feat(observability+tts): OTel logs for backend/runner/ui; add kokoro-fastapi (GPU) and pocket-tts (CPU) to homelab

- otelsetup.Init now returns a *slog.Logger wired to the OTLP log exporter
  so all slog output is shipped to Loki with embedded trace IDs
- backend and runner both adopt the new OTel-bridged logger
- runner.runScrapeTask and runAudioTask now emit structured OTel spans
- ui/hooks.server.ts adds BatchLogRecordProcessor alongside existing trace exporter
- homelab: add kokoro-fastapi GPU service (ghcr.io/remsky/kokoro-fastapi-gpu)
  using deploy.resources.reservations for NVIDIA GPU, exposed internally on :8880
- homelab: add pocket-tts CPU service (ghcr.io/kyutai-labs/pocket-tts) on :8000
- runner KOKORO_URL hardcoded to http://kokoro-fastapi:8880 (fixes DNS failure
  for the stale kokoro.kalekber.cc hostname)

backend/cmd/backend/main.go

@@ -71,14 +71,17 @@ func run() error {
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer stop()
 
-	// ── OpenTelemetry tracing ─────────────────────────────────────────────────
-	otelShutdown, err := otelsetup.Init(ctx, version)
+	// ── OpenTelemetry tracing + logs ──────────────────────────────────────────
+	otelShutdown, otelLog, err := otelsetup.Init(ctx, version)
 	if err != nil {
 		return fmt.Errorf("init otel: %w", err)
 	}
 	if otelShutdown != nil {
 		defer otelShutdown()
-		log.Info("otel tracing enabled", "endpoint", os.Getenv("OTEL_EXPORTER_OTLP_ENDPOINT"))
+		// Replace the plain slog logger with the OTel-bridged one so all
+		// structured log lines are forwarded to Loki with trace IDs attached.
+		log = otelLog
+		log.Info("otel tracing + logs enabled", "endpoint", os.Getenv("OTEL_EXPORTER_OTLP_ENDPOINT"))
 	}
 
 	// ── Storage ──────────────────────────────────────────────────────────────

backend/cmd/runner/main.go

@@ -25,6 +25,7 @@ import (
 	"github.com/libnovel/backend/internal/kokoro"
 	"github.com/libnovel/backend/internal/meili"
 	"github.com/libnovel/backend/internal/novelfire"
+	"github.com/libnovel/backend/internal/otelsetup"
 	"github.com/libnovel/backend/internal/runner"
 	"github.com/libnovel/backend/internal/storage"
 )
@@ -70,6 +71,19 @@ func run() error {
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer stop()
 
+	// ── OpenTelemetry tracing + logs ─────────────────────────────────────────
+	otelShutdown, otelLog, err := otelsetup.Init(ctx, version)
+	if err != nil {
+		return fmt.Errorf("init otel: %w", err)
+	}
+	if otelShutdown != nil {
+		defer otelShutdown()
+		// Switch to the OTel-bridged logger so all structured log lines are
+		// forwarded to Loki with trace IDs attached.
+		log = otelLog
+		log.Info("otel tracing + logs enabled", "endpoint", os.Getenv("OTEL_EXPORTER_OTLP_ENDPOINT"))
+	}
+
 	// ── Storage ─────────────────────────────────────────────────────────────
 	store, err := storage.NewStore(ctx, cfg, log)
 	if err != nil {

backend/go.mod

@@ -34,12 +34,16 @@ require (
 	github.com/rs/xid v1.6.0 // indirect
 	github.com/tinylib/msgp v1.6.1 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
+	go.opentelemetry.io/contrib/bridges/otelslog v0.17.0 // indirect
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.67.0 // indirect
 	go.opentelemetry.io/otel v1.42.0 // indirect
+	go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp v0.18.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.42.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.42.0 // indirect
+	go.opentelemetry.io/otel/log v0.18.0 // indirect
 	go.opentelemetry.io/otel/metric v1.42.0 // indirect
 	go.opentelemetry.io/otel/sdk v1.42.0 // indirect
+	go.opentelemetry.io/otel/sdk/log v0.18.0 // indirect
 	go.opentelemetry.io/otel/trace v1.42.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.9.0 // indirect
 	go.uber.org/atomic v1.11.0 // indirect

backend/go.sum

@@ -58,18 +58,26 @@ github.com/tinylib/msgp v1.6.1/go.mod h1:RSp0LW9oSxFut3KzESt5Voq4GVWyS+PSulT77ro
 github.com/xyproto/randomstring v1.0.5/go.mod h1:rgmS5DeNXLivK7YprL0pY+lTuhNQW3iGxZ18UQApw/E=
 go.opentelemetry.io/auto/sdk v1.2.1 h1:jXsnJ4Lmnqd11kwkBV2LgLoFMZKizbCi5fNZ/ipaZ64=
 go.opentelemetry.io/auto/sdk v1.2.1/go.mod h1:KRTj+aOaElaLi+wW1kO/DZRXwkF4C5xPbEe3ZiIhN7Y=
+go.opentelemetry.io/contrib/bridges/otelslog v0.17.0 h1:NFIS6x7wyObQ7cR84x7bt1sr8nYBx89s3x3GwRjw40k=
+go.opentelemetry.io/contrib/bridges/otelslog v0.17.0/go.mod h1:39SaByOyDMRMe872AE7uelMuQZidIw7LLFAnQi0FWTE=
 go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.67.0 h1:OyrsyzuttWTSur2qN/Lm0m2a8yqyIjUVBZcxFPuXq2o=
 go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.67.0/go.mod h1:C2NGBr+kAB4bk3xtMXfZ94gqFDtg/GkI7e9zqGh5Beg=
 go.opentelemetry.io/otel v1.42.0 h1:lSQGzTgVR3+sgJDAU/7/ZMjN9Z+vUip7leaqBKy4sho=
 go.opentelemetry.io/otel v1.42.0/go.mod h1:lJNsdRMxCUIWuMlVJWzecSMuNjE7dOYyWlqOXWkdqCc=
+go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp v0.18.0 h1:icqq3Z34UrEFk2u+HMhTtRsvo7Ues+eiJVjaJt62njs=
+go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp v0.18.0/go.mod h1:W2m8P+d5Wn5kipj4/xmbt9uMqezEKfBjzVJadfABSBE=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.42.0 h1:THuZiwpQZuHPul65w4WcwEnkX2QIuMT+UFoOrygtoJw=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.42.0/go.mod h1:J2pvYM5NGHofZ2/Ru6zw/TNWnEQp5crgyDeSrYpXkAw=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.42.0 h1:uLXP+3mghfMf7XmV4PkGfFhFKuNWoCvvx5wP/wOXo0o=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.42.0/go.mod h1:v0Tj04armyT59mnURNUJf7RCKcKzq+lgJs6QSjHjaTc=
+go.opentelemetry.io/otel/log v0.18.0 h1:XgeQIIBjZZrliksMEbcwMZefoOSMI1hdjiLEiiB0bAg=
+go.opentelemetry.io/otel/log v0.18.0/go.mod h1:KEV1kad0NofR3ycsiDH4Yjcoj0+8206I6Ox2QYFSNgI=
 go.opentelemetry.io/otel/metric v1.42.0 h1:2jXG+3oZLNXEPfNmnpxKDeZsFI5o4J+nz6xUlaFdF/4=
 go.opentelemetry.io/otel/metric v1.42.0/go.mod h1:RlUN/7vTU7Ao/diDkEpQpnz3/92J9ko05BIwxYa2SSI=
 go.opentelemetry.io/otel/sdk v1.42.0 h1:LyC8+jqk6UJwdrI/8VydAq/hvkFKNHZVIWuslJXYsDo=
 go.opentelemetry.io/otel/sdk v1.42.0/go.mod h1:rGHCAxd9DAph0joO4W6OPwxjNTYWghRWmkHuGbayMts=
+go.opentelemetry.io/otel/sdk/log v0.18.0 h1:n8OyZr7t7otkeTnPTbDNom6rW16TBYGtvyy2Gk6buQw=
+go.opentelemetry.io/otel/sdk/log v0.18.0/go.mod h1:C0+wxkTwKpOCZLrlJ3pewPiiQwpzycPI/u6W0Z9fuYk=
 go.opentelemetry.io/otel/trace v1.42.0 h1:OUCgIPt+mzOnaUTpOQcBiM/PLQ/Op7oq6g4LenLmOYY=
 go.opentelemetry.io/otel/trace v1.42.0/go.mod h1:f3K9S+IFqnumBkKhRJMeaZeNk9epyhnCmQh/EysQCdc=
 go.opentelemetry.io/proto/otlp v1.9.0 h1:l706jCMITVouPOqEnii2fIAuO3IVGBRPV5ICjceRb/A=

backend/internal/otelsetup/otelsetup.go

@@ -5,12 +5,13 @@
 //	OTEL_EXPORTER_OTLP_ENDPOINT  — OTLP/HTTP endpoint, e.g. http://otel-collector:4318
 //	OTEL_SERVICE_NAME            — service name reported in traces (default: "backend")
 //
-// When OTEL_EXPORTER_OTLP_ENDPOINT is empty the function is a no-op and
-// returns a nil shutdown func, so the caller never needs to branch on it.
+// When OTEL_EXPORTER_OTLP_ENDPOINT is empty the function is a no-op: it
+// returns a nil shutdown func and the default slog.Logger, so callers never
+// need to branch on it.
 //
 // Usage in main.go:
 //
-//	shutdown, err := otelsetup.Init(ctx, version)
+//	shutdown, log, err := otelsetup.Init(ctx, version)
 //	if err != nil { return err }
 //	if shutdown != nil { defer shutdown() }
 package otelsetup
@@ -18,22 +19,31 @@ package otelsetup
 import (
 	"context"
 	"fmt"
+	"log/slog"
 	"os"
 	"time"
 
+	"go.opentelemetry.io/contrib/bridges/otelslog"
 	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp"
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
+	otellog "go.opentelemetry.io/otel/log/global"
+	"go.opentelemetry.io/otel/sdk/log"
 	"go.opentelemetry.io/otel/sdk/resource"
 	sdktrace "go.opentelemetry.io/otel/sdk/trace"
 	semconv "go.opentelemetry.io/otel/semconv/v1.26.0"
 )
 
-// Init sets up a TracerProvider that exports spans via OTLP/HTTP.
-// Returns a shutdown function (or nil if OTel is disabled) and any error.
-func Init(ctx context.Context, version string) (shutdown func(), err error) {
+// Init sets up TracerProvider and LoggerProvider that export via OTLP/HTTP.
+//
+// Returns:
+//   - shutdown: flushes and stops both providers (nil when OTel is disabled).
+//   - logger:   an slog.Logger bridged to OTel logs (falls back to default when disabled).
+//   - err:      non-nil only on SDK initialisation failure.
+func Init(ctx context.Context, version string) (shutdown func(), logger *slog.Logger, err error) {
 	endpoint := os.Getenv("OTEL_EXPORTER_OTLP_ENDPOINT")
 	if endpoint == "" {
-		return nil, nil // OTel disabled — not an error
+		return nil, slog.Default(), nil // OTel disabled — not an error
 	}
 
 	serviceName := os.Getenv("OTEL_SERVICE_NAME")
@@ -41,14 +51,7 @@ func Init(ctx context.Context, version string) (shutdown func(), err error) {
 		serviceName = "backend"
 	}
 
-	exp, err := otlptracehttp.New(ctx,
-		otlptracehttp.WithEndpoint(endpoint),
-		otlptracehttp.WithInsecure(), // collector is on the internal Docker network
-	)
-	if err != nil {
-		return nil, fmt.Errorf("otelsetup: create OTLP exporter: %w", err)
-	}
-
+	// ── Shared resource ───────────────────────────────────────────────────────
 	res, err := resource.New(ctx,
 		resource.WithAttributes(
 			semconv.ServiceName(serviceName),
@@ -56,19 +59,50 @@ func Init(ctx context.Context, version string) (shutdown func(), err error) {
 		),
 	)
 	if err != nil {
-		return nil, fmt.Errorf("otelsetup: create resource: %w", err)
+		return nil, slog.Default(), fmt.Errorf("otelsetup: create resource: %w", err)
+	}
+
+	// ── Trace provider ────────────────────────────────────────────────────────
+	traceExp, err := otlptracehttp.New(ctx,
+		otlptracehttp.WithEndpoint(endpoint),
+		otlptracehttp.WithInsecure(), // collector is on the internal Docker network
+	)
+	if err != nil {
+		return nil, slog.Default(), fmt.Errorf("otelsetup: create OTLP trace exporter: %w", err)
 	}
 
 	tp := sdktrace.NewTracerProvider(
-		sdktrace.WithBatcher(exp),
+		sdktrace.WithBatcher(traceExp),
 		sdktrace.WithResource(res),
 		sdktrace.WithSampler(sdktrace.ParentBased(sdktrace.TraceIDRatioBased(0.2))),
 	)
 	otel.SetTracerProvider(tp)
 
-	return func() {
+	// ── Log provider ──────────────────────────────────────────────────────────
+	logExp, err := otlploghttp.New(ctx,
+		otlploghttp.WithEndpoint(endpoint),
+		otlploghttp.WithInsecure(),
+	)
+	if err != nil {
+		return nil, slog.Default(), fmt.Errorf("otelsetup: create OTLP log exporter: %w", err)
+	}
+
+	lp := log.NewLoggerProvider(
+		log.WithProcessor(log.NewBatchProcessor(logExp)),
+		log.WithResource(res),
+	)
+	otellog.SetLoggerProvider(lp)
+
+	// Bridge slog → OTel logs. Structured fields and trace IDs are forwarded
+	// automatically; Grafana can correlate log lines with Tempo traces.
+	otelLogger := otelslog.NewLogger(serviceName)
+
+	shutdown = func() {
 		shutCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 		defer cancel()
 		_ = tp.Shutdown(shutCtx)
-	}, nil
+		_ = lp.Shutdown(shutCtx)
+	}
+
+	return shutdown, otelLogger, nil
 }

backend/internal/runner/runner.go

@@ -22,6 +22,10 @@ import (
 	"sync/atomic"
 	"time"
 
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/codes"
+
 	"github.com/libnovel/backend/internal/bookstore"
 	"github.com/libnovel/backend/internal/domain"
 	"github.com/libnovel/backend/internal/kokoro"
@@ -301,6 +305,14 @@ func (r *Runner) newOrchestrator() *orchestrator.Orchestrator {
 
 // runScrapeTask executes one scrape task end-to-end and reports the result.
 func (r *Runner) runScrapeTask(ctx context.Context, task domain.ScrapeTask) {
+	ctx, span := otel.Tracer("runner").Start(ctx, "runner.scrape_task")
+	defer span.End()
+	span.SetAttributes(
+		attribute.String("task.id", task.ID),
+		attribute.String("task.kind", task.Kind),
+		attribute.String("task.url", task.TargetURL),
+	)
+
 	log := r.deps.Log.With("task_id", task.ID, "kind", task.Kind, "url", task.TargetURL)
 	log.Info("runner: scrape task starting")
 
@@ -340,8 +352,10 @@ func (r *Runner) runScrapeTask(ctx context.Context, task domain.ScrapeTask) {
 
 	if result.ErrorMessage != "" {
 		r.tasksFailed.Add(1)
+		span.SetStatus(codes.Error, result.ErrorMessage)
 	} else {
 		r.tasksCompleted.Add(1)
+		span.SetStatus(codes.Ok, "")
 	}
 
 	log.Info("runner: scrape task finished",
@@ -384,6 +398,15 @@ func (r *Runner) runCatalogueTask(ctx context.Context, task domain.ScrapeTask, o
 
 // runAudioTask executes one audio-generation task.
 func (r *Runner) runAudioTask(ctx context.Context, task domain.AudioTask) {
+	ctx, span := otel.Tracer("runner").Start(ctx, "runner.audio_task")
+	defer span.End()
+	span.SetAttributes(
+		attribute.String("task.id", task.ID),
+		attribute.String("book.slug", task.Slug),
+		attribute.Int("chapter.number", task.Chapter),
+		attribute.String("audio.voice", task.Voice),
+	)
+
 	log := r.deps.Log.With("task_id", task.ID, "slug", task.Slug, "chapter", task.Chapter, "voice", task.Voice)
 	log.Info("runner: audio task starting")
 
@@ -407,6 +430,7 @@ func (r *Runner) runAudioTask(ctx context.Context, task domain.AudioTask) {
 	fail := func(msg string) {
 		log.Error("runner: audio task failed", "reason", msg)
 		r.tasksFailed.Add(1)
+		span.SetStatus(codes.Error, msg)
 		result := domain.AudioResult{ErrorMessage: msg}
 		if err := r.deps.Consumer.FinishAudioTask(ctx, task.ID, result); err != nil {
 			log.Error("runner: FinishAudioTask failed", "err", err)
@@ -441,6 +465,7 @@ func (r *Runner) runAudioTask(ctx context.Context, task domain.AudioTask) {
 	}
 
 	r.tasksCompleted.Add(1)
+	span.SetStatus(codes.Ok, "")
 	result := domain.AudioResult{ObjectKey: key}
 	if err := r.deps.Consumer.FinishAudioTask(ctx, task.ID, result); err != nil {
 		log.Error("runner: FinishAudioTask failed", "err", err)