Lay the groundwork for collaborating on assistant panel (#13991)

This pull request introduces collaboration for the assistant panel by
turning `Context` into a CRDT. `ContextStore` is responsible for sending
and applying operations, as well as synchronizing missed changes while
the connection was lost.

Contexts are shared on a per-project basis, and only the host can share
them for now. Shared contexts can be accessed via the `History` tab in
the assistant panel.

<img width="1819" alt="image"
src="https://github.com/zed-industries/zed/assets/482957/c7ae46d2-cde3-4b03-b74a-6e9b1555c154">


Please note that this doesn't implement following yet, which is
scheduled for a subsequent pull request.

Release Notes:

- N/A

crates/text/src/network.rs

@@ -1,12 +1,15 @@
+use std::fmt::Debug;
+
 use clock::ReplicaId;
+use collections::{BTreeMap, HashSet};
 
 pub struct Network<T: Clone, R: rand::Rng> {
-    inboxes: std::collections::BTreeMap<ReplicaId, Vec<Envelope<T>>>,
-    all_messages: Vec<T>,
+    inboxes: BTreeMap<ReplicaId, Vec<Envelope<T>>>,
+    disconnected_peers: HashSet<ReplicaId>,
     rng: R,
 }
 
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 struct Envelope<T: Clone> {
     message: T,
 }
@@ -14,8 +17,8 @@ struct Envelope<T: Clone> {
 impl<T: Clone, R: rand::Rng> Network<T, R> {
     pub fn new(rng: R) -> Self {
         Network {
-            inboxes: Default::default(),
-            all_messages: Vec::new(),
+            inboxes: BTreeMap::default(),
+            disconnected_peers: HashSet::default(),
             rng,
         }
     }
@@ -24,6 +27,24 @@ impl<T: Clone, R: rand::Rng> Network<T, R> {
         self.inboxes.insert(id, Vec::new());
     }
 
+    pub fn disconnect_peer(&mut self, id: ReplicaId) {
+        self.disconnected_peers.insert(id);
+        self.inboxes.get_mut(&id).unwrap().clear();
+    }
+
+    pub fn reconnect_peer(&mut self, id: ReplicaId, replicate_from: ReplicaId) {
+        assert!(self.disconnected_peers.remove(&id));
+        self.replicate(replicate_from, id);
+    }
+
+    pub fn is_disconnected(&self, id: ReplicaId) -> bool {
+        self.disconnected_peers.contains(&id)
+    }
+
+    pub fn contains_disconnected_peers(&self) -> bool {
+        !self.disconnected_peers.is_empty()
+    }
+
     pub fn replicate(&mut self, old_replica_id: ReplicaId, new_replica_id: ReplicaId) {
         self.inboxes
             .insert(new_replica_id, self.inboxes[&old_replica_id].clone());
@@ -34,8 +55,13 @@ impl<T: Clone, R: rand::Rng> Network<T, R> {
     }
 
     pub fn broadcast(&mut self, sender: ReplicaId, messages: Vec<T>) {
+        // Drop messages from disconnected peers.
+        if self.disconnected_peers.contains(&sender) {
+            return;
+        }
+
         for (replica, inbox) in self.inboxes.iter_mut() {
-            if *replica != sender {
+            if *replica != sender && !self.disconnected_peers.contains(replica) {
                 for message in &messages {
                     // Insert one or more duplicates of this message, potentially *before* the previous
                     // message sent by this peer to simulate out-of-order delivery.
@@ -51,7 +77,6 @@ impl<T: Clone, R: rand::Rng> Network<T, R> {
                 }
             }
         }
-        self.all_messages.extend(messages);
     }
 
     pub fn has_unreceived(&self, receiver: ReplicaId) -> bool {

crates/text/src/text.rs

@@ -1265,6 +1265,10 @@ impl Buffer {
         }
     }
 
+    pub fn has_deferred_ops(&self) -> bool {
+        !self.deferred_ops.is_empty()
+    }
+
     pub fn peek_undo_stack(&self) -> Option<&HistoryEntry> {
         self.history.undo_stack.last()
     }