feat: one Poll Lane per Site, replacing the shared pace (#100)

Each Site runs its own poll goroutine, paced by Rest and Gap from the
registry (sites.go) instead of the shared cooldown/interval/stagger/batch
config. Rest is enforced by the due query's WHERE clause; the Lane sleeps
its effective gap between fetches (hour/eligible, floored at 1s).

Lane-local failures: two refusals stop that Site for 15m, a lost browser
stops only the round's remaining browser Lanes, and cover heals moved to
background goroutines so a slow CDN cannot consume a Lane's gap. The five
LATEST_CHAPTER_POLL_* pace env vars are gone; only the kill switch
remains.

backend/main.go

@@ -7,7 +7,6 @@ import (
 	"net/http"
 	"os"
 	"os/signal"
-	"strconv"
 	"strings"
 	"syscall"
 	"time"
@@ -61,30 +60,15 @@ type Config struct {
 
 // LatestPoll configures the background latest-chapter poller.
 //
-// Sizing: batch x (cooldown / interval) is how many series hold a true cooldown
-// cadence — 14 x (1h / 10m) = 84 with these defaults, which covers this
-// deployment. Past that nothing breaks; the effective cadence stretches to
-// N x interval / batch and the oldest-checked-first ordering keeps it uniform.
+// Only the kill switch lives here. Pace is per Site — rest time and gap are
+// registry properties (internal/latest/sites.go, issue #100), because each
+// Lane has to be able to differ from the others. The five environment
+// settings that used to size a shared pace (cooldown, browser cooldown,
+// interval, stagger, batch) are gone with it: no deployed .env may carry them.
 type LatestPoll struct {
-	Enabled         bool
-	Cooldown        time.Duration
-	BrowserCooldown time.Duration
-	Interval        time.Duration
-	Stagger         time.Duration
-	Batch           int
+	Enabled bool
 }
 
-const (
-	defaultPollCooldown        = time.Hour
-	defaultBrowserPollCooldown = 6 * time.Hour
-	defaultPollInterval        = 10 * time.Minute
-	defaultPollStagger         = 20 * time.Second
-	defaultPollBatch           = 14
-	// minPollCooldown keeps a typo from turning a polite background check into
-	// a hammer against sites that are already bot-scoring us.
-	minPollCooldown = 15 * time.Minute
-)
-
 func envOr(key, def string) string {
 	if v := os.Getenv(key); v != "" {
 		return v
@@ -107,66 +91,11 @@ func envBool(key string, def bool) bool {
 	}
 }
 
-// envDuration reads a duration env var. An unparseable or non-positive value
-// falls back to def and logs rather than failing startup: the poller is an
-// enhancement, and a typo in one of its knobs must not stop bookmark sync.
-func envDuration(key string, def time.Duration) time.Duration {
-	raw := strings.TrimSpace(os.Getenv(key))
-	if raw == "" {
-		return def
-	}
-	d, err := time.ParseDuration(raw)
-	if err != nil || d <= 0 {
-		log.Printf("config: %s=%q is not a positive duration, using %s", key, raw, def)
-		return def
-	}
-	return d
-}
-
-// envInt reads a positive integer env var, with the same fallback policy.
-func envInt(key string, def int) int {
-	raw := strings.TrimSpace(os.Getenv(key))
-	if raw == "" {
-		return def
-	}
-	n, err := strconv.Atoi(raw)
-	if err != nil || n <= 0 {
-		log.Printf("config: %s=%q is not a positive integer, using %d", key, raw, def)
-		return def
-	}
-	return n
-}
-
-func clampPollCooldown(name string, d time.Duration) time.Duration {
-	if d < minPollCooldown {
-		log.Printf("config: %s %s is below the %s floor, clamping", name, d, minPollCooldown)
-		return minPollCooldown
-	}
-	return d
-}
-
-// loadLatestPoll reads the poller's settings, clamping anything that would make
-// it antisocial.
+// loadLatestPoll reads the poller's settings. The pace knobs that used to be
+// clamped here are registry properties now (issue #100), so there is nothing
+// left to clamp.
 func loadLatestPoll() LatestPoll {
-	p := LatestPoll{
-		Enabled:         envBool("LATEST_CHAPTER_POLL_ENABLED", true),
-		Cooldown:        envDuration("LATEST_CHAPTER_POLL_COOLDOWN", defaultPollCooldown),
-		BrowserCooldown: envDuration("LATEST_CHAPTER_POLL_BROWSER_COOLDOWN", defaultBrowserPollCooldown),
-		Interval:        envDuration("LATEST_CHAPTER_POLL_INTERVAL", defaultPollInterval),
-		Stagger:         envDuration("LATEST_CHAPTER_POLL_STAGGER", defaultPollStagger),
-		Batch:           envInt("LATEST_CHAPTER_POLL_BATCH", defaultPollBatch),
-	}
-	p.Cooldown = clampPollCooldown("cooldown", p.Cooldown)
-	p.BrowserCooldown = clampPollCooldown("browser cooldown", p.BrowserCooldown)
-	// batch x stagger has to fit inside one tick or a batch is still running
-	// when the next one is due. Run() serialises them, so this degrades to a
-	// slower cadence rather than to overlapping fetches — worth a warning, not
-	// a failure.
-	if span := time.Duration(p.Batch) * p.Stagger; span > p.Interval {
-		log.Printf("config: batch(%d) x stagger(%s) = %s exceeds interval %s; batches will overrun their tick",
-			p.Batch, p.Stagger, span, p.Interval)
-	}
-	return p
+	return LatestPoll{Enabled: envBool("LATEST_CHAPTER_POLL_ENABLED", true)}
 }
 
 func loadConfig() Config {
@@ -377,7 +306,8 @@ func main() {
 	}
 }
 
-// newLatestPoller wires the configured cooldowns and fetchers into the poller.
+// newLatestPoller wires the fetcher seams into the poller. Pace is registry
+// property, not config (issue #100), so there are no knobs to pass through.
 func newLatestPoller(s *store.Store, cfg LatestPoll, fetch, browser latest.Fetcher) *latest.Poller {
 	var covers latest.BrowserCoverFetcher
 	if f, ok := browser.(latest.BrowserCoverFetcher); ok {
@@ -390,11 +320,6 @@ func newLatestPoller(s *store.Store, cfg LatestPoll, fetch, browser latest.Fetch
 		CoverFetch:      covers,
 		CoverBytesFetch: latest.NewCoverFetcher(),
 		Now:             time.Now,
-		Cooldown:        cfg.Cooldown,
-		BrowserCooldown: cfg.BrowserCooldown,
-		Interval:        cfg.Interval,
-		Stagger:         cfg.Stagger,
-		Batch:           cfg.Batch,
 	}
 }