Final piece of the os module graduation: the three try* wrappers
move off the (T | str) placeholder shape. `oserror` becomes a real
Hare-style error type (`!i64` instead of plain `i64`), so it's
picked up by ?-propagation as the error half without callers having
to name it.
tryread: (i64 | oserror) was (i64 | str)
trywrite: (i64 | oserror) was (i64 | str)
tryopen: (i32 | oserror) was (i32 | str)
Callsites updated: wwdump uses tryopen; the e2e trywrite probe
matches on os.oserror and validates -EBADF for a bad fd (-9 instead
of the old "write failed" string length).
selfhost/test/smoke.ww switched to raw os.open(2) instead of
os.tryopen for probe 7 — same reason as the os.readall switch in
the prior commit: probe 6 in 990_selfhost compiles smoke.ww
standalone, and cross-module type refs like `os.oserror` don't
resolve in that mode.
`type oserror = i64` carries -errno (Hare's errors::errno-shaped
named-i64). The three convenience wrappers move off the i64 = -1
sentinel and onto the tagged-union surface.
Callers updated across the selfhost (wwdump, w6c, w6a, w6l, ww
driver). The slurp paths in w6c/w6a/w6l/wwdump now match on the
filesize and readall results; the ELF-emitting writeall sites in
w6a/obj.ww are wrapped through two small local helpers (`wrn` for
"wrote N bytes ok?", `wrdrop` for fire-and-forget) so the existing
11-callsite write loop stays readable.
selfhost/test/smoke.ww kept using raw os.read instead of
os.readall: the 990 cgen-match probe compiles smoke.ww standalone
(no `use` expansion), and cross-module type references like
`os.oserror` can't be resolved in that mode.
Two selfhost-side gaps surfaced and got plugged:
- lib/ww/parse/parse.ww parsetype now collapses dotted type names
(`pkg.Type` → single N_TNAME with the joined string), mirroring C
parsetype's dotted-path loop. Local `joindotted` helper because
there's no arena-based string-concat in the selfhost lib yet.
- selfhost/cmd/wcc/check.ww name-resolver applies the dotted-prefix
rule from cmd/wcc/check.c's resolve_typename: split at the last
dot, look up the head as a `use` import, then the leaf as a type.
