Use Extension trait when registering extension context servers (#21070)

This PR updates the extension context server registration to go through
the `Extension` trait for interacting with extensions rather than going
through the `WasmHost` directly.

Release Notes:

- N/A

crates/extension/src/extension.rs

@@ -25,6 +25,10 @@ pub trait WorktreeDelegate: Send + Sync + 'static {
     async fn shell_env(&self) -> Vec<(String, String)>;
 }
 
+pub trait ProjectDelegate: Send + Sync + 'static {
+    fn worktree_ids(&self) -> Vec<u64>;
+}
+
 pub trait KeyValueStoreDelegate: Send + Sync + 'static {
     fn insert(&self, key: String, docs: String) -> Task<Result<()>>;
 }
@@ -87,6 +91,12 @@ pub trait Extension: Send + Sync + 'static {
         worktree: Option<Arc<dyn WorktreeDelegate>>,
     ) -> Result<SlashCommandOutput>;
 
+    async fn context_server_command(
+        &self,
+        context_server_id: Arc<str>,
+        project: Arc<dyn ProjectDelegate>,
+    ) -> Result<Command>;
+
     async fn suggest_docs_packages(&self, provider: Arc<str>) -> Result<Vec<String>>;
 
     async fn index_docs(

crates/extension/src/types.rs

@@ -10,6 +10,7 @@ pub use slash_command::*;
 pub type EnvVars = Vec<(String, String)>;
 
 /// A command.
+#[derive(Debug)]
 pub struct Command {
     /// The command to execute.
     pub command: String,