fix(browse): externalize @ngrok/ngrok in node server build

[exabird]

Problem

Running ./setup (or browse/scripts/build-node-server.sh directly) fails with:

Building Node-compatible server bundle...
error: cannot write multiple output files without an output directory

Reproduced on: bun 1.3.11, macOS arm64, gstack 0.16.2.0.

Root cause

@ngrok/ngrok was added (I believe in 0.16.x for /pair-agent tunneling). That package ships two native .node binaries as assets:

• ngrok.darwin-universal-*.node (~19 MB)
• ngrok.darwin-arm64-*.node (~9 MB)

When bun bundles server.ts, it statically analyzes @ngrok/ngrok (even though the actual import is dynamic via await import('@ngrok/ngrok')) and tries to emit those .node files as additional outputs next to server-node.mjs. Since --outfile can only produce a single file, bun aborts with the "cannot write multiple output files without an output directory" error.

Fix

Add --external "@ngrok/ngrok" to the bun build command in browse/scripts/build-node-server.sh.

This is safe because @ngrok/ngrok is already loaded dynamically at runtime in server.ts:

// server.ts:1568
const ngrok = await import('@ngrok/ngrok');
tunnelListener = await ngrok.forward(forwardOpts);

At runtime, Node resolves @ngrok/ngrok from node_modules/ just like the other runtime-loaded externals (playwright, playwright-core, diff).

Verification

$ bash browse/scripts/build-node-server.sh
Building Node-compatible server bundle...
Bundled 23 modules in 5ms

  server-node.mjs  0.31 MB  (entry point)

Node server bundle ready: /.../browse/dist/server-node.mjs

Both server-node.mjs (307 KB) and bun-polyfill.cjs are generated correctly.

Notes

• Tested on macOS arm64. I don't have a Windows box to smoke-test the actual Windows Node runtime, but since ngrok is loaded via dynamic import() on an opt-in code path (/tunnel/start), externalizing it should not break any eager initialization.
• Only 2 lines changed (one line + continuation backslash).

[lijishuai]

niubility