Owner Finish control on the Series detail page: confirm-gated finish, instant un-finish (#158)

backend/internal/web/admin_series_detail.go

@@ -56,6 +56,14 @@ type seriesDetailView struct {
 	// Series no Reader holds can be removed, so the owner is never offered a
 	// button the database will always refuse.
 	CanRemove bool
+	// Finished is the owner's finish stamp rendered for the control: while it
+	// stands, the page offers the instant Un-finish, not the confirm-gated
+	// Finish (issue #158).
+	Finished bool
+	// FinishedSince is the "finished <age> ago" line, "" while no finish
+	// stands. It rides the meta fragment both presses swap, so the answer
+	// itself shows how long the Series has been finished.
+	FinishedSince string
 }
 
 // adminSeriesDetail renders one Series' page, keyed by the composite
@@ -141,6 +149,8 @@ func (h *Handler) seriesDetailView(a store.AdminSeries) seriesDetailView {
 		v.Checked = since(time.Now(), time.UnixMilli(a.LatestCheckedAt))
 	}
 	v.Corrected = correctedAge(time.Now(), a.LatestCorrectedAt)
+	v.Finished = a.FinishedAt != 0
+	v.FinishedSince = finishedAge(time.Now(), a.FinishedAt)
 
 	// Provenance: the actor class behind the current number, evaluated in the
 	// order the classes outrank one another — the owner's stamp, which a
@@ -171,3 +181,13 @@ func correctedAge(now time.Time, at int64) string {
 	}
 	return "corrected " + since(now, time.UnixMilli(at))
 }
+
+// finishedAge is the finish marker's text: "finished <age> ago" while the
+// stamp is set, "" when zero — zero means never finished, and the reversal
+// (un-finish) must not read as history after a press (issue #158).
+func finishedAge(now time.Time, at int64) string {
+	if at == 0 {
+		return ""
+	}
+	return "finished " + since(now, time.UnixMilli(at))
+}