fix(monitor): trigger immediate recheck after site config edit

Monitor goroutine slept for the full check interval after a config
edit, so hostname/URL changes wouldn't take effect until the next
scheduled check. Added per-site recheck channel that wakes the
goroutine immediately when UpdateSiteConfig is called.

internal/monitor/monitor.go

@@ -53,6 +53,9 @@ type Engine struct {
 	alertHealthMu sync.RWMutex
 	alertHealth   map[int]AlertHealth
 
+	recheckMu sync.RWMutex
+	recheck   map[int]chan struct{}
+
 	db                  store.Store
 	insecureSkipVerify  bool
 	allowPrivateTargets bool
@@ -74,6 +77,7 @@ func newEngine(s store.Store, allowPrivateTargets bool) *Engine {
 		liveState:           make(map[int]models.Site),
 		histories:           make(map[int]*SiteHistory),
 		tokenIndex:          make(map[string]int),
+		recheck:             make(map[int]chan struct{}),
 		probeResults:        make(map[int]map[string]NodeResult),
 		alertHealth:         make(map[int]AlertHealth),
 		aggStrategy:         AggAnyDown,
@@ -335,7 +339,6 @@ func (e *Engine) Start(ctx context.Context) {
 
 func (e *Engine) UpdateSiteConfig(site models.Site) {
 	e.mu.Lock()
-	defer e.mu.Unlock()
 	if existing, ok := e.liveState[site.ID]; ok {
 		e.removeFromTokenIndex(site.ID)
 		site.Status = existing.Status
@@ -352,6 +355,28 @@ func (e *Engine) UpdateSiteConfig(site models.Site) {
 		e.liveState[site.ID] = site
 		e.addToTokenIndex(site)
 	}
+	e.mu.Unlock()
+
+	e.signalRecheck(site.ID)
+}
+
+func (e *Engine) getRecheckChan(id int) chan struct{} {
+	e.recheckMu.Lock()
+	defer e.recheckMu.Unlock()
+	ch, ok := e.recheck[id]
+	if !ok {
+		ch = make(chan struct{}, 1)
+		e.recheck[id] = ch
+	}
+	return ch
+}
+
+func (e *Engine) signalRecheck(id int) {
+	ch := e.getRecheckChan(id)
+	select {
+	case ch <- struct{}{}:
+	default:
+	}
 }
 
 func (e *Engine) RemoveSite(id int) {
@@ -360,6 +385,10 @@ func (e *Engine) RemoveSite(id int) {
 	delete(e.liveState, id)
 	e.mu.Unlock()
 	e.removeHistory(id)
+
+	e.recheckMu.Lock()
+	delete(e.recheck, id)
+	e.recheckMu.Unlock()
 }
 
 func (e *Engine) ToggleSitePause(id int) bool {
@@ -380,6 +409,8 @@ func (e *Engine) ToggleSitePause(id int) bool {
 }
 
 func (e *Engine) monitorRoutine(ctx context.Context, id int) {
+	recheckCh := e.getRecheckChan(id)
+
 	// Stagger initial check to avoid thundering herd on startup
 	stagger := time.Duration(rand.IntN(3000)) * time.Millisecond //nolint:gosec // non-security jitter
 	select {
@@ -401,6 +432,7 @@ func (e *Engine) monitorRoutine(ctx context.Context, id int) {
 			case <-time.After(pollInterval):
 			case <-ctx.Done():
 				return
+			case <-recheckCh:
 			}
 			continue
 		}
@@ -417,6 +449,7 @@ func (e *Engine) monitorRoutine(ctx context.Context, id int) {
 			case <-time.After(pollInterval):
 			case <-ctx.Done():
 				return
+			case <-recheckCh:
 			}
 			continue
 		}
@@ -430,6 +463,7 @@ func (e *Engine) monitorRoutine(ctx context.Context, id int) {
 		case <-time.After(time.Duration(interval)*time.Second + jitter):
 		case <-ctx.Done():
 			return
+		case <-recheckCh:
 		}
 		e.checkByID(id)
 	}