wcc/check: #11 def [_]T length-inference — stamp the def decl path, the #7 let-twin (both stages)

def xs:[_]T=arrlit was sized 0 (no DATA emitted, garbage indexed reads) on BOTH stages, byte-id-identical: #7 wired [_] length-inference only on the let decl path, never def. cstage check.c N_DEF pass-2 infers the length from the initialiser and re-points both d->type and the SK_DEF Sym (an indexed read resolves the def through its Sym); wwstage check.ww runs inferarraylen before resolvewalk. Checker-only — cgen lays the DATA correctly once the length is stamped. w6c and wwdump combined.ww regen'd (both embed the wcc checker).

Pin: table-driven test/wcc/814_def_arr_infer_len (index reads int/u8/2d + 1-elem edge + negative build-fail), teeth-proven against a reverted inference. Filed separately, not folded (rule-11): def-global .len GAP-A (#7 cgdot twin), def str-array element DATA GAP-B (#270), [0]T-vs-[_] alen==0 conflation (pre-existing in the #7 let path too).

Makefile

@@ -243,6 +243,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_arr_strslice_elem \
 	  $(BIN)/test_arr_tagged_elem \
 	  $(BIN)/test_arr_infer_len \
+	  $(BIN)/test_def_arr_infer_len \
 	  $(BIN)/test_slice_str_global_zero \
 	  $(BIN)/test_slice_literal_global \
 	  $(BIN)/test_global_arr_elem_field \
@@ -632,6 +633,12 @@ $(BIN)/test_arr_infer_len: test/wcc/684_arr_infer_len.c $(BIN)/ww \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_def_arr_infer_len: test/wcc/814_def_arr_infer_len.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_arr_tagged_elem: test/wcc/685_arr_tagged_elem.c $(BIN)/ww \
 		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \