Stop engagement-count store errors from zeroing For You rank features - #181
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Dragonfly Err was coerced to an empty map, then Ok(default) counts. CachedHydrator cached those zeros for 60s and Phoenix unwrap_or(0) ranked the slate as if nobody engaged. Co-authored-by: Jon Bailey <Pitchfork-and-Torch@users.noreply.github.com>
This was referenced Sep 8, 2026
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Dragonfly Err in EngagementCountsHydrator was coerced to an empty HashMap. Every candidate then got Ok(CachedCounts::default()). CachedHydrator caches Ok for 60s. as_tweet_info unwrap_or(0) stamps Phoenix InputBuffer and Thompson sampling as if the post had no favs, replies, or views.
Proof
This is not #171/#177 (notes). Not #172 (author diversity retweeter key). Not #173 (safemodel). Not #174 (UserCred). Not #175/#176 (cache mutual-follow / Phoenix rescore). Not #142 (empty Phoenix heads). Not #22 (cold-start thresholds). Not #21 (DPP missing embeddings).
Fix: on client Err, return Err for candidates that need a fetch. CachedHydrator does not insert. update_all leaves existing counts. Successful per-id misses stay Ok(default), same as a tweet with no row.
Tests cover store Err (no zero stamp), no cache poison, cached-post ineligible preserve, and successful miss unchanged.
cargo test cannot run here. Public dump has no Home Mixer manifest. Standalone rustc model of the stamp path passed 4/4.