Mechanical sweep of all .sx sources and plan docs (PLAN.md, current/,
.agents/) for the sx language rename (s8/s16/s32/s64 -> i8/i16/i32/i64).
Verified: make build + make test, 14/14.
Every abort site writes a CliFailure (stable dotted code + human message
naming the offending input); under --json the CLI emits a single
{"status":"error","error":{code,message}} object on stdout and exits 1 —
distinct from the parser's EX_USAGE 64. All aborts happen before db.save
and the repo transaction rolls back, so a failed publish never changes
db.json. Pinned test drives all five failure classes plus the
non-empty-store no-partial-state crux.
