Examine each batch once instead of every poll

The first full pass over all 42 feeds finished, then the server kept
re-deriving the same answers: Radiolab reported "53:29 of 59:39" four
times in one day. pollOne called detect unconditionally and the mirror
skips files it already has, so nothing had changed between passes. At
~6.5 minutes a show that is 4.5 hours a cycle against a two-hour poll
interval -- the machine never finished a cycle and never idled, burning
13h42m of CPU in 11h of wall clock, roughly 60% of it on the intro search
whose results are deliberately not published.

Show.DetectedBatch records the episode ids a completed pass examined.
The batch is the unit rather than the episode because every offset and
every break comes from comparing an episode against the others fetched
alongside it, so one arrival or one pruning legitimately changes all of
them. Order-independent, since feeds are not reliably sorted. Recorded
only on completion, so a cancelled or failed pass is retried.

Episode.DetectedAtUnix could not serve as the gate: it is only set for
episodes appearing in result.Offsets, so an episode nothing was found in
never got a timestamp and the gate would never close.

Also records what the first full corpus showed, including a disproven
hypothesis worth not retrying -- filtering breaks by partner count or run
length looks obviously right and makes agreement with the declared length
gap substantially worse -- and a correction: Sleepy History's 117 minutes
of "advertising" was a show-level sum sitting almost entirely inside the
two episodes its own guard already refused.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018AwnALZL6bD4VBtATDVv3B

1 files changed, 14 insertions, 4 deletions

diff --git a/server/cmd/listend/main.go b/server/cmd/listend/main.go
index 04c933f..3e5c65a 100644
--- a/server/cmd/listend/main.go
+++ b/server/cmd/listend/main.go
@@ -278,6 +278,7 @@ func (w *worker) pollOne(ctx context.Context, feedURL string) {
 // over weeks and lost it whenever retention reclaimed the file it was holding.
 func (w *worker) detect(ctx context.Context, show *store.Show, candidates []*store.Episode) {
 	var episodes []skips.Episode
+	var ids []string
 	byID := map[string]*store.Episode{}
 	for _, e := range candidates {
 		if !e.Mirrored() {
@@ -288,11 +289,15 @@ func (w *worker) detect(ctx context.Context, show *store.Show, candidates []*sto
 			Path:               filepath.Join(w.mirror.AudioDir, e.Path),
 			DeclaredDurationMs: e.DeclaredDurationMs,
 		})
+		ids = append(ids, e.ID)
 		byID[e.ID] = e
 	}
 	if len(episodes) < skips.DefaultConfirmThreshold || ctx.Err() != nil {
 		return
 	}
+	if !show.NeedsDetection(ids) {
+		return
+	}
 
 	started := time.Now()
 	result, err := skips.Detect(ctx, w.decoder, episodes, skips.DefaultConfig())
@@ -323,7 +328,9 @@ func (w *worker) detect(ctx context.Context, show *store.Show, candidates []*sto
 		result.OutroConfirmedOn, len(episodes), checkNote(result.OutroCheck),
 		time.Since(started).Round(time.Second))
 
-	w.detectAds(ctx, show, episodes, byID)
+	if w.detectAds(ctx, show, episodes, byID) {
+		show.RecordDetected(ids)
+	}
 }
 
 // detectAds finds the advertising a batch of episodes shares, which is what simultaneous
@@ -334,20 +341,22 @@ func (w *worker) detect(ctx context.Context, show *store.Show, candidates []*sto
 // is how it came to confirm an advertisement as an intro. This uses that dependence rather than
 // being defeated by it -- and reports what it found against the declared-versus-served length
 // gap, a figure it did not produce and which can therefore contradict it.
+// Reports whether the scan completed, so an interrupted or failed pass is examined again rather
+// than written off as done.
 func (w *worker) detectAds(
 	ctx context.Context,
 	show *store.Show,
 	episodes []skips.Episode,
 	byID map[string]*store.Episode,
-) {
+) bool {
 	if ctx.Err() != nil {
-		return
+		return false
 	}
 	started := time.Now()
 	ads, err := skips.DetectAds(ctx, w.decoder, episodes, skips.DefaultAdConfig())
 	if err != nil {
 		log.Printf("%s: ad scan failed: %v", show.Title, err)
-		return
+		return false
 	}
 
 	var withBreaks, refused int
@@ -381,6 +390,7 @@ func (w *worker) detectAds(
 	log.Printf("%s: ads on %d/%d episode(s)%s, accounted %s of %s inserted, took %s",
 		show.Title, withBreaks, len(episodes), refusedNote(refused),
 		clock(foundTotal), clock(insertedTotal), time.Since(started).Round(time.Second))
+	return true
 }
 
 func refusedNote(refused int) string {