Wasm and host sizes
A libwasm SPA is one wasm module and one vibe.0 host. Those two files are what the user downloads and what the operator runs. Debug builds keep DWARF, the wasm name section, and /DEBUG so a failing _start or a vibe.0 stack still names ClickField.go. Release builds ask DUB for optimize + inline and pass lflags -strip-all (on Windows the host also gets /OPT:REF /OPT:ICF /DEBUG:NONE). After the wasm link, Binaryen ≥123 wasm-opt parses the LDC 1.43 try_table module and, on release, runs -Oz --converge --strip-debug --strip-dwarf --strip-producers with --enable-exception-handling. That is the official ship path. It is not --asyncify — Flatten still cannot rewrite try_table.
bun run dev / svelte-d wasm --debug / svelte-d host stay on debug. bun run build / svelte-d build / svelte-d wasm / svelte-d host --release are release + strip, then wasm-opt -Oz when Binaryen ≥123 is on the machine (bunx svelte-d setup downloads it). Switching modes rebuilds; reprint-skip will not reuse a debug module as a release one.
The numbers below are the simplified kit-admin tree compiled with LDC 1.43 into that package’s own svelte-engine-ws — the same IR the language section prints, not a hello-world stub.
| Artifact | Debug | LDC release + strip | wasm-opt -Oz (ship) |
|---|---|---|---|
public/svelte-engine.wasm | 12.64 MiB (13,255,662) | 1.59 MiB (1,667,361) | 0.93 MiB (971,820) |
same, gzip -9 | — | 217 KiB (222,176) | 224 KB (223,909) |
webserver/svelte-engine-server | 14.08 MiB (14,759,424) | 10.85 MiB (11,377,664) | (host is not wasm-opt) |
The wasm cell is where strip and -Oz pay. Debug wasm carries the name section and DWARF so wasm-names.json and a browser DevTools wasm frame can still say lib.ClickField.go. LDC -strip-all drops most of that and leaves 1.59 MiB. Binaryen then folds the leftover DWARF (~134 KiB after LDC strip) and shrinks the CTFE NodeDef graph, spa-phobos, and WebIDL bindings to 0.93 MiB. Gzip of the -Oz module is slightly larger than gzip of the unopt release (transfer is similar; the raw ship size is the win). There is no React, no virtual DOM, and no second JS runtime. A real admin shell (layout, list, :id, {#await}, host JSON) still fits in a module smaller than a typical JS SPA source map.
The twelve exports stay after -Oz: memory, __indirect_function_table, svelte_engine_eh_probe, svelte_engine_phobos_probe, _start, dumpApp, loadApp, domEvent, allocString, jsCallback0, jsCallback, __heap_base.
The host shrinks less because vibe.0, botan, and OpenSSL stay in the image. Release still drops the debug directory and unused COMDAT. The matching .pdb is a debug leftover, not the ship artifact.
Those figures live in svelte-engine-ws/.svelte-d/artifact-sizes.json after bun run build in packages/svelte-d-kit-admin. They are measurements, not a budget. A page that news on every click will grow the heap at runtime without changing this file size. See memory and wasm vs host.