Probably a more future proof fix would be to initialise the detail directions if they don't exist instead of only in the first stroke step in SCULPT_enhance_details_brush. This way the code would be ready for when the brush engine supports inverting the direction during the stroke.

In sculpt-dev the strength of the shift-smooth mode is controlled by a global property so it does not depend on arbitrary brush presets from an different tool.

In that file, the object has a Z scale value set to almost 0. Sculpt mode is not intended to work with non uniform scaling (it already shows a warning). Applying the scale fixes the issue.

In particular for sculpt mode and some of those operators, it would be ideal to keep the paint cursor updating and redrawing when waiting for input (as it has the active vertex/face set and surface orientation preview). Not sure if the patch already supports that. If it does, then those tools should work as expected.

A lot of sculpt mode related operators fall into this category, some of them have the modal callback just to show the picker and update the cursor. Not sure if you want to tackle this as part of this patch, but I can update and test all of them later after committing it.
This includes:

• Expand (all modes)
• Shrink/Grow Face Sets
• Face Set extract
• Set pivot to surface under cursor
• Transfer Sculpt mode
• Dyntopo/Voxel detail size picker