Candidates
Three ways a post enters the pool.
In-network and out-of-network are retrieved separately, then ranked together. Being retrieved is not the same as being shown.
thunder/
Thunder — in-network
Holds recent posts from accounts you follow in memory as they are published. Home Mixer asks Thunder for your following list. Already-seen IDs are passed in so Thunder can skip them. This is the "people I follow" slice of For You, not the Following tab.
phoenix/ retrieval
Phoenix retrieval — out-of-network
Embeds your history and looks up the nearest posts in the RankAll index. The index is maintained by phoenix-rankall as events arrive; phoenix-rankall-strato decides which shard a post belongs in after consulting visibility filtering. Semantic IDs let the tower generalize to posts it has never scored.
simclusters/
SimClusters — out-of-network
Clusters accounts and posts by who engages with what. Retrieval is cluster overlap, not embedding nearest-neighbor. NSFW authors on this source are stripped for non-followers by OONNsfwSimclustersFilter before scoring.