<p>I've put together a flashlight mount for a camera coldshoe in OpenSCAD.  I originally modeled it in FreeCAD and it was easy to round the edges of the clamp with a fillet and that makes it a little easier to get the light in and out of the mount.</p>
<p>I'm not sure how to do it in OpenSCAD.  Naively, I'm sure I could calculate where on my semicircle I would need to add some cylinders in order to round the sharp corners, but it seems like there'd be something a little easier than that.</p>
<p>Am I missing something?</p>
<p>Here's the <a href="https://github.com/tncbbthositg/cold_shoe_light_mount/blob/795489c90f412502a2545536e906ad8971cfd691/cold_shoe_light_mount.scad" rel="nofollow noreferrer">coldshoe light mount SCAD file</a> and this is what it looks like:
<a href="https://i.stack.imgur.com/StF93.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/StF93.png" alt="coldshoe light mount" /></a></p>

I'm far from a wizard with OpenSCAD, but enjoy using the program, learning something new every time. In your case, it's likely that you can use the
roundanything library
to accomplish your objective.
The library will present various implementations in the samples, making it an exercise for the reader to determine which module calls will present the solution.
The image below shows a part which has had the radii applied in a manner similar to your image: