Latest Chapter correction: one numeric input, owner-gated (#149)

backend/internal/store/store.go

@@ -904,6 +904,11 @@ func (s *Store) Upsert(readerID int64, b Bookmark) (Bookmark, error) {
 	// xmax is zero only on a row this statement inserted, which is how a
 	// Series nobody had bookmarked before is told apart from one that already
 	// existed — DO UPDATE returns a row either way.
+	// latest_corrected_at is the one clause conditional on the value moving
+	// (#149): after a Correction a Reader's cached row holds the corrected
+	// number and resends it on the next Progress PUT, so unconditional
+	// zeroing would erase the fact while the value is still the owner's. The
+	// stamp survives a same-number PUT and dies the moment the number moves.
 	var created bool
 	if err := tx.QueryRow(`
 		INSERT INTO series (site, series_id, title, series_url, kind,
@@ -914,7 +919,10 @@ func (s *Store) Upsert(readerID int64, b Bookmark) (Bookmark, error) {
 		ON CONFLICT (site, series_id) DO UPDATE SET
 		  kind=excluded.kind,
 		  latest_chapter=excluded.latest_chapter,
-		  latest_chapter_num=excluded.latest_chapter_num
+		  latest_chapter_num=excluded.latest_chapter_num,
+		  latest_corrected_at = CASE
+		    WHEN series.latest_chapter_num IS DISTINCT FROM excluded.latest_chapter_num
+		    THEN 0 ELSE series.latest_corrected_at END
 		RETURNING xmax = 0`,
 		b.Site, b.SeriesID, b.Title, b.SeriesURL, b.Kind,
 		b.LatestChapter, latestNum).Scan(&created); err != nil {
@@ -1320,10 +1328,13 @@ func (s *Store) LatestCheckedAt(site, seriesID string) (int64, error) {
 // SetLatestChapter records the newest chapter the poll found on a series page.
 // The poller walks Series rather than Bookmarks, so this is a series-level
 // write: the row is shared, and updating it once refreshes every bookmark that
-// joins to it. Touching a missing series is not an error.
+// joins to it. Touching a missing series is not an error. The correction stamp
+// is zeroed unconditionally: checkOne only calls this when the number differs,
+// so a second copy of the condition would drift (#149).
 func (s *Store) SetLatestChapter(site, seriesID, label string, num float64) error {
 	if _, err := s.db.Exec(
-		`UPDATE series SET latest_chapter = $3, latest_chapter_num = $4
+		`UPDATE series SET latest_chapter = $3, latest_chapter_num = $4,
+		                   latest_corrected_at = 0
 		 WHERE site = $1 AND series_id = $2`,
 		site, seriesID, label, num); err != nil {
 		return fmt.Errorf("set latest chapter %s:%s: %w", site, seriesID, err)
@@ -1331,8 +1342,27 @@ func (s *Store) SetLatestChapter(site, seriesID, label string, num float64) erro
 	return nil
 }
 
-// RecordSighting notes that a Reader's browser reported this Series' Latest
-// Chapter, which is the half of a Sighting the client body cannot express
+// CorrectLatestChapter makes the Latest Chapter the owner's: one UPDATE
+// carrying the number, the derived label and the correction stamp. The label
+// shape is the poller's and the userscript's ("Chapter " + the number as
+// printed), so chapterLeadIn strips it and the UI renders "Ch N" with no
+// special case. latest_checked_at is not touched: a Correction is not a check.
+// A raising Reader is cleared without judgement: the number is the owner's
+// now, and no Sighting counter moves (spec #135).
+func (s *Store) CorrectLatestChapter(site, seriesID string, num float64, at int64) error {
+	if _, err := s.db.Exec(
+		`UPDATE series SET
+		   latest_chapter = $3,
+		   latest_chapter_num = $4,
+		   latest_corrected_at = $5,
+		   latest_raised_by = NULL
+		 WHERE site = $1 AND series_id = $2`,
+		site, seriesID, "Chapter "+strconv.FormatFloat(num, 'f', -1, 64), num, at); err != nil {
+		return fmt.Errorf("correct latest chapter %s:%s: %w", site, seriesID, err)
+	}
+	return nil
+}
+
 // (issue #103). It must be called *before* the Upsert that stores the reported
 // value: the raise test compares against what is still on the row, and after
 // the Upsert there is nothing left to compare with. A Series that does not