Bitcoin Forum

I have been here for a while now, but I chose to study the technical aspects of bitcoin before I can move forward to any other part of it. I find this question difficult to comprehend, and I need more clarification about it.

The basic script for a lightning network HTLC output has a conditional branch, which requires a user to know the preimage of a hash. It also requires the user to give a valid signature, but it got me thinking: what if, before P2SH was a thing (back in the day), a user created a locking script that just so happens to match the P2SH template? For whatever reason, the user only intended to lock the bitcoin with a "spender must know the preimage of this hash" requirement. But this preimage is not a bitcoin script itself, so it can't be executed even though it matches the P2SH template. Do P2SH-knowing nodes lock this bitcoin forever?

Yes.
If the top stack item which has to be interpreted as a script (the redeem script to be exact) is not a valid script for any reason, that output is unspendable forever because according to the consensus rules the transaction spending it would be invalid.