cgen: B6-c1 assign/reassign family single peels fold into type_chase_named — 9 lines, cs-only

The exact B6-c1 set (rob b6 spec §2): cgexpr :6359 (tagged-local plain
reassign lu), :6403/:6405 (deref-target assign pu/vt), :6460/:6462
(deref compound-assign pu/vt), :6518 (str/slice/struct reassign lu) +
cgstmt :11696 (nomem null-propagate r), :12047 (assign base peel bu),
:13625 (destructure-reassign rhs ru — chased; the #64 citation above it
stays, the deferral is about the tuple-literal rhs ROUTE, not this
peel). Raw `->under` in cgen.c 58→49.

TRAIN INVARIANT: cs-only — zero selfhost/ or lib/ bytes move; w6c_ww/
ww_ww bit-identical to ken's 4cac1cb baselines (md5
b6bddc8eb5c3ed8e805e50371d4b7017 / 4e9ca8741f19e1f68219ff799a5e5a14).
cs movers bounded to exactly: kb6_streassign, kb5_wstore_a (the
named c1 family); the rest of the kb4/kb5/kb6/kna corpus + five
selfhost mains byte-NEUTRAL both stages; kw1_101 / fill2 / tuparg_c /
xampdef / amplen1 detectors unmoved. 989 lib ratchet: zero flips.

LIVE graduation: kb6_streassign (the :6518 lu single-peel missed
TY_STR at 2 alias levels, fell to the scalar default — `b = a` copied
the ptr WORD0 only, len/cap stale, cs silent exit 1; ww was the
runtime-correct full 3-word reference) → 0/0 byte-id. Designed
graduation: kb5_wstore_a (ken C1-CORR-2 seed — the ident-lhs N_ASSIGN
tagged gate :6359 is cgexpr INLINE, never reached B5's :2456 funnel)
→ wstore_a_2lvl re-pinned K_RUN_NOID→K_RUN in the b5 suite (84→85
checks). kb6_sreassign / kb6_dassign latent controls byte-NEUTRAL as
ken's structural bound predicts.

New 944_alias_cgen_b6_run row table (3 rows, 9 checks): streassign_2lvl
+ sreassign_2lvl/dassign_2lvl controls; Makefile wires
test_alias_cgen_b6_run into the unit list. All 944-family suites green;
sizelint 0.

Makefile

@@ -309,6 +309,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_alias_def_addr_run \
 	  $(BIN)/test_alias_global_decl_run \
 	  $(BIN)/test_alias_cgen_b5_run \
+	  $(BIN)/test_alias_cgen_b6_run \
 	  $(BIN)/test_tuple_nary_destructure_run \
 	  $(BIN)/test_rvalue_tuple_destructure_run \
 	  $(BIN)/test_overcap_tuple_field_store_run \
@@ -1495,6 +1496,12 @@ $(BIN)/test_alias_cgen_b5_run: test/wcc/944_alias_cgen_b5_run.c \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_alias_cgen_b6_run: test/wcc/944_alias_cgen_b6_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 \