Series URL repair: owner-typed, gated by the poller's own fetch gate (#151)

backend/internal/store/store.go

@@ -60,10 +60,11 @@ type Bookmark struct {
 // exists once no matter how many bookmarks point at it (ADR-0003).
 //
 // Title, SeriesURL and Cover are written once, at creation: a PUT naming an
-// existing Series has them ignored, and only the backend's own Poll may change
-// them. Kind and the latest-chapter fields are last-write-wins like the
-// bookmark's own fields. Never serialized: the wire format is the flat
-// Bookmark (ADR-0004).
+// existing Series has them ignored, and only the backend's own Poll may
+// change them. The one exception is SeriesURL, which the owner's
+// SetSeriesURL may repair (issue #151). Kind and the latest-chapter fields
+// are last-write-wins like the bookmark's own fields. Never serialized: the
+// wire format is the flat Bookmark (ADR-0004).
 type Series struct {
 	Site      string
 	SeriesID  string
@@ -1394,6 +1395,21 @@ func (s *Store) SetLatestChapter(site, seriesID, label string, num float64) erro
 	return nil
 }
 
+// SetSeriesURL stores the owner's repair for a Series' source address
+// (issue #151): the one write that lifts the write-once rule documented on
+// Series.SeriesURL. It is a store, not a verification — the caller has
+// already passed the poller's fetch gate. The handler 404s on an unknown row
+// before calling; the write itself is a plain single-column UPDATE like
+// MarkLatestChecked.
+func (s *Store) SetSeriesURL(site, seriesID, seriesURL string) error {
+	if _, err := s.db.Exec(
+		`UPDATE series SET series_url = $3 WHERE site = $1 AND series_id = $2`,
+		site, seriesID, seriesURL); err != nil {
+		return fmt.Errorf("set series url %s:%s: %w", site, seriesID, err)
+	}
+	return nil
+}
+
 // 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