The decompiled per-edge branches computing the surrounding nine squares had two
independent defects.
1. Field letters stepped past the alphabet
Every branch moved a field with raw character arithmetic (`str[0] - 1`,
`str5[0] + 1`) and Maidenhead fields only run A..R, so coordinates near the
edges of the world produced squares outside the alphabet:
(-89.9, -179.9) -> [@A91, AA01, AA11, @A90, AA00, @A10, @@99, A@09, A@19]
( 89.9, 179.9) -> [RS80, RS90, SS00, RR89, RR99, SR09, RR88, RR98, SR08]
2. Some moved cells kept the old field letter
The north-edge branch advanced the latitude field for the top-centre cell only,
leaving the two top corners in the previous field:
centre AA19 -> ported [AA00, AB10, AA20, ...]
correct [AB00, AB10, AB20, ...]
Cross-checked against the shared qthNeighbors helper, which is already covered
by QthConverterTest including the AA00 and RR99 wrap cases:
before: 64,800 sampled coordinates, 6,480 disagreed (all with centre square
digits 00 or x9, i.e. the north edge and the 00 corner)
after: 64,800 sampled coordinates, 0 disagree
The ring is plain Maidenhead arithmetic with no QTH-Locator-specific behaviour,
so call qthNeighbors instead of keeping a second, wrong implementation. The
now-unreferenced buildGrids branches are removed (grep confirmed the definition
was the only remaining occurrence). The existing OL42 reference grid and the
four ported edge-case tests still pass unchanged.
Reverting the fix fails both new regression tests; with it
:feature:roaming:testDebugUnitTest and :core:domain:test are green.
mckero
2da7127fd3