erlang: wasm32 -O2 miscompilation coverage (kd-r8h7 steps 1-4)

[brandonpayton]

Implements the low-risk core (steps 1-4) of the kd-r8h7 design
(#832,
docs/plans/2026-07-02-erlang-wasm32-o2-miscompilation-coverage-design.md):
turn the reactive per-file -O1 posture for LLVM wasm32 -O2 miscompilations
into a systematic, bounded, detected one — without a blanket -O1.

What & why

ERTS dodges known wasm32 -O2 miscompilations with per-file -O1 + a
global.h init patch, discovered one production incident at a time (unicode
garbage, ETS OOB, and md5-over-iolist breaking beam_asm → on-Kandelo erlc).
This adds detection + a bounded process so a new instance fails CI, not a user.

• Step 1 — Audit. ESTACK/WSTACK/EQUEUE/DMC risk audit of OTP 28.2 ERTS
  (test-runs/kd-jin7/audit-*). Corrects the design's guessed list: refutes
  erl_bif_binary.c/erl_bif_re.c (no idiom), adds erl_term_hashing.c
  (phash), erl_iolist.c/erl_io_queue.c (EQUEUE iodata); flags that the
  facet-1 global.h init patch covers only ESTACK/WSTACK, not EQUEUE/DMC.
• Step 2 — Registry. packages/registry/erlang/wasm32-miscompilations.md:
  greppable source of truth — triage runbook, applied-workaround table (chksum
  marked PR erlang: fix erlang:md5/1 badarg on iolist input (unblocks on-Kandelo compilation) #824), detection-only table, CI wiring, removal checklist, OTP-bump
  re-audit trigger. Referenced from build-erlang.sh. Doc/comment-only → no
  build output byte change → build.toml revision intentionally not bumped.
• Step 3 — Detection matrix + local runner.
  test/wasm32-miscompilation-matrix.ts (single {name, expr, expected} source,
  native-OTP-28 oracles, inputs sized past DEF_*_SIZE == 16 to force the
  heap-stack path); test/erlang.test.ts runs the whole matrix in one BEAM boot
  under skipIf.
• Step 4 — CI gate runner. test/run-wasm32-miscompilation-smoke.ts: one
  boot; fails on mismatch, on incompletion, and on the false-coverage case (no
  active case ran = missing OTP tree — the design's highest-listed risk). Emits
  passed/failed/skipped outcome lists.

Verification (native OTP 28 — the oracle source)

A from-source erlang.wasm build was not run (erlang is CI-disabled, "too slow"
to rebuild); the matrix was validated on native OTP 28 via dev-shell, exactly
where the design says oracles come from:

• Positive: 8/8 active pass, 2 pending skip, matrix_done, gate exit 0.
• Negative control: a corrupted oracle → FAIL … expected=… got=…, non-zero.
• False-coverage guard: no OTP tree → GATE FAIL, exit 1.
• md5/crc32/adler32 oracle cross-checked byte-for-byte vs Python
  hashlib/zlib. All 3 TS files pass esbuild transform.

Full write-up + outcome lists: test-runs/kd-jin7/SUMMARY.md.

Scope / follow-ups

• chksum_iolist + compile_module are pending PR erlang: fix erlang:md5/1 badarg on iolist input (unblocks on-Kandelo compilation) #824 (kd-qe2c) — reported
  as expected skips until that -O1 lands (flip pendingPr in the same change).
• PR-gate promotion is documented, not landed: the bottle-build/smoke job +
  framebuffer gate (kd-ivdr/kd-jg94) are not on main and no current CI job has
  the OTP runtime tree, so a hard gate today would trip the false-coverage guard.
  The verified runner + exact wiring block are ready in the registry.
• Deferred design steps 5-7 (coverage closure, perf baseline, upstream LLVM) stay
  future beads.

🤖 Generated with Claude Code

[github-actions]

Phase B-1 matrix build status — pr-835-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	ba15af22
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	61c3bb81
lamp	wasm32	built	f5445d80
node-vfs	wasm32	built	75f6e69a
wordpress	wasm32	built	1c1bcff5

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