banditcallback: shorten default TTL to 60s for absence-detection heartbeat

banditcallback/banditcallback.go

@@ -51,11 +51,17 @@ type Emitter struct {
 
 // New returns an emitter. token and callbackURL come from the daemon's
 // INI (banditcallbacktoken / banditcallbackurl). ttl is the per-device
-// dedup window — typically matches the API-side ProbeTTLForPollInterval
-// at the daemon's expected poll. Zero ttl uses 10m as a sensible default.
+// dedup window — also the heartbeat cadence: while a device keeps
+// using the proxy, it triggers a callback at most once per ttl. The
+// API side uses absence of those heartbeats as its only available
+// signal for censorship blocking (the proxy itself can't observe a
+// blocked connection because the client never reaches it), so ttl
+// must stay short enough that an absence is detected before users
+// suffer. Zero ttl uses 60s as a sensible default. Keep this in lock-
+// step with bandit.ArmCallbackHeartbeatWindow on the API side.
 func New(token, callbackURL string, ttl time.Duration) *Emitter {
 	if ttl <= 0 {
-		ttl = 10 * time.Minute
+		ttl = 60 * time.Second
 	}
 	return &Emitter{
 		token:       token,

http-proxy/main.go

@@ -95,7 +95,7 @@ var (
 	// the same binary without firing any callbacks.
 	banditCallbackToken = flag.String("banditcallbacktoken", "", "Per-arm bandit callback token plumbed by the provisioner")
 	banditCallbackURL   = flag.String("banditcallbackurl", "", "Full URL of the /v1/bandit/callback endpoint")
-	banditCallbackTTL   = flag.Duration("banditcallbackttl", 10*time.Minute, "Per-device dedup window for bandit callback emission")
+	banditCallbackTTL   = flag.Duration("banditcallbackttl", 60*time.Second, "Per-device dedup window and heartbeat cadence for bandit callback emission. The API's absence-reaper expects a callback within ArmCallbackHeartbeatWindow (~90s) of the previous one; values much smaller than that just amplify callback traffic, values larger risk false-positive negative rewards on idle clients.")
 
 	throttleRefreshInterval = flag.Duration("throttlerefresh", throttle.DefaultRefreshInterval, "Specifies how frequently to refresh throttling configuration from redis. Defaults to 5 minutes.")