[NVIDIA#12560][fix] Fix disagg serving hang on block reuse after eviction

Claim block from eviction policy free queue before pinning in
storeBlocks so that the later unpinBlocksById / releaseBlock cycle
does not create a duplicate queue entry.

Signed-off-by: Iman Tabrizian <itabrizian@nvidia.com>

Author: Tabrizian

cpp/tensorrt_llm/batch_manager/kvCacheManager.cpp

@@ -1618,6 +1618,14 @@ std::pair<SizeType32, std::optional<KVCacheBlock::IdType>> WindowBlockManager::s
         }
         if (pinBlocks)
         {
+            // Claim block from free queue before pinning so that
+            // unpinBlocksById can safely releaseBlock it back later.
+            // Without this, the block stays in the free queue while pinned,
+            // and the subsequent releaseBlock creates a duplicate entry.
+            if (!searchRoot->hasRefs())
+            {
+                mEvictionPolicy->claimBlock(searchRoot, searchRoot->getPriority(), searchRoot->getDurationMs());
+            }
             searchRoot->incRefCount();
         }
         lastStoredId = searchRoot->getBlockId();