windows: Add support for fetching shell environment in remote projects (#39831)

Closes #39216

Note that this affects all platforms, I'm just using the prefix to make
auto-cherry-picking easier.

Release Notes:

- Fixed shell commands run by agents failing to find installed programs
in some cases.

crates/remote_server/src/headless_project.rs

@@ -50,6 +50,7 @@ pub struct HeadlessProject {
     pub languages: Arc<LanguageRegistry>,
     pub extensions: Entity<HeadlessExtensionStore>,
     pub git_store: Entity<GitStore>,
+    pub environment: Entity<ProjectEnvironment>,
     // Used mostly to keep alive the toolchain store for RPC handlers.
     // Local variant is used within LSP store, but that's a separate entity.
     pub _toolchain_store: Entity<ToolchainStore>,
@@ -199,7 +200,7 @@ impl HeadlessProject {
             let mut agent_server_store = AgentServerStore::local(
                 node_runtime.clone(),
                 fs.clone(),
-                environment,
+                environment.clone(),
                 http_client.clone(),
                 cx,
             );
@@ -255,6 +256,7 @@ impl HeadlessProject {
         session.add_entity_request_handler(Self::handle_open_new_buffer);
         session.add_entity_request_handler(Self::handle_find_search_candidates);
         session.add_entity_request_handler(Self::handle_open_server_settings);
+        session.add_entity_request_handler(Self::handle_get_directory_environment);
         session.add_entity_message_handler(Self::handle_toggle_lsp_logs);
 
         session.add_entity_request_handler(BufferStore::handle_update_buffer);
@@ -295,6 +297,7 @@ impl HeadlessProject {
             languages,
             extensions,
             git_store,
+            environment,
             _toolchain_store: toolchain_store,
         }
     }
@@ -764,6 +767,26 @@ impl HeadlessProject {
 
         Ok(proto::GetProcessesResponse { processes })
     }
+
+    async fn handle_get_directory_environment(
+        this: Entity<Self>,
+        envelope: TypedEnvelope<proto::GetDirectoryEnvironment>,
+        mut cx: AsyncApp,
+    ) -> Result<proto::DirectoryEnvironment> {
+        let shell = task::Shell::from_proto(envelope.payload.shell.context("missing shell")?)?;
+        let directory = PathBuf::from(envelope.payload.directory);
+        let environment = this
+            .update(&mut cx, |this, cx| {
+                this.environment.update(cx, |environment, cx| {
+                    environment.get_local_directory_environment(&shell, directory.into(), cx)
+                })
+            })?
+            .await
+            .context("failed to get directory environment")?
+            .into_iter()
+            .collect();
+        Ok(proto::DirectoryEnvironment { environment })
+    }
 }
 
 fn prompt_to_proto(