A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 8 November 2007
What are the correct steps for a performing personality during the following cases.
Player A attacking. Player B is the defender. Player B plays Doomed Intentions for the move in action on personality XX. When is he allowed to attach Pincers and Tail as per the item's text? When does he take the additional action?
Player B now attacking. Player A defends. Player B attaches random follower on Naval personality XX. When is he allowed to attach Pincers and Tail as per the item's text? When is the extra stronghold action granted?
Martin Lund (rules official), 9 November 2007
Whenever an effect grants an additional action while another action of the same designator is in progress, the timing of the additional action is delayed until after the current action resolves. This makes sure that Battle actions can not occur within other Battle actions, and so on. ["After" ADDED August 14 2007]
So Pincers and Tail and the additional Action from Doomed Intentions both share the same trigger.
According to the Comprehensive Rules on Timing, the Delayed Effects always come before the Triggered Traits, which always come before Reactions.
So the Additional Action from Doomed Intentions happens first.
This might prevent you from ever attaching Pincers and Tail, and consequently stop you from benefiting from Eastern Hub Port too.