Modifying Melee Weapon: How to make a melee weapon with a telescoping handle?

[smin32]

Hello, Steve Jackson Games GURPS forum users.
I hope you are having a good day today.
Before we get into the full-fledged thread, let's first clarify the core agenda.

"What modifiers or other methods can I use to make a weapon with a telescoping handle?"

This time, I joined as a player in a campaign featuring a giant robot powered by magic.
In this campaign, I'm going to use a piece of gear that can be worn around the waist like a regular Broadsword until held in hand, but transforms like a Polearm with a long handle once pulled out.

I've been looking for a couple of telescopic ways to apply this transformation to a weapon, and as a result I've found a way to stretch into the inside of the handle, just like a collapsible umbrella or collapsible baton.
(Reference image: https://cdn.shopify.com/s/files/1/03...g?v=1623184002)

And as another example, I found a way to fold and unfold by attaching an elastic material, such as a rubber band, to the inside of the handle, commonly used in folding walking canes.
(Reference image: https://ae01.alicdn.com/kf/H43eeb720...de80ab7e2F.jpg)

Of course, this is a case that takes into account the case of using a realistic method, and the background of the campaign I am participating in this time is a fantasy world where magic is real, so there is no need to stick to this method.
The best results will be achieved if we can use a stretchable method while maintaining density, such as "Ruyi Jingu Bang" by Son Goku in "Journey to the West", a popular fantasy novel popular in Northeast Asian cultures. (Of course, the handle doesn't have to be infinitely long like Ruyi Jingu Bang)

So far, I've researched a few GURPS Supplements, and searched the forums for related threads, but to no avail.
GURPS Power-Ups 1: I know that Imbuements' Telescoping Weapon skill (p. 10 of that book) allows the user to extend the reach of the weapon in their hand.
However, what I want is not to increase the reach of all the weapons the character holds in his hand, but to transform the handle of that specific weapon into a stretchable form.
There is a way to implement this with Innate Attack Advantage, but in that case, it is difficult to estimate the weight of the equipment, and I think it is difficult to preserve the original characteristic of transforming from Broadsword form to Polearm form (and I did not understand the Gadget limitation properly yet) .
I also looked for ways to lengthen or shorten the handle of a weapon in the Weapons And Armor section of GURPS Low-Tech Companion 2: Weapons and Warriors, but it wasn't a way to dynamically change shape at any time as needed.

I've seen some threads suggesting that if you want to implement something like this you can use Stretching Advantage plus the Force Extension enhancement (GURPS Powers p.78).
But it's not in the form I want.
(It feels to me like Gwen Tennyson, the wizard character from the anime "Ben 10", wields a weapon with telekinesis)

So, after a lot of thought, I came to the forum thinking that it would be difficult to find an answer on my own.
At first, I wondered if someone had already implemented the weapon "Combi Stick" of the alien "Predators" from the old movie "Predator" series with GURPS 4e. (Because the Predator series is famous)
But I couldn't find any related threads.
In a similar case, someone tried to implement a similar weapon to the stretchable Quater Staff used by a character in the TV series "Babylon 5".
(Reference thread: http://forums.sjgames.com/showthread.php?t=17222)
But I couldn't find the exact answer in that thread either.

So, I ask you.
How can I implement a weapon that can be transformed from a Boardsword shape to a Polearm shape by stretching the handle when needed?

[Written by Google Translator ;D]