I've gotten to a point where I get a single frame in a debugger ...
Here's a healthy halt run from a playground:

and here's the empty halt:

When I open a debugger I only see the one frame .. this is not quite
right ... The other thing that happens in this mode is that halts
don't halt the ui process and I can end up with a screen full of
halt if I put a halt in a loop or worse I end up with infinite
errors, because the UI process is not halted (at least that's my
current hypothesis) ...
There is a UI process and I have saved and restarted the image at
this point:

In a helathy image the UI process stack looks very similar, but I do
notice that I've got an OSSubprocess child watcher in the healthy
image and it is missing from the sick image:

It appears that I create this problem when I terminate a debugger
that was brought up in an ensure block ... once I've done this the
image becomes completely unusable (for development and debugging)
and I have to create a new image from scratch ...
I'm hoping that someone can give me the secret formula for repairing
things ...
Is the UI process instance cached somewhere and when I nuke the
process running ensure blocks the debugger's ensure block doesn't
run or some such thing?
I'll follow this route as I investigate ... any help would be
appreciated as this makes debugging very time consuming
Dale