Carry project memory in the repo, with tools/memory-sync.sh

Claude Code keeps per-project memory at <home>/.claude/projects/<key>/,
where <key> is the project's absolute path with every separator and the
drive colon turned into a dash. That makes it both rename-fragile and
machine-specific, and this project has hit each of those once:

  - D:\DEV\Schunix -> D:\DEV\SchOS changed the key, and 43 memories were
    invisible until moved across by hand.
  - Development happens from Windows and from Linux, and each looks in a
    different place for the same checkout.

Committing .claude/memory/ fixes both -- git carries it across renames
and between hosts -- and `import` puts it wherever the local machine
expects. .claude/settings.local.json stays ignored: those are per-machine
permissions.

The colon maps to a dash rather than being dropped. Deleting it gives
D-DEV-SchOS, which matches nothing and silently finds zero memories; that
was the first attempt. On Git Bash the key comes from `cygpath -w`,
because Claude Code is a Windows program and sees D:\DEV\SchOS, not
/d/DEV/SchOS.

.claude/memory/schunix-build-speed.md

@@ -0,0 +1,50 @@
+---
+name: schunix-build-speed
+description: The build is fast now (no-op ~2s); the four things that made it slow and the traps that will make it slow again
+metadata: 
+  node_type: memory
+  type: project
+  originSessionId: a665e14b-86bd-4b41-a228-51377f3e9225
+  modified: 2026-08-04T17:27:56.099Z
+---
+
+**A no-op `make` went from 1m48s to ~2s on 2026-08-04**, and a full kernel
+rebuild from ~110s to ~7s. Almost none of it was compilation — with only 2.4s
+of CPU in that 1m48, it was I/O across WSL's `/mnt/d` boundary. Four causes,
+all still worth not reintroducing:
+
+- **`tools/mkfs` built the image on the file**, one `lseek` + one 512-byte
+  `write` per block: 300,000 syscall pairs, 150,000 of them just to zero it.
+  It now assembles the image in RAM and writes once. It also stops at the last
+  non-zero block and `ftruncate`s, so ~2 MB is written instead of 147 MB.
+- **The image was rebuilt on every invocation.** `sysroot-install` is phony, so
+  everything depending on it always ran. There is now a `build/sysroot.stamp`
+  whose mtime only advances when a `find`-based summary of the staged tree
+  actually changes (the `cmp -s ... || mv` idiom — **do not add a `touch`, and
+  note `touch -c` still updates an existing file's mtime**, which is exactly
+  the bug I wrote and had to remove).
+- **`ports/toybox` re-linked its 236 applets every build**, because port.mk
+  declares `install` .PHONY for every port. It hangs off
+  `$(BUILDDIR)/toybox.installed` now. This was the sneaky one: it bumped the
+  mtime of 236 files in `sysroot/` and so invalidated the stamp above.
+- **mkfs and mkschfs re-read every file to dedup it.** They now check
+  `(st_dev, st_ino)` first — toybox's applets are real hard links, so 236 of
+  them are settled by one `fstat` instead of ~500 MB of reads.
+
+Two real bugs found in the Makefile while doing this:
+
+- **`$(BUILD)/kernel/**/*.d` only matched one directory level.** make's wildcard
+  has no recursive `**`. `arch/x86_64/` and `fs/schfs/` therefore had **no
+  header dependency tracking at all** — editing `include/schfs.h` left stale
+  objects that linked fine. It uses `$(shell find ...)` now.
+- **`CFLAGS` is recursively expanded and had a `$(shell)` appended**, so the
+  stack-protector probe re-ran on every expansion: one extra gcc per object
+  file. Probed once into `NO_SSP :=` now.
+
+`schunix.img` is no longer `.PHONY` (it is a real file), and `MAKEFLAGS +=
+-j$(nproc)` is on by default — use `make -j1` for readable output from a
+failing build.
+
+Verify with `make schfs-check` plus [[schunix-verify-by-driving-shell]]; the
+superblock checksum is printed by mkfs and should not change when only build
+mechanics change.