Red dev caught it ninety minutes after the merge: smoke_plan_drawing_repairs
and smoke_resize_pointer_real_plan went red because the new "a 0° wedge is
always a duplicate" rule refused two ordinary edits — creating a room over
an existing partition ring (#308's legal overlay) and resizing a wall until
it lands on a neighbour's. The premise was wrong at the model level: a
shared wall of two adjacent rooms IS two co-located owner atoms on one line,
so every shared-wall node carries a legitimate 0° pair by construction.
Bisection pinned the exact cut: with only the 0° rule reverted, both smokes
are green again; keys, incidence, the iterative walk and fail-closed stay.
Spec revision 4 records the revert and returns "an exact duplicate wall is
invisible to П1" to the status of a KNOWN LIMITATION — an honest detector
needs owner identity, which is a separate decision for the owner to make.
The zero-wedge mutant is removed with its rule; the .5-tick parity unit now
observes quantisation through valence instead of the retired duplicate
visibility; changelogs drop the over-promise.
Issue: #331
User-Visible: yes