muslis built the first time, it is upgraded during the build of the immediate next package:
... >>> lzip: Building system/lzip 1.23-r0 (using abuild 3.4.2-r0) started Mon, 10 Apr 2023 00:42:51 +0000 >>> lzip: Checking sanity of /usr/src/packages/system/lzip/APKBUILD... >>> lzip: Analyzing dependencies... (1/4) Upgrading musl (1.2.0-r2 -> 1.2.3-r1) (2/4) Upgrading musl-dev (1.2.0-r2 -> 1.2.3-r1) (3/4) Upgrading musl-utils (1.2.0-r2 -> 1.2.3-r1) (4/4) Installing .makedepends-lzip (20230410.004251) ...
This is proof that
musl(and others) are up-to-date prior to the start of the second pass.
The second pass is still required, since it is built with the upgraded tools produced by the first pass.