cgen: B5-c1 helper+funnel single peels fold into type_chase_named — 19 sites, cs-only

The exact F2b c1 set (rob next-arc spec + B5 re-rule): node_tuplearg:249,
fld_issigned:409, castsrcprim:501/:531, struct_float_class:598,
tagged_arg_size:640, tagged_memarg_size:661, type_isnullable:740,
nullable_ptr_tag:750, cg_tagged_success_tag:860, cg_variant_is_error:876,
cg_tag_for_variant:899, type_istagged:953, type_unwrap:1269 + the widen/
fill funnel entries cg_widen_tagged_store:2456/:2480/:2483,
cg_widen_tagged_push:2905, cg_structlit_fill:3195. Raw `->under` in
cgen.c 88→69. Riding per re-rule R1: peel-ok-#218 annotations at
cg_variant_match/cg_variant_struct_match (citing ken's b5 oracle §4 —
chasing those four peels graduates zero v2_struct rows; the real fix is
a both-stage NAMED-source arm, task #95) and the :755 peel-ok annotation
mirroring ww cgenutil.ww:2758 (probe-cleared, 018ef66). :447 untouched
(c2's grant).

TRAIN INVARIANT: cs-only — zero selfhost/ or lib/ bytes move; w6c_ww/
ww_ww/w6a_ww/w6l_ww bit-identical to the bcd948d baselines (md5
28ad889042bad8006f1997cbcec94805 / 4e9ca8741f19e1f68219ff799a5e5a14).
cs movers bounded to exactly: kb5_targ, kb5_tmem, kb5_wpush, kb5_null,
kb5_f32p, kb5_fill2, kb5_tuparg_c; five selfhost mains + the rest of the
kb2/kb3/kb4/kb5/kna corpus byte-NEUTRAL both stages.

LIVE graduations: kb5_targ (tagged_arg_size sized a 2-level alias union
param 0 → wrong arg path, cs silent exit 1) and kb5_tmem (>48B memarg
twin) → 0/0 byte-id. Divergence flips to byte-id: wpush/null/f32p.

#85 CLOSES as SITE-CLOSURE with ZERO live graduations: type_unwrap's
two consumers (:14716/:14907, both tuple-global layout walks that want
the chased view) are checker-DEAD on cs for alias tuples (#86 upstream)
— correctness there is by-construction, pinned by tupglobal_bound86.

DESIGNED DIVERGENCE (re-rule R4, task #100): the :3195 chase flips
kb5_fill2 from both-wrong-IDENTICAL-silent (gate-blind, both stages
accepted and ran wrong byte-identically) to cs-LOUD / ww-silent-wrong.
A loud, disclosed, pinned divergence over a silent miscompile; rejected
programs emit no asm so the byte-id gates hold. Dual-cell pin
(fill2_bound100): cs experr + ww run-exit-1 both asserted; fill0
both-loud control holds. #100 (the ww twin gate) fires immediately
after B5 so the window is one train wide.

Oracle corrections at the c1 boundary (ken c1-BOUNDARY ADDENDUM,
verified on his independent scratch build; rob ack'd, scope unchanged):
  C1-CORR-1: kb5_succ does NOT flip here — its residual divergence is
  exactly three paired return-position tag syntheses, the cgreturn
  return-route family (:12278/:12318/:12322). Joins c3's graduation
  set; pinned succ_bound_c3 K_RUN_NOID until then.
  C1-CORR-2 (corrects re-rule R2): kb5_wstore_a does NOT flip — the
  ident-lhs N_ASSIGN tagged store gates in the cgexpr INLINE set (B6),
  never reaching the :2456 funnel; cs byte-neutral here. Pinned
  wstore_a_bound_b6 K_RUN_NOID; byte-id rides B6.
  C1-CORR-3 (corrects re-rule R3 + ken FLAG-2): the :249 chase is NOT
  purely latent — the CAST spelling (kb5_tuparg_c) earned a LIVE cs
  graduation (cs ok/1 → ok/0, correct tuple-arg classify); ww still
  runs wrong (task #99). Two-key pin tuparg_cast_bound99: cs-0 earned +
  ww-1 pinned observed-wrong; byte-id re-pins to full 0/0 when #99's ww
  fix lands.

New 944_alias_cgen_b5_run row table (16 rows, 40 checks): controls
signed/wstore/wstore1 byte-NEUTRAL as predicted (kind-keyed tests are
the only behavior-visible peels — type.c classifiers already recurse);
literal tuparg spellings stay dual-cell bounds (#99/#86). All 944-family
suites green; sizelint 0.

Makefile

@@ -308,6 +308,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_alias_amp_idx_run \
 	  $(BIN)/test_alias_def_addr_run \
 	  $(BIN)/test_alias_global_decl_run \
+	  $(BIN)/test_alias_cgen_b5_run \
 	  $(BIN)/test_tuple_nary_destructure_run \
 	  $(BIN)/test_rvalue_tuple_destructure_run \
 	  $(BIN)/test_overcap_tuple_field_store_run \
@@ -1488,6 +1489,12 @@ $(BIN)/test_alias_global_decl_run: test/wcc/944_alias_global_decl_run.c \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_alias_cgen_b5_run: test/wcc/944_alias_cgen_b5_run.c \
+		$(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
+		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_tuple_nary_destructure_run: test/wcc/945_tuple_nary_destructure_run.c \
 		$(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \