However, I tested it live, and it aborts like this (this is with Guile
2.0.11.109-e1d29 on x86_64-linux-gnu):

--8<---------------cut here---------------start------------->8---
retrieving 1 files from 'wildebeest.jxself.org'...
importing file or directory '/gnu/store/prrwzx5v33miiz5fh8653m1izl5f8d4k-brasero-3.8.0'...

;;; (sigport #f #<input: r6rs-custom-binary-input-port 1eee0d0>)
guile: ../../libguile/ports.c:2527: scm_i_port_iconv_descriptors: Assertion `pti->encoding_mode == SCM_PORT_ENCODING_MODE_ICONV' failed.
builder for `/gnu/store/izjx4wllhcy66nsn9pxbkghaq2cy06qv-brasero-3.8.0.drv' failed due to signal 6 (Aborted)
@ hook-failed /gnu/store/izjx4wllhcy66nsn9pxbkghaq2cy06qv-brasero-3.8.0.drv - 6 builder for `/gnu/store/izjx4wllhcy66nsn9pxbkghaq2cy06qv-brasero-3.8.0.drv' failed due to signal 6 (Aborted)
guix build: error: build failed: build of `/gnu/store/izjx4wllhcy66nsn9pxbkghaq2cy06qv-brasero-3.8.0.drv' failed
--8<---------------cut here---------------end--------------->8---

(The ‘sigport’ pk shows the port encoding, in nar.scm.)

This sounds like a memory corruption, as you noted on IRC.

To be continued...

Ludo’.