perl-vfs: fix image build overflow that masked ENOSPC as a parent-dir ENOENT

[brandonpayton]

Purpose

Building the browser Perl VFS image (bash images/vfs/scripts/build-perl-vfs-image.sh) crashed with SFSError: No such file or directory at pathResolveParent, and no perl.vfs.zst was produced (kd-n6vr; discovered during kd-gtxa browser verification). This restores the build and, more importantly, makes the underlying failure mode honest.

Root cause (a product bug, not a perl-src artifact)

The builder allocated a fixed, non-growable 16 MiB SharedArrayBuffer, but the Perl 5.40.3 stdlib payload is ~25.68 MiB across 1288 files (+238 dirs). The in-memory VFS ran out of space mid-write; the ENOSPC from mkdir in the parent-dir loop was silently swallowed by ensureDir's catch-all, so the directory was never created and the failure resurfaced far away as a misleading ENOENT when the next file write could not resolve its missing parent.

Static analysis of the merged PRIVLIB namespace reproduced exactly 1288 included paths and found zero file/dir name collisions, ruling out the perl-src-layout hypothesis. pathResolveParent threw -2 (ENOENT) (parent path unresolved), not -20 (ENOTDIR) (file-in-the-way) — consistent with a masked, never-created parent.

Changes

• images/vfs/scripts/build-perl-vfs-image.ts — allocate a growable SharedArrayBuffer(64 MiB, { maxByteLength: 256 MiB }) + create(sab, 256 MiB), matching the mariadb/redis/sqlite image builders. The full stdlib fits (and can grow); the empty tail compresses away (64 MB raw → 3.4 MB zstd).
• host/src/vfs/image-helpers.ts — ensureDir and symlink now swallow only EEXIST and rethrow every other error, so a real failure (ENOSPC/ENOTDIR/ENOENT) is reported at its true origin instead of being masked. Per CLAUDE.md: prefer truthful failure over convenient illusion.
• host/test/vfs-image.test.ts — 4 regression tests pinning the honest-failure contract.

Verification

• Original crash reproduced in-worktree (changes stashed): exact ENOENT at pathResolveParent, code -2, while "Writing 1288 files to VFS".
• Fix rebuilds the image: all 1288 files written; apps/browser-demos/public/perl.vfs.zst produced (64.0 MB raw → 3.4 MB zstd).
• Host vitest gate (cd host && npx vitest run): 586 passed / 29 failed / 204 skipped with the fix vs 582 / 29 / 201 on a clean baseline → +4 passed (the new tests), 0 new failures. The 29 failures are an identical pre-existing set (kernel/spawn/pthread/wasm/wasi suites needing built kernel.wasm/example binaries absent from this worktree) — unrelated to this change.

Durable evidence: test-runs/kd-n6vr/DISPOSITION.md and test-runs/kd-n6vr/outcome-lists/.

Scope / follow-ups

• Fixes building perl.vfs.zst; booting perl in-browser remains kd-yuef/kd-gtxa scope (gated on trusted-CI GHCR bottle publish). No browser smoke run here.
• The erlang (16 MiB) and python (32 MiB) VFS builders still use non-growable buffers; with the now-honest ensureDir a future overflow there fails loudly as ENOSPC. Candidate follow-up to adopt the growable pattern proactively.

🤖 Generated with Claude Code

[github-actions]

Phase B-1 matrix build status — pr-829-staging

ABI v16. 67 built, 0 failed, 67 total.

Package	Arch	Status	Sha
libcurl	wasm32	built	b01be826
libcxx	wasm32	built	bd2dd5a6
libcxx	wasm64	built	926cfc96
libpng	wasm32	built	25e56ef0
libxml2	wasm32	built	eb77d16a
libxml2	wasm64	built	9743c3c9
openssl	wasm32	built	296793ae
openssl	wasm64	built	b53a16d9
sqlite	wasm32	built	93b98c80
sqlite	wasm64	built	7079a1ac
zlib	wasm32	built	4543740c
zlib	wasm64	built	4ccf5221
bc	wasm32	built	0c54e287
bzip2	wasm32	built	614536d6
coreutils	wasm32	built	e1a33298
curl	wasm32	built	ecbc3967
dash	wasm32	built	4f2caf8b
diffutils	wasm32	built	34f174f8
dinit	wasm32	built	97a7849b
fbdoom	wasm32	built	3799bb5e
file	wasm32	built	535dd689
findutils	wasm32	built	4b727dbf
gawk	wasm32	built	92e5184d
git	wasm32	built	42b4d1cb
grep	wasm32	built	fd4d79fa
gzip	wasm32	built	8f54d8ac
kandelo-sdk	wasm32	built	3829dcd2
kernel	wasm32	built	917959d2
less	wasm32	built	7f3184f8
lsof	wasm32	built	4dc5ae5b
m4	wasm32	built	5fbbe8b3
make	wasm32	built	57a6d854
mariadb	wasm32	built	9ed4aa94
mariadb	wasm64	built	eaf29411
modeset	wasm32	built	d9f12284
msmtpd	wasm32	built	23172a3a
nano	wasm32	built	763f56f8
ncurses	wasm32	built	a7862ee0
netcat	wasm32	built	57bdd0cd
nginx	wasm32	built	933bdcd3
php	wasm32	built	e047ea3c
posix-utils-lite	wasm32	built	2aec933c
sed	wasm32	built	9d958a03
spidermonkey	wasm32	built	ef0ac7d5
tar	wasm32	built	050e7cb3
tcl	wasm32	built	ee9ae67a
unzip	wasm32	built	b176c19f
userspace	wasm32	built	a9e013a2
vim	wasm32	built	8194ff88
wget	wasm32	built	378dca44
xz	wasm32	built	763b854c
zip	wasm32	built	1c834314
zstd	wasm32	built	bcd693e5
bash	wasm32	built	d435c352
mariadb-test	wasm32	built	74e71062
mariadb-vfs	wasm32	built	85427981
mariadb-vfs	wasm64	built	6c3ac528
nethack	wasm32	built	5b7fc658
node	wasm32	built	cdad27ac
spidermonkey-node	wasm32	built	6d8dc738
vim-browser-bundle	wasm32	built	ef862c6f
nethack-browser-bundle	wasm32	built	d4992e6b
rootfs	wasm32	built	ae3df667
shell	wasm32	built	82682bda
lamp	wasm32	built	43815b7e
node-vfs	wasm32	built	fd9e7949
wordpress	wasm32	built	a1d15adb

_{Auto-generated; replaced on each push. Raw data in the publish-status workflow artifact.}