fix(simulation): address PR #39 review — 3 warnings + 6 suggestions

Warnings fixed:
- contraband.rs: scan event now always emits even when NPC already
  knows (was skipped by early `continue`). Contract matches doc.
- test_world/mod.rs: ScanEventBuffer added to player spawn bundle
  so check_contraband_scan doesn't silently no-op in gauntlet mode.
- npc/mod.rs → simulation/mod.rs: moved check_contraband_scan
  registration to SimulationPlugin (operates on player inventory and
  snapshot pipeline, consistent with process_talk_interaction).

Suggestions addressed:
- cross_room_transitions.rs T1: clarified standalone position vs
  constants.rs observer position in comment.
- dialogue.rs: Vec<&str> dedup replaced with BTreeSet<&str> for
  deterministic iteration (project convention).
- contraband.rs: added test for multiple simultaneous ScanAuthority
  NPCs in range (564 tests total).
- dialogue.rs: doc-comment on relationship_to_trust explaining
  KnowledgeConfidence ordering and Suspects default.
- cross_room_transitions.rs T5: noted direct KG API usage vs full
  perception system.
- sprint_gauntlet.rs: documented intentional Contentment { level: 0 }.
- content_scaling.rs: noted GAUNTLET_NPC_COUNT is manually maintained.
- contraband.rs: doc-comment on cross-plugin registration rationale.

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

server/src/simulation/dialogue.rs

@@ -15,6 +15,8 @@
 //! - Writes DialogueResponseBuffer for snapshot inclusion
 //! - Uses SimRng for deterministic weighted random selection
 
+use std::collections::BTreeSet;
+
 use bevy_ecs::prelude::*;
 use rand::Rng;
 
@@ -177,6 +179,19 @@ pub fn available_access_tiers(relationship: RelationshipState) -> Vec<AccessTier
 ///   - Secret: Friendly + KnowsDetails+ (deep rapport + actionable knowledge)
 ///   - Real: (Friendly or Known) + KnowsOf+ (rapport + substantive knowledge)
 ///   - Surface: everything else (baseline, always available)
+/// Map relationship + knowledge confidence to trust tier (D-075).
+///
+/// Trust tier gates which dialogue lines are available. The layered gate
+/// requires BOTH sufficient relationship AND sufficient KG confidence:
+///   Surface: any relationship, any confidence (baseline)
+///   Real:    (Friendly|Known) + KnowsOf+  (rapport + substantive knowledge)
+///   Secret:  Friendly + KnowsDetails+     (deep rapport + actionable knowledge)
+///
+/// KnowledgeConfidence ordering is load-bearing here — the >= comparison
+/// relies on the derive(PartialOrd) order: Suspects < KnowsOf < KnowsDetails < Direct.
+///
+/// Unknown NPCs (no KG entry) default to Suspects, yielding Surface tier.
+/// This is correct: you can't have deep dialogue with someone you know nothing about.
 pub fn relationship_to_trust(
     relationship: RelationshipState,
     confidence: crate::knowledge::types::KnowledgeConfidence,
@@ -383,6 +398,8 @@ pub fn process_talk_interaction(
     let situations = derive_situations(time.day_phase(), relationship);
 
     // Layer 3: Trust tier from relationship + confidence (D-075)
+    // Default to Suspects for unknown NPCs — no KG entry means no basis for
+    // deeper dialogue, which correctly yields Surface trust tier.
     let confidence = target_stable
         .and_then(|sid| observer_kg.confidence_of(&sid))
         .unwrap_or(crate::knowledge::types::KnowledgeConfidence::Suspects);
@@ -390,7 +407,7 @@ pub fn process_talk_interaction(
 
     // Query Layers 1-3: collect candidates across all available access tiers
     let mut candidates: Vec<&IndexedDialogueLine> = Vec::new();
-    let mut seen_ids: Vec<&str> = Vec::new();
+    let mut seen_ids: BTreeSet<&str> = BTreeSet::new();
 
     for access in &access_tiers {
         let results = line_pool.0.query_dialogue(
@@ -401,9 +418,8 @@ pub fn process_talk_interaction(
             trust,
         );
         for line in results {
-            // Deduplicate across access tiers
-            if !seen_ids.contains(&line.id.as_str()) {
-                seen_ids.push(&line.id);
+            // Deduplicate across access tiers (BTreeSet for deterministic iteration)
+            if seen_ids.insert(&line.id) {
                 candidates.push(line);
             }
         }