fix: update can_append and may_append logic for block allocation

nanovllm/engine/block_manager.py

@@ -92,22 +92,20 @@ def deallocate(self, seq: Sequence):
         seq.block_table.clear()
 
     def can_append(self, seq: Sequence) -> bool:
-        return len(self.free_block_ids) >= (len(seq) % self.block_size == 1)
+        return len(self.free_block_ids) >= (len(seq) > 0 and len(seq) % self.block_size == 0)
 
     def may_append(self, seq: Sequence):
         block_table = seq.block_table
         last_block = self.blocks[block_table[-1]]
-        if len(seq) % self.block_size == 1:
-            assert last_block.hash != -1
-            block_id = self.free_block_ids[0]
-            self._allocate_block(block_id)
-            block_table.append(block_id)
-        elif len(seq) % self.block_size == 0:
+        if len(seq) > 0 and len(seq) % self.block_size == 0:
             assert last_block.hash == -1
-            token_ids = seq.block(seq.num_blocks-1)
+            token_ids = seq.block(seq.num_blocks - 1)
             prefix = self.blocks[block_table[-2]].hash if len(block_table) > 1 else -1
             h = self.compute_hash(token_ids, prefix)
             last_block.update(h, token_ids)
             self.hash_to_block_id[h] = last_block.block_id
+            block_id = self.free_block_ids[0]
+            self._allocate_block(block_id)
+            block_table.append(block_id)
         else:
             assert last_block.hash == -1