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/knowledge/graph.rs

@@ -268,7 +268,17 @@ pub fn filter_by_access(
             .entities
             .get(&target_id)
             .and_then(|k| k.known_attributes.get("faction_id"))
-            .and_then(|v| v.parse::<u64>().ok())
+            .and_then(|v| match v.parse::<u64>() {
+                Ok(id) => Some(id),
+                Err(_) => {
+                    tracing::warn!(
+                        target_id = target_id.0,
+                        value = %v,
+                        "FactionOnly: non-numeric faction_id attribute, denying access"
+                    );
+                    None
+                }
+            })
             .is_some_and(|id| id == faction_id.0),
 
         // RelationshipGated: observer must have a relationship score >= threshold.
@@ -713,4 +723,27 @@ mod tests {
             "FactionOnly must block when faction attribute is not known"
         );
     }
+
+    #[test]
+    fn filter_by_access_faction_only_passes_with_matching_faction() {
+        let observer = StableId(1);
+        let target = StableId(2);
+        let mut kg = KnowledgeGraph::new();
+
+        // Observer knows target's faction via known_attributes
+        kg.observe_entity(target, make_position(5, 5), 10);
+        kg.entities
+            .get_mut(&target)
+            .unwrap()
+            .known_attributes
+            .insert("faction_id".into(), "99".into());
+
+        let faction = StableId(99);
+        let rule = ObserverAccess::FactionOnly(faction);
+
+        assert!(
+            filter_by_access(observer, target, &rule, &kg),
+            "FactionOnly must pass when observer knows the matching faction_id"
+        );
+    }
 }