boards/BRINGUP.md A6, FABRIC-3 SXLIII (ruled: one image, switch at boot).
A STARFORTH_V4 kernel carries v3 too; system= in the boot arguments
chooses, else the build's default (V4_DEFAULT: 1 for plain STARFORTH_V4
builds as before, 0 for board images). make boot_image builds both and
always writes starforth.cfg / cmdline.txt with system=v3 first, and cleans
its ISA's objects first -- that clean was removing build/<arch>/SER5, not
the kernel's objects, until fixed here.
Each ISA: v3 by default (hash unchanged), v4 with system=v4 (538/538).
The SER5 image under OVMF: v3 as built, v4 after a one-word edit on it.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
