The tray says why the engine is not running, and setup will not run under a live app

Seen on the demo PC: Start did nothing and Stop stayed grey. The
supervisor's engine had failed because a second engine already held
port 8010, and the tray reported that as nothing at all. The supervisor
now keeps the engine's last lines and turns the known ones into a
sentence - 'port 8010 is already in use - another Behavision or its
engine is still running', 'run behavision-setup again' - which the tray
and the window show. Tray clicks no longer run on the menu loop, so a
stop that waits for the process cannot make the menu look dead.

Two ways that second process came to exist are closed: setup refuses to
run while Behavision.exe or the agent is up, and the app watches
agent.json so a claim made underneath it - which rotates the API token
- is picked up instead of leaving camera sync refused until a restart.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KGcjxF1cNLcuwc3DAPcnfj

desktop/app.go

@@ -125,6 +125,7 @@ func (a *App) startup(ctx context.Context) {
 	})
 
 	a.startPipeline(ctx)
+	go a.watchConfig(ctx)
 
 	// Recognition starts with the app. Until this, the engine only ever
 	// started when somebody pressed Start - which meant a till that rebooted
@@ -467,6 +468,62 @@ func (a *App) Claim(code string) (SessionInfo, error) {
 // the current config. Only Claim needs it today; it exists as its own method
 // because "stop everything that reads the config, then start it" is the part
 // that is easy to get half right.
+// watchConfig reloads agent.json when something else writes it.
+//
+// behavision-setup re-run on a PC with the app open re-claims the shop and
+// rotates its API token; the running app kept the old one and every camera
+// sync was refused from then on - heartbeats still flowed, so head office
+// looked fine while the cameras went stale. A claim from `behavision-agent
+// claim` does the same. Rather than ask people to restart the app, the app
+// watches the file and picks the new credentials up itself.
+func (a *App) watchConfig(ctx context.Context) {
+	path := agentpaths.AgentConfig()
+	last := mtime(path)
+	t := time.NewTicker(10 * time.Second)
+	defer t.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-t.C:
+		}
+		now := mtime(path)
+		if now.IsZero() || now.Equal(last) {
+			continue
+		}
+		last = now
+		fresh, err := agentcfg.Load(path)
+		if err != nil {
+			continue
+		}
+		fresh = fresh.WithEngineCredentials(agentpaths.APICredentials())
+		a.mu.Lock()
+		changed := fresh.AgentToken != a.cfg.AgentToken || fresh.SiteID != a.cfg.SiteID ||
+			fresh.BrokerPassword != a.cfg.BrokerPassword || fresh.CloudBase != a.cfg.CloudBase ||
+			fresh.Standalone != a.cfg.Standalone
+		if changed {
+			// Keep this process's live session; a claim clears it in the file
+			// deliberately, and that is honoured too.
+			a.cfg = fresh
+			if fresh.SessionToken == "" {
+				a.cloud.Clear()
+			}
+		}
+		a.mu.Unlock()
+		if changed {
+			a.restartPipeline()
+		}
+	}
+}
+
+func mtime(path string) time.Time {
+	st, err := os.Stat(path)
+	if err != nil {
+		return time.Time{}
+	}
+	return st.ModTime()
+}
+
 func (a *App) restartPipeline() {
 	if a.stopBridge != nil {
 		a.stopBridge()