rss: provenance + score calibration in items

Item titles gain a rune-capped source-feed suffix so list views (which
only ever show the channel title) display provenance inline. Item bodies
open with feed, model score, and the batch-wide score median; the median
is computed over every scored entry at poll time and stored on the run
row as a nil-safe pointer, so old rows render without it. /api/status
exposes the median too.

1 files changed, 23 insertions, 0 deletions

diff --git a/cmds/serve.go b/cmds/serve.go
index 9d82d38..0df5003 100644
--- a/cmds/serve.go
+++ b/cmds/serve.go
@@ -257,6 +257,7 @@ func (c *ServeCommand) pollOnce(client *miniflux.Client, vec *core.TFIDFVectoriz
 		Kept:           assembleBatch(scored, c.TopN, c.ExploreFrac, rng),
 		DurationMs:     time.Since(started).Milliseconds(),
 		ModelCreatedAt: model.CreatedAt,
+		ScoreMedian:    medianScore(scored),
 	}
 	if err := core.AppendRun(c.Runs, row); err != nil {
 		return err
@@ -275,6 +276,27 @@ type scoredEntry struct {
 	score float64
 }
 
+// medianScore returns the median score across every scored entry in a
+// poll — the batch-wide background (typical-entry) calibration rendered
+// alongside kept items' scores in the RSS body. Nil when nothing was
+// scored, so the run row omits the field rather than logging a fake 0.00.
+func medianScore(entries []scoredEntry) *float64 {
+	if len(entries) == 0 {
+		return nil
+	}
+	scores := make([]float64, len(entries))
+	for i, e := range entries {
+		scores[i] = e.score
+	}
+	sort.Float64s(scores)
+	n := len(scores)
+	median := scores[n/2]
+	if n%2 == 0 {
+		median = (scores[n/2-1] + scores[n/2]) / 2
+	}
+	return &median
+}
+
 // assembleBatch ranks scored entries by score descending and selects the
 // batch: the top (topN minus the exploration budget) are ranked; the
 // budget splits at a fixed 1/3 : 2/3 into runner-ups (highest-scored just
@@ -443,6 +465,7 @@ func (c *ServeCommand) routes(mins []int, modelCreatedAt time.Time) http.Handler
 				"kept":             len(last.Kept),
 				"duration_ms":      last.DurationMs,
 				"model_created_at": last.ModelCreatedAt,
+				"score_median":     last.ScoreMedian,
 			}
 		}
 		w.Header().Set("Content-Type", "application/json")