The formalism presented in this post turned out to be erroneous (as opposed to the formalism in the previous post). The problem is that the step in the proof of the main proposition in which the soundness schema is applied cannot be generalized to the ordinal setting since we don't know whether ακ is a successor ordinal so we can't replace it by ακ'=ακ-1. I'm not deleting this post primarily to preserve the useful discussion in the comments.
Followup to: Parametric polymorphism in updateless intelligence metric
In the previous post, I formulated a variant of Benja's parametric polymorphism suitable for constructing updateless intelligence metrics. More generally, this variants admits agents which are utility maximizers (in the informal sense of trying their best to maximize a utility function, not in the formal sense of finding the absolutely optimal solution; for example they might be "meliorizers" to use the terminology of Yudkowsky and Herreshoff) rather than satisficers. The agents using this formalism labor under a certain "delusion", namely, since they believe that κ ("the number of ineffable mystery") is an actual finite number (whereas it is secretly infinite, in a sense), they think that the chain of tiling agents is effectively finite as well (since at some point agent #n in the chain will discover that κ > n is false and will fail to construct a subsequent agent of the same "epistemic strength"). The same problem exists in Weaver's intuitionistic assertability predicate formalism.
To overcome this limitation, I suggest to extend κ's semantics from natural numbers to elements of a certain recursive ordinal (at least morally; technically it is done a bit differently, see below). In Benja's original formulation this doesn't appear a valid option, since κ is interpreted as a time interval. However, in my variant κ is just an abstract parameter queries about which can be directed to a special "oracle", so there is no such limitation.
Formalism
Fix α a recursive ordinal and αi a system of notations for ordinals smaller than α such that α0=0, the function f defined by αf(i)=αi+1 is recursive and the bit-valued function g(i,j) which equals 1 iff αi < αj is also recursive. We also assume that
(0) T |- For all i: g(i,f(i))=1
where T is our starting theory. We define Tκ(α) to be T extended by the symbol κ (which stands for the index of the ordinal, not the ordinal itself) and the following self-referential soundness schema:
(1) For all formulae φ: For all n, i: ((@_Tκ(α) "φ(n)" and g(i,κ)=1) -> φ(n)[κ\i])
Tκ(α) is proven to be sound analogously to Yudkowsky and Herreshoff, with transfinite induction over ordinals below α replacing the ordinary induction.
The licensing condition for agent A0 to perform action b0 is
(2) Exists n: Tκ(α) |- (g(n,κ)=1 -> (A0()=b0 -> G))
The property which is sufficient for agent B1 to be creatable by agent A0 is
(3) Tκ(α) |- For all b1: (B1()=b1 -> (b1=0 or Exists n: (g(n,κ)=1 and @_Tκ(α) "(g(n,f(κ))=1 and B1()[κ\f(κ)]=b1) -> G[κ\f(κ)]")))
The proof that (3) indeed enables tiling is analogous to the previous post (but requires using (0)).
Discussion
In order for A0 to know that the tiling chain is infinite, it is enough for her to verify ακ >= ω. In order for her to know that A1 is going to know the tiling chain is infinite, she needs to verify ακ >= ω+1. In order for her to know that all agents are going to know the tiling chain is infinite, she needs to verify ακ >= 2ω. In order for her to know that all agents are going to know that, she needs to verify ακ >= 3ω et cetera.
It remains to decide which ordinal should we actually use. My intuition is that the correct ordinal is the least α with the property that α is the proof-theoretic ordinal of Tκ(α) extended by the axiom schema {g(i,κ)=1}. This seems right since the agent shouldn't get much from ακ > β for β above the proof theoretic ordinal. However, a more formal justification is probably in order.
OK, firstly I found an error in what I wrote, namely condition (3) was missing a piece which I erroneously thought was redundant. Fixed it in both posts.
It surely is. However, the problem goes away once we restrict to goals G such that given a time sequence {a_m} that doesn't satisfy G, there is an initial segment {a_m}_{m<N} s.t. any sequence beginning with this initial segment also doesn't satisfy G. For example, assume the "motor action space" consists of natural numbers and the goal is as follows: either a_m = m^2+1 for all m or a_m = 0 for the first m violating the previous equation. 0 serves us as the "fallback action". The agent is guaranteed to achieve any goal of this form.
I'm guessing that the unclear part is how are conditions (3) and (4) satisfied. I'll use the goal I described in the previous paragraph to avoid the procrastination paradox (otherwise the tiling still happens but the goal isn't guaranteed to be really achieved). Let's start with the "finite" system.
The sequence Am is recursively defined within T_κ by A_m() = a_m = (a_m, A_{m+1}). Here a_m are the motor actions which are used to define G.
Condition (4) is T_κ | (A0() = b_0 and B1() = 0) -> G. Because of the way fallback works with this goal, we need to introduce the further assumption that b_0 = 0^2+1 = 1 where b_0 = (b_0, B0). The T_κ-proof of (4) now goes as follows. A0() = b_0 implies A1 = B1. B1() = 0 implies A1() = 0 implies a_1 = 0. A0() = b_0 also implies a_0 = b_0 = 1. a_0 = 1 and a_1 = 0 imply G by definition of G.
Condition (3) is T_κ | For all b_1: (B1() = b_1 -> (b_1 = 0 or Exists n: (κ > n and @_{T_κ} "(κ+1 > n and B1()[κ\κ+1] = b_1) -> G[κ\κ+1]"))). This condition is T_κ-proved by inspecting B1's code. B1 looks for T_κ-proofs of theorems of the form "κ > n-1 and B1()[κ\κ+1] = b_1 -> G[κ\κ+1]". It is licensed to act on such a proof only when the oracle affirms the stronger premise κ > n. Note that G[κ\κ+1] looks the same as G except that the oracle used in evaluating Am() is "twisted" (in a way that doesn't affect the secret real implementation of the oracle). B1 performs fallback action 0 when it fails to find any proof as above. In practice, if a_0=(0^2+1=1,B1) then B1 is able to prove it (for example by running A0; more precisely since its goal is twisted it has to run a twisted A0 but it doesn't change the result). It can then go on to prove that a suitable motor action and a suitable successor agent will lead to the goal (since B1 and G are twisted in the same way within the theorem). If B1 is an "L-zombie" i.e. it wasn't really constructed by A0 then it a priori might fail to find a suitable proof in which case it will fallback.
I'll stop at this point. If this clarification was insufficient, please point me in the direction of the problem. If this clarification was sufficient for the "finite" system but the analogical argument for the ordinal system is unclear, tell me and I will produce it.