Deliver SIGEV_THREAD timers to pthread helpers

[brandonpayton]

Purpose

Vim's POSIX start_timeout() path uses timer_create(..., SIGEV_THREAD, ...). Musl implements that contract with a helper pthread and lowers the timer notification to Linux-compatible SIGEV_THREAD_ID. Kandelo rejected that exact notification mode with EINVAL, so Vim reported E1286, remained in its timer error path, and left Git waiting indefinitely for the default editor.

This fixes the platform timer contract instead of suppressing Vim timers or adding package-specific behavior.

What changed

• Keep authoritative per-timer notification state in the kernel, including exact thread targets, SI_TIMER metadata, overrun state, and cleanup.
• Deliver host timer expirations through a kernel export so both Node and browser hosts use the same queueing and wakeup semantics.
• Preserve finite sigtimedwait() deadlines across retries and wake the matching blocked thread channel.
• Build musl with the SDK's Wasm EH/SjLj lowering so its timer helper does not leave unresolved setjmp/longjmp imports.
• Add an end-to-end pthread SIGEV_THREAD timer fixture and targeted host coverage.
• Update the POSIX and SDK reference documentation.

ABI

This PR has an intentionally reviewable two-commit shape:

1. 1382547ac5b6083830bba336d17c5aab7e31348e is the complete functional change.
2. 0d03f899103408c6c233379072c93b0407c81ced is the isolated ABI 19 bump and generated snapshot/binding update.

The timer delivery export and semantics are ABI-visible, so the standalone PR correctly bumps ABI_VERSION to 19. The ABI batching work in #871 should cherry-pick the functional commit and replace or omit this PR's standalone bump when assigning the consolidated epoch.

No package archives, VFS images, or release indexes are changed here. They must be rebuilt for the final merged ABI epoch.

Validation

Run through scripts/dev-shell.sh on the functional head, followed by ABI consistency checks on the exact PR head:

• kernel unit tests: 972 passed
• focused host timer/signal tests: 15 passed
• targeted POSIX sigtimedwait tests: 5 passed
• host production build: passed
• focused POSIX timer pthread fixture: passed on the functional head
• scripts/check-abi-version.sh: passed on exact head
• git diff --check: passed
• independent exact-head review: accepted

The standalone ABI bump has not been followed by a full local ABI 19 artifact rebuild. Full browser, libc conformance, POSIX conformance, and Sortix suites were not run locally; CI is the evidence gate for those claims.

[brandonpayton]

Independent exact-head review completed for 0d03f899103408c6c233379072c93b0407c81ced: ACCEPT.

• The branch is exactly the accepted functional commit 1382547ac5b6083830bba336d17c5aab7e31348e followed by the isolated ABI commit.
• The ABI commit is limited to ABI_VERSION 19, the authoritative snapshot, and generated C/TypeScript constants.
• The combined snapshot includes kernel_posix_timer_fire with its optional host-adapter classification.
• scripts/check-abi-version.sh and git diff --check pass at exact head; the worktree and index are clean.

No review blocker was found. CI still owns the full ABI 19 artifact rebuild and broad browser/conformance evidence.

[github-actions]

Phase B-1 matrix build status — pr-906-staging

ABI v19. 69 built, 0 failed, 69 total.

Package	Arch	Status	Sha
libcurl	wasm32	built	d91660ac
libcxx	wasm32	built	6ab57bf4
libcxx	wasm64	built	95a9b1db
libpng	wasm32	built	3cd08346
libxml2	wasm32	built	9bd3619f
libxml2	wasm64	built	03616b63
openssl	wasm32	built	5ae4fe50
openssl	wasm64	built	d9d249d6
sqlite	wasm32	built	06655b03
sqlite	wasm64	built	ad7294fe
zlib	wasm32	built	347ca36b
zlib	wasm64	built	0c033641
bc	wasm32	built	ef20578a
bzip2	wasm32	built	cf7f30e0
coreutils	wasm32	built	7f0b7802
curl	wasm32	built	d0187845
dash	wasm32	built	f802bddb
diffutils	wasm32	built	674b8f44
dinit	wasm32	built	a8168ccb
fbdoom	wasm32	built	0f4818ed
file	wasm32	built	0b9fac52
findutils	wasm32	built	b636d32c
gawk	wasm32	built	0a8f6795
git	wasm32	built	5ba8c0c6
grep	wasm32	built	2aac26f9
gzip	wasm32	built	3698a07a
hello	wasm32	built	6553ed19
kandelo-sdk	wasm32	built	4062f2d6
kernel	wasm32	built	be880b01
less	wasm32	built	7f9297f6
lsof	wasm32	built	dbdabdbb
m4	wasm32	built	6fd6a44b
make	wasm32	built	cfb18f6e
mariadb	wasm32	built	deaffec4
mariadb	wasm64	built	4adc1d3b
modeset	wasm32	built	24d1188e
msmtpd	wasm32	built	275d3474
nano	wasm32	built	e88a4c8d
ncurses	wasm32	built	4c36b411
netcat	wasm32	built	319765d3
nginx	wasm32	built	76a029d6
php	wasm32	built	2d325e8d
posix-utils-lite	wasm32	built	818c4bb5
ruby	wasm32	built	7c32e926
sed	wasm32	built	dc5d015b
spidermonkey	wasm32	built	72ee84d8
tar	wasm32	built	3c8d4efe
tcl	wasm32	built	13ec97f7
unzip	wasm32	built	1c8bc9c1
userspace	wasm32	built	95446055
vim	wasm32	built	088793df
wget	wasm32	built	099fffa4
xz	wasm32	built	3f435f79
zip	wasm32	built	cd9a1e95
zstd	wasm32	built	9bc9f13e
bash	wasm32	built	8b4bd77a
mariadb-test	wasm32	built	b0273594
mariadb-vfs	wasm32	built	317f8ee0
mariadb-vfs	wasm64	built	b6fa7e8a
nethack	wasm32	built	10851493
node	wasm32	built	9a4036cf
spidermonkey-node	wasm32	built	0516a7ee
vim-browser-bundle	wasm32	built	c3e294a1
nethack-browser-bundle	wasm32	built	2b945cc9
rootfs	wasm32	built	0036fdc9
shell	wasm32	built	5f332d81
lamp	wasm32	built	ade2ef08
node-vfs	wasm32	built	d2b85408
wordpress	wasm32	built	29a03d35

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

[brandonpayton]

Merged PR #907 supersedes this work through the strengthened timer-delivery implementation now on main at e15edcef3. This head was not merged verbatim; the merged commit preserves the intended behavior in the ABI39 batch.