Load PHP intl as a runtime-optional C++ side module

[mho22]

Why

• PHP's intl extension needs ICU, but base php.wasm must stay ICU-free: ~30 MB of ICU should not burden every PHP boot and download. So intl must ship as a runtime-optional side module loaded via extension=intl.so (the way opcache is), not be statically compiled in.
• This is the first self-contained C++ side module in the repo (mariadb is C++ but a main module), and loading it exposed a real host dynamic-linker gap. A self-contained C++ side module both defines and imports its weak COMDAT symbols — virtual destructors, template instantiations, replaceable operator new/delete — because wasm-ld routes default-visibility weak symbols through env so a main module could interpose them. A pure-C main module (php.wasm) exports none of them, so instantiation failed with "function import requires a callable". That is a host-runtime contract that must hold on Node and browser, not an intl-specific quirk.

What

• host/src/dylink.ts — resolve a side module's weak C++ self-imports: an unresolved env function import is satisfied from the module's own post-instantiation exports via a trampoline. A genuinely absent symbol throws loudly at call time instead of returning a silent 0, so a real ABI gap stays truthful. Also provide the env.__cpp_exception tag that -fwasm-exceptions modules import.
• packages/registry/icu — new ICU4C 74.2 wasm32 library package (two-stage host/cross build, static PIC, common data staged as share/icu.dat).
• packages/registry/libcxx — emit position-independent libc++-pic.a / libc++abi-pic.a variants for -shared PIC side modules; the non-PIC pair is unchanged for main-module consumers.
• packages/registry/php — link intl.so by hand with wasm32posix-cc -shared (the libtool workaround opcache uses), naming the libc++ PIC archives; force the 25 pure-musl symbols intl.so imports but base PHP never references (allocator, wide-char, math, and the pthread mutex/cond/TLS ICU's UMutex uses) into php.wasm via -u so the side module shares one libc state with the main module. ICU is kept out of the main link entirely; its ~30 MB common data ships as the separate icu.dat, fed to ICU at load time by a constructor in intl-icu-data-loader.c.

Validation

• clean rebuild: bash build-php.sh reproduces php.wasm (35,590,340 B) and intl.so (5,867,877 B) byte-for-byte from the committed sources (icu rev3 + libcxx rev6 resolver caches).
• host/test/dylink.test.ts: 19 passed, including a new "weak self-import handling" suite that assembles synthetic WAT side modules to cover the trampoline route-to-self, the loud missing-symbol failure, and the __cpp_exception tag — no full PHP/ICU build needed.
• packages/registry/php/test/php-intl.test.ts: 4 passed — base php.wasm lacks intl; extension=intl.so loads; Locale::getDisplayLanguage("fr","en")→"French"; Collator sort off icu.dat.
• no regression: dlopen-e2e (3), fork-dlopen-replay-e2e (1), opcache-prewarm (2) pass; opcache.so is pure C so the trampoline branch never fires for it.

Host parity

dylink.ts is shared Node/browser host logic and uses only standard WebAssembly APIs, so the fix covers both hosts; run on Node. No browser demo is added here (no VFS-image staging yet), so no browser run was required.

ABI

No ABI change — host-side linking plus package artifacts, not kernel/process ABI, syscall, memory layout, or fd semantics. Conformance suites (libc/posix) were not run because no syscall or kernel behavior changed.

🤖 Generated with Claude Code

[github-actions]

Phase B-1 matrix build status — pr-839-staging

ABI v16. 17 built, 0 failed, 17 total.

Package	Arch	Status	Sha
icu	wasm32	built	aa03c107
libcxx	wasm32	built	35eec6d6
libcxx	wasm64	built	9364e8f4
dinit	wasm32	built	4fbff30d
kandelo-sdk	wasm32	built	22d40b0f
mariadb	wasm32	built	4ac2398c
mariadb	wasm64	built	265a4b97
php	wasm32	built	889c740b
spidermonkey	wasm32	built	e7d3a887
lamp	wasm32	built	9d840407
mariadb-test	wasm32	built	b7195948
mariadb-vfs	wasm32	built	86c048cf
mariadb-vfs	wasm64	built	b94b0a28
node	wasm32	built	77ec2f34
spidermonkey-node	wasm32	built	5db86c0e
wordpress	wasm32	built	99a0763d
node-vfs	wasm32	built	b2901d6c

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