What happens if two columns have the same timestamp in Apache Cassandra?

I want to understand how Cassandra resolves conflicts when two updates for the same key and column have the same timestamp.

From my understanding, Cassandra follows a Last Write Wins (LWW) approach, but if two writes have the same timestamp, how does Cassandra determine which value to keep?

I am particularly interested in the following two scenarios where I expect a comparison to happen-

1. update within memtable (two writes for a key, with the same timestamp, before memtable can flush)
2. merging of two columns during the compaction process

I understand Cassandra may compare values Lexicographically, but I could not find a reference for the above two scenarios.

Please also provide a reference to documentation or source code mentioning the Comparator used for the above two scenarios.

For the sake of scenarios, please assume (even if not possible or has low probability) that 2 timestamps can collide for 2 different writes.