[eriksvedang]

This is a follow up PR to #1598 (it contains its changes too).

It makes things super fast but needs thorough review before we merge it. I just pushed it so that interested parties can try it out :)

Disclosure: also written by Claude

[hellerve]

i think this means i cannot override deleters anymore if i already had an instance. concretely, the new check skips an existing specialization without checking whether its source changed.

i specced out a repro with codex:

(deftype (Crate a) [value a])

(defmodule Crate
  (sig delete (Fn [(Crate a)] ()))
  (defn delete [x] (IO.println "old")))

; we find it here and specialize
(defn before []
  (let [x (Crate.init 1)] ()))

(defmodule Crate
  (defn delete [x] (IO.println "new")))

; old deleter here too
(defn main [] (let [x (Crate.init 2)] ()))