'ww test' gains the istest build path (-T injection in build_one/
buildone) and do_test/dotest accept -I, mirroring do_run - both twins.
The 35 converted lib tests drop their interim bare mains (-T
synthesizes the entry from @test fns and rejects a user main); their
35 C run-drivers flip 'ww run' -> 'ww test'; 989_lib_byteid compiles
lib tests under -T (8 user-main probe fixtures stay non-T, gated on
the fixture field). Abort-on-first-failure stands until the deferred
record-and-continue harness lands with the multi-package arc.
Hare-faithful port of errors::errno (ref/hare/errors/{rt,common,opaque}.ha): the 13 named common error conditions, opaque_data/opaque_ (the type-erased tail whose strerror fn-ptr defers to os.strerror), and errno(os.errno) error mapping the ~12 mapped errnos to named conditions and wrapping the unmapped tail in opaque_. The raw errno type (!i32, kernel-int width, distinct from oserror's !i64 negative raw return), the E* constants, and the strerror message table live in lib/os: ww folds Hare's sys role into os, so os is the import floor that lib/io and lib/errors build on -- documented in lib/CLAUDE.md (os never imports io or errors). errors.error is explicitly enumerated, matching Hare; the ...errors::error spread is only io.error's (blocked by #199b). Prereq for post-eFinal #5's faithful io error mapping; retires the nomem-collapse interim. Adds errnotest (mapping / opaque-tail / strerror) + test/wcc/902_errno_run. Landing required two wwstage cgen fixes (#9 struct-variant-large-union return, #11 deref-store alias narrow). Divergences cited at-site: bare-type-name return -> let+return; switch fall-through vs Hare's exhaustiveness-only default; opaque_ const dropped.
