[HiCache] Label radix-cache metrics per rank and split the "shrunk" prefetch reason (#39280)

test/registered/unit/mem_cache/test_unified_radix_cache_unittest.py

@@ -10177,7 +10177,7 @@ class TestAnchorLockOutcomePolicy(CustomTestCase):
         cache.dec_host_lock_ref.assert_not_called()
         self.assertEqual(controller.prefetch_tokens_occupied, 8)
 
-    def test_positive_hit_with_lost_anchor_is_reported_as_shrunk(self):
+    def test_positive_hit_with_lost_anchor_reports_anchor_lost(self):
         cache = UnifiedRadixCache.__new__(UnifiedRadixCache)
         cache.storage_prefetch_retries = StoragePrefetchRetries()
         cache.ongoing_prefetch = {
@@ -10191,7 +10191,7 @@ class TestAnchorLockOutcomePolicy(CustomTestCase):
         cache._handle_storage_prefetch_anchor_loss(self._REQ)
 
         cache._finish_storage_prefetch.assert_called_once_with(
-            self._REQ, fulfilled_tokens=0, reason="shrunk"
+            self._REQ, fulfilled_tokens=0, reason="anchor_lost"
         )
         # The eviction widened the span, so the request replans over it --
         # skipping the query, the prior hit having proved it stored, and the