diff --git a/src/core/platform.c b/src/core/platform.c
index bad99c91d..5251a6712 100644
--- a/src/core/platform.c
+++ b/src/core/platform.c
@@ -369,7 +369,7 @@ static uint64_t cache_sysfs_llc_bytes(void) {
 }
 #endif
 
-uint64_t ray_cache_llc_bytes(void) {
+static uint64_t cache_llc_probe(void) {
     static uint64_t cached = UINT64_MAX;
     if (cached != UINT64_MAX) return cached;
     uint64_t bytes = 0;
@@ -642,7 +642,7 @@ uint32_t ray_physical_core_count(void) {
 /* Sum of every level-3 cache instance reported by the processor topology
  * (each SYSTEM_LOGICAL_PROCESSOR_INFORMATION cache record is one instance).
  * 0 when the query fails. */
-uint64_t ray_cache_llc_bytes(void) {
+static uint64_t cache_llc_probe(void) {
     static uint64_t cached = UINT64_MAX;
     if (cached != UINT64_MAX) return cached;
     uint64_t bytes = 0;
@@ -800,7 +800,7 @@ ray_err_t ray_thread_join(ray_thread_t t) {
 }
 
 uint32_t ray_thread_count(void) { return 1; }
-uint64_t ray_cache_llc_bytes(void) { return 0; }
+static uint64_t cache_llc_probe(void) { return 0; }
 
 /* Semaphore — counter-only.  Single-threaded so wait never blocks (the
  * counter must already be positive when wait fires). */
@@ -818,3 +818,21 @@ void ray_sem_wait(ray_sem_t* s) {
 void ray_sem_signal(ray_sem_t* s) { (*s)++; }
 
 #endif /* RAY_OS_WASM */
+
+#ifdef DEBUG
+/* Test pin for the probed LLC size: routing that bounds replicated state by
+ * the cache (group dense slabs) otherwise picks a different strategy on
+ * every CI runner.  0 restores the platform probe. */
+static uint64_t g_llc_for_test = 0;
+
+void ray_cache_llc_set_for_test(uint64_t bytes) {
+    g_llc_for_test = bytes;
+}
+#endif
+
+uint64_t ray_cache_llc_bytes(void) {
+#ifdef DEBUG
+    if (g_llc_for_test) return g_llc_for_test;
+#endif
+    return cache_llc_probe();
+}
diff --git a/src/core/platform.h b/src/core/platform.h
index ea3633c56..e2d137856 100644
--- a/src/core/platform.h
+++ b/src/core/platform.h
@@ -180,6 +180,10 @@ uint32_t ray_physical_core_count(void);
  * 0 when the platform cannot report it.  Bounds replicated per-task state
  * whose random-access working set must stay cache-resident to scale. */
 uint64_t ray_cache_llc_bytes(void);
+#ifdef DEBUG
+/* Pin ray_cache_llc_bytes to `bytes` (0 = probe again). */
+void ray_cache_llc_set_for_test(uint64_t bytes);
+#endif
 
 void ray_parallel_begin(void);
 void ray_parallel_end(void);
diff --git a/test/test_agg_contract.c b/test/test_agg_contract.c
index 2134755cf..3f61880c3 100644
--- a/test/test_agg_contract.c
+++ b/test/test_agg_contract.c
@@ -1734,7 +1734,13 @@ static test_result_t test_cancelled_group(void) {
  * 20-worker pool and a 100k-slot slab the raw replication (20 slabs) leaves
  * most caches, and the run must use at most floor(0.75 * LLC / slab) task
  * slabs (never fewer than the pool when everything fits).  The result is
- * identical either way. */
+ * identical either way.
+ *
+ * The LLC is pinned to 32 MB (the size the route assumes when none is
+ * reported) for the routed query: ~10 slabs fit, so the bound bites but the
+ * run is not cache-starved.  Unpinned, a small-cache runner (a macOS CI VM
+ * reports a few MB of L2) fits fewer than three slabs and the route rightly
+ * switches to partition ownership, failing the strategy assertion. */
 static test_result_t test_dense_cache_bound(void) {
     ray_pool_destroy();
     TEST_ASSERT_EQ_I(ray_pool_init_total(20), RAY_OK);
@@ -1743,21 +1749,24 @@ static test_result_t test_dense_cache_bound(void) {
         "(set cb_t (table [k v] (list (as 'I32 (% (* cb_i 7919) 100000)) (% cb_i 13))))");
     TEST_ASSERT_NOT_NULL(setup); TEST_ASSERT_FALSE(RAY_IS_ERR(setup)); ray_release(setup);
     agg_route_reset();
+    ray_cache_llc_set_for_test(32ull << 20);
     ray_t* r = ray_eval_str("(select {from:cb_t by:k s:(sum v)})");
-    TEST_ASSERT_NOT_NULL(r); TEST_ASSERT_FALSE(RAY_IS_ERR(r));
     agg_route_stats_t stats = agg_route_stats();
+    uint64_t llc = ray_cache_llc_bytes();
+    ray_cache_llc_set_for_test(0);  /* before any assert can return */
+    TEST_ASSERT_NOT_NULL(r); TEST_ASSERT_FALSE(RAY_IS_ERR(r));
     TEST_ASSERT_EQ_I(stats.routes[AGG_ROUTE_V2_DENSE], 1);
     TEST_ASSERT_EQ_I(stats.dense_strategy, AGG_DENSE_TASK_LOCAL);
     TEST_ASSERT_TRUE(stats.dense_tasks >= 2 && stats.dense_tasks <= 20);
     TEST_ASSERT_EQ_I(ray_table_nrows(r), 100000);
-    uint64_t llc = ray_cache_llc_bytes();
-    if (llc > 0) {
+    {
         size_t block = agg_resolve(OP_SUM, RAY_I64)->state_size;
         double slots = (double)stats.dense_local_slots / stats.dense_tasks;
         double slab = slots * (block + sizeof(int64_t) + 1);
         double budget = (double)llc * 0.75;
         uint32_t cap = slab * 20 > budget ? (uint32_t)(budget / slab) : 20;
         if (cap < 2) cap = 2;
+        TEST_ASSERT_TRUE(cap >= 3 && cap < 20);  /* the pin makes the bound bite */
         TEST_ASSERT_EQ_I(stats.dense_tasks, cap);
     }
     /* The bounded run computes the same sums as the serial engine. */