Store shared buffers on LocalWorktree

It's okay for our domain objects to model remote state. We should minimize what we need to store in the rpc::ClientState struct.

zed-rpc/src/peer.rs

@@ -51,11 +51,18 @@ pub struct Receipt<T> {
 
 pub struct TypedEnvelope<T> {
     pub sender_id: ConnectionId,
-    pub original_sender_id: Option<PeerId>,
+    original_sender_id: Option<PeerId>,
     pub message_id: u32,
     pub payload: T,
 }
 
+impl<T> TypedEnvelope<T> {
+    pub fn original_sender_id(&self) -> Result<PeerId> {
+        self.original_sender_id
+            .ok_or_else(|| anyhow!("missing original_sender_id"))
+    }
+}
+
 impl<T: RequestMessage> TypedEnvelope<T> {
     pub fn receipt(&self) -> Receipt<T> {
         Receipt {