edgesync: WASM Targets

EdgeSync ships two WebAssembly builds. Both are produced by the leaf module — same agent API (New -> Start -> Stop) — but with different runtimes, networking models, and SQLite drivers.

Target	GOOS	GOARCH	SQLite driver	Build entry	Output
WASI	`wasip1`	`wasm`	`ncruces` (WASM-based)	`leaf/cmd/leaf`	`bin/leaf.wasm`
Browser	`js`	`wasm`	`ncruces` + OPFS VFS	`leaf/cmd/wasm`	`bin/leaf-browser.wasm` + `bin/wasm_exec.js`

Building

Both targets are driven from the repo root:

make wasm-wasi      # produces bin/leaf.wasm
make wasm-browser   # produces bin/leaf-browser.wasm and copies wasm_exec.js
make wasm           # both

The Makefile cds into leaf/ because the leaf agent lives in its own Go module. The browser recipe copies wasm_exec.js from $(go env GOROOT)/lib/wasm/ (Go 1.26+ path); older Go releases used misc/wasm/.

SQLite driver selection

leaf/cmd/leaf/main.go uses build-tagged blank imports to pick the right driver:

driver_default.go (!wasip1) — modernc (pure Go, the standard driver)
driver_wasi.go (wasip1) — ncruces (WASM-based; modernc.org/libc has no wasip1 port)

The browser entry (leaf/cmd/wasm/main.go) is //go:build js and imports ncruces directly.

Runtimes

WASI runs under any wasip1 host: wasmtime, wasmer, wazero, browser WebAssembly.Module instantiated with WASI shims. Full HTTP serving works (host networking).
Browser runs in a Web Worker via wasm_exec.js. NATS connects via nats.SetCustomDialer() over a WebSocket. Exposes JS globals: edgesync.newAgent, .start, .stop, .syncNow. See leaf/cmd/wasm/worker.js.

Known limitations

Browser cannot listen. serve_http_js.go and signals_js.go are build-tagged no-ops — there is no HTTP server in browser builds.
stash/ and undo/ are excluded (//go:build !js) — checkout features, not needed for sync.
Telemetry is a no-op on both wasm targets (leaf/telemetry/noop.go covers wasip1 || js). OTel exporters require host networking that browser builds cannot reach.
Binaries are large. leaf.wasm and leaf-browser.wasm are each ~50 MB unstripped — the SQLite driver dominates. Compression (gzip/brotli) on the serving layer is recommended.

See agent-deployment.md (WASM Targets section) for the agent lifecycle in WASM and testing-strategy.md for how WASM builds are exercised in CI.