v1.2.5 - Fix alignment above alignof(max_align_t) and stale marker rewinds

test.c

@@ -160,6 +160,45 @@ static void test_snapshot_rewind_trim_logic(void)
     arena_free(&arena);
 }
 
+static void test_invalid_markers(void)
+{
+    printf("Running invalid marker tests...\n");
+    Arena arena = arena_create(128);
+
+    void *first = arena_alloc(&arena, 100); // Region 1 (Cap: 128)
+    assert(is_aligned(first));
+    ArenaMarker mark_r1 = arena_snapshot(&arena);
+
+    arena_alloc(&arena, 200); // Region 2 (Cap: 256)
+    ArenaMarker mark_r2 = arena_snapshot(&arena);
+
+    // Free Region 2, invalidating mark_r2
+    arena_rewind(&arena, mark_r1);
+    arena_trim(&arena);
+    assert(count_regions(&arena) == 1);
+
+    // Stale marker must be rejected without touching freed memory
+    arena_rewind(&arena, mark_r2);
+    assert(arena.tail == mark_r1.region);
+    assert(arena.tail->count == mark_r1.count);
+
+    // Marker from another arena
+    Arena other = arena_create(128);
+    arena_alloc(&other, 10);
+    arena_rewind(&arena, arena_snapshot(&other));
+    assert(arena.tail == mark_r1.region);
+    assert(arena.tail->count == mark_r1.count);
+    arena_free(&other);
+
+    // Marker with a count beyond the region capacity
+    ArenaMarker forged = mark_r1;
+    forged.count = mark_r1.region->capacity + 1;
+    arena_rewind(&arena, forged);
+    assert(arena.tail->count == mark_r1.count);
+
+    arena_free(&arena);
+}
+
 static void test_massive_string_formatting(void)
 {
     printf("Running massive string formatting tests...\n");
@@ -204,6 +243,7 @@ int main(void)
     test_overflows();
     test_geometric_growth_and_stress();
     test_snapshot_rewind_trim_logic();
+    test_invalid_markers();
     test_massive_string_formatting();
     test_zero_capacity_fallback();