Fetch older messages when scrolling up in the chat message list

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

zrpc/proto/zed.proto

@@ -32,6 +32,8 @@ message Envelope {
         SendChannelMessage send_channel_message = 27;
         SendChannelMessageResponse send_channel_message_response = 28;
         ChannelMessageSent channel_message_sent = 29;
+        GetChannelMessages get_channel_messages = 30;
+        GetChannelMessagesResponse get_channel_messages_response = 31;
     }
 }
 
@@ -130,6 +132,7 @@ message JoinChannel {
 
 message JoinChannelResponse {
     repeated ChannelMessage messages = 1;
+    bool done = 2;
 }
 
 message LeaveChannel {
@@ -159,6 +162,16 @@ message ChannelMessageSent {
     ChannelMessage message = 2;
 }
 
+message GetChannelMessages {
+    uint64 channel_id = 1;
+    uint64 before_message_id = 2;
+}
+
+message GetChannelMessagesResponse {
+    repeated ChannelMessage messages = 1;
+    bool done = 2;
+}
+
 // Entities
 
 message Peer {

zrpc/src/proto.rs

@@ -125,6 +125,8 @@ messages!(
     ChannelMessageSent,
     CloseBuffer,
     CloseWorktree,
+    GetChannelMessages,
+    GetChannelMessagesResponse,
     GetChannels,
     GetChannelsResponse,
     GetUsers,
@@ -158,6 +160,7 @@ request_messages!(
     (SaveBuffer, BufferSaved),
     (ShareWorktree, ShareWorktreeResponse),
     (SendChannelMessage, SendChannelMessageResponse),
+    (GetChannelMessages, GetChannelMessagesResponse),
 );
 
 entity_messages!(