oh, no

<no location info>: error:
    panic! (the 'impossible' happened)
  GHC version 9.12.4.20260607:
	ASSERT failed!
  in_scope InScope {ds_aP9t $dMonoid_s26Ke $dFunctor_s26Kg
                    $dApplicative_s26Ki lvl_s26Ox lvl_s26OA lvl_s26Wj lvl_s26Wk
                    lvl_s26Wl lvl_s26Wm}
  tenv [a1gar :-> f_a1ga3, a1gas :-> t_a1ga4, a1gat :-> a_a1ga5,
        a1gau :-> r_a1ga6]
  tenvFVs {f_a1ga3, t_a1ga4, a_a1ga5, r_a1ga6}
  cenv []
  cenvFVs {}
  tys []
  cos [<t_a1gas a_a1gat -> Traversed f_a1gar r_a1gau>_R
       %<'Many>_N ->_R Sym (N:Forget
                                <Traversed f_a1gar r_a1gau>_R
                                <ZonkAny 1>_P
                                <t_a1gas a_a1gat>_R
                                <()>_P)]
  Call stack:
      CallStack (from HasCallStack):
        assertPpr, called at compiler/GHC/Core/TyCo/Subst.hs:680:5 in ghc-9.12.4.20260607-inplace:GHC.Core.TyCo.Subst
        checkValidSubst, called at compiler/GHC/Core/TyCo/Subst.hs:848:17 in ghc-9.12.4.20260607-inplace:GHC.Core.TyCo.Subst
        substCo, called at compiler/GHC/Core/Subst.hs:261:39 in ghc-9.12.4.20260607-inplace:GHC.Core.Subst
        substExpr, called at compiler/GHC/Core/Subst.hs:268:37 in ghc-9.12.4.20260607-inplace:GHC.Core.Subst
        substExpr, called at compiler/GHC/Core/Subst.hs:272:37 in ghc-9.12.4.20260607-inplace:GHC.Core.Subst
        substExpr, called at compiler/GHC/Core/Subst.hs:272:37 in ghc-9.12.4.20260607-inplace:GHC.Core.Subst
        substExpr, called at compiler/GHC/Core/Subst.hs:306:28 in ghc-9.12.4.20260607-inplace:GHC.Core.Subst
        substBind, called at compiler/GHC/Core/Subst.hs:274:44 in ghc-9.12.4.20260607-inplace:GHC.Core.Subst
        substExpr, called at compiler/GHC/Core/Subst.hs:272:37 in ghc-9.12.4.20260607-inplace:GHC.Core.Subst
        substExpr, called at src/Test/Inspection/Core.hs:609:18 in inspection-testing-0.6.3-152826bba0790f422bcf299ee350f11f2d91c1b0e54a3e3d07dd75e90d5a68a4:Test.Inspection.Core

Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug