refactor(web): share poll-state derivation; keep zebra parity across a row swap (#146)

Review round: pollState() unifies the CanPoll/Pending/Requested derivation
used by the list row and the detail page, and the row anchor carries its
band parity with the press (hx-vals) so the swapped answer keeps the
alternation.

backend/internal/web/admin_series.go

@@ -149,7 +149,8 @@ func (h *Handler) adminSeriesPoll(w http.ResponseWriter, r *http.Request) {
 	// Re-read after the stamp: the answer must describe the state after the
 	// press. The detail page's control swaps its meta in place and the list
 	// row's swaps the row; htmx names an id target in HX-Target, so the
-	// response matches the surface it came from.
+	// response matches the surface it came from. The row's band parity travels
+	// with the press (hx-vals), so the swap keeps the zebra alternation.
 	a, found, err := h.adminSeriesByKey(site, seriesID)
 	if err != nil {
 		log.Printf("series poll %s: %v", site+":"+seriesID, err)
@@ -164,7 +165,11 @@ func (h *Handler) adminSeriesPoll(w http.ResponseWriter, r *http.Request) {
 		h.render(w, http.StatusOK, "series-detail-meta", h.seriesDetailView(a))
 		return
 	}
-	h.render(w, http.StatusOK, "series-row", seriesRow(a, 0, time.Now()))
+	band := 0
+	if r.PostFormValue("band") == "1" {
+		band = 1
+	}
+	h.render(w, http.StatusOK, "series-row", seriesRow(a, band, time.Now()))
 }
 
 // seriesListView assembles one Series list view from the request's query
@@ -267,18 +272,32 @@ func (h *Handler) seriesFilterOptions(selected string, cutoff int64) ([]seriesFi
 
 // seriesRow shapes one store row for the template, capping its chips at two
 // plus a +N tail; attention marks a row that carries any.
-func seriesRow(a store.AdminSeries, i int, now time.Time) seriesRowView {
-	row := seriesRowView{
-		Key:     a.Key(),
-		Title:   a.Title,
-		Site:    a.Site,
-		Readers: a.ReaderCount,
-		Band:    i%2 == 1,
-		CanPoll: a.SeriesURL != "" && a.ReaderCount > 0,
-	}
+// pollState derives the Check now control and the pending marker (issue
+// #146), shared by the list row and the detail page: CanPoll is false on a
+// Series with no page to fetch and on an orphan, so the owner is never
+// offered a button that can never do anything. Pending is derived — the
+// request stamp is newer than the check stamp — and requested is its ageing
+// label, which never expires.
+func pollState(a store.AdminSeries, now time.Time) (canPoll, pending bool, requested string) {
+	canPoll = a.SeriesURL != "" && a.ReaderCount > 0
 	if a.ForcePollAt > a.LatestCheckedAt {
-		row.Pending = true
-		row.Requested = requestedAge(now, a.ForcePollAt)
+		pending = true
+		requested = requestedAge(now, a.ForcePollAt)
+	}
+	return canPoll, pending, requested
+}
+
+func seriesRow(a store.AdminSeries, i int, now time.Time) seriesRowView {
+	canPoll, pending, requested := pollState(a, now)
+	row := seriesRowView{
+		Key:       a.Key(),
+		Site:      a.Site,
+		Title:     a.Title,
+		Readers:   a.ReaderCount,
+		Band:      i%2 == 1,
+		CanPoll:   canPoll,
+		Pending:   pending,
+		Requested: requested,
 	}
 	if a.LatestChapterNum != nil {
 		row.Ch = strconv.FormatFloat(*a.LatestChapterNum, 'f', -1, 64)

backend/internal/web/admin_series_detail.go

@@ -96,6 +96,7 @@ func (h *Handler) adminSeriesByKey(site, seriesID string) (store.AdminSeries, bo
 // seriesDetailView shapes one AdminSeries row for display: every judgement in
 // Go, the template left to print strings and flags.
 func (h *Handler) seriesDetailView(a store.AdminSeries) seriesDetailView {
+	canPoll, pending, requested := pollState(a, time.Now())
 	v := seriesDetailView{
 		Key:            a.Key(),
 		Site:           a.Site,
@@ -107,11 +108,9 @@ func (h *Handler) seriesDetailView(a store.AdminSeries) seriesDetailView {
 		NoCover:        a.CoverAddress == "",
 		Orphan:         a.ReaderCount == 0,
 		SightingRaised: a.RaisedByReader,
-		CanPoll:        a.SeriesURL != "" && a.ReaderCount > 0,
-	}
-	if a.ForcePollAt > a.LatestCheckedAt {
-		v.Pending = true
-		v.Requested = requestedAge(time.Now(), a.ForcePollAt)
+		CanPoll:        canPoll,
+		Pending:        pending,
+		Requested:      requested,
 	}
 	if a.LatestChapterNum == nil {
 		v.Chapter = "—"

backend/internal/web/templates/series-list.html

@@ -48,6 +48,6 @@
   <span>{{.Age}}</span>
   <span class="c-rd">{{.Readers}}</span>
   <span class="c-note">{{range .Notes}}<span class="mark">{{.}}</span>{{end}}{{if .More}}<span class="mark mark-faint">+{{.More}}</span>{{end}}</span>
-  <span class="c-act">{{if .CanPoll}}<a class="ghost act" hx-post="/admin/series/{{.Key}}/poll" hx-target="closest .trow" hx-swap="outerHTML" href="#">Check now</a>{{end}}</span>
+  <span class="c-act">{{if .CanPoll}}<a class="ghost act" hx-post="/admin/series/{{.Key}}/poll" hx-target="closest .trow" hx-swap="outerHTML" hx-vals='{"band":{{if .Band}}1{{else}}0{{end}}}' href="#">Check now</a>{{end}}</span>
 </div>
 {{end}}

backend/web_test.go

@@ -2645,6 +2645,20 @@ func TestSeriesPollRoundTrip(t *testing.T) {
 		t.Errorf("poll response lacks the pending marker:\n%s", body)
 	}
 
+	// The press answers with the row's own band parity (hx-vals), so the swap
+	// keeps the zebra alternation.
+	req = httptest.NewRequest(http.MethodPost, "/admin/series/asura:x/poll", strings.NewReader("band=1"))
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.AddCookie(sessionCookie(t, st))
+	rr = httptest.NewRecorder()
+	router.ServeHTTP(rr, req)
+	if rr.Code != http.StatusOK {
+		t.Fatalf("POST poll (banded) status = %d, want 200", rr.Code)
+	}
+	if !strings.Contains(rr.Body.String(), `class="trow`) || !strings.Contains(rr.Body.String(), ` band"`) {
+		t.Errorf("banded press answer lost the zebra parity:\n%s", rr.Body.String())
+	}
+
 	// Detail surface: the meta fragment carries the same marker.
 	req = httptest.NewRequest(http.MethodPost, "/admin/series/asura:x/poll", nil)
 	req.AddCookie(sessionCookie(t, st))