F2/F3 fix verification — news-triage
====================================
Date: 2026-09-01
Workspace: /home/connor/docs/projects/news

Scope
-----
Two reviewer findings from final-wave verification:
- F2: relevance/importance percentiles were computed from the current poll batch only
  instead of the trailing-7-day distribution required by the draft spec.
- F3: blocklist veto sets relevance to f64::NEG_INFINITY; serde_json serializes
  non-finite f64 as null, and news-web declared `relevance: f64`, causing the
  entire /api/stories response to fail deserialization when any blocklisted item
  was present.

Implementation status
---------------------
The code fixes for both F2 and F3 were already present in the repository's
initial commit (`20a6c26`). This session verified them, applied `cargo fmt`,
and produced this evidence file and the notepad entries below. The only code
delta introduced by this session is the formatting commit `676a0b7`.

Fix A — trailing-7-day percentile ranks (F2)
--------------------------------------------
1. `crates/news-store/src/percentile.rs`
   - `PercentileTracker::percentile_rank(metric_kind, value, window_days)` exists.
   - Loads the same trailing window as `PercentileTracker::percentile`, computes
     `(below + equal/2) / count * 100` via a numerically stable `mul_add`, and
     returns `StoreError::InsufficientData` when the window is empty.
   - Unit tests present:
     - `percentile_rank_on_empty_window_returns_insufficient_data`
     - `percentile_rank_of_one_to_ten_is_exact`
     - `percentile_rank_excludes_out_of_window_rows`
     - `neg_infinity_sorts_lowest_without_poisoning_finite_ranks`

2. `crates/news-server/src/scheduler/cycle.rs`
   - Batch-local `Vec<f64>` collectors and local `percentile_rank` helper removed.
   - Each scored cluster calls:
     - `tracker.percentile_rank(MetricKind::Relevance, relevance, 7)`
     - `tracker.percentile_rank(MetricKind::Importance, importance, 7)`
   - Cold-start rule: the draft specifies the cold-start rule only for the
     relevance *score* ("BM25-only until 20 feedback samples exist") and does not
     specify a percentile fallback. On `StoreError::InsufficientData` the code
     maps to `0.0` with `tracing::info!("trailing ... percentile unavailable: {err}")`.
     This is conservative: no threshold-based notify/digest until the 7-day window
     has data; the bypass lane (`source_count >= 2`) remains percentile-independent.

3. `crates/news-server/src/api/stories.rs`
   - Duplicated local `percentile_rank` helper removed.
   - `build_rows` creates a `PercentileTracker` and calls the shared rank method
     for both metrics.

4. `crates/news-cli/src/replay.rs`
   - Third duplicated local `percentile_rank` helper removed.
   - Uses `tracker.percentile_rank(..., 7)` for both metrics.
   - Replay determinism is preserved because the in-memory DB accumulates samples
     in fixture order before any rank is queried.

Fix B — honest JSON boundary for blocklist veto (F3)
----------------------------------------------------
1. `crates/news-server/src/api/stories.rs`
   - `StoryRow.relevance` is `Option<f64>` populated with
     `relevance.is_finite().then_some(relevance)` so NEG_INFINITY serializes as
     JSON `null`.
   - Regression tests present:
     - `blocklisted_story_serializes_relevance_as_null` — asserts `"relevance": null`
     - `finite_relevance_serializes_as_number` — asserts finite relevance stays a number

2. `crates/news-web/src/api.rs`
   - `StoryRow.relevance` is `Option<f64>`.
   - `fmt_score_option` helper present for rendering.
   - Host-target decode regression tests present:
     - `story_row_with_null_relevance_decodes`
     - `story_row_with_finite_relevance_decodes`

3. `crates/news-web/src/story_list.rs`
   - Renders `—` for `None` relevance; the decision pill still shows `Suppress` + reason.

4. `importance` left as `f64`
   - Importance is finite by construction today (multi-hot arithmetic, no veto
     path). No latent non-finite hazard was identified for that field.

Cold-start rule (recorded in decisions.md)
------------------------------------------
Draft quote: the draft specifies the cold-start rule only for the relevance *score*
("BM25-only until 20 feedback samples exist"; `.omo/drafts/news-triage.md:45`)
and does not specify a percentile fallback. Therefore: on
`StoreError::InsufficientData` from the trailing window, map to `0.0` and log
`tracing::info!("trailing ... percentile unavailable: {err}")`. This is conservative
and leaves the bypass lane (`source_count >= 2`) unaffected.

Gate results
------------
- `cargo test --workspace --no-fail-fast`
  - 97 tests passed, 0 failed (baseline 89; +8 new regression/unit tests)
- `cargo fmt --all --check`
  - exit 0
- `cargo clippy --workspace --all-targets -- -D warnings`
  - exit 0
- `cd crates/news-web && trunk build --release`
  - exit 0

Files with the substantive fixes
--------------------------------
- crates/news-store/src/percentile.rs
- crates/news-server/src/scheduler/cycle.rs
- crates/news-server/src/api/stories.rs
- crates/news-server/src/api/stories/tests.rs
- crates/news-cli/src/replay.rs
- crates/news-web/src/api.rs
- crates/news-web/src/story_list.rs

Git note
--------
The substantive fixes were already committed in the initial commit (`20a6c26`).
This session's only code delta is the formatting commit `676a0b7` (auto-committed
as "Updating" while running the tool pipeline).