test: migrate Fam13 misc checker/coercion value tests to @test (#5-C6)

Final fold-2 chunk. The 12 Fam13 single-file value drivers move from
test/wcc/*_run.c into in-language @test row-tables under test/lang/:

- value rows -> test/lang/*_test.ww (12 files)
- reject rows -> runww //ww:error carriers (13, dual-stage non-vacuous)
- nullable abort rows -> runww //ww:run-exit 1 carriers (3)
- 953_globalslice_arg -> _runonly (cs!=ww checker divergence, #28)
- 788 value_not_type_neg + 953_arrlit_slice reject_assign kept as slim
  rc-only .c pins (divergent-diag dual-reject, mutation-gated); 788 #29

Coverage parity verified row-by-row vs each retired driver; advisor-
ratified carve taxonomy; two-round reviewed. Floor ratchet follows.

test/lang/nullable_try_test.ww

@@ -0,0 +1,37 @@
+// nullable_try_test — #15 (F4): the `?` / `!` try operators on a nullable
+// `(*T|void)` operand must discriminate POINTER-vs-NULL, not tag-vs-success-
+// index. Migrated from test/wcc/949_nullable_try_run.c (non-abort value rows;
+// cs==ww byte-id rides T2). The must-abort-on-null polarity (`!` on null) stays
+// as a carrier (an abort cannot be a @test row).
+//
+// For a nullable operand AX holds the POINTER and successtag()=0, so pre-fix
+// wwstage cgtryprop/cgtryunw CMPQ'd $0,AX and treated NULL as success / a valid
+// pointer as the error (inverted). tryprop_valid pins the valid-ptr unwrap +
+// mutate; tryprop_null pins NULL propagates to the caller (pre-fix: null deref
+// SEGV); tryunw_valid pins the `!` valid-ptr unwrap.
+
+package nullable_try_test;
+
+fn gp(p: (*int|void)) (*int|void) = { let q = p?; *q = 7; return q; };
+fn hu(p: (*int|void)) int = { let q = p!; return *q; };
+
+@test fn tryprop_valid() void = {
+	let x: int = 1;
+	let r = gp(&x);
+	assert(x == 7);
+};
+
+@test fn tryprop_null() void = {
+	let r = gp(void);
+	let isvoid: bool = false;
+	match (r) {
+	case let q: *int => { };
+	case void => { isvoid = true; };
+	};
+	assert(isvoid);
+};
+
+@test fn tryunw_valid() void = {
+	let x: int = 42;
+	assert(hu(&x): i32 == 42);
+};