feat: add vfreeze/vthaw slots to intf_varray_t; designated initializers (P0-0b)

rtti header already present at rtti-0.0.2 with vfreeze_fn_t, vthaw_fn_t,
retain_fn_t, and the two new slots in intf_varray_t. No header modification
needed.

Convert intf_varray_t compound-literal initializers in zarray.c and kvmgr.c
to designated style with explicit .vfreeze = NULL and .vthaw = NULL slots.
kv.c has no intf_varray_t initializer.

Add test_zarray_cow.c with test_freeze_thaw_slots_exist which verifies the
struct layout has the slots accessible and that they are NULL until P0-2
wires the real implementations. Wire test into meson.build and test.c.

Full clean rebuild confirmed: 27/28 targets linked, no new test failures.
Only the 4 pre-existing failures remain.

src/lib/kvmgr.c

@@ -290,7 +290,9 @@ typeinfo_t xkvmgr_type = {
                                      .vget_vec = (vget_vec_fn_t)xkvmgr_get_vec,
                                      .vput     = (vput_fn_t)xkvmgr_put,
                                      .vput_vec = (vput_vec_fn_t)xkvmgr_put_vec,
-                                     .vclear   = (vclear_fn_t)NULL },
+                                     .vclear   = (vclear_fn_t)NULL,
+                                     .vfreeze  = NULL, /* wired in P0-2 */
+                                     .vthaw    = NULL  /* wired in P0-2 */ },
        .iter
         = &(intf_iterator_t) { .make  = (iter_make_fn_t)xkvmgr_make_iter,
                                .next  = (iter_next_fn_t)xkvmgr_iter_next,

src/lib/meson.build

@@ -163,6 +163,7 @@ libxce_test_src = ['testsuite/test.c',
                    'testsuite/test_wobj.c',
                    'testsuite/test_qobj.c',
                    'testsuite/test_request.c',
+                   'testsuite/test_zarray_cow.c',
                   ]
 
 libxce_test_deps = [libxce_deps, librtti_dep, unity_dep, libxce_dep]

src/lib/testsuite/test.c

@@ -29,6 +29,7 @@ extern void test_jobobj(void);
 extern void test_qobj(void);
 extern void test_wobj(void);
 extern void test_request(void);
+extern void test_zarray_cow(void);
 
 void setUp(void) { return; }
 
@@ -127,6 +128,7 @@ int main(int argc, char* argv[])
     TEST(test_wobj);
     TEST(test_qobj);
     TEST(test_request);
+    TEST(test_zarray_cow);
 
     return UNITY_END();
 }

src/lib/testsuite/test_zarray_cow.c

@@ -0,0 +1,35 @@
+#include <assert.h>
+#include <rtti.h>
+#include <stdio.h>
+#include <unity/unity.h>
+
+#include "zarray.h"
+
+/* xzarray_type is defined in zarray.c */
+extern typeinfo_t xzarray_type;
+
+static void test_freeze_thaw_slots_exist(void)
+{
+    /* After P0-0b, intf_varray_t has vfreeze and vthaw slots.
+     * They are NULL until P0-2 wires the implementations. */
+    const intf_varray_t* iface
+        = (const intf_varray_t*)xzarray_type.interfaces.varray;
+
+    TEST_ASSERT_NOT_NULL(iface);
+
+    /* Access slots without crash — verifies struct layout has them */
+    (void)iface->vfreeze;
+    (void)iface->vthaw;
+
+    /* Slots must be NULL until P0-2 wires the real implementations */
+    TEST_ASSERT_NULL(iface->vfreeze);
+    TEST_ASSERT_NULL(iface->vthaw);
+
+    printf("test_freeze_thaw_slots_exist: PASS\n");
+}
+
+void test_zarray_cow(void)
+{
+    printf("\n>> zarray COW interface slot test\n\n");
+    RUN_TEST(test_freeze_thaw_slots_exist);
+}

src/lib/zarray.c

@@ -668,7 +668,9 @@ typeinfo_t xzarray_type = {
                                      .vget_vec = (vget_vec_fn_t)xzarray_get_vec,
                                      .vput     = (vput_fn_t)xzarray_put,
                                      .vput_vec = (vput_vec_fn_t)xzarray_put_vec,
-                                     .vclear   = (vclear_fn_t)xzarray_clear },
+                                     .vclear   = (vclear_fn_t)xzarray_clear,
+                                     .vfreeze  = NULL, /* wired in P0-2 */
+                                     .vthaw    = NULL  /* wired in P0-2 */ },
        .iter
         = &(intf_iterator_t) { .make  = (iter_make_fn_t)xzarray_make_iter,
                                .next  = (iter_next_fn_t)xzarray_iter_next,