while I have looked at the rulebook and rules reference I'm still unsure about how units/attachments work with cards like ambush platform and earth cast technician

Ambush Platform reads

Interrupt : When you deploy an attachment, reduce its cost by 1.
Combat Action : Exhaust this support to deploy an attachment from your hand.

shadowsun's stealth cadre reads

This card may enter play as an attachment with the text, “Attach to a non- Vehicle army unit. Attached unit gets +2 ATK and +2 HP.”

Gun Drone reads

You may deploy this card as a Drone attachment with the text “Attach to a non- Vehicle army unit. Attached unit gains Area Effect (2). ”

I'm fairly sure that when used as an attachment gun drone gets the discount but I am unsure of shadowsun's stealth cadre and I'm not sure if either can be deployed with the combat action

Earth Cast Technician reads

Reaction : After this unit enters play, search the top 6 cards of your deck for an attachment or Drone card. Reveal it, add it to your hand, and place the remaining cards on the bottom of your deck in any order.

Obviously the gun drone can be selected as a drone but I don't think shadowsun's stealth cadre can be selected

what does everyone think?

do I get the discount when using those 2 cards?

can i use the combat action to deploy them?

can i chose the stealth cadre from the 6 cards searched?

I'm fairly sure that when used as an attachment gun drone gets the discount but I am unsure of shadowsun's stealth cadre and I'm not sure if either can be deployed with the combat action

I was talking this through with a friend a few weeks back, too.

The Gun Drone is fairly straight forward. It specifically says that it can be "deployed" as an attachment. Therefore, anything that references the "deploy" mechanic can be applied to it as well. So both effects of the Platform, which both use the "deploy" wording, can be used with the Gun Drone.

The Cadre I'm less sure about. The problem is that "entering play" is a far more general term than "deploy." Every time you deploy, something enters play, but just because something enters play does not mean something was deployed. (Kind of like, "All thumbs are fingers, but not all fingers are thumbs.") At first, it seemed to me that the Cadre's ability to become an attachment should work with any mechanic that sends a card into play (deploy, put into play, attach from your hand, etc.). But the more I think about it, "deploy" is such a specific mechanic that you can't backtrack directly from the result to the initiation.

All of that is a long way of saying that my take on it is that if it is legal to deploy the Cadre unit, the result can be that it enters play as an attachment (and you "deploy" an attachment). But that doesn't work in reverse and effects that let you deploy an attachment will not work on the Cadre unit. So the Platform's Interrupt ability should work when deploying the unit as an attachment, but the Combat Action ability should not since the Cadre is not an attachment in your hand.

Earth Cast Technician reads

Reaction : After this unit enters play, search the top 6 cards of your deck for an attachment or Drone card. Reveal it, add it to your hand, and place the remaining cards on the bottom of your deck in any order.

Obviously the gun drone can be selected as a drone but I don't think shadowsun's stealth cadre can be selected

The Technician allows you to add an attachment card (by type) or a card with the Drone trait to your hand. The Cadre is a unit card, not an attachment card, and it does not have the Drone trait - so it is off limits for this reaction.

also can shadowsun's ability be used on gun drones?

The rules forum is up at cardgamedb, and I've provided a fuller answer (largely confirming ktom's) there.

http://www.cardgamedb.com/forums/index.php?/topic/17734-tau-attachments-entering-play-shadowsun-cadre-gun-drones-ambush-platform/

I'd encourage rules questions to be posted to that forum instead of here going forward. Both are owned by FFG, but it has more traffic, better moderation and "best answer" facilities - plus deckbuilder facilities, card commentary, etc. Centralising rules answers on one forum should be a plus, and it saves the playtesters having to repeat answers here, there and BGG.

Hope to see you come over ...