Track A — FILE_DIRECTORY_FILE handling. NtCreateFile's 9th parameter
`create_options` (sp+0x54 per shim_utils.h:49-50) is now read and
forwarded to open_vfs_file/open_cache_file. When the
FILE_DIRECTORY_FILE bit (0x1) is set on a `cache:\<hash>` path,
the host-side handler `mkdir -p`s instead of `File::create`'ing a
0-byte sentinel that blocked subsequent hierarchical creates of
`cache:\<hash>\<sub>\<leaf>` with NAME_COLLISION. Confirmed by
`opts=0x4021` (incl. FILE_DIRECTORY_FILE) on `cache:\d4ea4615`
and `opts=0x4020` (no DIR bit) on the leaf `.tmp` files. NtOpenFile
forwards `open_options` (r8) into the same slot per
xboxkrnl_io.cc:118-122. Closes the AUDIT-053 ζ-class VFS layout
aliasing wedge.
Track B — opt-in persistent cache root. AUDIT-038's per-process
tmpdir + wipe stays the default (preserves lockstep/oracle
determinism + dodges Sylpheed's `<hash>.tmp` journal-append-on-
reboot self-inconsistency). Persistence is now opt-in via
* `XENIA_CACHE_ROOT=<path>` — explicit path (caller manages
wiping); hands a stable place to drop a canary-built cache
for cascade A/B oracle work.
* `XENIA_CACHE_PERSIST=1` — `$XDG_DATA_HOME/xenia-rs/cache`
(or `$HOME/.local/share/xenia-rs/cache`).
Cold-start (-n 500M, default tmpfs) with FILE_DIRECTORY_FILE fix:
swaps=1 draws=0 imports=40454 cxx_throw=0 — matches master baseline,
no regression. Cache hierarchy now mkdir-p'd correctly: `cache:/`
contains 9 hash dirs (e.g. `d4ea4615/e/`, `aab216c3/5/`) instead
of the 0-byte sentinel files AUDIT-053 found masquerading as
directories.
LOC: +88 / -14 = +74 net (≤80 budget). All 127 xenia-kernel unit
tests pass.
Trace: audit-runs/audit-054-vfs-layout-fix/
cold-start-digest.json + warm-start-digest.json (defaults)
persist-cold-digest.json + persist-warm-digest.json (opt-in)
baseline-master-digest.json (master 25704c5 reference)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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