Reject helpers checked only rc!=0, so a SEGFAULT (exit 139, or the
driver's "w6c failed" exit 1) counted as a clean reject -- a wwstage
crash could pass vacuously (it did, latently, on bodied bare-... pre
#11). Every reject row now captures stderr and requires the actual
diagnostic substring (rc!=0 AND strstr) across all 16 reject tests; a
crash emits no diagnostic, so it now fails. This is the
differential-reject backstop (#15): both stages must cleanly reject
with the expected message.
Two genuine cstage/wwstage diagnostic-body divergences are documented
inline via per-stage substrings, not papered over (845 tuple parse,
catA_f2 tuple arity); catalogued in #21.
The wwstage checker silently accepted a struct with repeated field names; cstage already rejects it (cmd/wcc/check.c:925-947). Add validatestructfields, dispatched once per struct decl from resolvewalk's eager type-decl arm (check.ww:792, sibling to the N_TENUM stampenumvals fire): a pure read-only O(n^2) named-field dup walk that emits "duplicate field 'X'" via cerr + c.errs, with no mutation -- valid-program codegen is unchanged so cstage==wwstage byte-id holds. Named fields only; ww has no struct embedding, so cstage's embed-collision arm is intentionally not ported (separate parser gap, catB-89).
Test: new table-driven both-stage reject test 849_dupfield_reject (adjacent / non-adjacent / different-type dup rows + a distinct-field control that builds and runs). Full make test: 451 green incl. 990-997 byte-id.
