wwstage named variadic-gather slots with mkvarargname off a separate
varargseq counter, never bumping the shared labelseq that names match
labels. cstage names them via mklabel (cmd/w6c/cgen.c:5427,5431), which
advances labelseq twice per gather. So by the time main.main reached its
`match (wr)`, wwstage's match-label counter ran two behind cstage's
(_4/_5/_6 vs _6/_7/_8) — a pure label-numbering divergence that kept fmt
cs/ww byte-id failing.
Drop varargseq and the mkvarargname helper; call the existing mklabel
for the two gather slots, matching cstage's order (vararg_d only when
nvar>0, vararg_sl always). The slot names are locals-table keys only —
they resolve to BP offsets and never reach the asm — so only the
labelseq advance is observable, which is exactly what realigns the
downstream match labels. cstage untouched (align wwstage up).
This was the match-label half of fmt's divergence; with the earlier
compound-assign fix it completes fmt byte-identity. Graduate
777/780/781 to STAGE_CS|STAGE_WW with byte_id, and drop the now-stale
(void)asm_byte_identical guard in 777.
The wwstage checker walked a match's raw AST variant list and never expanded a ...inner spread variant, so it rejected fmt's match over field = (...formattable | *mods) ('not a variant of scrutinee'). cstage's resolve_type flattens the spread at type-build. Mirror that in the AST exhaustiveness walk (casevariantin + a recursive checkvariantcovered): when a variant resolves to N_TTAGGED via a spread, recurse into its members. Additive + spread-gated -- typeeqast / casevariantpairmatch (#13) / casecovers untouched, so non-spread matches and 990-997 byte-id are unaffected. Also size a spread N_TTAGGED off each flattened member (mirror cstage check.c), dropping the inner union tag word (field 40B to 32B). Closes the #209 CHECKER reject; full fmt-byte-id still awaits cgen cluster #226 (io.read nominal-remap) + #227 (spread-widen ABI), so fmt tests stay cstage-only with retargeted comments. Adds test 792; regenerates w6c/wwdump combined.ww.
Graduates the fmt fprint family (fprint/fprintf/fprintln/fprintfln + internal putbytes/writeone/format*) from io.stream to io.handle, so a file (fd) prints directly through io.write's file-arm (commit-1). Removes the fdsink placeholder -- the fake-stream-vtable-over-os.write shim that stood in for the missing handle. The 8 stdio wrappers route over os.STD{OUT,ERR}_FILENO (new i32 filenos in lib/os; os is the import floor, so it can't hold an io.file-typed handle like Hare's os::stdout_file -- consumers cast i32 to io.file). Migrates the fd-shim sentinel tests 777/780/781 to fprint-over-handle as their headers designed, cstage-only per the pre-existing #209 (fmt is wwstage-uncompilable). Regenerates the 6 os-embedding combined.ww.
