review: verdigris patina, honest Lane figures, tests that can fail (#102)

Two-axis review found the shipped colour and three weak tests.

- --patina was a warm gold at the same hue family as --brass; the spec
  asked for a cool blue-green so an unhealthy Lane is unmistakably not
  ember. Now verdigris in both branches, with docs/design-system.md
  stating why the far side of the wheel is the point.
- A Lane pass that returns before computing its figures carries the
  previous pass's due count and gap forward instead of recording zeroes,
  and Checked rides beside Due so a stopped Lane is distinguishable from
  a quiet one.
- TestAdminPageWithoutAPollerSaysSo now separates the two causes it
  conflated, TestOwnerClearsReaderMarks seeds real counters so the
  clearing assertion can fail, and TestLaneStatus asserts Checked and
  the carry-forward.
- backend/AGENTS.md records the one deliberate owner comparison outside
  requireOwner and the carry-forward rule.

backend/internal/latest/poller.go

@@ -246,19 +246,23 @@ func (p *Poller) runLanePass(ctx context.Context, name string, paced bool) time.
 		// No fetcher at all right now (browser absent, no fallback): every
 		// Series stays unstamped and due, so a browser that appears after a
 		// restart finds its full queue waiting (issue #100).
+		st.Gap = defaultGap
 		return defaultGap
 	}
 
 	due, err := p.Store.DueForLatestCheck(name, now.Add(-s.Rest).UnixMilli())
 	if err != nil {
 		log.Printf("latest poll %s: due query: %v", name, err)
+		st.Gap = defaultGap
 		return defaultGap
 	}
 	st.Due = len(due)
 	if s.Browser != nil && f == p.BrowserFetch && !browserWakeDue(due, now, s.Rest) {
 		// Below both thresholds Chrome stays asleep (ADR-0005 on-demand
 		// browser): waking it for a single Poll would cost a challenge solve
-		// per request.
+		// per request. The Lane still paces at the default gap, which is what
+		// the owner's page must show rather than a zero.
+		st.Gap = defaultGap
 		return defaultGap
 	}
 	if s.Browser != nil {
@@ -274,6 +278,7 @@ func (p *Poller) runLanePass(ctx context.Context, name string, paced bool) time.
 	eligible, err := p.Store.EligibleSeriesCount(name)
 	if err != nil {
 		log.Printf("latest poll %s: eligible count: %v", name, err)
+		st.Gap = defaultGap
 		return defaultGap
 	}
 	gap, clamped := effectiveGap(s, eligible)
@@ -288,7 +293,6 @@ func (p *Poller) runLanePass(ctx context.Context, name string, paced bool) time.
 	}
 
 	refusals := 0
-	checked := 0
 	for i, sr := range due {
 		if ctx.Err() != nil {
 			break
@@ -323,10 +327,10 @@ func (p *Poller) runLanePass(ctx context.Context, name string, paced bool) time.
 		} else {
 			refusals = 0
 		}
-		checked++
+		st.Checked++
 	}
-	if checked > 0 {
-		log.Printf("latest poll %s: due=%d checked=%d", name, len(due), checked)
+	if st.Checked > 0 {
+		log.Printf("latest poll %s: due=%d checked=%d", name, len(due), st.Checked)
 	}
 	if refusals >= 2 {
 		p.setRefusalBackoff(name, now.Add(refuseBackoff))