In fact, it was while thinking about the application design that I encountered the Cell Output Reusing Attack problem mentioned in the Exploring the CKB OTX Paradigm: Accomplishments and Insights from Building a Transaction Streaming Prototype, prompting me to seek a more finer-grained design.
In certain scenarios, the output value is not fixed but is constrained by Action. Under the current design, I can only completely exclude the needed output from signing message to exert control, forcing the application to scan all outputs to find one that meets the requirements. This leaves the possibility of Cell Output Reusing Attack open.
Suppose the OTX’s signing message could leave some attributes of the output uncovered, or even leave the corresponding position blank. In that case, the application could at least determine which OTX the specific output belongs to and which Action it is tied to, thereby making Cell Output Reusing Attack no longer possible.