SCFF: the live root ships compressed, with Xorg and Window Maker

SCFF, the SchOS Compressed File Format (include/fs/scff.h), is a block
image cut into 128 KB chunks, each its own zstd frame, behind an index.
tools/mkscff writes it from fs-ram.img on every core (-19, 11 s) and
checks each chunk decompresses to itself. The kernel carries the .scff
as its ramdisk and unpacks a chunk the first time a block in it is
read; zero blocks share one page. The kernel and the ISO are the
compressed size, and the root costs memory only for what is touched.
See docs/architecture/scff.md.

zstd 1.5.7 comes from ports/zstd like uACPI: the decoder is compiled
into the kernel at -O2, with a static context and a 64 KB stack of its
own, and mkscff builds the whole library from the same release.

world now has xorg-server, the fbdev and evdev drivers, xinit, Window
Maker, xterm and DejaVu, and /root/.xinitrc runs wmaker. That root is
358 MB, 102 MB as SCFF.

The ISO no longer carries the root a third time as an ISO 9660 tree,
which nothing read. schos.iso: 1389 MB -> 318 MB. El Torito keeps its
own copy of the EFI image, the layout real machines have booted.

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

kernel/scff/scff_zstd.h

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+// The SCFF decoder's interface, in types both the kernel's headers and zstd's
+// agree on. See kernel/scff/scff.c.
+#ifndef SCHOS_SCFF_ZSTD_H
+#define SCHOS_SCFF_ZSTD_H
+
+// 0, or -1 if the workspace is too small for this zstd.
+int  scff_zstd_init(void);
+// Decompress one zstd frame. The length written, or -1 for a bad frame.
+// One caller at a time.
+long scff_zstd_decompress(void *dst, unsigned long cap, const void *src, unsigned long n);
+
+#endif