store restored channel immediately

When we restore a channel from a peer backup, we need to store the
channel in database as soon as possible, so we are exactly in the same
state as if the channel was restored from local db.

This applies whether we are restoring from empty or outdated local db.

src/commonMain/kotlin/fr/acinq/lightning/channel/Syncing.kt

@@ -63,7 +63,13 @@ data class Syncing(val state: ChannelStateWithCommitments, val waitForTheirReest
                             yourLastCommitmentSecret = PrivateKey(yourLastPerCommitmentSecret),
                             myCurrentPerCommitmentPoint = myCurrentPerCommitmentPoint
                         ).withChannelData(nextState.commitments.remoteChannelData)
-                        val actions = listOf<ChannelAction>(ChannelAction.Message.Send(channelReestablish))
+                        val actions = buildList {
+                            if (nextState != state) {
+                                // we just restored from backup
+                                add(ChannelAction.Storage.StoreState(nextState))
+                            }
+                            add(ChannelAction.Message.Send(channelReestablish))
+                        }
                         // now apply their reestablish message to the restored state
                         val (nextState1, actions1) = Syncing(nextState, waitForTheirReestablishMessage = false).processInternal(event)
                         Pair(nextState1, actions + actions1)

src/commonMain/kotlin/fr/acinq/lightning/io/Peer.kt

@@ -613,6 +613,7 @@ class Peer(
                                 is Try.Success -> {
                                     logger.warning { "n:$remoteNodeId restoring channelId=${msg.channelId} from peer backup" }
                                     val backup = decrypted.result
+                                    db.channels.addOrUpdateChannel(backup)
                                     val state = WaitForInit(StaticParams(nodeParams, remoteNodeId), currentTipFlow.filterNotNull().first(), onChainFeeratesFlow.filterNotNull().first())
                                     val event1 = ChannelEvent.Restore(backup as ChannelState)
                                     val (state1, actions1) = state.process(event1)