platform: modularize api/gui, add docs-tests-web foundation, and refresh root config

selective-vpn-api/app/transport_health_refresh.go

@@ -0,0 +1,37 @@
+package app
+
+import (
+	"sync"
+	"time"
+)
+
+const (
+	transportHealthFreshTTL           = 45 * time.Second
+	transportHealthBackoffMin         = 5 * time.Second
+	transportHealthBackoffMax         = 2 * time.Minute
+	transportHealthPersistMinAge      = 90 * time.Second
+	transportHealthMaxConcurrentProbe = 2
+)
+
+type transportHealthRefreshEntry struct {
+	swr refreshCoordinator
+}
+
+type transportHealthRefresher struct {
+	mu      sync.Mutex
+	entries map[string]*transportHealthRefreshEntry
+	sem     chan struct{}
+}
+
+func newTransportHealthRefresher(maxConcurrent int) *transportHealthRefresher {
+	n := maxConcurrent
+	if n <= 0 {
+		n = transportHealthMaxConcurrentProbe
+	}
+	return &transportHealthRefresher{
+		entries: map[string]*transportHealthRefreshEntry{},
+		sem:     make(chan struct{}, n),
+	}
+}
+
+var transportHealthSWR = newTransportHealthRefresher(envInt("SVPN_TRANSPORT_HEALTH_MAX_PARALLEL", transportHealthMaxConcurrentProbe))