wcc_ww/cgen: #62 Layer-2 (ww half) — rhsstructpayload chases the alias chain; widen-store su at entry

The wwstage tagged widen's struct-payload classify was name-keyed:
rhsstructpayload's N_IDENT arm did a bare structlookup on the local's
declared TNAME, so an alias name (ali->base) missed the registered
structinfo and the value fell past the struct arm to the SCALAR widen
arm — word0-only box payload, words 1+ zero-filled. At normal decl
order this was BOTH-WRONG-IDENTICAL with cstage pre-F1 (byte-id YES,
gate-blind; F0 m5b_match1 exit 2/2). Choke-point fix: route the arm
through structlookupchain (the name-domain twin of cstage's
su = type_chase_named, c138605) and return the REGISTERED struct
name so every consumer's re-lookup hits. All three consumers
graduate through the one funnel (proof-grep: rhsstructpayload is the
only struct-payload classifier): cgwidentaggedstorebp's struct arm
(let/assign/match), pushargsrev's widen route (the call-arg twin),
and cgreturn's needswiden (cgenstmt.ww:1022). The variant TAG still
keys on the un-chased stamped type — the member's nominal identity
is the alias (cg_tag_for_variant precedent).

Rider, same store family: cgwidentaggedstorebp now chases the source
classify ONCE at entry (post cast peels, where src is final) —
`su = tichase(src.type_)` replaces the five per-arm chases
(nested-arm su / memread su37 / >32B+cast-guard sf37 / tuple-guard
stu72 / tuple-arm stu, all reading the same src.type_), mirroring
cstage cg_widen_tagged_store's su position. dt entry loop + the
remaining in-function plain chases (castu/ceti/fti/fvt) collapse to
tichase — mechanical, excluded from c1 only because the function was
c2 scope wholesale.

Runtime graduation (banked rows .ai/impl62r_layer2_rows.md):
m5b_match1 (L2-1 norm) + m5_match (L2-2 fwd) cs0/ww2 -> 0/0 byte-id;
L2-4 3-word (last payload word) 0/0; push-twin arg row 0/0; control
m5b_match0 holds 0/0 (ken confirms at verdict). test 944: the four
K_RUN_CS rows flip to K_RUN (both drivers + byte-id), 129/129.

SURFACED, FILED NOT FIXED (task #89): the RETURN-position leg
(`return x` of an alias struct into a (void|ali) fn return) was
both-wrong-identical (cs1/ww1 byte-id) and is now transiently
cs1/ww0 byte-id NO — ww is the runtime-correct side; cstage
cgreturn's own route into the widen misses the alias (F1 c138605
covered store+push only). F1-precedent transient divergence, noted
per the L2 rows file's acceptance clause.

Selfhost byte-id: new w6c_ww on the c1-HEAD five main.combined.ww —
byte-identical to the c1 build's output (the fix is asm-neutral on
the corpus); cs==ww on the regenerated five. make test-unit green
(288). Closes task #62's ww half — fix-landed-pending-gate (#71
precedent). combined.ww regens ride along.

test/wcc/944_alias_accept_run.c

@@ -43,11 +43,11 @@
  *                        | struct-lit, walk leaves, reads);     |
  *                        | unprobed gates LOUD-tripwired (#73,  |
  *                        | K_BUILDERR_CS pin)                   | 0
- *   union_store_* +      | task #62 Layer-2 (cs half): alias-   |
- *   union_push_arg       | NAMED struct as union member — widen |
- *                        | store/push word0-only; CS-ONLY until |
- *                        | F2 lands the wwstage half; base ctl  |
- *                        | + the #54-bound `as` row pinned loud | 0(cs)
+ *   union_store_* +      | task #62 Layer-2: alias-NAMED struct |
+ *   union_push_arg       | as union member — widen store/push   |
+ *                        | word0-only; cs half c138605, ww half |
+ *                        | F2a batch-2 c2 — graduated K_RUN;    |
+ *                        | base ctl + #54-bound `as` row loud   | 0
  *   nested_alias_field_* | task #71: alias-typed nested-field   |
  *                        | store/read/addr-of walks fold to     |
  *                        | direct offsets (byte-id graduation,  |
@@ -657,14 +657,17 @@ static const struct row rows[] = {
 	  "	if (take(x) != 26) { return 1; };\n"
 	  "	return 0;\n"
 	  "};\n", 0, K_RUN, NULL },
-	/* ---- task #62 Layer-2 (cstage half): alias-NAMED struct as a
-	 * UNION MEMBER. The widen store/push su single peel fell past the
-	 * struct arm to the scalar arm — word0-only payload (the banked
-	 * rows /tmp/impl62r_layer2_rows.md; both-wrong-identical with
-	 * wwstage at normal decl order = gate-blind byte-id). CS-ONLY
-	 * until F2 routes wwstage rhsstructpayload/push through
-	 * structlookupchain — flip these to K_RUN then. Values distinct
-	 * per word; the LAST payload word is always checked. */
+	/* ---- task #62 Layer-2: alias-NAMED struct as a UNION MEMBER.
+	 * The widen store/push source classify fell past the struct arm
+	 * to the scalar arm — word0-only payload (the banked rows
+	 * /tmp/impl62r_layer2_rows.md; both-wrong-identical at normal
+	 * decl order = gate-blind byte-id). cs half c138605
+	 * (cg_widen_tagged_store/push su chase); ww half F2a batch-2 c2
+	 * (rhsstructpayload -> structlookupchain) — K_RUN, byte-id.
+	 * Values distinct per word; the LAST payload word is always
+	 * checked. The RETURN-position leg stays both-stage divergent —
+	 * cs cgreturn residual, task #89 (ww runtime-correct since c2;
+	 * not pinned here until the cs half lands). */
 	{ "union_store_norm",	/* banked row L2-1 (= F0 m5b_match1) */
 	  "package main;\n"
 	  "type base = struct { a: size, b: size };\n"
@@ -681,7 +684,7 @@ static const struct row rows[] = {
 	  "	case void => { return 3; };\n"
 	  "	};\n"
 	  "	return 0;\n"
-	  "};\n", 0, K_RUN_CS, NULL },	/* ww: task #62 F2 */
+	  "};\n", 0, K_RUN, NULL },
 	{ "union_store_fwd",	/* banked row L2-2 (= F0 m5_match) */
 	  "package main;\n"
 	  "type ali = base;\n"
@@ -698,7 +701,7 @@ static const struct row rows[] = {
 	  "	case void => { return 3; };\n"
 	  "	};\n"
 	  "	return 0;\n"
-	  "};\n", 0, K_RUN_CS, NULL },	/* ww: task #62 F2 */
+	  "};\n", 0, K_RUN, NULL },
 	{ "union_store_3word",	/* banked row L2-4: pins the width LOOP */
 	  "package main;\n"
 	  "type base = struct { a: size, b: size, c: size };\n"
@@ -715,7 +718,7 @@ static const struct row rows[] = {
 	  "	case void => { return 3; };\n"
 	  "	};\n"
 	  "	return 0;\n"
-	  "};\n", 0, K_RUN_CS, NULL },	/* ww: task #62 F2 */
+	  "};\n", 0, K_RUN, NULL },
 	{ "union_push_arg",	/* the cg_widen_tagged_push twin (F1 find) */
 	  "package main;\n"
 	  "type base = struct { a: size, b: size };\n"
@@ -731,7 +734,7 @@ static const struct row rows[] = {
 	  "	x.a = 4; x.b = 9;\n"
 	  "	if (peek(x) != 9) { return 1; };\n"
 	  "	return 0;\n"
-	  "};\n", 0, K_RUN_CS, NULL },	/* ww: task #62 F2 */
+	  "};\n", 0, K_RUN, NULL },
 	/* banked row L2-5: the m5b_match0 gold invariant — base spelling
 	 * indistinguishable (ken oracle PART 1.7). */
 	{ "union_store_base_ctl",