[TF2] During the first wave of an MvM mission, the Engineer can store more metal than intended

[KalleKokosnott]

To achieve what title says, one has to know these two game mechanics:

1. "During the first wave, upgrades can be individually refunded by pressing the minus button to regain the money spent for it and forfeit the upgrade." (Wiki - Upgrade Station)
2. During setup time, the Engineer's metal capacity is always set to the current maximum metal capacity.

There is an oversight with the metal capacity, regarding the second aforementioned game mechanic, where it stops adding and subtracting 100 metal for each metal capacity upgrade, once the wave starts. With this oversight, an Engineer can start a wave with 600 metal without any metal capacity upgrades invested.

For example, if you have 800 credits to spend, and you upgrade the metal capacity to 600 during setup time before the first wave starts, you will receive the said 600 instantly, because of the second aforementioned game mechanic. Once the wave starts, use the first aforementioned game mechanic to regain the 800 credits, and simultaneously keep the 600 metal. Once you carry more metal than your current max metal capacity, you cannot gain extra metal from ammo pickups and Dispensers.

Steps to reproduce:

1. Play MvM as Engineer before the first wave starts (setup time).
2. With at least 200 credits, upgrade metal capacity.
3. Once the wave starts, refund metal capacity.
4. Credits are refunded, and can be spent on desired upgrades.

It can also be reproduced during the first wave, by picking up metal from sources and then refund, but isn't that effective.