BLE transport: recv buffer sizing, advertising interval, socket tuning, PHY logging

- Size receive buffer from negotiated recv_mtu instead of hardcoded 4096
  (prevents silent truncation if MTU exceeds buffer size)
- Set advertising interval to 400-600ms for deterministic behavior
  instead of depending on BlueZ driver defaults
- Enable power_forced_active on L2CAP sockets to prevent sniff-mode
  latency spikes during data transfer (best-effort, logged on failure)
- Log negotiated PHY and MTU at connection establishment for diagnostics

src/transport/ble/io.rs

@@ -165,6 +165,13 @@ mod bluer_impl {
             let recv_mtu = conn
                 .recv_mtu()
                 .map_err(|e| map_io_err("recv_mtu", e))? as u16;
+
+            // Log negotiated PHY for diagnostics (2M vs 1M)
+            match conn.as_ref().phy() {
+                Ok(phy) => debug!(addr = %remote, phy, send_mtu, recv_mtu, "BLE connection established"),
+                Err(_) => debug!(addr = %remote, send_mtu, recv_mtu, "BLE connection established (PHY query unsupported)"),
+            }
+
             Ok(Self { conn, remote, send_mtu, recv_mtu })
         }
     }
@@ -339,6 +346,11 @@ mod bluer_impl {
                 .set_recv_mtu(self.mtu)
                 .map_err(|e| map_io_err("set_recv_mtu", e))?;
 
+            // Prevent sniff mode to reduce latency during data transfer
+            if let Err(e) = listener.as_ref().set_power_forced_active(true) {
+                debug!(error = %e, "BLE listener: set_power_forced_active not supported");
+            }
+
             debug!(psm, mtu = self.mtu, "BLE listener bound");
 
             Ok(BluerAcceptor {
@@ -363,6 +375,11 @@ mod bluer_impl {
                 .set_recv_mtu(self.mtu)
                 .map_err(|e| map_io_err("set_recv_mtu", e))?;
 
+            // Prevent sniff mode to reduce latency during data transfer
+            if let Err(e) = socket.set_power_forced_active(true) {
+                debug!(error = %e, "BLE connect: set_power_forced_active not supported");
+            }
+
             let conn = socket
                 .connect(target_sa)
                 .await
@@ -381,6 +398,8 @@ mod bluer_impl {
                     s
                 },
                 local_name: Some("fips".to_string()),
+                min_interval: Some(std::time::Duration::from_millis(400)),
+                max_interval: Some(std::time::Duration::from_millis(600)),
                 ..Default::default()
             };
 

src/transport/ble/mod.rs

@@ -401,6 +401,7 @@ impl<I: BleIo> BleTransport<I> {
             self.packet_tx.clone(),
             self.transport_id,
             Arc::clone(&self.stats),
+            recv_mtu,
         ));
 
         let conn = BleConnection {
@@ -491,6 +492,7 @@ impl<I: BleIo> BleTransport<I> {
                         packet_tx,
                         transport_id,
                         Arc::clone(&stats),
+                        recv_mtu,
                     ));
 
                     let conn = BleConnection {
@@ -757,6 +759,7 @@ async fn accept_loop<A>(
                     packet_tx.clone(),
                     transport_id,
                     Arc::clone(&stats),
+                    recv_mtu,
                 ));
 
                 let conn = BleConnection {
@@ -802,8 +805,9 @@ async fn receive_loop<S: BleStream>(
     packet_tx: PacketTx,
     transport_id: TransportId,
     stats: Arc<BleStats>,
+    recv_mtu: u16,
 ) {
-    let mut buf = vec![0u8; 4096];
+    let mut buf = vec![0u8; recv_mtu as usize];
     loop {
         match stream.recv(&mut buf).await {
             Ok(0) => {