[manager] document EventReport reclaim accounting boundaries

Keep reporter-owned locations out of generic physical deletion without granting false predicted-key credit when ordinary and EventReport locations coexist.

Document that EventReport bytes remain in the group-wide capacity watermark while being excluded from per-storage-type watermarks. Add regression coverage ensuring reporter locations cannot satisfy migration cold-tier spec coverage.

Author: charpty

docs/design/cache_reclaimer_async_delete.md

@@ -221,6 +221,14 @@ size 的 Location 按 0 bytes 记账，但仍加入 pending 并受数量上限
 只有本次请求覆盖某个 block 的全部有效 Location 时，才增加一个 `predicted_deleted_keys`。V1 不跨
 多个 `DeleteHandler` 合并推断，允许保守少计。
 
+EventReport Location 由外部 reporter 拥有，只能由 ReportEvent snapshot、delta 或 host lifecycle 清理，不能进入
+通用物理存储回收请求。它仍然是 metadata key 上的有效 Location：若一个 block 同时包含 EventReport 与普通
+Location，删除全部普通 Location 后 key 仍然存在，因此不得产生 `predicted_deleted_keys` credit。EventReport usage
+不参与按 storage type 的水位，但仍计入 group 总 byte 水位；通用 Reclaimer 即使因此触发，也只能选择普通
+Location，EventReport-only 场景会按 no-progress 退避，不能进入物理删除。EventReport Location 也不能作为
+migration cold-tier spec coverage。key-count 水位继续使用 MetaIndexer 的官方总 key 数，无法证明可删除时保持
+fail-closed、允许保守多触发而不能提前抵扣。
+
 水位判断改为：
 
 ```text
@@ -362,6 +370,10 @@ V1 提供以下指标：
     有效 Location。
 15. Meta 异步请求跳过 `CLS_DELETING`，重复提交不会再次安排物理删除。
 16. Admission 已进入队列但尚未执行时停止 Executor，cancel callback 使 Future 以错误终态完成。
+17. EventReport Location 不进入物理删除请求，但与普通 Location 共存时仍阻止错误的
+    `predicted_deleted_keys` credit。
+18. EventReport usage 仍可触发 group 总 byte 水位，但不触发 EventReport storage-type 水位。
+19. reporter URI host 即使与 migration target storage 同名，也不能补齐 cold-tier spec coverage。
 
 ### 8.2 集成测试关注点
 

kv_cache_manager/manager/cache_reclaimer.cc

@@ -1488,6 +1488,10 @@ bool CacheReclaimer::FilterLocID(RequestContext *request_context,
             if (!loc_ptr) {
                 continue;
             }
+            // Reporter-owned locations are not reclaim candidates, but still
+            // keep the metadata key alive after all ordinary locations have
+            // been removed. Count them before filtering so key-count credit is
+            // only granted when the deletion can actually remove the key.
             ++valid_location_count;
             const auto &loc = *loc_ptr;
             if (IsEventReportStorageType(loc.type())) {

kv_cache_manager/manager/test/cache_reclaimer_test.cc

@@ -4499,10 +4499,20 @@ TEST_F(CacheReclaimerTest, TestFilterLocIDDoesNotEvictHotWhenColdSpecsIncomplete
         DataStorageType::DATA_STORAGE_TYPE_DUMMY,
         1,
         std::vector<LocationSpec>{LocationSpec("TP0", "dummy://cold_01/cold_partial/tp0")});
+    // A reporter may use the migration target name as its URI host and carry
+    // the otherwise missing spec. It is not an ordinary cold-tier replica and
+    // must not make the hot location eligible for physical reclamation.
+    auto event_report_loc = std::make_shared<CacheLocation>(
+        "event_report#mem#cold_01:9600",
+        CacheLocationStatus::CLS_SERVING,
+        DataStorageType::DATA_STORAGE_TYPE_EVENT_REPORT_L2,
+        1,
+        std::vector<LocationSpec>{LocationSpec("TP1", "event_report://cold_01:9600/mem?size=1")});
 
     CacheLocationMap loc_map;
     loc_map.emplace("hot_full", hot_loc);
     loc_map.emplace("cold_partial", partial_cold_loc);
+    loc_map.emplace("event_report", event_report_loc);
     batch_get_loc_out_maps = {std::move(loc_map)};
     batch_get_loc_result = ErrorCode::EC_OK;