selfhost/cmd+test: run check before cgen in wwstage drivers

w6c_ww and wwdump_ww (-c mode) silently passed source into cgen
without type-checking it; any type error flowed through as broken
asm with exit 0. Mirror cstage cmd/w6c/main.c:73-75: between the
parse-error gate and cgeninit, install typesinit + checkinit +
checkfile + `if (ck.errs > 0) return 1;`. Cgen path unchanged —
drivers own check, cgen owns emit (checkfile not idempotent due to
installdecl scopedefine).

The wire-up was blocked by five latent check.ww divergences from
cstage, all landed first: cross-module type refs (#51), enum-int
reinterprets (#52), per-block scoping (#53), nominal-first
tagged-variant inclusion (#55), and same-module N_IDENT callee
preference (#56). With those clear, the broader exercise of
check across every selfhost driver reaches 131/131 first try.

994_w6c_ww grows by one row: a trivially-wrong `let x: i32 =
"hello";` smoke pins both stages to exit-non-zero. Pre-#50 it
emitted 202 bytes of broken asm with exit=0.

Unblocks #42 (size/align/offset wwstage intercepts) and the
audit-§1.8 UP-polarity refactor (node.type_ population can now
land in the same check pass we just wired up).

selfhost/cmd/w6c/main.ww

@@ -147,6 +147,19 @@ export fn main(argc: i32, argv: **u8) i32 = {
 	// cgen and emits junk asm with a zero exit (silent miscompile).
 	if (l.errs > 0 || ps.errs > 0) { return 1; };
 
+	// #50: run check before cgen so AST mutations from #42 (size/align/
+	// offset fold) and the audit §1.8 node.type_ population land before
+	// cgen walks the file. Mirrors cmd/w6c/main.c:73-75. Five precondition
+	// fixes for fixture cleanliness: #51 cross-module type refs, #52
+	// enum↔int reinterpret, #53 N_BLOCK scoping, #55 nominal-first variant
+	// compare, #56 bare-leaf same-module preference.
+	let tc: tctx;
+	typesinit(&tc, ar);
+	let ck: checker;
+	checkinit(&ck, ar, &tc);
+	checkfile(&ck, f);
+	if (ck.errs > 0) { return 1; };
+
 	let cg: cgen;
 	cgeninit(&cg, ar);
 	cgfile(&cg, f);