Flip T3 to substrate-initiated actuator commands

substrate/src/config.rs

@@ -25,6 +25,13 @@ pub struct QuicConfig {
     pub t1_capacity: usize,
     pub t2_capacity: usize,
     pub t3_capacity: usize,
+    /// Bench-only knob. When > 0, the substrate spawns a synthetic T3
+    /// driver that issues toggling Relay commands to every connected device
+    /// at the configured rate, exercising the real outbound code path.
+    /// Off by default (0.0) in production. Override via env:
+    /// `APP_NETWORK__SYNTHETIC_T3_RATE_HZ=100`.
+    #[serde(default)]
+    pub synthetic_t3_rate_hz: f64,
 }
 
 #[derive(Debug, Serialize, Deserialize)]
@@ -47,6 +54,7 @@ impl Default for AppConfig {
                 t1_capacity: 1024,
                 t2_capacity: 512,
                 t3_capacity: 256,
+                synthetic_t3_rate_hz: 0.0,
             },
             simulation: SimulationConfig {
                 tick_rate_hz: 60,
@@ -65,7 +73,9 @@ impl AppConfig {
         Figment::new()
             .merge(Serialized::defaults(Self::default()))  // compiled-in defaults
             .merge(Toml::file(config_file))                // config file
-            .merge(Env::prefixed("APP_"))            // env overrides, e.g. APP_NETWORK__PORT=9000
+            // env overrides — `__` is the nesting separator so
+            // `APP_NETWORK__SERVER_PORT=9001` overrides `network.server_port`.
+            .merge(Env::prefixed("APP_").split("__"))
             .extract()
     }
 }