TRI-27 emulator: loader.load writes eight-byte words but run fetches four-byte units at pc * 4 #1166

Where: loader.zig and the fetch in executor.zig at 976df51.

What happens. loader.load writes each code word into an eight-byte memory word from word 3 on, while run fetches four-byte units at pc * 4.

• A loaded program executes a NOP between every two of its instructions.
• Its absolute jump targets miss.
• The path the owner's tests drive copies the file to byte 0 and starts at word 3, so the tests never see this.
• loader.load is used only by tri_emu_main.zig, which has no build target.

Source: specs/isa/tri27_machine.t27, FINDINGS.

Expected. The loader and the fetch agree on the word size: one code word per fetch unit.

Vector. loader-entry in conformance/trinity/tri27_programs.json. After loader.load, six zero fetches run as NOP before the first real instruction.

Found while writing the S05 specs of #988 (gHashTag/t27#3581); until now it lived only in the spec's FINDINGS. The vectors are replayed by tools/trinity_tri27.py in gHashTag/t27. Tracked in #1164.