feat: add FTS5 full-text message search

Leverage Room 3.0.0-alpha04's FTS5 support to enable searching
message history. Uses external content table backed by Packet entity.

Schema changes (migration 38→39):
- Add message_text column to Packet entity
- Create PacketFts virtual table with FTS5 index on message_text
- Content triggers auto-sync FTS index on INSERT/UPDATE/DELETE

Search stack:
- PacketDao: searchMessages/searchMessagesInConversation queries
- DatabaseManager: backfillSearchIndexIfNeeded on DB switch
- PacketRepository: searchMessages with FTS query sanitization
- MessageViewModel: debounced search (300ms, min 2 chars)
- MessageSearchBar: M3 TopAppBar replacement pattern

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

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

@@ -149,6 +149,9 @@ open class DatabaseManager(
         // One-time cleanup: remove legacy DB if present and not active
         managerScope.launch(dispatchers.io) { cleanupLegacyDbIfNeeded(activeDbName = dbName) }
 
+        // Backfill FTS search index for any text messages missing messageText
+        managerScope.launch(dispatchers.io) { backfillSearchIndexIfNeeded(db) }
+
         Logger.i { "Switched active DB to ${anonymizeDbName(dbName)} for address ${anonymizeAddress(address)}" }
     }
 
@@ -290,6 +293,26 @@ open class DatabaseManager(
         datastore.edit { it[legacyCleanedKey] = true }
     }
 
+    /**
+     * Backfills [Packet.messageText] for existing text-message packets that predate the FTS5 schema. Iterates packets
+     * with empty messageText, extracts text from [DataPacket], and updates. Finally rebuilds the FTS index so search
+     * covers historical messages.
+     */
+    private suspend fun backfillSearchIndexIfNeeded(db: MeshtasticDatabase) {
+        val packetDao = db.packetDao()
+        val packets = packetDao.getAllUserPacketsForMigration()
+        val toUpdate = packets.filter { it.messageText.isEmpty() && it.data.text != null }
+        if (toUpdate.isEmpty()) return
+
+        Logger.i { "Backfilling FTS search index for ${toUpdate.size} messages" }
+        for (packet in toUpdate) {
+            val text = packet.data.text ?: continue
+            packetDao.updateMessageText(packet.uuid, text)
+        }
+        packetDao.rebuildFtsIndex()
+        Logger.i { "FTS search index backfill complete" }
+    }
+
     /** Closes all open databases and cancels background work. */
     fun close() {
         managerScope.cancel()

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

@@ -39,6 +39,7 @@ import org.meshtastic.core.database.entity.MetadataEntity
 import org.meshtastic.core.database.entity.MyNodeEntity
 import org.meshtastic.core.database.entity.NodeEntity
 import org.meshtastic.core.database.entity.Packet
+import org.meshtastic.core.database.entity.PacketFts
 import org.meshtastic.core.database.entity.QuickChatAction
 import org.meshtastic.core.database.entity.ReactionEntity
 import org.meshtastic.core.database.entity.TracerouteNodePositionEntity
@@ -49,6 +50,7 @@ import org.meshtastic.core.database.entity.TracerouteNodePositionEntity
         MyNodeEntity::class,
         NodeEntity::class,
         Packet::class,
+        PacketFts::class,
         ContactSettings::class,
         MeshLog::class,
         QuickChatAction::class,
@@ -95,8 +97,9 @@ import org.meshtastic.core.database.entity.TracerouteNodePositionEntity
         AutoMigration(from = 35, to = 36),
         AutoMigration(from = 36, to = 37),
         AutoMigration(from = 37, to = 38),
+        AutoMigration(from = 38, to = 39),
     ],
-    version = 38,
+    version = 39,
     exportSchema = true,
 )
 @androidx.room3.ConstructedBy(MeshtasticDatabaseConstructor::class)
@@ -120,7 +123,9 @@ abstract class MeshtasticDatabase : RoomDatabase() {
     companion object {
         /** Configures a [RoomDatabase.Builder] with standard settings for this project. */
         fun <T : RoomDatabase> RoomDatabase.Builder<T>.configureCommon(): RoomDatabase.Builder<T> =
-            this.fallbackToDestructiveMigration(dropAllTables = false).setQueryCoroutineContext(ioDispatcher)
+            this.fallbackToDestructiveMigration(dropAllTables = false)
+                .setMultipleConnectionPool(maxNumOfReaders = 4, maxNumOfWriters = 1)
+                .setQueryCoroutineContext(ioDispatcher)
     }
 }
 

core/database/src/commonMain/kotlin/org/meshtastic/core/database/dao/PacketDao.kt

@@ -547,4 +547,29 @@ interface PacketDao {
         "UPDATE packet SET filtered = :filtered WHERE (myNodeNum = 0 OR myNodeNum = (SELECT myNodeNum FROM my_node)) AND data LIKE :senderIdPattern",
     )
     suspend fun updateFilteredBySender(senderIdPattern: String, filtered: Boolean)
+
+    // region ── FTS5 Search ──
+
+    @Query(
+        "SELECT packet.* FROM packet JOIN packet_fts ON packet.rowid = packet_fts.rowid " +
+            "WHERE packet_fts MATCH :query AND packet.myNodeNum = (SELECT myNodeNum FROM my_node) " +
+            "ORDER BY packet.received_time DESC LIMIT 100",
+    )
+    suspend fun searchMessages(query: String): List<Packet>
+
+    @Query(
+        "SELECT packet.* FROM packet JOIN packet_fts ON packet.rowid = packet_fts.rowid " +
+            "WHERE packet_fts MATCH :query AND packet.contact_key = :contactKey " +
+            "AND packet.myNodeNum = (SELECT myNodeNum FROM my_node) " +
+            "ORDER BY packet.received_time DESC LIMIT 100",
+    )
+    suspend fun searchMessagesInConversation(query: String, contactKey: String): List<Packet>
+
+    @Query("UPDATE packet SET message_text = :text WHERE uuid = :uuid")
+    suspend fun updateMessageText(uuid: Long, text: String)
+
+    @Query("INSERT INTO packet_fts(packet_fts) VALUES('rebuild')")
+    suspend fun rebuildFtsIndex()
+
+    // endregion
 }

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

@@ -94,6 +94,7 @@ data class Packet(
     @ColumnInfo(name = "hopsAway", defaultValue = "-1") val hopsAway: Int = -1,
     @ColumnInfo(name = "sfpp_hash") val sfpp_hash: ByteString? = null,
     @ColumnInfo(name = "filtered", defaultValue = "0") val filtered: Boolean = false,
+    @ColumnInfo(name = "message_text", defaultValue = "") val messageText: String = "",
 ) {
     companion object {
         const val RELAY_NODE_SUFFIX_MASK = 0xFF

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

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2026 Meshtastic LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.meshtastic.core.database.entity
+
+import androidx.room3.ColumnInfo
+import androidx.room3.Entity
+import androidx.room3.Fts5
+
+/**
+ * FTS5 virtual table that mirrors [Packet.messageText] for full-text search. Room auto-generates INSERT/UPDATE/DELETE
+ * triggers to keep this table in sync with the content entity ([Packet]).
+ */
+@Fts5(contentEntity = Packet::class)
+@Entity(tableName = "packet_fts")
+data class PacketFts(@ColumnInfo(name = "message_text") val messageText: String)