Challenge 2: Extruding at Zero Distance Still Creates Geometry — Solution Walkthrough

The answer:

Per this chapter's own warning box, Extrude always creates new
geometry the moment it's activated, even if it's then confirmed at
zero distance without moving the mouse. The student's model isn't
actually unchanged — an invisible, overlapping duplicate face now sits
exactly on top of the original.

Why this looks like nothing happened:

Since the duplicate sits at exactly the same position as the original
face, there's no visible difference in the model's own appearance
right now, which is exactly why the student assumed nothing occurred.

Why this can cause problems later:

Per this chapter's own warning box, that hidden duplicate can cause
confusing selection or shading problems once it gets caught up in a
future edit — selecting what looks like one face might actually select
two overlapping ones, or a later transform might move only one of the
two duplicates, suddenly revealing a visible gap or overlap that seems
to come from nowhere.

What should have happened instead:

Moving the mouse at least slightly before confirming, or explicitly
cancelling with Escape if no extrusion was actually intended, avoids
leaving this invisible duplicate behind in the first place.

WHY THIS WORKS AS AN ANSWER
------------------------------
This exercise checks that a zero-distance extrude is correctly
understood as still creating real, overlapping geometry, not a
no-op action.