fix: EventBus panic on SSE disconnect + JWT secret persistence + recover() guards

- eventbus.go: Fix send-on-closed-channel panic in SubscribeGlobal by
  using a done channel; add recover() in fan-out goroutine; track active
  global subs for proper cleanup on unsubscribe
- config.go: Persist JWT secret to $DATA_DIR/.jwt_secret instead of
  regenerating a random one on every restart (which invalidated all sessions)
- handlers_ws.go: Replace time.After with time.Ticker to fix timer leak in
  SSE keepalive loop
- handlers_jobs.go: Add recover() in fire-and-forget job goroutine; fix nil
  pointer deref when GetByID fails after job creation
- handlers_machines.go: Add recover() in ProbeAllMachines goroutine
- scheduler.go: Add recover() in scheduled job run goroutine
- engine.go: Add recover() in per-machine probe goroutines

internal/api/handlers_jobs.go

@@ -4,6 +4,7 @@ import (
 	"database/sql"
 	"encoding/json"
 	"fmt"
+	"log/slog"
 	"net/http"
 	"os"
 	"strconv"
@@ -150,11 +151,20 @@ func (h *JobHandler) TriggerRun(w http.ResponseWriter, r *http.Request) {
 	}
 
 	go func() {
+		defer func() {
+			if r := recover(); r != nil {
+				slog.Error("job run goroutine panicked", "job_id", jobID, "panic", r)
+			}
+		}()
 		h.engine.Run(r.Context(), jobID, pairID)
 	}()
 
 	jobRepo := models.NewJobRepository(h.db)
-	j, _ := jobRepo.GetByID(jobID)
+	j, err := jobRepo.GetByID(jobID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to fetch created job")
+		return
+	}
 	writeJSON(w, jobToResp(*j), http.StatusCreated)
 }
 

internal/api/handlers_machines.go

@@ -3,6 +3,7 @@ package api
 import (
 	"database/sql"
 	"encoding/json"
+	"log/slog"
 	"net/http"
 	"regexp"
 	"strconv"
@@ -216,7 +217,14 @@ func (h *MachineHandler) Refresh(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusInternalServerError, "engine not available")
 		return
 	}
-	go h.engine.ProbeAllMachines()
+	go func() {
+		defer func() {
+			if r := recover(); r != nil {
+				slog.Error("ProbeAllMachines panicked", "panic", r)
+			}
+		}()
+		h.engine.ProbeAllMachines()
+	}()
 	w.WriteHeader(http.StatusAccepted)
 	writeJSON(w, map[string]string{"status": "probing"})
 }

internal/api/handlers_ws.go

@@ -38,6 +38,9 @@ func (h *SSEHandler) StreamAll(w http.ResponseWriter, r *http.Request) {
 	events, unsub := h.engine.SubscribeGlobal()
 	defer unsub()
 
+	ticker := time.NewTicker(30 * time.Second)
+	defer ticker.Stop()
+
 	for {
 		select {
 		case evt := <-events:
@@ -46,7 +49,7 @@ func (h *SSEHandler) StreamAll(w http.ResponseWriter, r *http.Request) {
 			flusher.Flush()
 		case <-r.Context().Done():
 			return
-		case <-time.After(30 * time.Second):
+		case <-ticker.C:
 			fmt.Fprintf(w, ": keepalive\n\n")
 			flusher.Flush()
 		}
@@ -84,6 +87,9 @@ func (h *SSEHandler) StreamJob(w http.ResponseWriter, r *http.Request) {
 	events, unsub := h.engine.SubscribeJob(jobID)
 	defer unsub()
 
+	ticker := time.NewTicker(30 * time.Second)
+	defer ticker.Stop()
+
 	for {
 		select {
 		case evt := <-events:
@@ -92,7 +98,7 @@ func (h *SSEHandler) StreamJob(w http.ResponseWriter, r *http.Request) {
 			flusher.Flush()
 		case <-r.Context().Done():
 			return
-		case <-time.After(30 * time.Second):
+		case <-ticker.C:
 			fmt.Fprintf(w, ": keepalive\n\n")
 			flusher.Flush()
 		}

internal/config/config.go

@@ -1,6 +1,8 @@
 package config
 
 import (
+	"crypto/rand"
+	"encoding/hex"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -80,19 +82,23 @@ func Load(configPath, dataDir, addr string) (*Config, error) {
 		}
 	}
 
+	secretPath := filepath.Join(cfg.DataDir, ".jwt_secret")
+	if cfg.Auth.JWTSecret == "" {
+		if data, err := os.ReadFile(secretPath); err == nil && len(data) >= 32 {
+			cfg.Auth.JWTSecret = strings.TrimSpace(string(data))
+		}
+	}
 	if cfg.Auth.JWTSecret == "" {
 		b := make([]byte, 32)
-		f, err := os.Open("/dev/urandom")
-		if err == nil {
-			defer f.Close()
-			n, _ := f.Read(b)
-			if n == 32 {
-				cfg.Auth.JWTSecret = fmt.Sprintf("%x", b)
-			}
+		if _, err := rand.Read(b); err == nil {
+			cfg.Auth.JWTSecret = hex.EncodeToString(b)
 		}
 		if cfg.Auth.JWTSecret == "" {
 			cfg.Auth.JWTSecret = "insecure-dev-secret-change-in-production"
 		}
+		if dirErr := os.MkdirAll(cfg.DataDir, 0700); dirErr == nil {
+			_ = os.WriteFile(secretPath, []byte(cfg.Auth.JWTSecret+"\n"), 0600)
+		}
 	}
 
 	if dataDir := os.Getenv("SYNCSERVER_DATA_DIR"); dataDir != "" {

internal/scheduler/scheduler.go

@@ -83,6 +83,11 @@ func (s *Scheduler) tick() {
 
 		ctx := context.Background()
 		go func(jobID int64, pairID int64, schID int64) {
+			defer func() {
+				if r := recover(); r != nil {
+					slog.Error("scheduler: job run panicked", "job_id", jobID, "panic", r)
+				}
+			}()
 			if err := s.engine.Run(ctx, jobID, pairID); err != nil {
 				slog.Warn("scheduler: job failed", "job_id", jobID, "error", err)
 			}

internal/syncengine/engine.go

@@ -368,7 +368,12 @@ func (e *Engine) ProbeAllMachines() {
 		sem <- struct{}{}
 		go func(m *models.Machine) {
 			defer wg.Done()
-			defer func() { <-sem }()
+			defer func() {
+				if r := recover(); r != nil {
+					slog.Error("probe goroutine panicked", "machine_id", m.ID, "panic", r)
+				}
+				<-sem
+			}()
 
 			ctx, cancel := context.WithTimeout(context.Background(), probeTimeout)
 			defer cancel()

internal/syncengine/eventbus.go

@@ -10,6 +10,12 @@ type EventBus struct {
 	mu          sync.RWMutex
 	global      chan Event
 	bufferSize  int
+	globalSubs  []globalSub
+}
+
+type globalSub struct {
+	ch   chan Event
+	done chan struct{}
 }
 
 func NewEventBus(bufferSize int) *EventBus {
@@ -17,6 +23,7 @@ func NewEventBus(bufferSize int) *EventBus {
 		subscribers: make(map[int64]map[chan Event]struct{}),
 		global:      make(chan Event, bufferSize),
 		bufferSize:  bufferSize,
+		globalSubs:  nil,
 	}
 }
 
@@ -43,20 +50,42 @@ func (eb *EventBus) Subscribe(jobID int64) (chan Event, func()) {
 }
 
 func (eb *EventBus) SubscribeGlobal() (chan Event, func()) {
-	eb.mu.RLock()
 	ch := make(chan Event, eb.bufferSize)
-	eb.mu.RUnlock()
+	done := make(chan struct{})
+	eb.mu.Lock()
+	eb.globalSubs = append(eb.globalSubs, globalSub{ch: ch, done: done})
+	eb.mu.Unlock()
 	go func() {
-		for evt := range eb.global {
+		defer func() {
+			if r := recover(); r != nil {
+				slog.Error("SubscribeGlobal goroutine panicked", "reason", r)
+			}
+			close(ch)
+		}()
+		for {
 			select {
-			case ch <- evt:
-			default:
-				slog.Warn("global event subscriber buffer full, dropping event", "type", evt.Type)
+			case evt := <-eb.global:
+				select {
+				case ch <- evt:
+				default:
+					slog.Warn("global event subscriber buffer full, dropping event", "type", evt.Type)
+				}
+			case <-done:
+				return
 			}
 		}
-		close(ch)
 	}()
-	return ch, func() { close(ch) }
+	return ch, func() {
+		close(done)
+		eb.mu.Lock()
+		for i, s := range eb.globalSubs {
+			if s.ch == ch {
+				eb.globalSubs = append(eb.globalSubs[:i], eb.globalSubs[i+1:]...)
+				break
+			}
+		}
+		eb.mu.Unlock()
+	}
 }
 
 func (eb *EventBus) Publish(evt Event) {