when maglevd rehashes its config:

- when a backend gets newly added or restarted, an event should fire; perhaps transition to 'unknown'
- when a backend gets removed, an event should fire; perhaps transition to 'removed'
- when a backend is in 'unknown' state, fast-interval is appropriate

internal/health/state.go

@@ -33,6 +33,7 @@ const (
 	StateUp
 	StateDown
 	StatePaused
+	StateRemoved // backend was removed from configuration
 )
 
 func (s State) String() string {
@@ -45,6 +46,8 @@ func (s State) String() string {
 		return "down"
 	case StatePaused:
 		return "paused"
+	case StateRemoved:
+		return "removed"
 	default:
 		return "unknown"
 	}
@@ -118,7 +121,7 @@ func New(name string, addr net.IP, rise, fall int) *Backend {
 // failure means the backend is not yet confirmed reachable), and to StateUp
 // once the counter reaches Rise consecutive passes.
 func (b *Backend) Record(r ProbeResult, maxHistory int) bool {
-	if b.State == StatePaused {
+	if b.State == StatePaused || b.State == StateRemoved {
 		return false
 	}
 	if r.OK {
@@ -157,12 +160,15 @@ func (b *Backend) Resume(maxHistory int) bool {
 }
 
 // NextInterval returns the appropriate probe interval based on state and counter:
-//   - Unknown (no probes yet):        interval  — probe promptly to establish initial state
-//   - Fully healthy (counter at max): interval
-//   - Fully down (counter at 0):      downInterval (falls back to interval)
-//   - Degraded (anywhere in between): fastInterval (falls back to interval)
+//   - Unknown (initial / post-resume): fastInterval (falls back to interval) — probe quickly to establish state
+//   - Fully healthy (counter at max):  interval
+//   - Fully down (counter at 0):       downInterval (falls back to interval)
+//   - Degraded (anywhere in between):  fastInterval (falls back to interval)
 func (b *Backend) NextInterval(interval, fastInterval, downInterval time.Duration) time.Duration {
 	if b.State == StateUnknown {
+		if fastInterval > 0 {
+			return fastInterval
+		}
 		return interval
 	}
 	if b.Counter.Health == b.Counter.Max() {
@@ -180,6 +186,21 @@ func (b *Backend) NextInterval(interval, fastInterval, downInterval time.Duratio
 	return interval
 }
 
+// Start records the initial StateUnknown transition when a backend is first
+// created or restarted. It exists solely to populate the transition history
+// and fire a reload event; the state does not change.
+func (b *Backend) Start(maxHistory int) Transition {
+	b.transition(StateUnknown, ProbeResult{Code: "start"}, maxHistory)
+	return b.Transitions[0]
+}
+
+// Remove transitions the backend to StateRemoved. Returns the transition.
+// After this call no further probe results are accepted.
+func (b *Backend) Remove(maxHistory int) Transition {
+	b.transition(StateRemoved, ProbeResult{Code: "removed"}, maxHistory)
+	return b.Transitions[0]
+}
+
 // transition appends a new Transition and updates State.
 func (b *Backend) transition(to State, r ProbeResult, maxHistory int) {
 	t := Transition{From: b.State, To: to, At: time.Now(), Result: r}