What is the timing for Sabotaged Armaments versus weapons like Power Punch?

Sabotaged Armaments is revealed when one of your characters defends, before Battle Cards are flipped. Power Punch will be scrapped before it can affect that battle.

If an opponent attacks me with a Sturdy Javelin on a ranged character and I reveal a Sabotaged Armaments I played last turn, how do the cards resolve? Does the Javelin scrap and deal two damage before the secret action takes effect or does the secret action scrap the Javelin before the two damage is dealt?

The attacking player will scrap the Javelin to do 2 Damage. Because attacker effects resolve before defender effects.

When you use Sabotaged Armaments, and your opponent has a Power Punch on the attacker, do they get the Bold before Sabotaged Armaments activates?

No. This all happens before Battle Cards are flipped. Speaking of which, what happens when a character upgraded with Anticipation Engine swings into a Sabotaged Armaments? Anticipation Engine and Sabotaged Armaments will both trigger at the same time. The attacker will resolve Anticipation Engine first, then the defender will resolve Sabotaged Armaments.

What happens if I get the trigger, but my opponent reveals a Sabotaged Armaments?

The Trigger grants the ability to the Character; therefore you would keep +2 Attack and Pierce 2 for that Battle, similar to cards like Kinetic Intensifier Whip.

Does my character keep the bonuses from the “attacks” triggers if my opponent reveals a Sabotaged Armaments?

You would keep the bonus ATK from the second and third abilities, if applicable. However, you would lose the Weapon’s static +1 ATK, Bold 1, and Pierce 1 that it normally gives.