start contextuel : am start sans argument lance l'agent par defaut du projet (issue #30) - resolution pure resolve_start_target, restart identique, REPL sans agent obligatoire

tests/instrumentation_test.rs

@@ -100,7 +100,7 @@ fn start_and_stop_emit_a_matching_pair() {
     app.state.set(&entry).unwrap();
 
     let opts = StartArgs {
-        agent: "sleeper".to_string(),
+        agent: Some("sleeper".to_string()),
         background: true,
         ..Default::default()
     };

tests/projects_test.rs

@@ -75,5 +75,18 @@ projects:
     );
     // Hors du projet : pas de profil.
     assert!(projects::default_agent_for_dir(&app, &std::env::temp_dir()).is_none());
+
+    // am start contextuel (issue #30) : résolution pure sans changer de cwd.
+    use agent_manager::commands::run_cmd;
+    assert_eq!(
+        run_cmd::resolve_start_target(&app, &sub, None).unwrap(),
+        "claude-code"
+    );
+    assert_eq!(
+        run_cmd::resolve_start_target(&app, &sub, Some("aider")).unwrap(),
+        "aider"
+    );
+    assert!(run_cmd::resolve_start_target(&app, &std::env::temp_dir(), None).is_err());
+
     let _ = std::fs::remove_dir_all(&dir);
 }