fix(ble): stop BLE scan on background and downgrade connection priority (#5644)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

core/ble/src/androidMain/kotlin/org/meshtastic/core/ble/KablePlatformSetup.kt

@@ -79,3 +79,10 @@ internal actual fun Peripheral.requestHighConnectionPriority(): Boolean {
         .onFailure { Logger.w(it) { "requestConnectionPriority(High) threw" } }
         .getOrDefault(false)
 }
+
+internal actual fun Peripheral.requestBalancedConnectionPriority(): Boolean {
+    val androidPeripheral = this as? AndroidPeripheral ?: return false
+    return runCatching { androidPeripheral.requestConnectionPriority(AndroidPeripheral.Priority.Balanced) }
+        .onFailure { Logger.w(it) { "requestConnectionPriority(Balanced) threw" } }
+        .getOrDefault(false)
+}

core/ble/src/commonMain/kotlin/org/meshtastic/core/ble/BleConnection.kt

@@ -78,6 +78,13 @@ interface BleConnection {
      * Default implementation returns `false` for platforms that don't support it.
      */
     fun requestHighConnectionPriority(): Boolean = false
+
+    /**
+     * Requests the platform to return to balanced BLE connection priority (default ~30–50 ms interval). Call after
+     * latency-sensitive operations (initial config drain, DFU) to reduce ongoing battery draw. Default implementation
+     * returns `false` for platforms that don't support it.
+     */
+    fun requestBalancedConnectionPriority(): Boolean = false
 }
 
 /** Represents a BLE service for commonMain. */

core/ble/src/commonMain/kotlin/org/meshtastic/core/ble/KableBleConnection.kt

@@ -245,6 +245,8 @@ class KableBleConnection(private val scope: CoroutineScope, private val loggingC
 
     override fun requestHighConnectionPriority(): Boolean = peripheral?.requestHighConnectionPriority() == true
 
+    override fun requestBalancedConnectionPriority(): Boolean = peripheral?.requestBalancedConnectionPriority() == true
+
     /** Ensures the previous peripheral's GATT resources are fully released. */
     private suspend fun cleanUpPeripheral(tag: String) {
         withContext(NonCancellable) { safeClosePeripheral(tag) }

core/ble/src/commonMain/kotlin/org/meshtastic/core/ble/KablePlatformSetup.kt

@@ -38,3 +38,9 @@ internal expect fun Peripheral.negotiatedMaxWriteLength(): Int?
  * no-op returning `false`. Used by latency-sensitive flows such as DFU firmware streaming.
  */
 internal expect fun Peripheral.requestHighConnectionPriority(): Boolean
+
+/**
+ * Requests balanced BLE connection priority (default ~30–50 ms interval) to reduce battery draw after latency-sensitive
+ * operations complete. On platforms without an equivalent API (JVM/iOS) this is a no-op.
+ */
+internal expect fun Peripheral.requestBalancedConnectionPriority(): Boolean

core/ble/src/iosMain/kotlin/org/meshtastic/core/ble/NoopStubs.kt

@@ -30,3 +30,5 @@ internal actual fun createPeripheral(address: String, builderAction: PeripheralB
 internal actual fun Peripheral.negotiatedMaxWriteLength(): Int? = null
 
 internal actual fun Peripheral.requestHighConnectionPriority(): Boolean = false
+
+internal actual fun Peripheral.requestBalancedConnectionPriority(): Boolean = false

core/ble/src/jvmMain/kotlin/org/meshtastic/core/ble/KablePlatformSetup.kt

@@ -33,4 +33,6 @@ internal actual fun Peripheral.negotiatedMaxWriteLength(): Int? = DEFAULT_JVM_MT
 
 internal actual fun Peripheral.requestHighConnectionPriority(): Boolean = false
 
+internal actual fun Peripheral.requestBalancedConnectionPriority(): Boolean = false
+
 private const val DEFAULT_JVM_MTU = 512

core/network/src/commonMain/kotlin/org/meshtastic/core/network/radio/BleRadioTransport.kt

@@ -78,6 +78,16 @@ private val HEARTBEAT_DRAIN_DELAY = 200.milliseconds
 private val SCAN_TIMEOUT = 5.seconds
 private val GATT_CLEANUP_TIMEOUT = 5.seconds
 
+/**
+ * Delay after onConnect before downgrading BLE connection priority to Balanced.
+ *
+ * The initial config drain (fromRadio burst) typically completes within 2–5 seconds on most devices, but slower radios
+ * (ESP32 with large node databases, many channels, or dense position history) can take significantly longer. 30 seconds
+ * provides generous margin while still ensuring we don't sustain the 7.5 ms connection interval indefinitely, which
+ * significantly increases battery draw on both the phone and the radio.
+ */
+private val PRIORITY_DOWNGRADE_DELAY = 30.seconds
+
 /**
  * A [RadioTransport] implementation for BLE devices using the common BLE abstractions (which are powered by Kable).
  *
@@ -361,15 +371,7 @@ class BleRadioTransport(
                 val maxLen = bleConnection.maximumWriteValueLength(BleWriteType.WITHOUT_RESPONSE)
                 Logger.i { "[$address] BLE Radio Session Ready. Max write length (WITHOUT_RESPONSE): $maxLen bytes" }
 
-                // Ask the platform for a low-latency / high-throughput connection interval
-                // (~7.5 ms on Android). The Meshtastic firmware happily accepts this and it
-                // materially speeds up the initial config drain and any bulk fromRadio reads.
-                if (bleConnection.requestHighConnectionPriority()) {
-                    Logger.d { "[$address] Requested high BLE connection priority" }
-                    // Wait for the connection parameter update to succeed before starting the heavy traffic
-                    // in onConnect(). Otherwise, the Android BLE stack may disconnect with GATT 147.
-                    delay(1.seconds)
-                }
+                requestHighPriorityAndScheduleDowngrade()
 
                 this@BleRadioTransport.callback.onConnect()
             }
@@ -398,6 +400,24 @@ class BleRadioTransport(
         }
     }
 
+    /**
+     * Requests high BLE connection priority for the initial config burst, then schedules a downgrade to balanced
+     * priority after [PRIORITY_DOWNGRADE_DELAY] to conserve battery.
+     */
+    private suspend fun CoroutineScope.requestHighPriorityAndScheduleDowngrade() {
+        if (bleConnection.requestHighConnectionPriority()) {
+            Logger.d { "[$address] Requested high BLE connection priority" }
+            // Wait for the connection parameter update before starting heavy traffic.
+            delay(1.seconds)
+        }
+        launch {
+            delay(PRIORITY_DOWNGRADE_DELAY)
+            if (bleConnection.requestBalancedConnectionPriority()) {
+                Logger.d { "[$address] Downgraded to balanced BLE connection priority" }
+            }
+        }
+    }
+
     @Volatile private var radioService: MeshtasticRadioProfile? = null
 
     // --- RadioTransport Implementation ---