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-rewrite-priorities.md

@@ -0,0 +1,45 @@
+---
+name: schunix-rewrite-priorities
+description: "The ordered list of what actually blocks Schunix, established by a full read of the kernel on 2026-08-01"
+metadata: 
+  node_type: memory
+  type: project
+  originSessionId: d1a1ea76-f919-411c-b0ef-0e1bc5064563
+  modified: 2026-08-01T19:01:25.126Z
+---
+
+Assessed the whole Schunix kernel (~12k hand-written lines) on 2026-08-01.
+Code quality is good; the problem is that xv6 lacks the *concepts* a real UNIX
+needs, so the fix is missing struct fields and subsystems, not bug fixing.
+
+Order to work in (each item unblocks the next):
+
+1. ~~**`struct proc` fields.**~~ **DONE 2026-08-01.** `xstate`, `killsig`,
+   `pgid`, `sid`, and uid/euid/suid + gid/egid/sgid added; `exit()` takes a
+   wait(2)-encoded status; waitpid() reports it. Verified: `sh -c "exit 42"`
+   yields `rc=42`, `id` prints `uid=0(root)`. Also required coupling
+   TIOCGPGRP to the real pgid — see [[schunix-tty-fg-pgrp-coupling]].
+2. **Signal delivery on the trap return path.** Currently only fires on
+   syscall return (`kernel/sys/syscall.c`), so a process spinning in userland
+   never receives a signal.
+3. **Fault-recoverable `copy_from_user`/`copy_to_user` with an exception
+   table.** `uva2ka()` returns a P2V alias valid for exactly one page; two
+   separate historical crashes trace to that single design flaw.
+4. **A page-fault handler.** `trap.c` has no `T_PGFLT` case at all — hence no
+   demand paging, no COW, no lazy stack growth.
+5. **SCHFS directory format.** Every directory is ≥113KB on disk, capped at
+   119KB; `DIRSIZ` is 14; `dirent.inum` is a `ushort` (65535-inode ceiling).
+   Disk-format break, so decide before accumulating images worth keeping.
+6. **Then** the Ring 0A/0B split. Its own Phase 1 is "just file moves" — doing
+   it before 1-5 means moving the same files twice.
+
+Separately, a real confirmed bug: `kernel/arch/x86_64/trapasm.S` saves
+`rax/rcx/rdx` to three **global** scratch words (`_sc_rax` etc. in `vm.c`) with
+a comment claiming "IF is off, no race" — but the Makefile runs `-smp 2`, and
+`cli` only masks the local CPU. Two CPUs in `syscall_entry` clobber each
+other's saved user `rip`. Use per-CPU storage.
+
+Also: `KSTACKSIZE` is 4096 (one page) on x86-64; Linux uses 16K. The stack
+canary exists because it really did overflow.
+
+See [[schunix-linux-abi-decision]], [[schunix-layout-migration]].