rose-ash/plans/NOTE-wasm-try-deprecation.md

Follow-up: WASM kernel uses deprecated try exception instruction (+ sync XHR)

Found: 2026-06-30, from a real browser console on blog.rose-ash.com (modern Chrome/Firefox). Severity: not yet breaking — deprecation warnings. The SPA still boots (a hard refresh cleared a stale cached loader, which was the day's actual symptom). But when browsers remove the legacy try instruction, the WASM kernel will fail to instantiate → "SxKernel not found after 5s" → no SPA (server-rendered pages + native-form writes still work; only SPA nav + the interactive picker need the kernel).

The two warnings

1. WebAssembly exception handling 'try' instruction is deprecated … use 'try_table' instead (×6). The kernel shared/static/wasm/sx_browser.bc.wasm.assets/*.wasm was compiled (Jun-29 artifact) with the legacy exception-handling encoding. wasm_of_ocaml standardized on try_table; current toolchain is 6.3.2.
2. Synchronous XMLHttpRequest on the main thread is deprecated — sx-platform.js:575, loadManifest() does xhr.open("GET", …module-manifest.sx…, false) (sync). Browsers increasingly restrict sync XHR.

Fix

1. A plain rebuild does NOT fix it — TESTED 2026-06-30, dead end. Ran bash hosts/ocaml/browser/build-all.sh with the current wasm_of_ocaml 6.3.2. The output .wasm units came out byte-identical to the Jun-29 backup (same content hashes, e.g. dune__exe__Sx_browser-4878f9e1.wasm; diff -rq clean). So 6.3.2 still emits the legacy try — rebuilding gains nothing. The fix needs a newer wasm_of_ocaml (or a flag) that emits try_table — a toolchain upgrade (opam upgrade wasm_of_ocaml-compiler to a version that defaults to try_table, or find the relevant --enable flag), then rebuild + verify. (Disassembly check note: apt's wasm2wat/wabt is too old for these wasm-GC binaries — error: unexpected type form (got 0x5e); need wasm-tools for wasm-GC, or verify in a real up-to-date browser. Playwright's older chromium still accepts try, so it won't tell you.)
2. loadManifest → async. Change to an async fetch and restructure the boot so the manifest is awaited before module loading (it's currently consumed synchronously). Contained to hosts/ocaml/browser/sx-platform.js + its copy in shared/static/wasm/.

Scope / ownership

hosts/ocaml/browser/ is the OCaml→WASM toolchain — generally out of the host loop's lane, though the host loop has committed there for the blog SPA (b21ae05e, 689dae7d). A kernel rebuild affects the LIVE SPA, so do it when the box is quiet, with real-browser verification, and a quick rollback path (the Jun-29 .assets are the known-good artifact — keep a copy before overwriting). Not urgent; schedule rather than rush.