[PHP] fix: implement stopped-child wait4 semantics

[brandonpayton]

Supersedes fork-headed PR #719. This replacement keeps the same head commit (5ab7927) but moves the PR head onto an Automattic/kandelo branch and adds the PHP prefix to the title.

Why this is needed

PHP pcntl PHPTs expect stopped children to be waitable with WUNTRACED, wait4 WNOHANG to remain nonblocking, SIGCONT to resume stopped children, and wait4 rusage pointers to receive a valid structure. The old behavior reported stopped children incorrectly and left rusage unavailable, so the PHP failures were exposing process-runtime gaps rather than PHP problems.

Why this shape makes sense

The change belongs as a focused runtime PR because stopped-child state, wait4 polling, host worker parking/resume, and ABI/rusage copy-out are one process lifecycle contract. Keeping this separate from the PHPT harness makes the harness a consumer of the fixed semantics rather than the place where we hide them.

Why this is the correct fix

Implementing stopped-child state and zeroed rusage copy-out in Kandelo aligns the Node and browser host paths with Unix wait semantics. That is the correct fix because pcntl is testing normal process behavior that other packages will also need, and the branch includes focused kernel and host coverage for that behavior.

Validation

Evidence from the superseded PR remains valid because this replacement has the identical head SHA: Node focused pcntl wait PHPTs PASS 3/3; browser focused pcntl wait PHPTs PASS 3/3; browser offset 9800 limit 100 refresh had 84 pass, 16 skip, 0 fail/time/error; cargo lib tests passed 960 tests; poll_waitable_child passed 5 tests; host process-wait-lifecycle vitest passed 11 tests; ABI check and git diff --check passed.

[github-actions]

Phase B-1 matrix build status — pr-759-staging

ABI v16. 66 built, 1 failed, 67 total.

Package	Arch	Status	Sha
libcurl	wasm32	built	a6f6534d
libcxx	wasm32	built	0d3c1977
libcxx	wasm64	built	3117bdac
libpng	wasm32	built	697eac68
libxml2	wasm32	built	f3af4b10
libxml2	wasm64	built	478af4d0
openssl	wasm32	built	96fbd5a6
openssl	wasm64	built	b53b8ff0
sqlite	wasm32	built	10a86a4f
sqlite	wasm64	built	e74c37db
zlib	wasm32	built	1b3d5c6f
zlib	wasm64	built	8470f519
bc	wasm32	built	6cfa350d
bzip2	wasm32	built	f119ff7e
coreutils	wasm32	built	0540afb5
curl	wasm32	built	f33f8926
dash	wasm32	built	fcc25397
diffutils	wasm32	built	ea99d8f1
dinit	wasm32	built	17078406
fbdoom	wasm32	built	e7caae32
file	wasm32	built	5947df7a
findutils	wasm32	built	612b36ac
gawk	wasm32	built	5e5b1e9f
git	wasm32	built	05247e65
grep	wasm32	built	d7110a09
gzip	wasm32	failed	—
kandelo-sdk	wasm32	built	1049924e
kernel	wasm32	built	04eaa270
less	wasm32	built	1694caf3
lsof	wasm32	built	f4fa0fa4
m4	wasm32	built	7d19cec7
make	wasm32	built	5671e538
mariadb	wasm32	built	e0c597fc
mariadb	wasm64	built	3e9d5eea
modeset	wasm32	built	af820f3f
msmtpd	wasm32	built	8c1bda31
nano	wasm32	built	27d25982
ncurses	wasm32	built	e2383aa6
netcat	wasm32	built	83261f5c
nginx	wasm32	built	097a5c70
php	wasm32	built	3006a5b4
posix-utils-lite	wasm32	built	6defd412
sed	wasm32	built	70f07e03
spidermonkey	wasm32	built	d1b3e35c
tar	wasm32	built	98b34b7a
tcl	wasm32	built	68c04865
unzip	wasm32	built	55097103
userspace	wasm32	built	f5a1ab12
vim	wasm32	built	a8847879
wget	wasm32	built	163ebe69
xz	wasm32	built	c4d2e82a
zip	wasm32	built	07f4db5d
zstd	wasm32	built	5c1b3192
bash	wasm32	built	96cb7de6
mariadb-test	wasm32	built	1720b71f
mariadb-vfs	wasm32	built	6fd5ea84
mariadb-vfs	wasm64	built	e5b9a397
nethack	wasm32	built	6057e6cf
node	wasm32	built	cfe2bfc0
spidermonkey-node	wasm32	built	eee81883
vim-browser-bundle	wasm32	built	1299a1eb
nethack-browser-bundle	wasm32	built	b0496c19
rootfs	wasm32	built	8baa9688
shell	wasm32	built	6c8eff17
lamp	wasm32	built	75c74a6e
node-vfs	wasm32	built	bf002f07
wordpress	wasm32	built	dda049c8

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