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

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

core/database/src/commonMain/kotlin/org/meshtastic/core/database/MeshtasticDatabase.kt

@@ -130,8 +130,9 @@ import org.meshtastic.core.database.entity.TracerouteNodePositionEntity
         AutoMigration(from = 48, to = 49),
         AutoMigration(from = 49, to = 50),
         AutoMigration(from = 50, to = 51),
+        AutoMigration(from = 51, to = 52),
     ],
-    version = 51,
+    version = 52,
     exportSchema = true,
 )
 @androidx.room3.ConstructedBy(MeshtasticDatabaseConstructor::class)

core/database/src/commonMain/kotlin/org/meshtastic/core/database/entity/Packet.kt

@@ -102,7 +102,8 @@ data class Packet(
     @ColumnInfo(name = "data") val data: DataPacket,
     @ColumnInfo(name = "packet_id", defaultValue = "0") val packetId: Int = 0,
     @ColumnInfo(name = "routing_error", defaultValue = "-1") var routingError: Int = -1,
-    @ColumnInfo(name = "snr", defaultValue = "0") val snr: Float = 0f,
+    /** Null when the packet carried no snr. Rows written before schema 52 store 0 for both absent and 0 dB. */
+    @ColumnInfo(name = "snr") val snr: Float? = null,
     /** Null when the radio reported no rssi. Rows written before schema 51 store 0 for both absent and 0 dBm. */
     @ColumnInfo(name = "rssi") val rssi: Int? = null,
     @ColumnInfo(name = "hopsAway", defaultValue = "-1") val hopsAway: Int = -1,
@@ -162,7 +163,8 @@ data class ReactionEntity(
     @ColumnInfo(name = "user_id") val userId: String,
     val emoji: String,
     val timestamp: Long,
-    @ColumnInfo(name = "snr", defaultValue = "0") val snr: Float = 0f,
+    /** Null when the packet carried no snr. Rows written before schema 52 store 0 for both absent and 0 dB. */
+    @ColumnInfo(name = "snr") val snr: Float? = null,
     /** Null when the radio reported no rssi. Rows written before schema 51 store 0 for both absent and 0 dBm. */
     @ColumnInfo(name = "rssi") val rssi: Int? = null,
     @ColumnInfo(name = "hopsAway", defaultValue = "-1") val hopsAway: Int = -1,

core/database/src/jvmTest/kotlin/org/meshtastic/core/database/MeshtasticDatabaseMigrationTest.kt

@@ -108,6 +108,29 @@ class MeshtasticDatabaseMigrationTest {
         }
     }
 
+    @Test
+    fun snrColumnsGoNullableWithoutLosingRows() = runTest {
+        helper.createDatabase(SNR_NULLABLE_FROM_VERSION).use { connection ->
+            connection.execSQL(
+                "INSERT INTO packet (uuid, myNodeNum, port_num, contact_key, received_time, read, data, snr, rssi) " +
+                    "VALUES (1, 42, 1, '0^all', 1000, 1, '{}', 0.0, -70)",
+            )
+            connection.execSQL(
+                "INSERT INTO reactions (myNodeNum, reply_id, user_id, emoji, timestamp, snr, rssi) " +
+                    "VALUES (42, 7, '!abc', 'X', 2000, -12.5, -70)",
+            )
+        }
+
+        helper.runMigrationsAndValidate(SNR_NULLABLE_TO_VERSION, emptyList()).use { connection ->
+            // A stored 0 dB must survive the recreate as 0, not become NULL: it is a real reading.
+            assertEquals(listOf("0.0"), queryColumn(connection, "SELECT snr FROM packet"))
+            assertEquals(listOf("-12.5"), queryColumn(connection, "SELECT snr FROM reactions"))
+            // A NULL is now storable where the column was previously NOT NULL DEFAULT 0.
+            connection.execSQL("UPDATE packet SET snr = NULL WHERE uuid = 1")
+            assertEquals(listOf(null), queryColumn(connection, "SELECT snr FROM packet"))
+        }
+    }
+
     /** Reads one column of every row as a string, with SQL NULL surfaced as Kotlin null. */
     private fun queryColumn(connection: SQLiteConnection, sql: String): List<String?> =
         connection.prepare(sql).use { statement ->
@@ -130,5 +153,7 @@ class MeshtasticDatabaseMigrationTest {
         const val EARLIEST_SCHEMA_VERSION = 3
         const val RSSI_NULLABLE_FROM_VERSION = 50
         const val RSSI_NULLABLE_TO_VERSION = 51
+        const val SNR_NULLABLE_FROM_VERSION = 51
+        const val SNR_NULLABLE_TO_VERSION = 52
     }
 }