fix: fix potential infinite recursion in simplify_optimization_system

Author: AayushSabharwal

src/systems/systems.jl

@@ -196,8 +196,9 @@ function simplify_optimization_system(sys::System; split = true, kwargs...)
     nlsys = System(econs, dvs, parameters(sys); name = :___tmp_nlsystem)
     snlsys = mtkcompile(nlsys; kwargs..., fully_determined = false)
     obs = observed(snlsys)
-    subs = Dict(eq.lhs => eq.rhs for eq in observed(snlsys))
     seqs = equations(snlsys)
+    trueobs, _ = unhack_observed(obs, seqs)
+    subs = Dict(eq.lhs => eq.rhs for eq in trueobs)
     cons_simplified = similar(cons, length(icons) + length(seqs))
     for (i, eq) in enumerate(Iterators.flatten((seqs, icons)))
         cons_simplified[i] = fixpoint_sub(eq, subs)