By strict RAW of your question, situation 1 is correct. You have already rolled initiative, so you have to act in turn order. However, that isn't the only way your DM could have played this scenario.
Combat begins when the DM says so
There isn't any explicit guidance as to when combat encounters technically begin. We know what a combat encounter is, an ...
David laid a lot of great foundation here, but I think I found a few ways that we can improve on this a bit.
1) Use a "Hold X" spell. This spell is going to be your best friend. This is because they are paralyzed which means that a) you attack with advantage and b) any attack that hits will CRIT automatically if the attacker is within 5 feet. While gaining ...
They’re hostile creatures, they can be claimed.
(Jade Ripley, author of the harbinger, personal communication May 26, 2020)
There was no mistake, oversight, or otherwise involved here: it is fully intended that the harbinger can Claim any hostile creature, period.
So far as I can tell, there's no mention of a harbinger being unable to use on a nonsentient or nonsapient creature the supernatural ability dark claim.1 To rephrase this positively: So far as I can tell, a harbinger can use the supernatural ability dark claim on any opponent
For example, the ability maneuvers readied, in part, says
[F]or the harbinger ...
Assuming you are fighting said object, yes you can Claim non-sapients*
Dark Claim has "specific" (really, non-specific) targeting requirements; you must consider them an enemy.
As a swift action, the harbinger may Claim an opponent that she can see...
Other portions of the ability refer to Creatures, which is a game-term in Pathfinder
A harbinger ...
There are some available rule options
As SomeoneEvil answered, the DMG provides an optional rule for allowing a specific disarming attack.
This suggests that this attack is purely an optional rule that a DM can choose to employ, but that's not entirely correct.
The PHB covers this as well with the Disarming Maneuver by the Battlemaster Fighter.
The DMG suggests an attack roll for Disarming
There's no standard option for disarming opponents, however there is an optional rule in the Dungeon Master's Guide (page 271). It has the attacker (disarmer) make an attack roll contested by Strength (Athletics) or Dexterity (Acrobatics). It also gives some clauses for advantage/disadvantage neither of which ...
They must be done separately
Whirlwind attack states:
When you use the full attack action, you can give up your regular
attacks and instead make one melee attack at your full base attack
bonus against each opponent within reach.
When you use the Whirlwind Attack feat, you also forfeit any bonus or
extra attacks granted by other feats, spells, ...