fix(simulation): address PR #42 review — 8 items from Hoshe and Tyre

1. Sound producers: document empty v0.1 pipeline explicitly (critical)
2. Routine tests: add ActiveSim to 3 tests that passed trivially
3. Rename _observer_pos → observer_pos (used at line 191)
4. Add FactionOnly positive test case (matching faction_id)
5. Fix stale doc comment "Current: 9" → 10 in ObserverSnapshot
6. Remove orphaned SimulationTier/LastInteraction/ScopeTag types
7. Add tracing::warn on FactionOnly non-numeric parse failure
8. Document Medium-range occlusion gap as TODO in audible_at
9. Insert SoundEventQueue in observer test setup_world

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/simulation/sound.rs

@@ -83,7 +83,9 @@ impl SoundEvent {
     }
 
     /// Whether this sound is audible at `listener_pos`.
-    /// Simple tile-distance check; occlusion is a future concern (D-018 note).
+    /// Simple tile-distance check — no wall/obstruction occlusion.
+    /// TODO: Medium-range sounds should be attenuated or blocked by walls
+    /// per D-018. Requires LOS integration (backlog — not in v0.1 scope).
     pub fn audible_at(&self, listener_pos: &TilePosition) -> bool {
         let ceil = Self::max_range_tiles(self.range);
         let dx = (self.x.floor() as i32).abs_diff(listener_pos.x);
@@ -157,6 +159,13 @@ impl SoundEventQueue {
 /// Runs each tick after movement/monologue/dialogue systems have fired.
 /// Removes the emitter component after draining. Ordering: after movement,
 /// before `compute_observer_snapshot`.
+///
+/// NOTE: v0.1 has no sound producers — no system currently inserts
+/// SoundEventEmitter components. The pipeline (emitter → queue → snapshot →
+/// client bridge) is fully wired but produces zero events at runtime.
+/// Sound producers (Footstep on movement, Voice on dialogue) are backlog
+/// scope and will be added when the client audio bus routing (#125) is
+/// integrated. See D-018 for the sound model specification.
 pub fn collect_sound_events(
     mut commands: Commands,
     mut queue: ResMut<SoundEventQueue>,