lem-electron fails to spawn lem-rpc

[Symbolics]

Installation proceeds with no errors. Running lem-electron brings up a blank windows. Looking at developer tools:

events.js:187 Uncaught Error: spawn lem-rpc ENOENT
    at Process.ChildProcess._handle.onexit (internal/child_process.js:264)
    at onErrorNT (internal/child_process.js:456)
    at processTicksAndRejections (internal/process/task_queues.js:80)
security-warnings.ts:182 Electron Security Warning (Insecure Content-Security-Policy) This renderer process has either no Content Security
    Policy set or a policy with "unsafe-eval" enabled. This exposes users of
    this app to unnecessary security risks.

For more information and help, consult
https://electronjs.org/docs/tutorial/security.
This warning will not show up
once the app is packaged.
(anonymous) @ security-warnings.ts:182
C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\node_modules\vscode-jsonrpc\lib\main.js:613 Uncaught Error: Connection is closed.
    at new ConnectionError (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\node_modules\vscode-jsonrpc\lib\main.js:138)
    at throwIfClosedOrDisposed (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\node_modules\vscode-jsonrpc\lib\main.js:613)
    at Object.sendNotification (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\node_modules\vscode-jsonrpc\lib\main.js:667)
    at HTMLElement.emitInput (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\frontends\electron\lem-editor\lem-editor.js:287)
    at HTMLElement.resize (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\frontends\electron\lem-editor\lem-editor.js:299)
    at resizeHandler (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\frontends\electron\lem-editor\lem-editor.js:199)
C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\node_modules\vscode-jsonrpc\lib\main.js:138 Uncaught Error: Connection is closed.
    at new ConnectionError (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\node_modules\vscode-jsonrpc\lib\main.js:138)
    at throwIfClosedOrDisposed (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\node_modules\vscode-jsonrpc\lib\main.js:613)
    at Object.sendNotification (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\node_modules\vscode-jsonrpc\lib\main.js:667)
    at HTMLElement.emitInput (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\frontends\electron\lem-editor\lem-editor.js:287)
    at HTMLElement.resize (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\frontends\electron\lem-editor\lem-editor.js:299)
    at resizeHandler (C:\Users\symbolics\AppData\Roaming\npm\node_modules\lem\frontends\electron\lem-editor\lem-editor.js:199)

The cause seems to be there is no lem_rpc to spawn. The build process must have silently failed somewhere. This is on MS Windows 10, with the latest versions of npm (6.14.10) and node.js (14.15.3).