test: 954 16B tuple-from-call receive cs==ww byte-id + cstage run (#102)

Per-row: cstage build+run exit assert AND w6c vs w6c_ww .s cmp.
Three scalar-pair single-var bug-rows — (f64,i64), (i64,f64) order-swap,
(i64,i64) all-integer — each diverge on master 60c3e51 by one dropped
MOVQ DX and are byte-identical after the fix. The all-integer row proves
the fix is not f64-gated. Two control rows stay byte-id pre- and
post-fix: the destructure form `let (a,b) = mk()` (cgmlet + tupstore
cursor, the path bootstrap/990-997 rely on) and a 32B str-element
single-var tuple (excluded by the fix's sz==16 gate). Modelled on
953_f64crossmod_run. Master gate: 3 bug rows FAIL, 2 controls clean.

Makefile

@@ -329,6 +329,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_checked_run \
 	  $(BIN)/test_f64cgen_run \
 	  $(BIN)/test_f64crossmod_run \
+	  $(BIN)/test_tuprecv_run \
 	  $(BIN)/test_floats_run \
 	  $(BIN)/test_bufio_run $(BIN)/test_random_run
 
@@ -1076,6 +1077,11 @@ $(BIN)/test_f64crossmod_run: test/wcc/953_f64crossmod_run.c $(BIN)/ww \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_tuprecv_run: test/wcc/954_tuprecv_run.c $(BIN)/ww \
+		$(BIN)/w6c $(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 sizelint:
 	@sh tools/sizelint