fish: version 4.7.1
terminal: Ghostty 1.3.1
OS: Linux 7.0.6 #1-NixOS SMP PREEMPT_DYNAMIC x86_64 GNU/Linux

Reproduction

❯ echo foo-{bar, baz-{far, faz}}
foo-bar foo-baz-far foo-baz- faz # leading space is not ignored in nested brace
❯ echo foo-{bar, baz-{far ,faz}}
foo-bar foo-baz-far  foo-baz-faz # trailing space is not ignored in nested brace
❯ echo foo-{bar, baz-{far,faz}}
foo-bar foo-baz-far foo-baz-faz # normal/expected

Expected Behaviour:
Spaces around commas should be stripped consistently at all nesting levels, matching the top-level behavior. All three commands above should have no stray spaces in the output.

Observed Behaviour:
Leading/Trailing spaces are not ignored