diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index b54a4239..b4c407eb 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -67,7 +67,9 @@ jobs:
         run: python tools/ci_build.py linux release
 
       - name: Test
-        run: python -m pytest -q tools/test_linux_port.py
+        run: |
+          python -m pytest -q tools/test_linux_port.py
+          python tools/test_light_storage.py
 
       - name: Compile cache
         run: ccache --show-stats
@@ -200,6 +202,9 @@ jobs:
       - name: Release
         run: python tools/ci_build.py windows release
 
+      - name: Test light storage
+        run: python tools/test_light_storage.py
+
       - name: Compile cache
         run: ccache --show-stats
 
diff --git a/port/linux/src/halo_linker_common.c b/port/linux/src/halo_linker_common.c
index 4362a601..1fd6b332 100644
--- a/port/linux/src/halo_linker_common.c
+++ b/port/linux/src/halo_linker_common.c
@@ -125,7 +125,9 @@ HALO_COMMON(hs_global_data, 4); /* struct data_array *hs_global_data */
 HALO_COMMON(hs_thread_data, 4); /* struct data_array *hs_thread_data */
 HALO_COMMON(hud_msg_def, 4); /* struct hud_messaging_parameters_definition *hud_msg_def */
 HALO_COMMON(interrupt_result, 24); /* HRESULT interrupt_result */
-HALO_COMMON(light_cluster_partition, 12); /* struct cluster_partition light_cluster_partition */
+/* object_lights.c owns light_cluster_partition. On COFF a weak fallback
+can override its tentative COMMON definition; let the owner allocate the
+native struct cluster_partition, including its reference-cache fields. */
 HALO_COMMON(light_data, 4); /* struct data_array *light_data */
 HALO_COMMON(local_player_index_for_draw_string_and_hack_in_icons, 4); /* short local_player_index_for_draw_string_and_hack_in_icons */
 HALO_COMMON(looping_sound_data, 4); /* struct data_array *looping_sound_data */
diff --git a/tools/test_light_storage.py b/tools/test_light_storage.py
new file mode 100644
index 00000000..cc12325b
--- /dev/null
+++ b/tools/test_light_storage.py
@@ -0,0 +1,153 @@
+"""Link the real light-partition definitions and initialize their native caches.
+
+No game assets, SDK, C runtime or profile needed. Windows uses COFF/i686;
+Linux uses ELF/i386. Exercise both ordinary and full-LTO links. The Windows
+negative control reinstates the retail-sized weak fallback and must corrupt
+the light-data pointer, proving this checks storage selected by the linker.
+"""
+
+import argparse
+import re
+import subprocess
+import sys
+import tempfile
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parent.parent
+
+
+def function(source, name):
+    start = re.search(r"(?:static )?void " + re.escape(name) + r"\([^;{]*\)\s*\{", source).start()
+    end = source.index("{", start) + 1
+    depth = 1
+    while depth:
+        depth += (source[end] == "{") - (source[end] == "}")
+        end += 1
+    return source[start:end]
+
+
+def owner_definition(source, declaration, export):
+    # Use the owning source's tentative definition, not another typed fallback.
+    assert declaration in source
+    return export + declaration + "\n"
+
+
+def run(cc):
+    windows = sys.platform == "win32"
+    common = (ROOT / "port/linux/src/halo_linker_common.c").read_text()
+    lights = (ROOT / "source/objects/object_lights.c").read_text()
+    partitions = (ROOT / "source/structures/cluster_partitions.c").read_text()
+    macro = common[common.index("#define HALO_COMMON"):common.index("HALO_COMMON(ai_globals")]
+    fallbacks = "\n".join(re.findall(
+        r"^HALO_COMMON\((?:light_cluster_partition|light_data),[^\n]+", common, re.M))
+    header = (ROOT / "source/structures/cluster_partitions.h").as_posix()
+    prefix = f'''
+/* Suppress header dependencies unrelated to the partition's layout. */
+#define __REAL_MATH_H
+#define __DATA_H
+typedef union real_point3d real_point3d;
+struct location;
+struct data_array {{ unsigned long signature; }};
+#include "{header}"
+typedef char require_32_bit_abi[sizeof(void *) == 4 && sizeof(long) == 4 ? 1 : -1];
+'''
+    # Keep symbol layout observable under whole-program scalar replacement.
+    export = '__declspec(dllexport) ' if windows else ''
+    owner = prefix + owner_definition(lights, 'struct cluster_partition light_cluster_partition;', export)
+    owner += owner_definition(lights, 'struct data_array *light_data;', export)
+    owner += r'''
+#define FALSE 0
+#define MAXIMUM_CLUSTERS_PER_STRUCTURE 8
+#define HALO_PORT_MAXIMUM_CLUSTER_REFERENCES 16
+#define MAXIMUM_PORT_CLUSTER_PARTITIONS 8
+static struct cluster_partition *cluster_partitions_port[MAXIMUM_PORT_CLUSTER_PARTITIONS];
+static short cluster_partitions_port_count;
+static unsigned long arena[1024], allocated;
+static void *allocate(unsigned long bytes) {
+    unsigned long words = (bytes + 3) / 4;
+    void *result = arena + allocated;
+    allocated += words;
+    return result;
+}
+#define game_state_malloc(name, label, bytes) allocate(bytes)
+#define reference_list_new(name, count) ((struct data_array *)allocate(sizeof(struct data_array)))
+#define debug_malloc(bytes, clear, file, line) allocate(bytes)
+#define sprintf(buffer, ...) ((void)0)
+#define error(...) ((void)0)
+static void csmemset(void *destination, int value, unsigned long bytes) {
+    unsigned char *out = destination;
+    while (bytes--) *out++ = (unsigned char)value;
+}
+'''
+    forget = function(partitions, 'cluster_partition_port_forget')
+    owner += forget
+    owner += function(partitions, 'cluster_partition_new')
+    owner += '''
+void initialize_partition(void) {
+    cluster_partition_new(&light_cluster_partition, "light");
+    cluster_partition_port_forget(&light_cluster_partition);
+}
+'''
+    caller = prefix + r'''
+extern struct cluster_partition light_cluster_partition;
+extern struct data_array *light_data;
+void initialize_partition(void);
+static struct data_array lights = { 0x64407440UL };
+__attribute__((noinline,optnone)) static int check(void) {
+    light_data = &lights;
+    initialize_partition();
+    if (light_data != &lights || light_data->signature != 0x64407440UL) return 71;
+    if (!light_cluster_partition.cluster_first_data_references ||
+        !light_cluster_partition.data_reference_data ||
+        !light_cluster_partition.cluster_reference_data) return 72;
+    if (!light_cluster_partition.port_previous_references ||
+        !light_cluster_partition.port_cluster_data_references) return 73;
+    if (light_cluster_partition.port_modification_count != 2) return 74;
+    for (int i = 0; i < 16; i++) {
+        if (light_cluster_partition.port_previous_references[i] != -1 ||
+            light_cluster_partition.port_cluster_data_references[i] != -1) return 75;
+    }
+    return 0;
+}
+'''
+    caller += 'int mainCRTStartup(void) { return check(); }\n' if windows else r'''
+void _start(void) {
+    int result = check();
+    __asm__ volatile("int $0x80" : : "a"(1), "b"(result) : "memory");
+    __builtin_unreachable();
+}
+'''
+    with tempfile.TemporaryDirectory(prefix='halo-light-storage-') as directory:
+        work = Path(directory)
+        (work / 'owner.c').write_text(owner)
+        (work / 'caller.c').write_text(caller)
+        for lto in (False, True):
+            for legacy in ((False, True) if windows and lto else (False,)):
+                fallback = fallbacks
+                if legacy:
+                    fallback = re.sub(r'^HALO_COMMON\(light_cluster_partition,[^\n]+\n?', '', fallback, flags=re.M)
+                    fallback = 'HALO_COMMON(light_cluster_partition, 12);\n' + fallback
+                (work / 'fallback.c').write_text(macro + fallback + '\n')
+                executable = work / ('probe.exe' if windows else 'probe')
+                abi = ['--target=i686-pc-windows-msvc'] if windows else ['-m32']
+                link = ['-Wl,/entry:mainCRTStartup', '-Wl,/subsystem:console'] if windows else [
+                    '-Wl,-e,_start', '-Wl,--export-dynamic', '-no-pie', '-static']
+                command = [cc, *abi, '-std=gnu99', '-O2', '-fcommon', '-ffreestanding',
+                           '-fno-builtin', '-nostdlib', '-fuse-ld=lld', '-I' + str(ROOT / 'source'), *link]
+                if lto:
+                    command.append('-flto=full')
+                command += [str(work / name) for name in ('owner.c', 'caller.c', 'fallback.c')]
+                command += ['-o', str(executable)]
+                subprocess.run(command, check=True, timeout=60)
+                result = subprocess.run([str(executable)], timeout=10)
+                expected = 71 if legacy else 0
+                assert result.returncode == expected, (command, result.returncode, expected)
+                print(f'PASS: {"COFF" if windows else "ELF"} {"full LTO" if lto else "ordinary"}: '
+                      f'{"legacy pointer corruption detected" if legacy else "light data and native caches preserved"}')
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument('--cc', default='clang')
+    args = parser.parse_args()
+    run(args.cc)