feat(queue): replace PocketBase polling with Asynq + Redis

Introduce a Redis-backed Asynq task queue so the runner consumes TTS
jobs pushed by the backend instead of polling PocketBase.

- backend/internal/asynqqueue: Producer and Consumer wrappers
- backend/internal/runner: AsynqRunner mux, per-instance Prometheus
  registry (fixes duplicate-collector panic in tests), redisConnOpt
- backend/internal/config: REDIS_ADDR / REDIS_PASSWORD env vars
- backend/cmd/{backend,runner}/main.go: wire Redis when env set; fall
  back to legacy poll mode when unset
- Caddyfile: caddy-l4 TCP proxy for redis.libnovel.cc:6380 → homelab
- caddy/Dockerfile: add --with github.com/mholt/caddy-l4
- docker-compose.yml: Caddy exposes 6380, backend/runner get Redis env
- homelab/runner/docker-compose.yml: Redis sidecar, runner depends_on
- homelab/otel/grafana: Grafana dashboards (backend, catalogue, runner)
  and alerting rules / contact-points provisioning

backend/cmd/backend/main.go

@@ -22,12 +22,16 @@ import (
 	"time"
 
 	"github.com/getsentry/sentry-go"
+	"github.com/hibiken/asynq"
+	"github.com/libnovel/backend/internal/asynqqueue"
 	"github.com/libnovel/backend/internal/backend"
 	"github.com/libnovel/backend/internal/config"
 	"github.com/libnovel/backend/internal/kokoro"
 	"github.com/libnovel/backend/internal/meili"
 	"github.com/libnovel/backend/internal/otelsetup"
+	"github.com/libnovel/backend/internal/pockettts"
 	"github.com/libnovel/backend/internal/storage"
+	"github.com/libnovel/backend/internal/taskqueue"
 )
 
 // version and commit are set at build time via -ldflags.
@@ -100,6 +104,15 @@ func run() error {
 		kokoroClient = &noopKokoro{}
 	}
 
+	// ── Pocket-TTS (voice list + sample generation; audio generation is the runner's job) ──
+	var pocketTTSClient pockettts.Client
+	if cfg.PocketTTS.URL != "" {
+		pocketTTSClient = pockettts.New(cfg.PocketTTS.URL)
+		log.Info("pocket-tts voices enabled", "url", cfg.PocketTTS.URL)
+	} else {
+		log.Info("POCKET_TTS_URL not set — pocket-tts voices unavailable in backend")
+	}
+
 	// ── Meilisearch (search reads only; indexing is the runner's job) ────────
 	var searchIndex meili.Client
 	if cfg.Meilisearch.URL != "" {
@@ -110,6 +123,24 @@ func run() error {
 		searchIndex = meili.NoopClient{}
 	}
 
+	// ── Task Producer ────────────────────────────────────────────────────────
+	// When REDIS_ADDR is set the backend dual-writes: PocketBase record (audit)
+	// + Asynq job (immediate delivery). Otherwise it writes to PocketBase only
+	// and the runner picks up on the next poll tick.
+	var producer taskqueue.Producer = store
+	if cfg.Redis.Addr != "" {
+		redisOpt, parseErr := parseRedisOpt(cfg.Redis)
+		if parseErr != nil {
+			return fmt.Errorf("parse REDIS_ADDR: %w", parseErr)
+		}
+		asynqProducer := asynqqueue.NewProducer(store, redisOpt)
+		defer asynqProducer.Close() //nolint:errcheck
+		producer = asynqProducer
+		log.Info("backend: asynq task dispatch enabled", "addr", cfg.Redis.Addr)
+	} else {
+		log.Info("backend: poll-mode task dispatch (REDIS_ADDR not set)")
+	}
+
 	// ── Backend server ───────────────────────────────────────────────────────
 	srv := backend.New(
 		backend.Config{
@@ -125,10 +156,11 @@ func run() error {
 			PresignStore:  store,
 			ProgressStore: store,
 			CoverStore:    store,
-			Producer:      store,
+			Producer:      producer,
 			TaskReader:    store,
 			SearchIndex:   searchIndex,
 			Kokoro:        kokoroClient,
+			PocketTTS:     pocketTTSClient,
 			Log:           log,
 		},
 	)
@@ -165,3 +197,16 @@ func (n *noopKokoro) GenerateAudio(_ context.Context, _, _ string) ([]byte, erro
 func (n *noopKokoro) ListVoices(_ context.Context) ([]string, error) {
 	return nil, nil
 }
+
+// parseRedisOpt converts a config.Redis into an asynq.RedisConnOpt.
+// Handles full "redis://" / "rediss://" URLs and plain "host:port".
+func parseRedisOpt(cfg config.Redis) (asynq.RedisConnOpt, error) {
+	addr := cfg.Addr
+	if len(addr) > 7 && (addr[:8] == "redis://" || (len(addr) > 8 && addr[:9] == "rediss://")) {
+		return asynq.ParseRedisURI(addr)
+	}
+	return asynq.RedisClientOpt{
+		Addr:     addr,
+		Password: cfg.Password,
+	}, nil
+}

backend/cmd/runner/main.go

@@ -20,6 +20,7 @@ import (
 	"time"
 
 	"github.com/getsentry/sentry-go"
+	"github.com/libnovel/backend/internal/asynqqueue"
 	"github.com/libnovel/backend/internal/browser"
 	"github.com/libnovel/backend/internal/config"
 	"github.com/libnovel/backend/internal/kokoro"
@@ -29,6 +30,7 @@ import (
 	"github.com/libnovel/backend/internal/pockettts"
 	"github.com/libnovel/backend/internal/runner"
 	"github.com/libnovel/backend/internal/storage"
+	"github.com/libnovel/backend/internal/taskqueue"
 )
 
 // version and commit are set at build time via -ldflags.
@@ -151,9 +153,23 @@ func run() error {
 		MetricsAddr:                 cfg.Runner.MetricsAddr,
 		CatalogueRefreshInterval:    cfg.Runner.CatalogueRefreshInterval,
 		SkipInitialCatalogueRefresh: cfg.Runner.SkipInitialCatalogueRefresh,
+		RedisAddr:                   cfg.Redis.Addr,
+		RedisPassword:               cfg.Redis.Password,
 	}
+
+	// In Asynq mode the Consumer is a thin wrapper: claim/heartbeat/reap are
+	// no-ops, but FinishAudioTask / FinishScrapeTask / FailTask write back to
+	// PocketBase as before.
+	var consumer taskqueue.Consumer = store
+	if cfg.Redis.Addr != "" {
+		log.Info("runner: asynq mode — using Redis for task dispatch", "addr", cfg.Redis.Addr)
+		consumer = asynqqueue.NewConsumer(store)
+	} else {
+		log.Info("runner: poll mode — using PocketBase for task dispatch")
+	}
+
 	deps := runner.Dependencies{
-		Consumer:    store,
+		Consumer:    consumer,
 		BookWriter:  store,
 		BookReader:  store,
 		AudioStore:  store,