Cover the partition offset branches and raise the coverage floor #112

fx_partition_offset_calculate.c holds 21 of the 30 uncovered branches in the merged coverage report, 11 of them on a single line where only one of twelve outcomes is taken. Nothing else in the tree comes close: the next largest contributor has two.

That is why the merged branch rate sits at 99.38% and why the branch floor in test/cmake/coverage.sh had to be set below it rather than above. The floor is a tripwire at that level, not a quality bar — it catches the next change that adds an uncovered branch rather than a real regression in coverage.

Cover those branches, then raise the floor deliberately to sit above the new rate with room to spare. The script compares whole tenths of a percent, so the floor can only move in steps of 0.1.

The line floor is a related but smaller case: the tree measures 99.92% against a floor of 99.9%, which is one covered line of headroom out of 7,657. It is green today and was left alone, but it will fail on the removal of a single covered line.