fix: session sim tests expect .marker.main not .marker

Way markers are now scoped per-agent: .marker.{agent_id} where
agent_id defaults to "main". The session sim tests were checking
for the old unscoped .marker path.

10/10 scenarios pass. make test, make setup, make test-sim all green.

Author: aaronsb

tools/ways-cli/tests/session_sim.rs

@@ -199,15 +199,15 @@ fn clean_markers(session_id: &str) {
 // ── Assertion helpers ──────────────────────────────────────────
 
 fn assert_marker_exists(way_id: &str, session_id: &str) {
-    let path = format!("{}/{session_id}/ways/{way_id}/.marker", sessions_root());
+    let path = format!("{}/{session_id}/ways/{way_id}/.marker.main", sessions_root());
     assert!(
         Path::new(&path).exists(),
         "Expected marker for '{way_id}' but it doesn't exist at {path}"
     );
 }
 
 fn assert_marker_absent(way_id: &str, session_id: &str) {
-    let path = format!("{}/{session_id}/ways/{way_id}/.marker", sessions_root());
+    let path = format!("{}/{session_id}/ways/{way_id}/.marker.main", sessions_root());
     assert!(
         !Path::new(&path).exists(),
         "Expected NO marker for '{way_id}' but found one at {path}"