build: an apk-managed root, with SchOS as a package

make aroot builds a SchFS root from Alpine's minirootfs, the packages
ports/alpine/world lists, and SchOS itself as the signed apk package
schos-base, in its own repository inside the root. apk add installs from
Alpine; apk upgrade updates both. Booted: zsh is Alpine's, apk update
sees 28669 packages, apk add htop works, and so does xorg-server.

world.lock pins every package with its sha256; a build fetches only what
dist/alpine/ lacks and never looks for newer versions. make alpine-lock
is the one step that does.

Alpine's zsh, busybox commands and hwdata replace SchOS's copies; SchOS
keeps its own tools, toybox's other commands, and static mksh, which
schinit's recovery shell now tries first.

Also: the dependency-file include matched Alpine's usr/lib/sysctl.d, a
directory, and stopped every make. See docs/plan/alpine.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

cmd/schinit/main.c

@@ -623,7 +623,11 @@ main(int argc, char *argv[])
             ioctl(0, TIOCSCTTY, 0);
             char *sh[] = { (char *)"-zsh", 0 };
             execve((char *)"/bin/zsh", sh, 0);
+            // mksh first: on an apk-managed root /bin/sh is busybox, which
+            // needs musl's dynamic linker, and the recovery shell should need
+            // nothing. On the ramdisk root mksh is /bin/sh and this misses.
             char *fb[] = { (char *)"sh", 0 };
+            execve((char *)"/bin/mksh", fb, 0);
             execve((char *)"/bin/sh", fb, 0);
             exit();
         }
@@ -643,6 +647,7 @@ main(int argc, char *argv[])
         if (fork() == 0) {
             setsid();
             char *argv[] = { (char *)"sh", 0 };
+            execve((char *)"/bin/mksh", argv, 0);
             execve((char *)"/bin/sh", argv, 0);
             exit();
         }