feat(backend): polywasm-backed undici on iOS, re-enable maps plugin

[gmaclennan]

Summary

• Replaces the iOS undici stub with polywasm, a pure-JS WebAssembly polyfill, so undici (and therefore the maps fastify plugin) works under nodejs-mobile's jitless V8 on iOS.
• Re-enables the real maps fastify plugin in the iOS bundle by deleting backend/lib/maps-stub.js and removing the iOS-only stubComapeoMapsPlugin from rollup. Tile fetching is no longer broken on iOS by construction.

Why polywasm + a SIMD alias

nodejs-mobile on iOS runs V8 with --jitless and is built with v8_enable_webassembly=false, so globalThis.WebAssembly is absent. The previous workaround stubbed the only direct undici user (@comapeo/core's maps plugin) and passed --no-experimental-fetch to keep the bundled fetch out of the same load path.

Polywasm fills the gap, but its 0.2 release doesn't implement WASM SIMD (opcode 0xfd). Undici's lazyllhttp() tries the SIMD-optimized llhttp wasm first, falls back to non-SIMD on compile error — but polywasm compiles SIMD bytes successfully and only throws lazily on the first export call, which undici's catch doesn't intercept. The aliasUndiciSimdWasmPlugin redirects require('../llhttp/llhttp_simd-wasm.js') to the non-SIMD bytes beside it, scoped to importers in undici/lib/dispatcher/ so unrelated packages aren't caught. iOS-only — Android keeps the native, SIMD-capable WASM path.

Files

File	Change
backend/index.ios.js	New iOS entry. Imports lib/install-polywasm.js first so polywasm is in place before index.js (and undici through the maps plugin) evaluates. ESM source order guarantees this. Filename uses RN's .<platform>.js convention.
backend/lib/install-polywasm.js	New. Installs polywasm whenever native WebAssembly.compile isn't callable. Tighter than typeof globalThis.WebAssembly === "undefined" because partial stubs would otherwise slip past.
backend/index.js	Unchanged behavior; only minor doc edit.
backend/rollup.config.ts	Drops stubComapeoMapsPlugin. Adds aliasUndiciSimdWasmPlugin (iOS-only). Switches iOS input to index.ios.js.
backend/lib/maps-stub.js	Deleted.
backend/package.json	Adds polywasm@0.2.0.

Verification

• ✅ Polywasm install verified on Node 18 jitless desktop: WebAssembly.compile + WebAssembly.instantiate + llhttp_alloc(1) returns a valid pointer.
• ✅ Bundled iOS path verified to use non-SIMD wasm: 48,615 bytes (matches node_modules/undici/lib/llhttp/llhttp-wasm.js); both WebAssembly.compile calls in the bundled lazyllhttp now reference the same bytes function.
• ✅ End-to-end fetch through bundled undici verified on iPhone 16 simulator under nodejs-mobile jitless V8 via a temporary smoke test (now removed — see commit be91565). The smoke test wrote PASS to <privateStorageDir>/undici-smoke-result.txt during diagnostic, confirming polywasm + non-SIMD undici handles HTTP through llhttp at runtime.

Pre-existing iOS test failure (unrelated)

apps/example/tests/ios/CoreManagerSmokeTest fails locally with service.state == .error — but the same failure reproduces against 8655ff8 (the base of this branch) without any of these changes. Not introduced by this PR; the IPC handshake between native sending init and the backend receiving it doesn't complete on the local simulator. Filing separately.

Test plan

• npm run backend:build produces ios/nodejs-project/index.mjs containing the polywasm install (search for globalThis.WebAssembly) and a single non-SIMD wasm bytes function.
• On a real iOS device or fresh simulator: app reaches STARTED lifecycle state, no undici/WASM errors in node logs.
• Android: existing build path unchanged — Android bundle still uses native WebAssembly, no polywasm cost. Verify Android tests still green.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds an iOS-specific backend bundle entry that installs a WebAssembly polyfill so undici can load under nodejs-mobile’s jitless V8, and re-enables the real maps Fastify plugin on iOS by removing the previous maps stub. This is implemented by introducing a polywasm bootstrap on iOS and a Rollup-time alias to force undici’s non-SIMD llhttp WASM module.

Changes:

• Add backend/index.ios.js + backend/lib/install-polywasm.js to install polywasm before the shared backend entry evaluates on iOS.
• Update backend/rollup.config.ts to use the iOS-specific input and to alias undici’s SIMD WASM module to the non-SIMD module on iOS.
• Remove the iOS maps stub and add polywasm@0.2.0 to backend dependencies.

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
backend/rollup.config.ts	Switch iOS input to index.ios.js and add an iOS-only alias plugin to redirect undici SIMD WASM to non-SIMD.
backend/package.json	Add polywasm dependency for the iOS WebAssembly polyfill.
backend/lib/maps-stub.js	Delete the iOS-only maps plugin stub to re-enable real maps behavior on iOS.
backend/lib/install-polywasm.js	Install polywasm when native WebAssembly.compile isn’t callable.
backend/index.ios.js	New iOS-only entry that imports the polywasm installer before the shared index.js.

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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	@​comapeo/​default-categories@​1.0.1
	@​types/​tar-stream@​3.1.4
	@​comapeo/​map-server@​1.1.3
	@​comapeo/​ipc@​8.0.0
	framed-stream@​1.0.1
	polywasm@​0.2.0
	tiny-typed-emitter@​2.1.0
	rollup-plugin-esbuild@​6.2.1
	@​rollup/​plugin-esm-shim@​0.1.8
	@​rollup/​plugin-json@​6.1.0
	@​rollup/​plugin-alias@​6.0.0
	@​rollup/​plugin-node-resolve@​16.0.3
	magic-string@​0.30.21
	rollup@​4.60.2
	@​rollup/​plugin-commonjs@​29.0.2
	tar-stream@​3.1.8
	typescript@​5.9.3
	@​sentry/​rollup-plugin@​5.2.1

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