So, I can connect to the Bangle from the IDE, send it commands and all works as expected. However the problem seems to be that sending it a "reset()" command causes the connection to drop and it then can't be restored without re-pairing. As the app upload issues a reset() then all commands it sends subsequent to that are lost.
Issuing "reset()" causes the Bangle to reply "=undefined" (presumably expected), then either the IDE or the Bangle prints "-> Terminal", but after that there is no more response from it until I disconnect and reconnect (see screenshot).
I observe this behaviour on both my desktop Mac and my iPad using the special Bluetooth-enabled browser.