Logs the two step-2a commits (223ec3d lock-in, cd36784 fix):
pack-fn bodies' `args[<int_literal>]` now substitutes the i-th
call-site argument's lowered value directly, propagating the
concrete type through field access and typed coercion.
Out-of-scope follow-ups noted: non-literal comptime indices,
type-position `$args[$i]` (step 3), per-mono mangling, and the
pre-existing nested-comptime-call scope bug (a pack-fn body
calling `print(...)` AND containing `return X;` trips
"unresolved 'result'" — same shape as the issue-0045 family,
worth filing separately if a later slice needs it).
4d9a7eda5a