w6c: forrange bind cap loud; drain widen gates keyed on type-eq (#55)

Two silent seams in one sweep. The for-range destructure silently
dropped the 9th+ binding in both stages (bind arrays are sized 8);
the cap now hard-stops per the DEFER_MAX/LOOP_MAX discipline (the
shape is unreachable today -- every wide-tuple construction path
already loud-stops). argtaggedwidensz, the drain-side SSoT for
widened call args, still keyed "natural push" on slot-size equality
while pushargsrev flipped to type equality with #55 -- a same-slot
subset was classified widen by push, natural by drain (counts
coincide today; a classification reader desyncs, the #48 shape).
Both sides now share the wsame key; the widen-branch tag miss for a
concrete source joins the task-2 loud-stop family (tagged subset
sources keep t=0 -- their widentag is never read, the scratch store
remaps).

Lead 17 (enum fold-failure prev+1) DISPROVED: enumvalfold gates
every member init in the checker and its fold set is op-for-op
equal to cgen's enumevalmember, so the fallback only runs inside
already-failing compiles.

test/wcc/data/subset_arg_widen/case.ww

@@ -0,0 +1,17 @@
+//ww:run-exit 0
+// #55 drain-SSoT leg: a same-slot subset ((bool|void) -> (i64|bool|void),
+// both 16B) call arg is classified WIDEN by push AND drain — the old
+// slot-size drain gates called it natural. The 0->1 tag remap through
+// the widen scratch is what this pins.
+package main;
+type narrow = (bool | void);
+type wide = (i64 | bool | void);
+fn take(w: wide) i32 = {
+	if (w is bool) { return 7; };
+	return 1;
+};
+export fn main() i32 = {
+	let n: narrow = true;
+	if (take(n) != 7) { return 1; };
+	return 0;
+};