temporarily disable codebase_fast_start

it seems the llm gets "lazy" and assumes all the tool
calls meant it's done most of the work.
I need to revise this approach.

crates/g3-cli/src/lib.rs

@@ -204,6 +204,8 @@ use rustyline::DefaultEditor;
 use sha2::{Digest, Sha256};
 use std::path::Path;
 use std::path::PathBuf;
+use std::process::exit;
+use sha2::{Digest, Sha256};
 use tokio_util::sync::CancellationToken;
 use tracing::{error, info};
 
@@ -325,6 +327,10 @@ pub async fn run() -> Result<()> {
         .await;
     }
 
+    if cli.codebase_fast_start.is_some() {
+        print!("codebase_fast_start is temporarily disabled.");
+        exit(1);
+    }
     // Otherwise, continue with normal mode
 
     // Only initialize logging if not in retro mode