Dumb OMO commit

.omo/notepads/news-triage/learnings.md

@@ -664,3 +664,24 @@ Key gotchas that would otherwise silently corrupt the index:
 
 - **Do not auto-apply snippets**. The README is operator-facing; the QA used
   scratch copies in `/tmp/opencode`. No real estate file was touched.
+
+## F2/F3 final-wave fixes
+
+- **Trailing-window percentile ranks must live in one place**: the original
+  batch-local `percentile_rank` helper was duplicated across `cycle.rs`,
+  `api/stories.rs`, and `news-cli/src/replay.rs`. Centralizing it in
+  `news-store::PercentileTracker::percentile_rank` removes the duplication and
+  guarantees the scheduler, API, and replay harness all rank against the same
+  trailing-7-day distribution.
+- **Use a stable empirical-CDF formula**: `(below * 100 + equal * 50) / count`
+  (implemented via `f64::mul_add`) avoids the small floating-point drift that
+  `(below + equal / 2.0) / count * 100.0` introduces for values like 5.5/10.
+- **Model non-finite f64 honestly at the JSON boundary**: the backend keeps
+  `f64::NEG_INFINITY` as the blocklist-veto sentinel, but the API serializes it
+  as `null` by making `StoryRow.relevance` an `Option<f64>` mapped with
+  `is_finite().then_some(...)`. The frontend mirrors the option and renders
+  `—` so the entire story list no longer fails when a blocklisted item is
+  present.
+- **Host-target tests for the frontend DTO are viable**: `news-web` can host-run
+  small `serde_json::from_str` regression tests because they only exercise the
+  `serde`-derived DTOs and do not depend on `gloo-net` or Leptos runtime APIs.