assistant: Allow guests to create new contexts on the host (#15439)

This PR extends collaboration in the Assistant to allow guests to create
new contexts on the host when collaborating.

Release Notes:

- N/A

crates/proto/proto/zed.proto

@@ -199,7 +199,7 @@ message Envelope {
         StreamCompleteWithLanguageModel stream_complete_with_language_model = 228;
         StreamCompleteWithLanguageModelResponse stream_complete_with_language_model_response = 229;
         CountLanguageModelTokens count_language_model_tokens = 230;
-        CountLanguageModelTokensResponse count_language_model_tokens_response = 231; // current max
+        CountLanguageModelTokensResponse count_language_model_tokens_response = 231;
         GetCachedEmbeddings get_cached_embeddings = 189;
         GetCachedEmbeddingsResponse get_cached_embeddings_response = 190;
         ComputeEmbeddings compute_embeddings = 191;
@@ -255,6 +255,8 @@ message Envelope {
         AdvertiseContexts advertise_contexts = 211;
         OpenContext open_context = 212;
         OpenContextResponse open_context_response = 213;
+        CreateContext create_context = 232;
+        CreateContextResponse create_context_response = 233; // current max
         UpdateContext update_context = 214;
         SynchronizeContexts synchronize_contexts = 215;
         SynchronizeContextsResponse synchronize_contexts_response = 216;
@@ -2381,6 +2383,15 @@ message OpenContextResponse {
     Context context = 1;
 }
 
+message CreateContext {
+    uint64 project_id = 1;
+}
+
+message CreateContextResponse {
+    string context_id = 1;
+    Context context = 2;
+}
+
 message UpdateContext {
     uint64 project_id = 1;
     string context_id = 2;

crates/proto/src/proto.rs

@@ -398,6 +398,8 @@ messages!(
     (AdvertiseContexts, Foreground),
     (OpenContext, Foreground),
     (OpenContextResponse, Foreground),
+    (CreateContext, Foreground),
+    (CreateContextResponse, Foreground),
     (UpdateContext, Foreground),
     (SynchronizeContexts, Foreground),
     (SynchronizeContextsResponse, Foreground),
@@ -523,6 +525,7 @@ request_messages!(
     (RenameDevServer, Ack),
     (RestartLanguageServers, Ack),
     (OpenContext, OpenContextResponse),
+    (CreateContext, CreateContextResponse),
     (SynchronizeContexts, SynchronizeContextsResponse),
     (AddWorktree, AddWorktreeResponse),
 );
@@ -589,6 +592,7 @@ entity_messages!(
     LspExtExpandMacro,
     AdvertiseContexts,
     OpenContext,
+    CreateContext,
     UpdateContext,
     SynchronizeContexts,
 );