fix: prevent panic when tracing subscriber already initialized

Use try_init() instead of init() for tracing subscriber setup to
gracefully handle cases where a global subscriber is already set.

This fixes a panic in the scout agent subprocess when spawned by the
research tool, where a dependency may have already initialized tracing.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

crates/g3-cli/src/agent_mode.rs

@@ -26,17 +26,17 @@ pub async fn run_agent_mode(
     use g3_core::find_incomplete_agent_session;
     use g3_core::get_agent_system_prompt;
 
-    // Initialize logging
+    // Initialize logging (use try_init to avoid panic if subscriber already set by a dependency)
     use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt, EnvFilter};
     let filter = EnvFilter::from_default_env()
         .add_directive("g3_core=info".parse().unwrap())
         .add_directive("g3_cli=info".parse().unwrap())
         .add_directive("llama_cpp=off".parse().unwrap())
         .add_directive("llama=off".parse().unwrap());
-    tracing_subscriber::registry()
+    let _ = tracing_subscriber::registry()
         .with(tracing_subscriber::fmt::layer())
         .with(filter)
-        .init();
+        .try_init();
 
     let output = SimpleOutput::new();
 

crates/g3-cli/src/utils.rs

@@ -169,8 +169,8 @@ pub fn initialize_logging(verbose: bool) {
             .add_directive("llama=off".parse().unwrap())
     };
 
-    tracing_subscriber::registry()
+    let _ = tracing_subscriber::registry()
         .with(tracing_subscriber::fmt::layer())
         .with(filter)
-        .init();
+        .try_init();
 }