Celestial Shot effect

I am not sure if this is a bug or intended, but I played a Celestial Shot earlier followed immediately by Explosive Trap. Given the wording of Celestial Shot “Your next spell has +2 Spell Damage”, I was expecting the Secret to deal 4 damage to all enemies when someone attacked into me. But it didn’t. And because that was my next spell, I just lost the effect. I kind of expected this might be the case, but wanted to try it for Science since the text wording implies it should work.

The text for the effect doesn’t say the next Arcane spell, and doesn’t have any other text to indicate that it wouldn’t work on a spell like Explosive Trap. I’m guessing this means it also doesn’t upgrade Motion Denied either. But this is a little strange in my opinion, especially since we have cards in Hunter that can give spell damage to spells in hand and in the deck.

So why wouldn’t this also be capable using a combination like Celestial Shot and Explosive Trap? It just seems intuitive that it would apply, and be a way for Hunter to have a buffed up board clear when needed.

And I know Hunter doesn’t really need any help right now, but I just wanted to point it out as a matter of clarity and being a possible bug.

That’s a trap every one fell into.
Effects like “your next spell has +X spell damage” are enchantments applied to your hero/board/whatever and only apply at the exact moment when you cast the spell. Then, they are gone. But secrets check for spell damage only at the moment when they are triggered.
It would be more obvious if you think about it like it was a minion.
Play a spell damage minion, play explosive trap, lose your minion. Explosive trap will only deal 2.
Play explosive trap, play a spell damage minion. Explosiv trap will deal additionnal damage . Because the spell damage is present at the time of the trigger.

But yeah it could/should work in a logical world. Just like card effects improved by spell power didn’t work at first. Namely Unexpected Results when it was the first of its kind. It just wasted the buff and summoned 2 drops instead of 4 drops when you gave it +2 spell damage.