`KeyError: key :S not found` in `map_ssas_to_source`

julia> using FillArrays, InfiniteArrays

julia> @descend Matrix(Zeros(∞,∞))
ERROR: KeyError: key :S not found
Stacktrace:
  [1] getindex
    @ ./dict.jl:484 [inlined]
  [2] map_ssas_to_source(src::Core.CodeInfo, rootnode::JuliaSyntax.TreeNode{JuliaSyntax.SyntaxData}, Δline::Int64)
    @ TypedSyntax ~/.julia/packages/TypedSyntax/JHruX/src/node.jl:657
  [3] tsn_and_mappings(m::Method, src::Core.CodeInfo, rt::Any, sourcetext::SubString{String}, lineno::Int64; warn::Bool, strip_macros::Bool, kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
    @ TypedSyntax ~/.julia/packages/TypedSyntax/JHruX/src/node.jl:47
  [4] tsn_and_mappings(m::Method, src::Core.CodeInfo, rt::Any; warn::Bool, strip_macros::Bool, kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
    @ TypedSyntax ~/.julia/packages/TypedSyntax/JHruX/src/node.jl:34
  [5] tsn_and_mappings
    @ ~/.julia/packages/TypedSyntax/JHruX/src/node.jl:28 [inlined]
  [6] #get_typed_sourcetext#32
    @ ~/Dropbox/JuliaPackages/Cthulhu.jl/src/reflection.jl:350 [inlined]
  [7] get_typed_sourcetext
    @ ~/Dropbox/JuliaPackages/Cthulhu.jl/src/reflection.jl:348 [inlined]
  [8] find_callsites(interp::Cthulhu.CthulhuInterpreter, CI::Core.CodeInfo, stmt_infos::Vector{Core.Compiler.CallInfo}, mi::Core.MethodInstance, slottypes::Vector{Any}, optimize::Bool, annotate_source::Bool)
    @ Cthulhu ~/Dropbox/JuliaPackages/Cthulhu.jl/src/reflection.jl:28
  [9] _descend(term::REPL.Terminals.TTYTerminal, interp::Cthulhu.CthulhuInterpreter, curs::Cthulhu.CthulhuCursor; override::Nothing, debuginfo::Symbol, optimize::Bool, interruptexc::Bool, iswarn::Bool, hide_type_stable::Bool, verbose::Nothing, remarks::Bool, with_effects::Bool, inline_cost::Bool, type_annotations::Bool, annotate_source::Bool)
    @ Cthulhu ~/Dropbox/JuliaPackages/Cthulhu.jl/src/Cthulhu.jl:497
 [10] _descend(term::REPL.Terminals.TTYTerminal, interp::Cthulhu.CthulhuInterpreter, mi::Core.MethodInstance; kwargs::Base.Pairs{Symbol, Bool, Tuple{Symbol}, NamedTuple{(:iswarn,), Tuple{Bool}}})
    @ Cthulhu ~/Dropbox/JuliaPackages/Cthulhu.jl/src/Cthulhu.jl:766
 [11] _descend(term::REPL.Terminals.TTYTerminal, args::Any; interp::Core.Compiler.NativeInterpreter, kwargs::Base.Pairs{Symbol, Bool, Tuple{Symbol}, NamedTuple{(:iswarn,), Tuple{Bool}}})
    @ Cthulhu ~/Dropbox/JuliaPackages/Cthulhu.jl/src/Cthulhu.jl:782
 [12] __descend_with_error_handling(args::Any; terminal::Any, kwargs::Base.Pairs{Symbol, V, Tuple{Vararg{Symbol, N}}, NamedTuple{names, T}} where {V, N, names, T<:Tuple{Vararg{Any, N}}})
    @ Cthulhu ~/Dropbox/JuliaPackages/Cthulhu.jl/src/Cthulhu.jl:240
 [13] _descend_with_error_handling(f::Any, argtypes::Any; kwargs::Base.Pairs{Symbol, Bool, Tuple{Symbol}, NamedTuple{(:iswarn,), Tuple{Bool}}})
    @ Cthulhu ~/Dropbox/JuliaPackages/Cthulhu.jl/src/Cthulhu.jl:229
 [14] descend_code_typed(::Any, ::Vararg{Any}; kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
    @ Cthulhu ~/Dropbox/JuliaPackages/Cthulhu.jl/src/Cthulhu.jl:174
 [15] descend_code_typed(::Any, ::Any)
    @ Cthulhu ~/Dropbox/JuliaPackages/Cthulhu.jl/src/Cthulhu.jl:174
 [16] top-level scope
    @ REPL[8]:1

Run the reported Julia reproduction with FillArrays and InfiniteArrays, then inspect Cthulhu.jl/src/reflection.jl around get_typed_sourcetext and the TypedSyntax stack frame at src/node.jl:657. Trace why map_ssas_to_source requests the missing :S key; done means the @descend command no longer raises this KeyError.