feat(latest): split browser poll cooldown (#48)

## Summary

Split latest-chapter polling cooldowns by fetch cost. Browser-backed kagane and novelfull series now rest longer without changing the cadence of plain-TLS sites.

## Behavior

- Plain-TLS series keep the 1h default cooldown.
- Browser-backed series use `LATEST_CHAPTER_POLL_BROWSER_COOLDOWN`, defaulting to 6h.
- Both cooldowns share the existing 15m minimum floor; invalid values retain the existing fallback behavior.
- The poller still selects both classes in one due query per cycle.
- Existing ordering and exclusions remain unchanged: reader-count precedence, least-recently-checked ordering, finished exclusion, archived polling, and orphan exclusion.

## Implementation

- Added the browser cooldown to backend configuration and passed it through production poller construction.
- Added the browser-site list as the single routing source used for both due-query cutoff selection and fetcher choice.
- Kept all query values parameterized; the site list is passed as a bound PostgreSQL array parameter.
- Updated startup logging to report interval, plain cooldown, browser cooldown, batch, and stagger.
- Documented the variable, default, and floor in `README.md`, `.env.example`, `backend/AGENTS.md`, and `docker-compose.yml`.

## Review findings addressed

The first review found that configuration parsing was correct but `startLatestPoller` did not pass `BrowserCooldown` into `latest.Poller`; every browser-backed row would therefore have been due immediately. Production construction now goes through `newLatestPoller`, with a regression test covering both cooldown fields.

The review also identified duplicated browser-site knowledge in fetch routing. `slices.Contains(browserBackedSites, site)` now reuses the same list already supplied to the store query.

## Verification

- Focused backend tests pass: `go test ./internal/latest ./internal/store .`.
- Full suite passes: `go test ./...`.
- `graphify update .` completed.
- Issue #42 was updated and closed.

Reviewed-on: #48
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

backend/main.go

@@ -60,18 +60,20 @@ type Config struct {
 // deployment. Past that nothing breaks; the effective cadence stretches to
 // N x interval / batch and the oldest-checked-first ordering keeps it uniform.
 type LatestPoll struct {
-	Enabled  bool
-	Cooldown time.Duration
-	Interval time.Duration
-	Stagger  time.Duration
-	Batch    int
+	Enabled         bool
+	Cooldown        time.Duration
+	BrowserCooldown time.Duration
+	Interval        time.Duration
+	Stagger         time.Duration
+	Batch           int
 }
 
 const (
-	defaultPollCooldown = time.Hour
-	defaultPollInterval = 10 * time.Minute
-	defaultPollStagger  = 20 * time.Second
-	defaultPollBatch    = 14
+	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
@@ -129,20 +131,27 @@ func envInt(key string, def int) int {
 	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.
 func loadLatestPoll() LatestPoll {
 	p := LatestPoll{
-		Enabled:  envBool("LATEST_CHAPTER_POLL_ENABLED", true),
-		Cooldown: envDuration("LATEST_CHAPTER_POLL_COOLDOWN", defaultPollCooldown),
-		Interval: envDuration("LATEST_CHAPTER_POLL_INTERVAL", defaultPollInterval),
-		Stagger:  envDuration("LATEST_CHAPTER_POLL_STAGGER", defaultPollStagger),
-		Batch:    envInt("LATEST_CHAPTER_POLL_BATCH", defaultPollBatch),
-	}
-	if p.Cooldown < minPollCooldown {
-		log.Printf("config: cooldown %s is below the %s floor, clamping", p.Cooldown, minPollCooldown)
-		p.Cooldown = minPollCooldown
+		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
@@ -324,6 +333,21 @@ func main() {
 	}
 }
 
+// newLatestPoller wires the configured cooldowns and fetchers into the poller.
+func newLatestPoller(s *store.Store, cfg LatestPoll, fetch, browser latest.Fetcher) *latest.Poller {
+	return &latest.Poller{
+		Store:           s,
+		Fetch:           fetch,
+		BrowserFetch:    browser,
+		Now:             time.Now,
+		Cooldown:        cfg.Cooldown,
+		BrowserCooldown: cfg.BrowserCooldown,
+		Interval:        cfg.Interval,
+		Stagger:         cfg.Stagger,
+		Batch:           cfg.Batch,
+	}
+}
+
 // startLatestPoller launches the background poller unless it is disabled or its
 // HTTP client cannot be built. Any problem here is logged and skipped: this
 // feature going missing degrades the service to userscript-only latest-chapter
@@ -341,16 +365,7 @@ func startLatestPoller(ctx context.Context, s *store.Store, cfg LatestPoll, brow
 	// Nil browser: sites behind a JavaScript challenge are simply not polled,
 	// and their latest_chapter comes from the userscript alone — which is how
 	// the service behaved before the sidecar existed.
-	p := &latest.Poller{
-		Store:        s,
-		Fetch:        f,
-		BrowserFetch: browser,
-		Now:          time.Now,
-		Cooldown:     cfg.Cooldown,
-		Interval:     cfg.Interval,
-		Stagger:      cfg.Stagger,
-		Batch:        cfg.Batch,
-	}
+	p := newLatestPoller(s, cfg, f, browser)
 
 	go p.Run(ctx)
 }