Function isSubagentDescendant

coderd/x/chatd/subagent.go:1476–1509

isSubagentDescendant reports whether targetChatID is a descendant of ancestorChatID by walking up the parent chain from the target. This is O(depth) DB queries instead of O(nodes) BFS.

(
	ctx context.Context,
	store database.Store,
	ancestorChatID uuid.UUID,
	targetChatID uuid.UUID,
)

// of ancestorChatID by walking up the parent chain from the target.
// This is O(depth) DB queries instead of O(nodes) BFS.
func isSubagentDescendant(
	ctx context.Context,
	store database.Store,
	ancestorChatID uuid.UUID,
	targetChatID uuid.UUID,
) (bool, error) {
	if ancestorChatID == targetChatID {
		return false, nil
	}

	currentID := targetChatID
	visited := map[uuid.UUID]struct{}{} // cycle protection
	for {
		if _, seen := visited[currentID]; seen {
			return false, nil
		}
		visited[currentID] = struct{}{}

		chat, err := store.GetChatByID(ctx, currentID)
		if err != nil {
			if xerrors.Is(err, sql.ErrNoRows) {
				return false, nil // chain broken; not a confirmed descendant
			}
			return false, xerrors.Errorf("get chat %s: %w", currentID, err)
		}
		if !chat.ParentChatID.Valid {
			return false, nil // reached root without finding ancestor
		}
		if chat.ParentChatID.UUID == ancestorChatID {
			return true, nil
		}
		currentID = chat.ParentChatID.UUID
	}
}

func subagentFallbackChatTitle(message string) string {
	const maxWords = 6