fix(ui): give rx_snr real presence semantics end to end (#6523)

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: jamesarich

androidApp/src/fdroid/kotlin/org/meshtastic/app/map/discovery/DiscoveryOsmMap.kt

@@ -122,7 +122,7 @@ fun DiscoveryOsmMap(
                         position = nodeGeoPoint
                         setAnchor(Marker.ANCHOR_CENTER, Marker.ANCHOR_BOTTOM)
                         title = node.longName ?: node.shortName ?: "Unknown"
-                        snippet = "SNR: ${node.snr} dB / RSSI: ${MetricFormatter.rssi(node.rssi)}"
+                        snippet = "SNR: ${MetricFormatter.snr(node.snr)} / RSSI: ${MetricFormatter.rssi(node.rssi)}"
 
                         val drawableId =
                             if (node.isSensorNode) {

androidApp/src/google/kotlin/org/meshtastic/app/ai/appfunctions/AppFunctionModels.kt

@@ -126,10 +126,10 @@ data class GetNodeDetailsResponse(
     val hardwareModel: String,
     /** Firmware version string. */
     val firmwareVersion: String,
-    /** Signal-to-noise ratio of strongest signal. */
-    val snr: Float,
-    /** Received signal strength indicator in dB. */
-    val rssi: Int,
+    /** Signal-to-noise ratio in dB of the strongest signal, or null if this node has no reading. */
+    val snr: Float?,
+    /** Received signal strength indicator in dBm, or null if this node has no reading. */
+    val rssi: Int?,
     /** Number of hops away from local node (-1 if unknown). */
     val hopsAway: Int,
     /** Channel index this node is on. */

androidApp/src/google/kotlin/org/meshtastic/app/map/discovery/DiscoveryGoogleMap.kt

@@ -126,7 +126,7 @@ fun DiscoveryGoogleMap(
             MarkerComposable(
                 state = rememberUpdatedMarkerState(position = nodeLatLng),
                 title = node.longName ?: node.shortName ?: "Unknown",
-                snippet = "SNR: ${node.snr} dB / RSSI: ${MetricFormatter.rssi(node.rssi)}",
+                snippet = "SNR: ${MetricFormatter.snr(node.snr)} / RSSI: ${MetricFormatter.rssi(node.rssi)}",
             ) {
                 DiscoveryMarkerChip(label = node.shortName ?: "?", color = markerColor, icon = nodeIcon)
             }

core/common/src/commonMain/kotlin/org/meshtastic/core/common/util/MetricFormatter.kt

@@ -45,7 +45,12 @@ object MetricFormatter {
 
     fun pressure(hPa: Float, decimalPlaces: Int = 1): String = "${NumberFormatter.format(hPa, decimalPlaces)} hPa"
 
-    fun snr(value: Float, decimalPlaces: Int = 1): String = "${NumberFormatter.format(value, decimalPlaces)} dB"
+    /**
+     * Formats a signal-to-noise ratio, or [UNKNOWN_VALUE] when the packet carried no measurement. 0 dB is a legitimate
+     * reading, so it must never stand in for a missing one.
+     */
+    fun snr(value: Float?, decimalPlaces: Int = 1): String =
+        if (value == null) UNKNOWN_VALUE else "${NumberFormatter.format(value, decimalPlaces)} dB"
 
     /**
      * Formats a received signal strength, or [UNKNOWN_VALUE] when the radio reported none. 0 dBm is a legitimate

core/common/src/commonTest/kotlin/org/meshtastic/core/common/util/MetricFormatterTest.kt

@@ -74,6 +74,18 @@ class MetricFormatterTest {
     @Test
     fun snr() {
         assertEquals("5.5 dB", MetricFormatter.snr(5.5f))
+        assertEquals("-12.5 dB", MetricFormatter.snr(-12.5f))
+    }
+
+    @Test
+    fun snrAbsentIsUnknown() {
+        assertEquals("—", MetricFormatter.snr(null))
+    }
+
+    @Test
+    fun snrZeroIsARealReading() {
+        // Must not render as unknown: 0 dB is a signal at the noise floor, not a missing measurement.
+        assertEquals("0.0 dB", MetricFormatter.snr(0f))
     }
 
     @Test

core/data/src/commonMain/kotlin/org/meshtastic/core/data/ai/AiFunctionProviderImpl.kt

@@ -228,8 +228,9 @@ class AiFunctionProviderImpl(
                     voltage = node.deviceMetrics.voltage,
                     hardwareModel = node.metadata?.hw_model?.name ?: "Unknown",
                     firmwareVersion = node.metadata?.firmware_version ?: "Unknown",
-                    snr = node.snr,
-                    rssi = node.rssi,
+                    // Never surface the unset sentinels to a model — Float.MAX_VALUE reads as a superb signal.
+                    snr = node.snrOrNull,
+                    rssi = node.rssiOrNull,
                     hopsAway = node.hopsAway,
                     channel = node.channel,
                     lastHeard = node.lastHeard.toLong() * MS_PER_SEC,

core/data/src/commonMain/kotlin/org/meshtastic/core/data/ai/AiFunctionResult.kt

@@ -159,10 +159,10 @@ data class NodeDetails(
     val hardwareModel: String,
     /** Firmware version string. */
     val firmwareVersion: String,
-    /** Signal-to-noise ratio of the strongest received signal. */
-    val snr: Float,
-    /** Received signal strength indicator in dB. */
-    val rssi: Int,
+    /** Signal-to-noise ratio in dB of the strongest received signal, or null if this node has no reading. */
+    val snr: Float?,
+    /** Received signal strength indicator in dBm, or null if this node has no reading. */
+    val rssi: Int?,
     /** Number of hops away from the local node (-1 if unknown). */
     val hopsAway: Int,
     /** Channel index this node is on. */

core/data/src/commonMain/kotlin/org/meshtastic/core/data/manager/MeshDataHandlerImpl.kt

@@ -44,6 +44,7 @@ import org.meshtastic.core.model.textMentionsNode
 import org.meshtastic.core.model.util.MeshDataMapper
 import org.meshtastic.core.model.util.decodeOrNull
 import org.meshtastic.core.model.util.isValidCodePoint
+import org.meshtastic.core.model.util.snrOrNull
 import org.meshtastic.core.model.util.toOneLiner
 import org.meshtastic.core.repository.AdminPacketHandler
 import org.meshtastic.core.repository.DataPair
@@ -250,7 +251,13 @@ class MeshDataHandlerImpl(
         // Only actionable beacons (carrying a channel offer) that we haven't already seen warrant a notification.
         if (beacon?.offer_channel == null) return
         val offer =
-            MeshBeaconOffer(fromNodeNum = packet.from, beacon = beacon, snr = packet.rx_snr, rssi = packet.rx_rssi)
+            MeshBeaconOffer(
+                fromNodeNum = packet.from,
+                beacon = beacon,
+                // [MeshBeaconOffer.snr] is not nullable, so absent narrows to 0f. See [snrOrNull].
+                snr = packet.snrOrNull() ?: 0f,
+                rssi = packet.rx_rssi,
+            )
         if (meshBeaconRepository.add(offer)) {
             radioInterfaceService.launchSessionWork(scope, session) {
                 notificationManager.dispatch(
@@ -583,7 +590,8 @@ class MeshDataHandlerImpl(
                     user = fromNode.user,
                     emoji = emoji,
                     timestamp = nowMillis,
-                    snr = packet.rx_snr,
+                    // [Reaction.snr] is not nullable, so absent narrows to 0f here. See [snrOrNull].
+                    snr = packet.snrOrNull() ?: 0f,
                     rssi = packet.rx_rssi,
                     hopsAway =
                     if (packet.hop_start == 0 || packet.hop_limit > packet.hop_start) {

core/data/src/commonMain/kotlin/org/meshtastic/core/data/manager/MeshMessageProcessorImpl.kt

@@ -38,6 +38,7 @@ import org.meshtastic.core.model.MeshLog
 import org.meshtastic.core.model.Node
 import org.meshtastic.core.model.util.isLora
 import org.meshtastic.core.model.util.rxTimeOrNull
+import org.meshtastic.core.model.util.snrOrNull
 import org.meshtastic.core.model.util.toOneLineString
 import org.meshtastic.core.model.util.toPIIString
 import org.meshtastic.core.repository.FromRadioPacketHandler
@@ -319,7 +320,8 @@ class MeshMessageProcessorImpl(
             lastHeard = packet.rxTimeOrNull()?.let(::clampTimestampToNow) ?: node.lastHeard,
             viaMqtt = viaMqtt,
             lastTransport = packet.transport_mechanism.value,
-            snr = if (updateRadioMetrics) packet.rx_snr else node.snr,
+            // A packet carrying no snr must not clobber the node's last real reading either.
+            snr = if (updateRadioMetrics) packet.snrOrNull() ?: node.snr else node.snr,
             // A packet carrying no rssi must not clobber the node's last real reading.
             rssi = if (updateRadioMetrics) packet.rx_rssi ?: node.rssi else node.rssi,
             hopsAway = hopsAway,

core/data/src/commonMain/kotlin/org/meshtastic/core/data/manager/NeighborInfoHandlerImpl.kt

@@ -18,6 +18,7 @@ package org.meshtastic.core.data.manager
 
 import co.touchlab.kermit.Logger
 import org.koin.core.annotation.Single
+import org.meshtastic.core.common.util.MetricFormatter
 import org.meshtastic.core.repository.NeighborInfoHandler
 import org.meshtastic.core.repository.NodeManager
 import org.meshtastic.core.repository.NodeRepository
@@ -56,7 +57,7 @@ class NeighborInfoHandlerImpl(
             ni.neighbors.joinToString("\n") { n ->
                 val user = nodeRepository.getUser(n.node_id)
                 val name = "${user.long_name} (${user.short_name})"
-                "• $name (SNR: ${n.snr})"
+                "• $name (SNR: ${MetricFormatter.snr(n.snr)})"
             }
 
         val fromUser = nodeRepository.getUser(from)