Espruino command-line tool

Hmmm, 2 steps forward, 1 step back.
Happy with my mods, I've tried a build on a 'large' project and I'm having serial comms. problems with the espruino-cli dropping characters in both directions.
When I say large, I mean a combined 26Kb of source.

• I have checked it's not the code I am loading: I can capture it with -o and then load this file via the WebIDE successfully
  
• I have forced Espruino.Config.SERIAL_THROTTLE_SEND = true; and verified this is in effect, and it doesn't solve the problem.
  
  

When espruino -v source.js sends the code to the Pico there are dropped characters, even if I leave out the -v the result is the same. If I use espruino in terminal mode and do a dump(); on the full set of code (loaded with the WebIDE) then there are dropped characters in what I see. Again, I don't have these problems with the WebIDE.

Any ideas about what to try next? I currently think its somewhere in the 2 different code paths for serial comms. when you compare the WebIDE with espruino-cli.