next() {
+		var m domain.TaskListMember
+		if rows.Scan(&m.UserID, &m.DisplayName, &m.Email, &m.AvatarURL) == nil {
+			m.Role = "member"
+			if m.UserID == ownerID {
+				m.Role = "owner"
+			}
+			members = append(members, m)
+		}
+	}
+	return members
+}
+
 func (s *Store) DeleteList(userID, listID string) error {
 	var ownerID string
 	err := s.db.QueryRow(`SELECT user_id FROM lists WHERE id = ?`, listID).Scan(&ownerID)
@@ -3691,9 +3743,11 @@ func (s *Store) DeleteList(userID, listID string) error {
 
 func (s *Store) GetListItems(listID string) ([]domain.ListItem, error) {
 	rows, err := s.db.Query(
-		`SELECT id, list_id, content, category, quantity, is_completed, completed_by, completed_by_name, sort_order, created_at, completed_at
-		 FROM list_items WHERE list_id = ?
-		 ORDER BY is_completed ASC, sort_order ASC, created_at DESC`,
+		`SELECT li.id, li.list_id, li.content, li.category, li.quantity, li.is_completed, li.completed_by, li.completed_by_name,
+		        li.created_by, COALESCE(u.display_name, ''), li.sort_order, li.created_at, li.completed_at
+		 FROM list_items li LEFT JOIN users u ON u.id = li.created_by AND li.created_by != ''
+		 WHERE li.list_id = ?
+		 ORDER BY li.is_completed ASC, li.sort_order ASC, li.created_at DESC`,
 		listID,
 	)
 	if err != nil {
@@ -3705,7 +3759,7 @@ func (s *Store) GetListItems(listID string) ([]domain.ListItem, error) {
 	for rows.Next() {
 		var it domain.ListItem
 		var doneInt int
-		if err := rows.Scan(&it.ID, &it.ListID, &it.Content, &it.Category, &it.Quantity, &doneInt, &it.CompletedBy, &it.CompletedByName, &it.SortOrder, &it.CreatedAt, &it.CompletedAt); err == nil {
+		if err := rows.Scan(&it.ID, &it.ListID, &it.Content, &it.Category, &it.Quantity, &doneInt, &it.CompletedBy, &it.CompletedByName, &it.CreatedBy, &it.CreatedByName, &it.SortOrder, &it.CreatedAt, &it.CompletedAt); err == nil {
 			it.IsCompleted = doneInt != 0
 			items = append(items, it)
 		}
@@ -3713,7 +3767,7 @@ func (s *Store) GetListItems(listID string) ([]domain.ListItem, error) {
 	return items, nil
 }
 
-func (s *Store) CreateListItem(listID, content, category, quantity string, sortOrder int) (*domain.ListItem, error) {
+func (s *Store) CreateListItem(listID, content, category, quantity string, sortOrder int, createdBy string) (*domain.ListItem, error) {
 	content = strings.TrimSpace(content)
 	if content == "" {
 		return nil, errors.New("item content cannot be empty")
@@ -3743,13 +3797,17 @@ func (s *Store) CreateListItem(listID, content, category, quantity string, sortO
 		Quantity:    strings.TrimSpace(quantity),
 		IsCompleted: false,
 		SortOrder:   sortOrder,
+		CreatedBy:   createdBy,
 		CreatedAt:   now,
 	}
+	if createdBy != "" {
+		_ = s.db.QueryRow(`SELECT display_name FROM users WHERE id = ?`, createdBy).Scan(&it.CreatedByName)
+	}
 
 	_, err := s.db.Exec(
-		`INSERT INTO list_items (id, list_id, content, category, quantity, is_completed, sort_order, created_at)
-		 VALUES (?, ?, ?, ?, ?, 0, ?, ?)`,
-		it.ID, it.ListID, it.Content, it.Category, it.Quantity, it.SortOrder, it.CreatedAt,
+		`INSERT INTO list_items (id, list_id, content, category, quantity, is_completed, sort_order, created_at, created_by)
+		 VALUES (?, ?, ?, ?, ?, 0, ?, ?, ?)`,
+		it.ID, it.ListID, it.Content, it.Category, it.Quantity, it.SortOrder, it.CreatedAt, it.CreatedBy,
 	)
 	if err != nil {
 		return nil, err
@@ -4173,6 +4231,9 @@ func (s *Store) CreateTaskList(userID, spaceID, teamID, title, icon, color strin
 // ErrTaskListReadOnly is returned when a user with viewer permission tries to modify a task list or its tasks.
 var ErrTaskListReadOnly = errors.New("Keine Schreibrechte für diese Aufgabenliste (nur Lesen)")
 
+// ErrAssigneeNoAccess is returned when a task should be assigned to someone who cannot see its list.
+var ErrAssigneeNoAccess = errors.New("Aufgaben können nur Personen mit Zugriff auf die Liste zugewiesen werden")
+
 // GetTaskListPermission returns "owner", "editor", "viewer" or "" (no access) for the given user.
 func (s *Store) GetTaskListPermission(userID, listID string) string {
 	var ownerID, teamID string
@@ -4283,6 +4344,7 @@ func (s *Store) RemoveTaskListShare(taskListID, shareIDOrTargetID string) error
 	if targetType == "team" {
 		_, _ = s.db.Exec(`UPDATE task_lists SET team_id = '' WHERE id = ? AND team_id = ?`, taskListID, targetID)
 	}
+	s.PruneTaskAssignees()
 	return err
 }
 
@@ -4333,6 +4395,129 @@ func (s *Store) queryUserIDs(query string, args ...interface{}) []string {
 	return ids
 }
 
+// taskListAccessSQL selects every user ID with access to the task list given as the single parameter.
+// It mirrors GetTaskListUserIDs and is correlated into PruneTaskAssignees.
+const taskListAccessSQL = `SELECT user_id FROM task_lists WHERE id = %[1]s
+		 UNION SELECT target_id FROM task_list_shares WHERE task_list_id = %[1]s AND target_type = 'user'
+		 UNION SELECT tm.user_id FROM team_members tm
+		       WHERE tm.team_id IN (SELECT target_id FROM task_list_shares WHERE task_list_id = %[1]s AND target_type = 'team')
+		          OR tm.team_id IN (SELECT team_id FROM task_lists WHERE id = %[1]s AND team_id != '')`
+
+func (s *Store) getTaskAssignees(taskID string) []string {
+	ids := s.queryUserIDs(`SELECT user_id FROM task_assignees WHERE task_id = ? ORDER BY created_at ASC`, taskID)
+	return ids
+}
+
+// attachTaskAssignees fills Assignees for a batch of tasks with a single query.
+func (s *Store) attachTaskAssignees(tasks []domain.Thought) {
+	if len(tasks) == 0 {
+		return
+	}
+	idx := make(map[string]int, len(tasks))
+	placeholders := make([]string, 0, len(tasks))
+	args := make([]interface{}, 0, len(tasks))
+	for i := range tasks {
+		idx[tasks[i].ID] = i
+		placeholders = append(placeholders, "?")
+		args = append(args, tasks[i].ID)
+	}
+	rows, err := s.db.Query(
+		`SELECT task_id, user_id FROM task_assignees WHERE task_id IN (`+strings.Join(placeholders, ",")+`) ORDER BY created_at ASC`,
+		args...,
+	)
+	if err != nil {
+		return
+	}
+	defer rows.Close()
+	for rows.Next() {
+		var taskID, uid string
+		if rows.Scan(&taskID, &uid) == nil {
+			if i, ok := idx[taskID]; ok {
+				tasks[i].Assignees = append(tasks[i].Assignees, uid)
+			}
+		}
+	}
+}
+
+// SetTaskAssignees replaces the assignees of a task. Only editors of the task's list may assign, and only
+// people who can see the list are accepted.
+func (s *Store) SetTaskAssignees(userID, taskID string, assignees []string) ([]string, error) {
+	thought, err := s.GetThoughtByID(userID, taskID)
+	if err != nil {
+		return nil, err
+	}
+	if thought.TaskListID == "" {
+		if len(assignees) > 0 {
+			return nil, ErrAssigneeNoAccess
+		}
+		return []string{}, nil
+	}
+	if !s.CanEditTaskList(userID, thought.TaskListID) {
+		return nil, ErrTaskListReadOnly
+	}
+	allowed := make(map[string]bool)
+	for _, id := range s.GetTaskListUserIDs(thought.TaskListID) {
+		allowed[id] = true
+	}
+	clean := make([]string, 0, len(assignees))
+	seen := make(map[string]bool)
+	for _, id := range assignees {
+		id = strings.TrimSpace(id)
+		if id == "" || seen[id] {
+			continue
+		}
+		if !allowed[id] {
+			return nil, ErrAssigneeNoAccess
+		}
+		seen[id] = true
+		clean = append(clean, id)
+	}
+
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+	keep := make([]interface{}, 0, len(clean)+1)
+	keep = append(keep, taskID)
+	ph := make([]string, 0, len(clean))
+	for _, id := range clean {
+		keep = append(keep, id)
+		ph = append(ph, "?")
+	}
+	delQuery := `DELETE FROM task_assignees WHERE task_id = ?`
+	if len(ph) > 0 {
+		delQuery += ` AND user_id NOT IN (` + strings.Join(ph, ",") + `)`
+	}
+	if _, err := tx.Exec(delQuery, keep...); err != nil {
+		return nil, err
+	}
+	now := domain.NowISO()
+	for _, id := range clean {
+		if _, err := tx.Exec(`INSERT OR IGNORE INTO task_assignees (task_id, user_id, created_at) VALUES (?, ?, ?)`, taskID, id, now); err != nil {
+			return nil, err
+		}
+	}
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	return s.getTaskAssignees(taskID), nil
+}
+
+// PruneTaskAssignees drops every assignment whose user can no longer see the task's list (share removed,
+// left the team, team deleted, task moved to another list or out of any list). Called after each change
+// that can take access away, so assignments never outlive permissions.
+func (s *Store) PruneTaskAssignees() {
+	_, _ = s.db.Exec(
+		`DELETE FROM task_assignees WHERE rowid IN (
+		    SELECT ta.rowid FROM task_assignees ta
+		    LEFT JOIN thoughts t ON t.id = ta.task_id
+		    WHERE t.id IS NULL OR t.task_list_id = ''
+		       OR ta.user_id NOT IN (` + fmt.Sprintf(taskListAccessSQL, "t.task_list_id") + `)
+		 )`,
+	)
+}
+
 // GetTaskListUserIDs returns every user who can see the task list: owner, direct shares, members of shared teams
 // and members of the legacy team_id.
 func (s *Store) GetTaskListUserIDs(listID string) []string {
@@ -4574,6 +4759,9 @@ func (s *Store) UpdateTaskList(userID, listID string, title, icon, color, teamID
 	if err != nil {
 		return nil, err
 	}
+	if teamID != nil {
+		s.PruneTaskAssignees()
+	}
 	return s.GetTaskListByID(userID, listID)
 }
 
@@ -4581,6 +4769,7 @@ func (s *Store) DeleteTaskList(userID, listID string) error {
 	_, _ = s.db.Exec(`UPDATE thoughts SET task_list_id = '' WHERE task_list_id = ?`, listID)
 	_, _ = s.db.Exec(`DELETE FROM task_list_shares WHERE task_list_id = ?`, listID)
 	_, err := s.db.Exec(`DELETE FROM task_lists WHERE id = ? AND user_id = ?`, listID, userID)
+	s.PruneTaskAssignees()
 	return err
 }
 
@@ -4709,6 +4898,7 @@ func (s *Store) CreateTeam(orgID, name, description string) (*domain.Team, error
 
 func (s *Store) DeleteTeam(teamID string) error {
 	_, err := s.db.Exec(`DELETE FROM teams WHERE id = ?`, teamID)
+	s.PruneTaskAssignees()
 	return err
 }
 
@@ -4888,6 +5078,7 @@ func (s *Store) RemoveTeamMember(teamID, userID string) error {
 		}
 	}
 	_, err = s.db.Exec(`DELETE FROM team_members WHERE team_id = ? AND user_id = ?`, teamID, userID)
+	s.PruneTaskAssignees()
 	return err
 }