Wwstage checkisas fell straight through to the tagged-union arm on
`enum_val as i32` reinterprets, false-positiving on every enum→int
cast in lib/ (lib/time/instant.ww, lib/os, lib/os/lseek). Cstage
admits these at cmd/wcc/check.c:1346-1357: when N_TYPEASSERT has
LHS-or-RHS enum AND both ends are integer-typed, the target type
returns without the tagged check. `is` (TYPETEST) stays rejected —
cstage gates only N_TYPEASSERT.
isinttypeast helper covers N_TENUM + i8..i64/u8..u64/int/uint/
uintptr/rune. Excludes floats so `enum as f64` still rejects.
N_TYPEASSERT branch in checkisas detects enum on either side via
resolvealias-unwrap, gates on both-ends-int, returns target type
before the tagged-union check.
4/5 selfhost main.combined.ww files now resolve clean via
wwdump_ww -r. Residual on selfhost/cmd/ww tracked as #53
(separate checkletassign u64→i32 path).
Hojun-Cho
1b7fde21cd