Feature: watcher clients (#4487)

* initial implementation

* make Screen aware of watchers - slightly buggy

* fix: only render focused tab to watcher

* track watcher sizes on Screen

* pad watcher output as needed

* truncate watcher sizes as needed

* render on watcher resize

* fix watcher first resize

* allow watchers to quit with esc, ctrl-c or ctrl-q

* fix: send watcher size on initial connection message

* refactor: move  padding logic to output

* fix watcher rendering after all clients disconnected

* fix watcher rendering caching issues

* crop watcher cursor when out of bounds

* remove watchers cleanly on session close

* standardize watcher messages ignoring

* add e2e test for watcher functionality

* update snapshots

* add output tests

* rustfmt

* cleanups

* docs(changelog): add PR

1 files changed, 20 insertions, 6 deletions

diff --git a/zellij-utils/src/ipc/protobuf_conversion.rs b/zellij-utils/src/ipc/protobuf_conversion.rs
index 23c9f201..658c10f3 100644
--- a/zellij-utils/src/ipc/protobuf_conversion.rs
+++ b/zellij-utils/src/ipc/protobuf_conversion.rs
@@ -1,11 +1,12 @@
 use crate::{
     client_server_contract::client_server_contract::{
-        client_to_server_msg, server_to_client_msg, ActionMsg, AttachClientMsg, BackgroundColorMsg,
-        CliPipeOutputMsg, ClientExitedMsg, ClientToServerMsg as ProtoClientToServerMsg,
-        ColorRegistersMsg, ConfigFileUpdatedMsg, ConnStatusMsg, ConnectedMsg, DetachSessionMsg,
-        ExitMsg, ExitReason as ProtoExitReason, FailedToStartWebServerMsg, FirstClientConnectedMsg,
-        ForegroundColorMsg, InputMode as ProtoInputMode, KeyMsg, KillSessionMsg, LogErrorMsg,
-        LogMsg, QueryTerminalSizeMsg, RenamedSessionMsg, RenderMsg,
+        client_to_server_msg, server_to_client_msg, ActionMsg, AttachClientMsg,
+        AttachWatcherClientMsg, BackgroundColorMsg, CliPipeOutputMsg, ClientExitedMsg,
+        ClientToServerMsg as ProtoClientToServerMsg, ColorRegistersMsg, ConfigFileUpdatedMsg,
+        ConnStatusMsg, ConnectedMsg, DetachSessionMsg, ExitMsg, ExitReason as ProtoExitReason,
+        FailedToStartWebServerMsg, FirstClientConnectedMsg, ForegroundColorMsg,
+        InputMode as ProtoInputMode, KeyMsg, KillSessionMsg, LogErrorMsg, LogMsg,
+        QueryTerminalSizeMsg, RenamedSessionMsg, RenderMsg,
         ServerToClientMsg as ProtoServerToClientMsg, StartWebServerMsg, SwitchSessionMsg,
         TerminalPixelDimensionsMsg, TerminalResizeMsg, UnblockCliPipeInputMsg,
         UnblockInputThreadMsg, WebServerStartedMsg,
@@ -68,6 +69,11 @@ impl From<ClientToServerMsg> for ProtoClientToServerMsg {
                 pane_to_focus: pane_to_focus.map(|p| p.into()),
                 is_web_client,
             }),
+            ClientToServerMsg::AttachWatcherClient { terminal_size } => {
+                client_to_server_msg::Message::AttachWatcherClient(AttachWatcherClientMsg {
+                    terminal_size: Some(terminal_size.into()),
+                })
+            },
             ClientToServerMsg::Action {
                 action,
                 terminal_id,
@@ -177,6 +183,14 @@ impl TryFrom<ProtoClientToServerMsg> for ClientToServerMsg {
                     is_web_client: attach.is_web_client,
                 })
             },
+            Some(client_to_server_msg::Message::AttachWatcherClient(attach_watcher)) => {
+                Ok(ClientToServerMsg::AttachWatcherClient {
+                    terminal_size: attach_watcher
+                        .terminal_size
+                        .ok_or_else(|| anyhow::anyhow!("Missing terminal_size"))?
+                        .try_into()?,
+                })
+            },
             Some(client_to_server_msg::Message::Action(action)) => Ok(ClientToServerMsg::Action {
                 action: action
                     .action