Cover reconnect delivery and the trim

The reconnect case fails on main: a peer served once, then sent mail while
away, receives nothing when it returns.

The other three hold the properties the fix must not break — a reconnect
with no new mail still sends nothing, the trim leaves the cap in place
rather than emptying it, and a recently delivered message is not the one
forgotten.

app/src/test/kotlin/com/bitchat/android/mesh/StoreForwardManagerTest.kt

@@ -0,0 +1,124 @@
+package com.bitchat.android.mesh
+
+import com.bitchat.android.protocol.BitchatPacket
+import com.bitchat.android.protocol.MessageType
+import kotlinx.coroutines.runBlocking
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * Store-and-forward exists so mail for an offline peer is handed over when it
+ * comes back. Two things stopped that working.
+ */
+class StoreForwardManagerTest {
+    private val manager = StoreForwardManager()
+    private val delegate = RecordingDelegate()
+
+    init {
+        manager.delegate = delegate
+    }
+
+    @After
+    fun tearDown() = manager.shutdown()
+
+    @Test
+    fun `mail cached after a peer was served is delivered on the next reconnect`() = runBlocking {
+        // First contact: nothing held, peer is marked as served.
+        manager.sendCachedMessages(PEER)
+        waitForDelivery()
+        assertEquals(0, delegate.sent.size)
+
+        // Peer goes away; a message is queued for it.
+        manager.cacheMessage(privateMessage("m-1"), "m-1")
+
+        // It comes back. Before this fix the send was refused outright,
+        // because nothing ever removed the peer from the already-sent latch,
+        // and the message sat in the cache until it aged out.
+        manager.sendCachedMessages(PEER)
+        waitForDelivery()
+
+        assertEquals(1, delegate.sent.size)
+    }
+
+    @Test
+    fun `a peer with nothing new is still not re-sent the same batch`() {
+        // The latch has to keep working, or every reconnect replays whatever
+        // is still cached.
+        manager.cacheMessage(privateMessage("m-1"), "m-1")
+        manager.sendCachedMessages(PEER)
+        waitForDelivery()
+        val afterFirst = delegate.sent.size
+
+        manager.sendCachedMessages(PEER)
+        waitForDelivery()
+
+        assertEquals("A second connect with no new mail must send nothing more", afterFirst, delegate.sent.size)
+    }
+
+    @Test
+    fun `trimming delivery state drops the oldest rather than all of it`() {
+        repeat(StoreForwardManager.MAX_DELIVERED_MESSAGE_IDS + 50) { index ->
+            manager.markMessageAsDelivered("delivered-$index")
+        }
+
+        manager.forceCleanup()
+
+        // Wiping the set bounded memory by forgetting which messages had
+        // already been handed over.
+        val debug = manager.getDebugInfo()
+        assertTrue(
+            "Delivery state must be trimmed to the cap, not emptied: $debug",
+            debug.contains("Delivered Messages: ${StoreForwardManager.MAX_DELIVERED_MESSAGE_IDS}")
+        )
+    }
+
+    @Test
+    fun `the newest delivery records are the ones kept`() {
+        repeat(StoreForwardManager.MAX_DELIVERED_MESSAGE_IDS + 10) { index ->
+            manager.markMessageAsDelivered("delivered-$index")
+        }
+        manager.forceCleanup()
+
+        // A message delivered a moment ago must not be the one forgotten.
+        manager.cacheMessage(privateMessage("delivered-${StoreForwardManager.MAX_DELIVERED_MESSAGE_IDS + 9}"),
+            "delivered-${StoreForwardManager.MAX_DELIVERED_MESSAGE_IDS + 9}")
+        manager.sendCachedMessages(PEER)
+        waitForDelivery()
+
+        assertEquals("An already-delivered message must not be queued again", 0, delegate.sent.size)
+    }
+
+    private fun waitForDelivery() {
+        // sendCachedMessages dispatches on its own scope with a 10ms/message
+        // stagger; this is well clear of the single-message case under test.
+        Thread.sleep(300)
+    }
+
+    private fun privateMessage(id: String): BitchatPacket = BitchatPacket(
+        version = 1u,
+        type = MessageType.MESSAGE.value,
+        senderID = "1111222233334444".hexToBytes(),
+        recipientID = PEER.toByteArray(),
+        timestamp = 1u,
+        payload = id.toByteArray(),
+        ttl = 7u
+    )
+
+    private class RecordingDelegate : StoreForwardManagerDelegate {
+        val sent = mutableListOf<BitchatPacket>()
+        override fun isFavorite(peerID: String) = false
+        override fun isPeerOnline(peerID: String) = false
+        override fun sendPacket(packet: BitchatPacket) {
+            synchronized(sent) { sent.add(packet) }
+        }
+    }
+
+    private fun String.hexToBytes(): ByteArray =
+        chunked(2).map { it.toInt(16).toByte() }.toByteArray()
+
+    private companion object {
+        const val PEER = "aaaabbbbccccdddd"
+    }
+}