Fix: lots of various fixes

src/engine/sequencer.rs

@@ -1007,6 +1007,7 @@ impl SequencerState {
                                 speed: speed_mult,
                                 fill,
                                 nudge_secs,
+                                sr,
                                 cc_access: self.cc_access.as_deref(),
                                 speed_key,
                                 mouse_x,
@@ -1128,6 +1129,7 @@ impl SequencerState {
                     speed: speed_mult,
                     fill,
                     nudge_secs,
+                    sr,
                     cc_access: self.cc_access.as_deref(),
                     speed_key: "",
                     mouse_x,
@@ -1266,13 +1268,16 @@ fn sequencer_loop(
 ) {
     use std::sync::atomic::Ordering;
 
-    set_realtime_priority();
+    let has_rt = set_realtime_priority();
+    if !has_rt {
+        super::realtime::warn_no_rt("sequencer");
+    }
 
     let rng: Rng = Arc::new(Mutex::new(StdRng::seed_from_u64(0)));
     let mut seq_state = SequencerState::new(variables, dict, rng, cc_access);
 
-    // Lookahead window: ~20ms expressed in beats, recomputed each tick
-    const LOOKAHEAD_SECS: f64 = 0.02;
+    // Lookahead window: 20ms normally, 40ms on Linux without RT to compensate for jitter
+    let lookahead_secs: f64 = if cfg!(target_os = "linux") && !has_rt { 0.04 } else { 0.02 };
     // Wake cadence: how long to sleep between scheduling passes
     const WAKE_INTERVAL: std::time::Duration = std::time::Duration::from_millis(3);
 
@@ -1302,7 +1307,7 @@ fn sequencer_loop(
         let tempo = state.tempo();
 
         let lookahead_beats = if tempo > 0.0 {
-            LOOKAHEAD_SECS * tempo / 60.0
+            lookahead_secs * tempo / 60.0
         } else {
             0.0
         };