assistant: Fix panic when using /project (#20733)

This PR fixes a panic when using `/project` (which is staff-flagged).

We weren't initializing the `SemanticDb` global if the
`project-slash-command` feature flag was enabled.

Closes #20563.

Release Notes:

- N/A

crates/assistant/src/assistant.rs

@@ -18,6 +18,7 @@ mod terminal_inline_assistant;
 mod tool_working_set;
 mod tools;
 
+use crate::slash_command::project_command::ProjectSlashCommandFeatureFlag;
 pub use crate::slash_command_working_set::{SlashCommandId, SlashCommandWorkingSet};
 pub use crate::tool_working_set::{ToolId, ToolWorkingSet};
 pub use assistant_panel::{AssistantPanel, AssistantPanelEvent};
@@ -215,10 +216,20 @@ pub fn init(
         });
     }
 
-    if cx.has_flag::<SearchSlashCommandFeatureFlag>() {
     cx.spawn(|mut cx| {
         let client = client.clone();
         async move {
+            let is_search_slash_command_enabled = cx
+                .update(|cx| cx.wait_for_flag::<SearchSlashCommandFeatureFlag>())?
+                .await;
+            let is_project_slash_command_enabled = cx
+                .update(|cx| cx.wait_for_flag::<ProjectSlashCommandFeatureFlag>())?
+                .await;
+
+            if !is_search_slash_command_enabled && !is_project_slash_command_enabled {
+                return Ok(());
+            }
+
             let embedding_provider = CloudEmbeddingProvider::new(client.clone());
             let semantic_index = SemanticDb::new(
                 paths::embeddings_dir().join("semantic-index-db.0.mdb"),
@@ -231,7 +242,6 @@ pub fn init(
         }
     })
     .detach();
-    }
 
     context_store::init(&client.clone().into());
     prompt_library::init(cx);