Creating external geometry constraints in cross space
Enable "Sync placement"
Add a Part (Part001) to the root (the yellow stairway icon) Create all sub-shape binders (Binders) (may go to any active "Body"), move them into the Part001 (move between containers one by one to keep the Placement in sync (for now)) Click the appropriate face of any Binder, use Sketcher->Flat Face, close Drag and drop the Sketch001 into the Part001 Double click the Sketch001 to edit Use "External Geometry" tool to teleport constraints from outside geometry through the Binder(s) Draw the projection for your desired geometry, close "Extrude" the sketch (under Part WB) (possibly you may want to use "symmetric" option if this will be used as a virtual cutter) Drag and drop the Extrude001 into the Part001 container Move the Part001 into the Assembly container (one by one, again) (Use the "Extrude001" as cutter and not the Part001, if it would be used as a cutter)
Add a Body to the root (the blue stairway icon) Drag and drop the Body into the Assembly container (or you'll get Cyclic Dependency error in the end) Double click the Body to activate it Single click any object to create a sub-shape binder for that, and click "sub-shape binder" button. Binders will go into the Body automatically. Make visible and click the appropriate face of any binder, click Sketch to create a sketch Use "External Geometry" tool to teleport the remote constraints Draw the projection of your desired geometry, close Select the Sketch (it should be already selected), click Pad to generate the solid Switch to Assembly3 WB, move or set some constraints to locate.
double click PartBody/Extrude/Sketch arrange the visibility for the binders edit the projection
Create a sub-shape binder of PartBody/Extrude (not PartBody itself) within the upper Assembly container Use this Binder as Tool for a Cut operation