Difficulty in emulating "weaker" OP_SUCCESS and why it should be a real opcode

Implementing fraud proofs in Bitcoin script is significantly enhanced by the introduction of an opcode, "OP_SUCCESS," which allows for the immediate marking of script execution as successful upon its activation. This functionality is particularly beneficial in contexts like BitVM, where the objective is to identify a single mismatch efficiently without needing to demonstrate additional mismatches. The concept shares similarities with the OP_SUCCESSx opcode introduced in the Taproot upgrade, albeit the latter activates success upon any presence within the script, showcasing a broader application.

Rusty Russell's 2023 article titled "Covenants: Examining ScriptPubkeys in Bitcoin Script" acknowledges the utility of such an opcode in Bitcoin scripting. Despite the possibility of emulating this opcode's function through script rewriting, the complexity involved in such processes is considerable. An illustration of this complexity is provided through a comparison between scripts using OP_SUCCESS and their equivalent versions achieved via traditional opcodes and complex scripting mechanisms. For example, a simple script utilizing OP_SUCCESS can be translated into a much more cumbersome version without it, as demonstrated in the provided codes. The latter involves intricate stack manipulation to replicate the straightforward outcome facilitated by OP_SUCCESS.

The existence of tools like the one available on GitHub for script rewriting indicates the technical feasibility of such emulation. However, the complexity and less intuitive nature of these rewritten scripts make a strong case for the direct implementation of an opcode like OP_SUCCESS in Bitcoin's scripting language. Simplifying the development process by incorporating such opcodes could enhance efficiency and accessibility for developers engaged in creating fraud proof mechanisms within the Bitcoin network.